Almost everything about Soil


Mixing light is fun!
Mar 3, 2017
Reaction score
Luxury consumption

  • It is the tendency of some crops to absorb and accumulate nutrients far in excess of their actual needs if it is present in sufficiently large quantities in the soil. Potassium is one of the nutrient elements which is subjected to luxury consumption.
  • The absorption pattern of different nutrients by plants is varies greatly among the plant species and also their age and growth stages.

Consumption of Nitrogen by plants

  • Plants absorb the N mostly in nitrate (NO3-) form or in ammonical (NH4+) form by some plants. Plants usually absorb the N more during active growing period, but they do not always absorb it at the same rate. The amount of nitrogen absorbed is at a maximum when the plants are young and gradually declines as the plants age. Plants can absorb extra nitrogen when it is available and store it to be used later if needed.
  • An oversupply of N generally produces dark green, succulent, vegetative growth. In such cases there will be a decline in seed production of grain crops, fruit production in tomatoes and some tree crops. In sugar beets, sugar content decreases and in and potatoes, tubers become watery. The negative effects of too much of N on growing plants can be lessened if the P and K supplies are adequate.
  • The average utilization of applied N by crops is around 50 percent but with proper nitrogen management strategies the efficiency as high as 80 % or more can be increased. Low N use efficiency may be attributed to various losses such as Volatilization of Ammonia in alkaline soil, Denitrification of Nitrate ions in flodded soil, Leaching loss of Nitrates in coarse textured soil, soil erosion/run off and ammonium fixation in clay lattices.

Consumption of phosphorus by plants

  • Phosphorus application, unlike N is known to benefit the growth and productivity of more than one crop in rotation. The residual P contributes more of P to crop nutrition. Responses to applied P depend on soil properties, initial available P, variety, level of N applied and management practices.
  • Phosphorus is absorbed as phosphate ions such as H2PO4- and HPO42- form. It is concentrated more in the reproductive parts of plant and in seeds. Harvested crops contain considerable amounts of P. In general, seed crops contain largest percentages of P, and forage crops contain moderate percentages.
  • Consumption of ‘P’ by the crops is very less after their application to soil and it accounts even less than 10 % and remaining amount will be useful later. This is mainly because; P is subjected to immobilization or fixation (retention/adsorption/precipitation/sorption) and undergoes various transformations which render it unavailable to plants.
  • P fertilizers are not easily and completely soluble in water and their mobility is less within the soil. Therefore in order to get maximum benefit from them we have to adopt suitable methods and time of application.

Consumption of potassium by plants

  • Potassium uptake is often equal to or more than that of nitrogen. It is absorbed by plants by K+ form. Crop species differ in their K requirement. Tuber crops like potato, vegetables like cauliflower and cabbage, forages like alfalfa and fruits like banana, grapes and pineapple, plantation crops like coconut, tea, rubber are among the heavy feeders of K.
  • High crop yields and higher rates of N and P application accelerate K uptake from the soil. Crop responses to K are large on laterites, red and yellow and mixed red and black soils. Plants absorb and accumulate K far in excess of their needs if it present sufficiently in soil without affecting the metabolic activity or without any plant response. This is called as Luxury consumption.
  • Potassium also subjected for various losses
    • 1) Leaching losses of K- Especially in sandy soils and soils rich in kaolinite located heavy rainfall area.
    • 2) Soil erosion losses- It also leads to considerable loss of total K from the soil.
    • 3) Fixation of K by clay complex of illite type

Consumption of secondary nutrients by plants

  • The amount of secondary nutrients removed by crops depends on the soil type, crop species, fertilizer sources and yield level. Generally, legumes and root crops remove more Ca and Mg than do cereals and other grasses. Cereals may remove 10-20 kg Ca per ha, a good crop of Brassica oleracea may remove 150 kg Ca per ha. A continuous cropping may result in the reduction of exchangeable Ca in soil.
  • Banana and pineapple crops with yield levels of 40 to 50 t/ha may remove 120 to 140 kg of Ca and Mg . As a thumb rule, S removal per tonne grain production can be taken as 3-4 kg for cereals, about 8 kg for pulses, about 12 kg for oil seeds and 18 kg for cruciferous and 38 kg for mustards. In most of the crop species, the critical limits of S in plants are 0.20 to 0.25%. Plants use approximately as much S as P.

Consumption of micro nutrients by plants

  • High crop yields remove substantial amounts of micronutrients from the soil, especially Zinc and Boron. Micronutrients depletion in soil depends on soil fertility level and crop yields. Maize based cropping sequence depletes the maximum micronutrients form soil, especially Zn and Fe.
  • The deficiencies of Zn and B are prevalent in most soils especially red and laterite soils.

Nutrient interactions in plants and soils

  • Interaction can be defined as the influence of an element upon another in relation to growth and crop yield. There may be positive or negative interaction of nutrients occurs either in soil or plant. The positive interaction of nutrients gives higher crop yield and such interactions should be exploited in increasing the crop production. Conversely, all negative interactions will lead to decline in crop yield and should be avoided in formulating agronomic packages for a crop.
  • The knowledge about interactions occurring in soils or plants or both is basic to help develop appropriate and efficient technologies. Further this will help to refine the existing ones to increase agricultural production.
  • There are mainly two types of interactions effect viz. antagonistic and synergistic effects. Antagonistic effect means an increase in concentration of any nutrient element will decrease the activity of another nutrient (negative effect). While synergistic effects means an increase of concentration of any one nutrient element will influence the activity of another nutrient element (Positive effect). One must understand how the negative or positive interaction takes place within or outside the plant.
  • The following antagonistic effects have been well established on the uptake of micronutrients by crops:
    • 1. Excess of P adversely affects utilization of Zn, Fe and Cu
    • 2. Excess of Fe adversely affects utilization of Zn and Mn
    • 3. Excess of Zn, Mn, and Cu induces Fe-deficiency in crops
    • 4. Excess of S and Cu induces Mo-deficiency in crops
    • 5. Excess of Lime induces deficiency of all micronutrients.
    • 6. Presence of carbonate and bicarbonate ions in soil due to sodicity or over liming reduces the availability of micronutrient cations to crops which suffer most iron deficiency.
    • 7. Lime X P, Lime X Mo, Mo X P, and Na X K are common negative interactions.
    • 8. Excess of Ca may induce P deficiency
    • 9. Excess of Ca and Mg may depress K uptake
    • 10. Excess of Ca may reduce Mg uptake, if ratio is wider than 7:1
    • 11. Excess of K and NH+ may reduce Mg uptake
    • 12. Excess of N, K and Ca may reduce B toxicity
    • 13. Excess of N,P,K may induces Cu deficiency
    • 14. Excess of NO3-N may cause Fe deficiency
  • (Lime: CaO, Ca(OH)2, CaCO3)

A little excursion to something i found to this topic.

The "Mineral Wheel"

  • It describes the influence of an excessive element on the uptake of other minerals.
  • There are 2 types:
    • antagonistic interactions
    • stimulating/synergizing interactions

This picture only shows antagonistic interactions:


"How to read"

  • If there is an arrow pointing from "Element1" to "Element2" it means
  • An excess of "Element1" leads to an uptake-problem or a deficiency of "Element2".
  • Example: Fe -> Al | An excess of Fe leads to an uptake-problem or a deficiency of Al.

"Mulders Chart"


"How to read"

  • For the green Lines:
    • If there is an arrow pointing from "Element1" to "Element2" it means
  • An excess of "Element1" leads to an uptake-problem or a deficiency of "Element2".
  • For the dotted Lines:
    • If there is an arrow pointing from "Element1" to "Element2" it means
  • An excess of "Element1" leads to a higher need of "Element2".

Since these are a bit hard to read when u want to know a specific Element interaction I collected all data and wrote it down a excel file.

This is a screenshot of it:


"How to read"
  • On the right side is a info which sign goes for which element. Blue ones are essential ones.
  • Select your Element on the first row, then go down the coloum. On the left side you can the which element interaction it is.
  • Red fields are for antagonism, green fields for synergism, black fields are always the same element.
  • Example: (Mo)
    • Antagonism for: Ca, S, W
    • Synergism for: Cu, N
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score
N- Transformation in soils


  • Dynamics and transformation of nitrogen in soil is very important with respect to plant nutrition. A bulk of total N is present in the organic form (98%) and only about 2% in inorganic form. However there are continuous transformations between these two pools. The crops utilize nitrogen in the inorganic forms only such as NO3-N and NH4-N. The inorganic form of N is also liable to undergo different types of loses like runoff, ammonia volatilization, leaching, denitrification and fixation by clay minerals.
  • The cycling of N in the soil – plant – atmosphere system involves many transformations of N between inorganic and organic forms.

N transformations in aerobic soils
  • In aerobic soils, NO3-N is the dominant form of available N. The mineralization/transformation of added or native organic matter in soil proceeds up to nitrification stage and giving predominantly NO3-N and small amount of NH4-N. There is a quick transformation of NH4+ to NO3-N in the aerobic soils occur which will be utilized by plants.
  • Any fertilizer containing ammonium nitrogen when added to soil gets dissociated to NH4+ which readily gets oxidized to NO3- ion which is either taken up by the crop or leaches down to the lower horizon as it is readily soluble in water. Some amount of NO3-N is also immobilized by soil microbes during the process of mineralization of organic matter.

The organic form of N, particularly hydrolyzable form is slowly mineralized and is transformed to mineral nitrogen through following process
  • a. Amminization
  • b. Ammonification.
  • c. Nitrification
  • d. Denitrification

Nitrogen mineralization
  • Mineralization is the conversation of organic N to inorganic forms of N as a result of microbial decomposition. Mineralization increases with a rise in temperature and is enhanced by adequate, soil moisture and a good supply of O2. Mineralization of organic N involves in two reactions.

  • Aminization is the decomposition of proteins and the release of amines, amino acids and urea. A large number of soil microorganisms bring about this change.
  • Under aerobic condition the major end products are CO2, (NH4)2 SO4 and H2O. Under anaerobic conditions the end products are ammonia, amides, CO2 and H2S.
  • The organic compounds and proteins are mainly decomposed by various species of Pseudomonas, Bacilli, clostridium, serrotia, Micrococcus.

Conversion of urea
  • Urea is a product of aminization. The hydrolysis of urea by the action of urease enzyme is effected by Bacilli micrococcus, Pseudomonas, clostridium, Acromobactor and coryne bactor.
    • Co (NH2) + H+ + 2H2O--------------> 2NH4+ + HCO3-
    • NH4+ ----------------->NH3 + H+
    • 2NH3 + H2 CO3 ----------------------->(NH4)2 CO3 -------------------->NH4+ + CO3-
  • The optimum water holding capacity for these reactions is 50 – 75% and optimum temperature is 30 – 50°C.
  • “Amines and Amino acids produced during aminization of organic N are decomposed by other heterotrophs with release of NH4+ is termed Ammonifcation

  • Nitrification is the process of biological oxidation by which the ammonical (NH4+) form of N converts to nitrate (NO3-) form of N. There are two steps.
  • (a) NH4 is converted first to NO2- and then to NO3-.
  • Nitrosomonas are obligate autotropic bacteria that obtain their energy from the oxidations of N and their C from CO2.
  • 2NH4 + 3O2 ------------------------->2 NO2- + 2 H2O + 4 H+
  • (b) In the second reaction NO2- is further oxidized to NO3- by nitrobactor
  • 2 NO2- + O2 -------------------------->2 NO3-.

  • Denitrification is the biochemical reduction of NO3-N or NO2-N to gaseous N forms, either as molecular Nitrogen or an oxide of Nitrogen. The most probable bio chemical pathway is
  • NO3-----------------> NO2 ---------------------->NO--------------------- >N2O-----------------------------> N2
  • Nitrate Nitrite Nitrogen Nitrous monoxide Nitrous oxide Dinitrogen
  • This is loss mechanism of nitrogen happening in anaerobic soil conditions.
Nitrogen immobilization
  • “Immobilisation is the process of conversion of inorganic N (NH4+ or NO3-) to organic N and it is basically the reverse of N mineralization”. By this process plant available N forms are converted to unavailable organic forms. The Microorganisms accumulate NH4- N and NO3- N in the form of protein, nucleic acid and other complexes. If C:N ratio is wider than 30, it favors immobilization and lesser C:N ratio encourage mineralization.

Losses of Nitrogen
  • The major losses of N from the soil are due to (1) crop removal and leaching, however under certain conditions inorganic N ions can be converted to gases and lost to the atmosphere. The primary pathway of gaseous N losses are
    • 1. Denitrification
    • 2. NH3 volatilization.

Nitrogen fixation
  • The conversation of atmospheric nitrogen to plant available forms readily usable by biological process mediated by microorganisms. .

Nitrogen Transformation in anaerobic soils
  • The N-transformations from added or native sources stops at NH4+ stage, since nitrification is not possible due to lack of oxygen. When NH4+-N containing fertilizers are added to soil, then NH4+ is oxidized to NO3- in the top layer (aerobic) of flood water or oxidized layer and later which moves down to reduced layer. On the reduced layer NH4+-N remains as NH4-N only for plant uptake. If NO3-N exists, then it moves down to the reduced layer, where it undergoes denitrification by bacteria (NO3-NO2-N2). The denitrified NO3- is lost from the soil to the atmosphere in the form of N2O or N2.
  • If NH4+ ions present in the flood water it is subjected to volatilization to atmosphere as NH3 (ammonia gas) because of higher partial presence of CO2 and high pH value developed due to alkalinity. Therefore, there is an accumulation of NH4+ ions in the reduced layer, which is either absorbed by root or gets oxidized in the rhizosphere to NO3- ions and are lost due to dentrification. Some of the NH4+ and NO3- ions also get immobilized by the soil microbes & some NH4+ may get fixed by the clay lattice.
Phosphorus transformation & availability in soils


  • In P cycle the phosphorus is not involved in any exchange process with the atmosphere. The amount of dissolved or solution P mostly H2PO4- and HPO42- ions in the soil is very small and crops will utilize P from this source. The soil solution P can come from mineralization of organic matter, added fertilizers, adsorbed phosphate ions and solid P compounds (primary & secondary minerals).
  • Any P present in solution P form and it is available to plants is called Labile P, where as any P which is bounded in solid P compounds such as primary and secondary minerals is called Non Labile P which is not available to plants.

P- Transformation in aerobic soils:
  • P transformation depends on their solubility, interaction with other soil components. When a water soluble phosphate fertilizer, such as super phosphate is applied to a soil, P dissolves immediately and enters the soil solution and readily forms new compounds with Ca as Ca-PO4 and carbonates of hydroxyapatite in calcareous and alkaline soils respectively. While in acid soils rich in Al, Mn and Fe, applied P is converted as Al-PO4 , Mn –PO4 and Fe-PO4 which are are precipitated as newly formed insoluble compounds and thus reduce the availability of P to crops.

P Transformation in Anaerobic soils:
  • Submerged or flooded conditions/soils create reduced conditions (anaerobic soil) which lead to reduction of Ferric-PO4 to ferrous PO4 resulting in greater availability of P in the reduced soil. Organic acids formed under submerged conditions also solubilize PO4 there by P is available to plants.

K-transformations & availability in soils


  • Potassum is present in soil solution as K+ ion which is readily available to plants. But this form is in dynamic equilibrium with exchangeable K which intern with fixed K. Fixed K is in equilibrium with mineral K. The available K is the solution-K and Exchangeable K which can be easily absorbed by plants.

K- Transformations in soil:
  • When potassic fertilizers are added to the soil, K may either remain in soil solution or in exchangeable form on the clay surface or in non-exchangeable form held by illitic clay minerals as fixed K which is not available to plants directly. Plants get K mainly from solution-K and exchangeable-K form. As and when the exchangeable K fraction is depleted form the soil substantially or exhausted by crop uptake, the non exchangeable form of K replenishes the exchangeable K and supply of K to plants is maintained and equilibrium is attained. The reserve source of K is mineral lattice K which undergoes weathering and releases K to soil. In all these transformations some sort of equilibrium is maintained always in soil among different forms of K thereby plants get continuous supply of K.

Calcium and Magnesium availability in soils


  • Ca and Mg are the most abundant cations occupying the exchange sites of the soil colloids of both inorganic (clay) and organic (humus). Soil Ca and Mg mainly come from the weathering of rocks and minerals (Calcite and Apatite). Thus most soils contain enough Ca and Mg except highly weathered leached acid soils and alkali soils. Deficiencies of Ca and Mg most commonly occur in coarse textured soils, acidic soils of high rainfall area due to leaching losses. In soil solution occurs as cations and also adsorbed cation on the clay and humus surfaces and involved in exchange process. The critical limits of exchangeable Ca and Mg vary widely among soils. However average value of <2.0 m.eq/100g for exchangeable Ca and < 0.5 m.eq/ 100g for exchangeable Mg are considered critical limits for availability.

Ca & Mg Transformations:
  • Ca and Mg occupying the exchange sites of the soil colloids (clay & humus) are subjected to cation exchange reactions with other monovalent and divalent cations then released into soil solution for plants absorption or adsorbed on the clay and organic matter surfaces. Soils usually contain less Mg than Ca because Mg2+ ions are not adsorbed as strongly by clay and organic matter as Ca2+ ions and further Mg2+ ions are more susceptible to leaching than Ca2+ions. The solution Ca and Mg is subjected to leaching/erosion losses and crop uptake, thus it may deplete the Ca and Mg content soil.

Micronutrients Cycle and their Transformations in soil

  • Micro or trace elements in soil are derived from the parent materials and natural deposition from the atmosphere, organic manures and fertilizers. Trace elements are largely bound in mineral lattices, to be released by weathering. Iron, Cu, Mn, Zn, Co, Mo, Ni and Cr occur in ferromagnesian minerals common in ultrabasic and basic igneous rock.
  • The total content of Fe, Mn, Zn, Cu, Co, Cl & B varies considerably in different soils. Except Zn, Cu and B, all other micronutrients (Fe, Mn, Cl, Mo) are present in Indian soils in sufficient amounts to sustain agricultural productivity. Zn and Boron deficiency is found in all the soils of agro ecological regions of the country. The availability of micronutrient cations in soil is highly affected by inorganic ions in soil solution, soil solid constituents like free oxides of Fe & Al, soil organic matter, fertilizers and amendments applied to soil.
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score
Soil fertility evaluation?

The diagnosis of the nutrient status of the soil by using different techniques or methods is known as soil fertility evaluation.

Methods of soil fertility evaluation
There are various diagnostic techniques that are commonly used to evaluate fertility of the soils. They are;
  • I. Nutrient deficiency symptoms on plants
  • II. Plant analysis
  • III. Biological tests
  • IV. Soil testing
  • V. Modern approaches of soil fertility evaluation and fertilizer recommendation

I. Nutrient deficiency symptoms of plants

  • It is a qualitative measurement of availability of plant nutrients. It is the visual method of evaluating soil fertility and diagnosing the malady affecting the plant. An abnormal appearance of the growing plant may be caused by a deficiency of one or more nutrient elements. The appearance of deficiency symptoms on plants has been commonly used as an index of soil fertility evaluation.
  • If a plant is lacking in a particular element, more or less characteristics symptoms may appear. This visual method of soil fertility evaluation is very simple, not expensive and does not require elaborate equipments but it becomes difficult to judge the deficiency symptoms if many nutrients are involved. In such cases it requires experienced person to make proper judgment.
The common deficiency symptoms are
  • 1. Complete crop failure at seedling stage
  • 2. Retarded/stunted growth
  • 3. Abnormal color pattern. E.g.: Chlorosis (yellowing), necrosis (dying of tissue)
  • 4. Malformation of different plant parts. E.g.: rosette appearance of leaves
  • 5. Delayed maturity
  • 6. Poor quality of crops like low protein, oil, starch content, keeping/ storage quality reduced.
  • 7. Internal abnormality like Hidden hunger (It is a situation in which a crop needs more of a given element, yet has been shown no deficiency symptoms).

II. Plant Analysis

It is a valuable supplement to soil testing in the task of soil fertility evaluation. Plant analysis indicates the actual removal of nutrients from the soil and identifies nutrient status of plant and deficiency of nutrient element. It is a direct reflection of nutrient status of soil.
Advantages of plant analysis are
  • a. Diagnosing or confirming the diagnosis of visible symptoms
  • b. Identifying hidden hunger
  • c. Locating areas of incipient (early stage) deficiencies.
  • d. Indicating whether the applied nutrients have entered the plant
  • e. Indicating interactions or antagonisms among nutrient elements.

Plant analysis consists of three methods

  • Rapid tissue tests: It is a rapid test and qualitative or semi quantitative method. Fresh plant tissue or sap from ruptured cells is tested for unassimilated N, P, K and other nutrients. The cell sap is added with certain reagents to develop color. Based on intensity of color low, medium and high color is categorized which indicates the deficiency, adequate and high nutrients in the plants respectively. It is mainly used for predicting deficiencies of nutrients and it is possible to forecast certain production problems.
  • Total analysis: It is a quantitative method and performed on whole plant or on plant parts. The dried plant material is digested with acid mixtures and tested for different nutrients quantitatively by different methods. The determination gives both assimilated and unassimilated nutrients such as nitrogen, phosphorus, potassium calcium, magnesium, suphur, iron, manganese, copper, boron, molybdenum, cobalt, chlorine, silicon, zinc, aluminum etc., in plants. Recently matured plant material is preferable for accurate analysis.
Critical levels of nutrients in plants


III. Biological methods

It is conducted for calibrating the crop responses to added nutrients. Different methods are adopted for evaluating fertility status of soil.
Field tests:
  • Field tests are conducted on different fertilizers and crops with treatments impositions in replications. The treatment which gives highest yield will be selected. These experiments are helpful for making general recommendations of fertilizer to each crop and soil and we can also choose right type and quantity of fertilizer for various crops. It is laborious, time consuming, expensive but most reliable method. They are used in conjunction with laboratory and greenhouse studies as final proving technology and in the calibration of soil and plant tests. Thy widely used by experiment stations.
Indicator plants:
  • These are plants that are more susceptible to the deficiency of specific nutrients and develop clear deficiency symptoms if grown in that nutrient deficient soil. Hence these are called as indicator plants.
Some indicator plants are;


Microbiological test:
  • By using various cultures of microorganisms soil fertility can be evaluated. These methods are simple, rapid and need little space. Winogradsky was one of the first to observe in the absence of mineral elements certain microorganisms exhibited a behavior similar to that of higher plants. Microorganisms are sensitive to deficiency of nutrients and could be used to detect the deficiency of any nutrient. A soil is treated with suitable nutrient solutions and cultures of various microbial species (bacteria, fungi) and incubated for a few days. Then observing the growth and development of organisms in terms of weight or diameter of the mycelia pad, the amount of nutrient present in the soil is estimated.
  • a. Azotobactor method for Ca, P and K.
  • b. Aspergillus niger test for P and K
  • c. Mehlich’s Cunninghamella (Fungus)- plaque method for phosphorus
  • d. Sackett and Stewart techniques (Azotobacter culture) to find out P and K status in the soil.
Laboratory and Green house Tests:
  • These are simple and more rapid biological techniques for soil fertility evaluation. Here, higher plants and small amounts of soils are used for testing. All these techniques are based on the uptake of nutrients by a large number of plants grown on a small amount of soil. It is used to assess availability of several nutrients and they are quantitatively determined by chemical analysis of the entire plant and soil. Some common methods are;
  • a. Mitscherlich pot culture method for testing N,P, K status in oat
  • b. Jenny’s pot culture test using lettuce crop with NPK nutrients
  • c. Neubauer seedling method for NPK d. Sunflower pot-culture technique for boron

IV. Soil Testing

  • A soil test is a chemical method for estimating the nutrient supplying power of a soil. It is much more rapid and has the added advantage over other methods of soil fertility evaluation. One can determine the needs of the soil before the crop is planted. A soil test measures a part of the total nutrient supply in the soil.
  • Soil testing plays a key role in today’s modern and intensive agriculture production system as it involves continuous use and misuse of soil without proper care and management. Soil analysis is helpful for better understanding of the soils to increase the crop production and obtaining sustainable yield. Soil testing is an indispensable tool in soil fertility management for sustained soil productivity.
  • Objective of soil testing
    • a. To evaluate fertility status of soil by measuring available nutrient status
    • b. To prescribe or recommend soil amendments like lime and gypsum and fertilizers for each crop
    • c. To assess nutrient deficiencies, imbalances or toxicities in soil and crop
    • d. To test the suitability of soil for cultivation or gardening or orchard making
    • e. To know acidity, alkalinity and salinity problems
    • f. To know morphology, genesis and classification of soil
    • g. To find out the effect of irrigation on soil properties.
    • h. To prepare a soil fertility map of an area (village, taluk, district, state)
    • In the soil testing programme, “soil sampling” is most important step to be followed for getting accurate results. Soil sampling is a process by which a true representative sample of an area or orcahrd can be obtained. The soil sampling must be done scientifically by adopting appropriate time and depth of sampling given for each crop for accurate analysis of soils.
Interpretation of soil test results and critical levels of nutrients in soils.


V. Modern approaches of soil fertility evaluation and fertilizer recommendation

  1. Soil Test Crop Response (STCR)/Targeted Yield Concept
  2. Diagnosis and Recommendation Integrated System (DRIS) Approach

  • After introduction of high yielding varieties and hybrid crops, the need for systematic soil test crop response research in different soil agro-climatic regions become evident. ICAR established the AICRP on STCR in 1967 and the STCR concept was developed by Ramamoorthy, in 1987. STCR provides the relationship between a soil test value and crop yield.
  • The soil test values are needed to be correlated with actual crop response obtained under field conditions. Separate calibration charts are needed for each crop and soil. Fertility gradient and regression approach and targeted yield concepts were evolved. This is also called as “rationalized fertilizer prescription approach” in which inherent soil fertility and yield level of the crop are taken in to account while recommending the fertilizer doses.
Objective of STCR
  • To prescribe fertilizer doses for a given crop based on soil test values to achieve the “Targeted yields” in a specific soil agro-climatic region under irrigation or protective irrigation conditions by using mathematical equations for different crops and different soil agro-climatic zones separately.
  • This takes in to consideration-the efficiency of utilization of soil and added fertilizer nutrient by the crops and its nutrient requirements for a “desired yield level”.
Concept of STCR
  • STCR approach is aiming at obtaining a basis for precise quantitative adjustment of fertilizer doses under varying soil test values and response conditions of the farmers and for targeted levels of crop production. These are tested in follow up verification by field trials to back up soil testing laboratories for their advisory purpose under specific soil, crop, and agro climatic conditions. The fertilizers are recommended based on the following criterias.
    • Fertilizer recommendations based on regression analysis approach
    • Recommendations for certain % of maximum yield
  • STCR methodology takes in to account the three factors;
    • Nutrient requirement (NR) in kg/ quintal of the produce
    • Percentage contribution from soil available nutrients (SE)
    • Percentage contribution from added fertilizers towards making effective fertilizer prescriptions for specific yields.

  • With the help of above parameters, adjustment equations have been developed for a number of crops in various soils.
    • For Rice crop.
      • a. Fertilizer N = 4.39 T -0.6723 Soil N
      • b. Fertilizer P2O5 = 2.83 T – 6.110 Soil P
      • c. Fertilizer K2O = 1.41 T – 0.329 Soil K
      • Where T= Targeted yield of rice

  • Advantages
    • 1) Efficient and profitable site specific fertilizer recommendation for increased crop production and for maintenance of soil fertility.
    • 2) Aims to provide balanced, efficient and profitable nutrient application rates for pre- set yield targets giving due consideration to basic fertility status of soil
  • Targeted yield concepts:
    • These are soil test based recommendations but given for different yield goals and not for a single optimum yield level. A large variety of fertilizer prescription have been made available by putting soil test values in to certain mathematical equations and finding out the amounts of nutrients needed for a given yield target.

2) Diagnosis and Recommendation Integrated System (DRIS Method)

Concepts of DRIS
  • Concepts of DRIS: DRIS is a new approach to interpreting leaf or plant analysis which was first developed by “Beaufils” (1973) named as Diagnosis and Recommendation Integrated System (DRIS). It is a comprehensive system which identifies all the nutritional factors limiting crop production and increases the chances of obtaining high crop yields by improving fertilizer recommendations. The DRIS method uses “nutrient ratios” instead of absolute and or individual nutrient concentrations for interpretation of tissue analysis.
  • There is a set of optimum ratios among the nutrient elements (N/P or N/K or K/P) within a given plant for promoting the growth of the plant. DRIS mainly uses the “nutritional balancing” concept (Relationship among nutrients) in the detection of nutritional deficiencies or excess in the plant. Nutrient balance is a part of the proper interpretation of DRIS system because nutrient interactions to a larger extent determine crop yield and quality. The nutrient ratios are helpful to obtain special indexes which are called “Nutrient Index” or “Beaufills nutrient Indexes” (BNI).
  • The nutrient index values are used to rate the nutrients in order of their need by the plants analyzed. It also measures how far particular nutrients in the leaf or plant are from optimim are used in the calibration to classify yield factors in order of limiting importance. BNI are actually expression of the supplies of nutrients relative to each other. The concentration of each nutrient in the plant has an effect on the index value for each of the other nutrient. An abnormally high concentration of one or more nutrients will decrease the index values of other nutrients.
  • There will be positive and negative values for the nutrient index. The nutrients with positive indexes appeared to be in “excess” and nutrients with negative indexes appeared to be “deficient” in plants. DRIS indices can be calculated individually for each nutrient using the average nutrient ratio deviation obtained from the comparison with the optimum value of a given nutrient ratio. DRIS is a mathematical technique to apply plant analysis information (Nutrient concentration) for diagnosing the most limiting nutrient in a production system.
  • The evaluation is made by comparing the relative balance of nutrient content with norms established for that crop under high yield conditions. The evaluation is made by comparing the relative balance of nutrient content with norms established for that crop under high yield conditions.
To develop a DRIS for a crop, the following requirements must be met whenever possible.
  • 1. All factors suspected of having effect on crop yield must be defined
  • 2. The relationship between these factors and yield must be described
  • 3. Calibrated norms must be established
  • 4. Recommendations suited to particular sets of conditions and based on correct and judicious use of these norms must be continually refined.
  • The importance of nutritional balance is taken in to account in deriving the norms and making diagnosis. It helps to quantify the nutrient balance in the plant.
  • The norms for nutrient content in leaves can be universally applied to the particular crop.
  • Diagnosis can be made over a wide range of stages of crop development.
  • The nutrient limiting yield through either excess or insufficient can be readily identified and arranged in order of their limiting importance for yield.
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score
Organic matter and its composition

Soil organic matter is a complex matter obtained from the plants and animal residues containing both organic and inorganic chemical compounds.

Composition of Organic matter

A. Organic compounds
  • 1. Nitrogenous compounds
    • eg: Amine, amide compounds and amino acids (water soluble) proteins (simple, combined, derived), peptone, purine, peptide, nucleoprotein, protease, pyridine, alkaloid, pirimidin.
  • 2. Non nitrogenous compounds
    • Eg : -Carbohydrates (mono, di, poly and oligosaccharides, amino sugars, sugar acids, sugar alcohol),lignin (aliphatic hydroxyl and carbonyl group found), Cellulose and hemicelluloses, tannin, fat, wax and resin, pigments, organic acids (acetic, oxalic, saccharic, propionic, benzoic, pomitic), organic phosphorus compounds (nucleic acids, phospholipids, inositol phosphate) and organic sulphur compounds (cystein, cystine, methionine).
B. Inorganic compounds
  • Organic matter contains several inorganic elements such as H, O, N, P, Ca, Mg, S, Na, K, Fe, Al, Mn, Zn, Mo, Si, B, Co, Cl etc. All these are in metallic complex form hence organic matter is water insoluble and do not destroy by leaching.

  • It is the decaying or rottening of organic materials by various groups of microorganisms and enzymes and converted in to simple inorganic elements or compounds. It helps to improve softness of the materials for further mineralization process. It is basically a burning or oxidation process.
  • Two types of decomposition
    • Aerobic decomposition- oxygen is required
    • Anaerobic decomposition- oxygen is not required.

Involvement of microorganisms
  • What types microorganisms involved in organic matter decomposition?
    • Decomposition is a purely microbial process involves several species of microorganisms. They are; Bacteria, actinomycetes, fungi, protozoa
    • Supporting organisms are: Insects, worms, rodents, termite, ants
    • All the soil organic matter is not decomposed by the same group of microorganisms. At different stages of decomposition different species of microorganisms enter into the degradation process. As the degradation proceeds newer materials are synthesized by soil microorganisms.

Enzymes involved in decomposition process?
  • What Enzymes involved in decomposition process?
    • Cellulase-breaks cellulose
    • Urease – breaks urea {CO(NH2)2 } to CO2 and NH4
    • Phosphatase – breaks humus –O-P-(OH) 2 bond to produce humus, OH & H3PO4
    • Sulfatase-breaks the humus O-S-OH bond to produce humus, OH & H2SO4
    • Protease – breaks bond linking two amino acids to separate amino acids

Major Process of organic matter decomposition
  • Decomposition processes
  • Two major decomposition processes involved
    • 1. Mineralization
    • 2. Immobilization
1. Mineralization
  • Is the conversion of an element from organic form to an inorganic/mineral form is called mineralization. Mineralization occurs for each element present in the organic matter individually especially for N, P and S
A. Nitrogen mineralization:
  • It is the conversion of organic nitrogen into inorganic Nitrogen NH4 and NO3 by microorganisms
  • Organic N(proteins and amino acids) ----------> Proteose------------>Peptone-------------->Amino compounds- ammonia -----------> nitrite --------> nitrate
Different steps involved in N-mineralization
  • 1. Aminisation: proteins and other complex nitrogenous compounds are converted into amino acids and amino compounds by the action of enzymes and microorganisms, CO2 and energy is released.
  • 2. Ammonification: it is the biochemical conversion of amino compounds and amino acids into ammonia by bacterial decomposition.
  • This process is governed by aminase and deaminase enzymes. The liberated NH3 is utilized by plants.
  • 3. Nitrification :It is the biochemical oxidation of ammonia into nitrite and then finally into nitrate. This process carried out by by autotropic bacteria (Nitrosomanas and Nitrobacter) in aerobic condition. Two steps are involved
  • Rate of nitrification depends on suitable temperature, humidity, pH, season, aeration, addition of lime (increases), nature of organic matter etc.
  • 4. Denitrification :It is the biochemical reduction of nitrate or nitrite to gaseous nitrogen (N2), either as molecular N or oxides of N.
  • Loss of nitrate by reduction and assimilation

B. Phosphorus mineralization
  • The process of conversion of organic forms of P into inorganic forms of P by P decomposing microorganisms especially by micorrhiza species is known as P-mineralization.
  • The organic-P found in organic manures mainly as nucleic acids, phytin, phospho lipids, inositol PO4, lecithin etc. The organic P is not directly available to plants and it has to undergo decomposition by micro organisms especially mycorrhyzal species.

C. Sulphur mineralization
  • The organic forms of S compounds such as methionine, cystine, cysteine are converted into inorganic sulphate forms (available) by aerobic bacteria species especially Thiobacillus and thiobacter.

2. Immobilization
  • The conversion of an element from the inorganic to the organic form in microbial tissues or in plant tissues, thus rendering the element not readily available to other organisms or to plants.

Rate of decomposition of organic compounds
  • Rate of decomposition varies with the types of organic compounds, some may undergo decomposition very fast and others may very slow.
  • The following is the decreasing order of rate decomposition.
Starch , sugars and simple proteins > Crude proteins> Hemi cellulose > Cellulose > Lignin > fat > Fatty compounds and waxes etc.(Most resistant)​

  • When fresh organic manures are added to soil 60% of it decomposed within the first 6 months, 20% in the next 3-4 years and remaining 20% decomposed beyond 4 years. This results in accumulation of lignins, fats and waxes in large quantities.

Products of Decomposition of organic matter
  • Under well drained, aerated (oxidised) soil: CO2, NO-2, NO-3, H2O, PO-4, SO42-, H2 and other essential plant nutrients. Antibiotics, Auxins, hormones, phytohormones.
  • Under anaerobic condition (water logged and compacted soil): Methane (CH4) (swamp gas), organic acids (R-COOH, NH4 and amine groups (R-NH2), Toxic gases like H2S, dimethyl sulphide and ethylene (CH2=CH2) etc.

Factors affecting decomposition
  • The most important conditions that affect the rate of decomposition are
    • 1. Temperature: Cold periods retard the organic matter decomposition and there will be more accumulation of organic matter on the top soil compared to that of warm climates. The most suitable temperature is 30-40 degree celcius for proper decomposition.
    • 2. Soil moisture: Near or slightly wetter than field capacity moisture conditions are most favorable for decomposition. About 60-75 % water holding capacity (WHC) is optimum.
    • 3. Soil pH: 6-8 pH or neutral pH is required for optimum growth of microorganisms. Bacteria at 6 - 7 pH, Actinomycetes is more at pH 8 -10, Algae pH of 5.5 - 7.5, Fungi- pH 4.0, Protozoa – pH 3.0
    • 4. Nutrients: Lack of nutrients, particularly N reduces microbial growth and it slows decomposition. Addition of nutrients by N fertilizers (urea) increases the speed of decomposition
    • 5. Soil texture: Soils higher in clays tend to retain larger amounts of humus, other condition being equal.
    • 6. Aeration: Good aeration increases the rate of decomposition and supply oxygen.
    • 7. Nature of plant matter: composition and age of plants and vegetations affect much their decomposition. It is fast in young, tender, and juicy material, But slow with more cellulose and hemicelluloses content.
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score
Formation of humus

Definition of humus
  • Humus is defined as they are more or less stable fraction of the soil organic matter remaining after the major portions of added plant and animal residues have decomposed. Usually it is dark or brown in colour. They are high molecular weight compounds, complex, resistant, polymeric compounds. They are amorphous and colloidal organic substances.
Composition of humus
  • Humus is a heterogeneous mixture of complex organic compounds. It is mainly made up of 58% C, 3-6% of N- and C:N ratio of 10:1 to 12:1.
Humus formation
  • Humic substances are produced when plant residues and other organic debris are broken down and/or chemically altered by microorganisms and subsequently recombine under the influence of enzymes. Humus formation is a complex two stage process in which organic residues of plant and animal origin undergo profound transformation.
    • 1. The decomposition of the original components of tissues and their conversion by microorganisms in to simpler chemical compounds and partially to products of complete mineralization (CO2, NO2, NO3, NH3, CH4, H2O etc.)
    • 2. The synthesis of organic compounds with the formation of high molecular weight humic substances of specific nature.
      • Ex. Lignin --------------broken into polyphenols, phenolic acids
      • Proteins-----------polypeptides and amino acids
      • Carbohydrates ------------ simple sugars
      • High molecular weights humic acids (HAs) and Fulvic acids (FAs).

Fractions and properties of humus

Fractions of humus
  • Humus is mainly composed of two major groups, they are
    • I. Humic group
    • II. Non-humic group

I. Humic group:
  • The humic substances make up about 60-80 % of the soil organic matter. On the basis of resistance to degradation and of solubility in acids and alkalis, humic substances have been classified into five chemical groupings.
  • Fulvic acid: lowest in molecular weight, lightest in colour, soluble in both acid and alkali and most susceptible to microbial attack. Contain uronides, simple carbohydrates and their sugars, phenolic glycosides, tannin and other organics, also rich in N and P.
  • Humic acid : Medium in molecular weight and colour, soluble in alkali but insoluble in acid and intermediate in resistance to degradation forms largest bulk, responsible for importing its characteristics properties to humus.
  • Humin: Highest in molecular weight, darkest in colour, insoluble in both acid and alkali and most resistant to microbial attack. Polymerized product of a part of the FA and HA fractions. 4. Apocremic acid 5. Hematomelanic acid. All the five fractions are amorphous and show no signs of crystallization.
II. Non humic group:
  • It comprises about 20-30% of the organic matter in soils. They are less complex and less resistant to microbial attack than those of humic group. They are comprised of specific organic compounds with definite physical and chemical properties.
  • E.g.: a. Polysaccharides- Polymers with sugar like structures. They are effective in enhancing soil aggregates stability.
  • b. Polyuronoids- They are not found in plants but have been synthesized by the soil microbes and held as part of the organisms body tissues.
  • c. Organic acids and protein like materials.
Properties of humus
  • It is a light bulky amorphous material of dark brown to black colour. The black colour of surface soil is usually due to the presence of humus.
  • It has a great water absorbing and water holding capacity. 100 part humus-181 part of water.
  • It possesses the power of adhesion and cohesion (but less than clay) so it acts as a cementing agent in crumb formation. In Sandy soils- adhesive capacity and in clay soils – cohesive capacity increases
  • It has a high ion adsorbing capacity (4-6 times that of clay) and CEC is very high (300-350 m.eq./100gm)
  • It is insoluble in water.
  • It behaves like a weak acid and forms salts with bases.
  • It acts as buffering agent and also as an oxidation reduction buffer.
  • It serves as a source of energy and food for the development of various microorganisms.
  • An important source of nutrients for higher plants.

C: N ratio and its importance

C:N ratio?
  • It is defined as the ratio of the weight of organic carbon to the weight of total nitrogen in a soil or organic matter. It is the relationship between organic matter and nitrogen content of soils or plants.

Importance of C:N ratio
  • C:N ratio mainly controls decomposition rate in soil
    • The wide C:N ratio leads to slow decomposition rate, nutrient immobilization may occur, carbon and energy wastage in large quantities. Activity of microorganisms restricted total amount of N is limited
    • In Narrow C:N ratio, Carbon and energy starvation occur. Plant residues decompose quickly and release nitrates readily. Amount of CO2 released/unit of carbon decomposed is less as more of it is metabolized and converted into microbial tissues. When the residue with high C/N ratio is added to soils, there will be intense competition among the microorganism for available N. The C/ N ratio in residues helps determine their rate of decay and the rate at which N is made available to plants. Ex : Speed of decomposition becomes slow with more/wide C/N ratio residue or low N percentages. On the contrary low/narrow C/N ratio or high N percentages speeds the decomposition rate.
  • It is a source of food and energy for plants
    • Soil organisms require carbon for building essential organic compounds and to obtain energy for life process, but they must also obtain sufficient N to synthesize N containing cellular components, such as amino acids, enzymes and DNA. (Microbes need to find about 1 g of N for every 24 g of C in their food. Microbes have 8:1 ratio means – microbes must incorporate into their cells about 8 parts of carbon for every 1 part of N.
  • Influence of C/N ratio on N release
    • It controls N availability in soils/plants: It controls N availability in soils/plants. If C/N ratio of OM is about 25:1, the soil microbes will have to scavenge the soil solution to obtain enough N. Thus, the incorporation of high C/N residues will deplete the soil native N, causing higher plants to suffer from N deficiency. While low C/N ratio (<20) Organic matter helps in increase in N content of soil for plants and organisms.
  • The decay of organic matter can be delayed: if sufficient nitrogen to support microbial growth is neither present in the material nor available in the soil
  • Influence of C/N ratio on Soil ecology: The soil ecosystem consists of saprophytic bacteria and fungi and nematodes, protozoa and earthworms that grow rapidly on organic residues as food source.
  • It is related to release of available N, total organic content and accumulation of humus.
    • C:N ratio’s of some of the organic materials
    • 1. Alfalfa 20:1
    • 2. Microbial population 10:1
    • 3. Soil organic matter 10-12:1
    • 4. Maize stalk 40:1
    • 5. Rice straw 100:1
    • 6. Rye straw 200:1
  • Saw dust 400:1 8. Clovers (mature) 20:1 9. Soil humus 11:1 Ratio varies from about 10 for leguminous and young plant materials and >100 for cereal straws.

Importance of pH in plant nutrition
  • The soil pH or soil reaction is the chemical properties/characteristics of the soil showing the degree of acidity, alkalinity or neutral condition of soil. The pH is having many roles in crop production and particularly in plant nutrition.
    • 1. It significantly influences other chemical as well as biological properties and also affect the availability of most of the chemical elements of importance to plants and microbes.
    • 2. The soil pH greatly affects the solubility of minerals.
    • 3. The soil pH determines the amount and type of nutrient element availability in soils.
    • Eg : In strongly acidic soils (pH 4-5) usually have high and toxic concentration of soluble Al and Mn.
    • 4. The soil pH also influences plant growth by the effect of pH on activity of beneficial microorganisms.
    • 5. Soil pH affects the mobility of many pollutants in soil by influencing the rate of their biochemical breakdown, their solubility and adsorption to colloids.
    • 6. Better nutrient availability found at neutral pH (6.5-7.5) like N, P, K, S, Ca, Mg but in low pH acid soil toxicity of Fe, Al, Mn etc., and deficiency of P, Mo etc. while in saline and alkaline soils Fe, Mn, Zn and Cu may be deficient. Mo availability is more.
    • 7. It helps in recommendation of soil amendments and fertilizer applications.
    • 8. It is a good guide for predicting which plant nutrients are likely to be deficient.
    • 9. It determines the microbial activity and the rate of decomposition.
    • 10. Availability and mobility of both macro and micro nutrients in soil is greatly affected by soil pH.
    • 11. The pH level affects soil physical properties ex: dispersion of clays and formation of stable aggregate structure.
    • 12. Suitability of soil for crop production.

Definition of Fertilizer

Fertilizers are defined as materials having definite chemical composition with a high analytical value that supply essential plant nutrients in available form. They are usually manufactured by industries and sold with a trade name. They are commonly synthetic in nature and also called as
chemical fertilizers/inorganic fertilizers/commercial fertilizers other than lime and gypsum.​

  • Most of the chemical fertilizers are inorganic in nature. The only exception to this is urea and calcium cyanamide (CaCN2), the solid organic N fertilizer.
  • In India the use of artificial fertilizers was first initiated in 1896 when imported Chilean nitrate was used as a fertilizer.
  • Presently fertilizers have become an integral part of agricultural economy as they increase the fertility of soils and enable them to support high yields. About 50% of the increase in crop production during recent times has been attributed to fertilizer use; though the fertilizer use efficiency is very poor.

Classification of inorganic fertilizers

  • A. Based on number of nutrients present
    • 1. Straight fertilizers
    • 2. Complex fertilizers
    • 3. Mixed Fertilisers Or Fertiliser Mixtures
  • B. Classification of fertilizers based on particular plant nutrient element
    • 1. Nitrogenous fertilizers
    • 2. Phosphatic fertilizers
    • 3. Primary nutrient fertilizers
    • 4. Potassic fertilizers
    • 5. Secondary nutrient fertilizers
    • 6. Micronutrient fertilizers.

A. Based on number of nutrients present

  • 1. Straight fertilizers
    • Are those fertilizers containing or supplying only one plant nutrient element at a time. For e.g., Urea, Ammonium Sulphate (NH4SO4), Ammonium nitrate(NH4NO3), Single super phosphate (SSP), Muriate of potash(MOP- KCl).
  • 2. Complex fertilizers
    • Fertilizers containing at least 2 or more of the primary essential nutrients (NPK). They are chemical mixtures, granular and free flowing and easy to apply. There are two types of complex fertilizers;
      • a. Complete or compound fertilizer: They are the chemical mixtures of three or more primary or major nutrient elements (NPK) in one compound or mixture. They are usually in granular form and easy to apply.
        • Ex: 10-26-26, 17:17:17, 19:19:19
      • b. Incomplete complex fertilizers: A fertilizer material lacking any one of three major nutrients or containing only two of the primary nutrients like N, P and K
        • Ex: N-P complex fertilizer : -Nitro-phosphate(Suphala:-15-15-0,20:20:0, -Diammonium phosphate: 18-46-0

Characteristics of complex fertilizers (CF)
  • 1. They usually have a high content of plant nutrients. As such they are also called high analysis fertilizers.
  • 2. They usually have a uniform grain size, granular form and good physical condition during storage.
Advantage of complex fertilizers
  • 1. In one application we can supply more nutrients and need not apply separately.
  • 2. Balanced nutrition can be achieved.
  • 3. Less cost is involved in transportation and application.
  • 4. They are available in different grades according to need of the soils and crops.
  • 5. Being granular, it is easy to apply by broadcasting.
  • 6. Some complex fertilizers also provides some micronutrients to soil.
  • 7. Transport and distribution is easy
  • 8. They are non-caking and non- hygroscopic, thus safer for storage
  • 3. Mixed Fertilisers Or Fertiliser Mixtures
    • A mechanical/physical mixture of two or more straight fertilizer materials in suitable proportion is referred to as fertilizer mixture or mixed fertilizers. Sometimes, complex fertilizers containing two plant nutrients are also used in formulating fertilizer mixtures. Specific fertilizer grades are recommended for specific crops depending upon the soil and climatic conditions of the region.
    • The mixed fertilizers are usually in powder form or sometimes granular form. Fertilizer mixture (FM) are free flowing and easy to apply. The mixed fertilizers can be made according to the need of the crop and there is wide scope for adjusting the fertilizer ratio..
Guide for mixing fertilizers​
  • Some fertilizers cannot be mixed with other fertilizers. Mixing of incompatible fertilizer leads to a loss of some of the nutrients in the form of gas, converting soluble nutrients into insoluble form or caking. Certain fundamental principles are to be followed in mixing fertilizers are.
    • 1. Ammonium sulphate, ammonium chloride and other ammonical fertilizers and nitrogenous organic manures should not be mixed with lime
    • 2. Urea should not be mixed with Super phosphate(SP)
    • 3. Calcium cyanamide, basic slag, quick lime slaked lime should not be mixed with N in NH4-N form.
    • 4. Super phosphate should not be mixed with lime or CaCO3 or wood ashes.
    • 5. NaNO3 or KNO3 should not be mixed with Super phosphate.
    • 6. Ammonium sulphate, nitrate should not be mixed with lime.
    • 7. Nitrochalk should not be mixed with SP or lime.
    • The commonest fertilizer mixture can be made from SSP, Ammonium sulphate, SOP, Bonemeal, and MOP.
Advantages of fertilizer mixtures​
  • 1. Less labour is required to apply fertilizer mixture to soil. Individual crop wise fertilizer mixture can be made.
  • 2. Balanced nutrition can be achieved.
  • 3. The residual acidity of fertilizers can be effectively controlled by adding liming materials in the mixtures.
  • 4. Micronutrients can be incorporated in fertilizer mixtures.
  • 5. They have a better physical condition and more easily applied.
  • 6. There is no need of purchasing straight fertilizers separately.
Disadvantages of fertilizer mixtures​
  • 1. Does not permit application of individual nutrients according to the needs of crops during specific times.
  • 2. The unit cost of plant nutrients is higher than of straight fertilizer.
  • 3. Lack of knowledge about proper mixing and their use.
  • 4. Fertilizer mixture of particular grade suitable for particular crop cannot be applied for all crops.

B. Classification of fertilizers based on particular plant nutrient element

  • The element forms their principal constituent in the fertilizer.
    • 1. Nitrogenous fertilizers
    • 2. Phosphatic fertilizers
    • 3. Potassic fertilizers
    • 4. Primary nutrient fertilizers
    • 5. Secondary nutrient fertilizers
    • 6. Micronutrient fertilizers.

I. Nitrogenous fertilizers

  • There are 6 groups.
    • a. Ammonium fertilizers
      • i. Ammonium sulphate (NH4)2 SO4 – 20% N
      • ii. Ammonium chloride : NH4Cl2 -24-26%
      • iii. Ammonium phosphate : NH4H2 PO4 -20%N + 20% P2O5 or 16% N and 20% P2O5
      • iv. Anhydrous ammonium (82%N)
      • v. Ammonium solution- 20-25%N
      • vi. Ammonium carbonate- 21-24%N
      • vii. Ammonium bicarbonate- 17%N
    • b. Nitrate fertilizers
      • i. Sodium nitrate or Chilean nitrate : NaNO3 – 16%N
      • ii. Calcium nitrate: CaNO3 – 15.5% N
      • iii. Nitrophosphate
    • c. Both Ammonium and nitrate fertilizers
      • i. Ammonium nitrate: NH4NO3- 33-34%N
      • ii. Calcium ammonium nitrate (CAN) – 25, 26 and 28% N
      • iii. Ammonium sulphate nitrate (ASN) – 26%N
    • d. Amide fertilizers
      • i. Urea – 46% N
      • ii. Calcium cyanamide- 21 %N
      • iii. Urea phosphate
      • iv. Urea sulphate
    • e. Nitrogen solutions
      • i. Anhydrous ammonia
      • ii. Aqueous ammonia
      • iii. Solution containing one or more of the following urea, ammonium nitrate, ammonia
    • f. Slowly available nitrogenous fertilizers
      • i. Urea formaldehyde compounds
      • ii. Neem Cake coated Urea NCU
      • iii. Lac Coated Urea(LCU)
      • iv. Sulphur Coated Urea(SCU)
      • v. Urea super granules (USG)
      • vi. Prilled urea (PU)

II. Phosphatic fertilizers

  • They are broadly classified into 3 major groups on the basis of their solubility either in water or in citrate or citric acid.
    • a. Water soluble phosphatic fertilizers (Contain phosphoric acid or mono calcium phosphate.)
      • 1. Single Super phosphate (SSP)- 16-18 % P2O5
      • 2. Triple super phosphate (TSP) – 46-48 % P2O5
      • 3. Double super phosphate (DSP)- 32% P2O5
      • 4. Di-Ammonium phosphate (DAP)- 18%N and 46% P containing dicalcium phosphate
    • b. Citric acid soluble phosphatic fertilizers
      • 1. Dicalcium phosphate (DCP) - 34-39% P2O5
      • 2. Rhenamia phosphate- 23-26% P2O5
      • 3. Basic slag- 14-18% P2O5
      • 4. Raw or steamed bone meal- part of P2O5 soluble in citric acid.
      • 5. Fused calcium magnesium phosphate- 16.5% P2O5
    • c. Water insoluble or citric acid insoluble phosphatic fertilizers. Containing tricalcium phosphate [(Ca3 (PO4)2]
      • Ex: Rock phosphate- 20-40% P2O5
      • Raw bone meal- 20-25% P2O5
      • Steamed bone meal- 22% P2O5
      • Pyrophos - 17% P2O5

III. Potassic Fertilizers

  • A. Fertilizers having K in the Chloride form
    • 1. Muriate of Potash (MOP) – KCl- 60-62 % K2O
  • B. Fertilizers having K in Non-chloride form
    • 1. Sulphate of potash (SOP) -K2SO4: 48-52% K2O
    • 2. Potassium nitrateKNO3 - 44% K2O

IV. Secondary Nutrient Fertilizers

  • Secondary elements are as important as primary elements because they help in uptake of primary elements by plants. They are required in very little quantity as compared to primary elements. The most important secondary nutrients are Ca, Mg and S. The fertilizers carrying secondary nutrients are;
    • 1. Calcium cyanamide(39.57% Ca)
    • 2. Calcium Ammonium Nitrate (8.0% Ca & 4.5% Mg)
    • 3. Calcium nitrate (1.5% Mg)
    • 4. Super phosphate (20.0% Ca)
    • 5. Bone meal (23.1% Ca)
    • 6 Limestone (32.58% Ca)
    • 7. Dolomite (20.0% Mg)
    • 8 Gypsum (29.40% Ca & 21.0% S)
    • 9. Potassium sulphate18.5% S & 0.6 to 0.9% Mg)
    • 10. Ammonium sulphate (24% S)

V. Micronutrient Fertilizers

  • Micronutrients are those which required by plants in very minute quantities by plants but they have equal role as that of primary nutrients. They govern most of the physiological as well as biochemical reactions of plant growth and development.
  • The most important micronutrients are iron, manganese, zinc, copper, molybdenum, chlorine, boron and nickel. The fertilizers carrying micronutrients are;
    • Fe carrying fertilizers
      • 1. Ferrous sulphate(19.0% Fe)
      • 2. Ferric sulpahte(23.0% Fe)
      • 3. Ferrous ammonium sulphate(29.0%Fe)
      • 4. Ferric and ferrous oxide70.0 and 77.0% Fe)
    • Boron carrying fertilizers
      • 1. Borax(11.0% B)
      • 2. Boric acid(17.0% B)
      • 3. Sodium tetra borate(14.0% B)
      • 4. Borosite(21.0% B)
    • Manganese carrying fertilizers
      • 1. Manganese sulphate (20.0 to 28.0% Mn)
      • 2. Manganese carbonate (31.0% Mn)
      • 3. Manganese chloride(17.0% Mn)
    • Zinc carrying fertilizers
      • 1. Zinc sulphate (55.0% Zn)
      • 2. Zinc oxide (67.0% Zn)
      • 3. Zinc sulphide (67.0% Zn)
      • 4. Zinc ammonium sulphate(33.5% Zn)
    • Molybdenum carrying fertilizers
      • 1. Sodium molybdate (39.0% Mo)
      • 2. Ammonium molybdate (54.0% Mo)
    • Copper carrying fertilizers:
      • Copper sulphate. (50.0% Cu)
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score
Basic principles of fertilizer application
  • Fertilizers are chemically reactive substances and costly inputs which need to applied carefully either to soil or foliar by adopting scientific methods and principles. Various methods have been used to apply fertilizers to soil or crops and their advantage and disadvantage of application and principles of application need to be understood.

Methods of Fertilizer application
  • Two major methods are used to apply fertilizers
    • I) Application of fertilizers in solid form
      • 1) Broadcast:
        • a) Broadcasting at sowing/planting or before sowing/ planting time
        • b) Broadcasting at later stages of crop growth i.e., top dressing
      • 2) Placement:
        • a) plough sole placement
        • b) Deep placement
        • c) Sub soil placement
      • 3) Localized placement:
        • a) Contact or Combined drilling or drill placement
        • b) Band or hill placement:
          • i) Spot placement
          • ii) Row placement
          • iii) Side dressing
        • c) Pellet application
        • d) Basin application
    • II) Application of fertilizers in liquid forms
      • a) Starter solution: mixed with ratio of 1:2:1 or 1:1:2 of NPK respectively for vegetable Seedlings at the time of transplanting
      • b) Foliar application or spray fertilization: Spraying the nutrient solution with appropriate concentration over the foliage
      • c) Direct application to the soil or plant (injection to soil or plant)
      • d) Fertigation: Application fertilizer through irrigation water (Sprinkler or drip method)

I. Application of fertilizers in solid form
  • Solid fertilizers of straight or complex or mixed NPK fertilizers are directly applied to soil by adopting different methods of application based on the type of crop, season, age of the crop, type of fertilizer and their concentrations.
  • 1. Broadcasting:
    • It is a process where the fertilizer is spread over the entire soil area evenly and uniformly. This may be done before the land is ploughed, before planting or while the crop standing. It may be of two types
      • a. Broadcasting at planting or sowing: During sowing time, fertilizers are uniformly spread over the soil and mixed properly.
      • b. Broadcasting as top dressing: Followed for closely spaced crops. It may be made at the time of critical crop growth period. It is essential to note that the fertilizers are not to be applied when the leaves of plants are wet. This may create injury to the leaves or direct fall of fertilizer granules like urea or KCl on leaves leads to leaf scorching
    • Advantage: Easy, simple, less cost (Labour), no special equipment, large quantity of fertilizer can be applied.
    • Dis-advantages: (Over placement)
      • 1) Uneven distribution of fertilizer which causes a ranked (un uniform) growth of crop
      • 2) Loss of nitrogen through volatilization, erosion
      • 3) It requires relatively large quantity of fertilizers.
      • 4) Costly fertilizers cannot be applied by this method, requires experience and skill of application.
      • 5) Fixation of nutrients especially PO4 and K due to contact of large volume of soil compare to that of placement.
      • 6) Stimulates the more weed growth
  • 2. Placement:
    • Fertilizers are placed in the soils irrespective of the position of seed, seedling or growing plants before sowing or after sowing the crops. The following methods are most common;
      • a) Plough- sole placement: It is applied in a continuous band at the bottom of the furrow during the process of ploughing
      • b) Deep placement: It is specially followed in paddy fields for placement of N fertilizers ((NH4)2SO4 and urea) in the reduced zone. It prevents loss of ammonia and makes the nutrient easily available to crop. The fertilizer is applied under the plough furrow in the dry soil before flooding the land and making ready for transplanting.
      • c) Sub soil placement: It is recommended in humid and sub humid regions where sub soils are strongly acid. P & K fertilizers are used.
      • d) Localized placement: Application of fertilizers in to the soil close to the seed or plants in bands or in pockets. Only small quantities of fertilizers are applied. It reduces fixation of P & K. It includes
        • i) Drill placement or contact placement or combined drilling: Drilling of seeds and fertilizers together while sowing in the same row. Old method and useful for PO4 and potash fertilizers in rainfed areas.
        • ii) Band or hill placement: When the plants are placed 3 feet or more on both sides fertilizers are placed close to plants in bands on one or both sides of the plant. It is practiced for N & P Fertilizers to orange, banana, papaya, apple, pear, coconut, cashew nut and other fruit trees.
        • iii) Row placement-Fertilizers are applied in rows
        • iv) Side dressing- Fertilizers are applied between the rows (followed for Vegetables and fruit crops)
        • v) Pellet application – Make pellet form (1:10 ratio of fertilizer (N) & soil and make it to dough) and apply to soil.
    • Advantages of placement/Banding
      • 1) Fixation of nutrients appreciably reduced.
      • 2) Never harms plants and seeds.
      • 3) No weed growth (weeds do not get nutrients)
      • 4) There is no volatilization loss of N
      • 5) It gives better residual effects and every unit of nutrient is effectively utilized (better FUE)
      • 6) Smaller quantities of fertilizers can be effectively applied; both solid and liquid fertilizers are applied.
      • 7) It is best method for P & K application.
      • 8) It is useful for widely spaced crops, quick growing crops, dry land crops.
    • Dis advantage: High labour cost and requires specialized equipments.

II. Application of fertilizers in Liquid form
  • Solid form of fertilizers with known concentrations are dissolved in definite volume of water and sprayed over the leaves. Commercially liquid fertilizer solutions are available in the market may be applied to the plants or soil directly. Various methods are used to apply the fertilizer in liquid form.
    • i) Starter solution: Fertilizer solutions are prepared by dissolving the fertilizers in water at the ratio of 1:2:1 or 1:1:2 of N: P2O5: K2O and applied to young vegetable plants at the time of transplanting. It is used in place of watering which helps in better establishment & early growth of plants. Only small amount of fertilizer is needed.
    • ii) Foliar application: Spraying over the leaves of growing plants with suitable fertilizer solutions of lower concentrations (recommended) to supply one or combination of nutrients. Most of the micronutrient fertilizers (Zn or Boron) are applied as foliar spray and urea is also used for foliar spray.
    • iii) Direct application of Liquid fertilizers to soils: Liquid anhydrous ammonia or N, P, K fertilizers are applied to soils (10 cm depth) with the help of special equipment. Plant injury or wastage of ammonia is very much limited.
    • iv) Fertigation: It is the process of direct application of liquid fertilizers through irrigation water. Straight and mixed fertilizers of N P K which are easily soluble in irrigation water can applied through furrow or drip irrigation or sprinkler irrigation system.

Advantages of liquid forms of fertilizers
  • 1) Under acute deficiency of elements like N, P, K, and micronutrients during active growth period of plants can be corrected.
  • 2) Rapid plant absorption, quick response and for fruit trees more efficient and effective method.
  • 3) Along with fertilizer solutions we can apply insecticides and herbicides with sticking agents and also some soil amendments like lime and gypsum.
  • 4) Small amount/concentration of nutrients can be used.
Disadvantage of liquid forms
  • 1) Sometimes fertilizer solutions causes scorching or burning of leaves due to presence of acids in it like ammonium sulphate or chlorides in KCl fertilizer
  • 2) It is more expensive/ costly.
  • 3) Several applications are needed for moderate to high fertilizer rates.
  • 4) All the fertilizers cannot be applied. Ex: Ammonium sulphate is unsuitable for foliar spray.

Basic principles of fertilizer application
  • Nitrogen fertilizers must be applied in split doses so that the N loses through leaching and washing could be reduced as nitrogen being readily soluble and highly mobile.
  • Except in acidic and highly alkaline soils, the PO4 must be applied in one dose as basal placement but in acidic soils RP, bone meal or basic slag may be applied at least a fortnight before sowing or crop planting whereas in alkaline soils spraying of PO4 has given better results.
  • The potassic fertilizers should be applied in a single dose but split application along with N as top dressing has given better response in heavy soil types.
  • Sandy soils need split application of N and K
  • A combination of organic manures and fertilizers is always beneficial for achieving highest nutrient recovery and best fertilizer use efficiency.
  • Mixed or complex fertilizers should be applied as basal before sowing or planting.
  • Soil amendments and soil conditioners should always be applied at least one month before sowing or planting of crops through broadcasting or proper mixing in to the soil.

Integrated Plant Nutrient Management System (IPNMS)

  • IPNM is the intelligent and combined use of inorganic, organic and biological resources so as to sustain optimum yields, improve or maintain the soil chemical and physical properties and provide crop nutrition packages which are technically sound, economically attractive, practically feasible and environmentally safe. The principal aim of the integrated approach is to utilize all the possible sources of plant nutrition in a judicious and efficient manner.
Concept of IPNMS
  • The basic concept of IPNMS is the promotion and maintenance of soil fertility for sustaining crop productivity through optimum use of all possible sources of nutrients like organic, inorganic and biological in an integrated manner appropriate to each farming situation. Improvement of soil fertility and productivity on sustainable basis through appropriate use of fertilizers and organic manures is the key principle and their scientific management for optimum growth and yield of crops in a specific agro ecological conditions.

Main objectives of IPNMS or INM
  • 1. To reduce the dependence on chemical fertilizers.
  • 2. To maintain productivity on sustainable basis without affecting soil health.
  • 3. To conserve locally available resources & utilize them judiciously.
  • 4. To reduce the gap between nutrients used & nutrients harvested by the crop.
  • 5. To improve physical, chemical & biological properties of soil.
  • 6. To make soil healthy by providing balanced nutrients through different nutrient sources.
  • 7. To overcome or reduce the ill effects of continuous use of only inorganic chemical fertilizers.
  • 8. To improve economical status of farmers.
  • 9. To increase the fertilizer use efficiency (FUE).

Components of IPNM
  • IPNM mainly emphasizes the integrated use of all the essential nutrients from different sources like chemical fertilizers, organic manures, green manures, bio-fertilizers, legume crops, locally available plant resources in a balanced proportion for sustainable soil health and productivity.
  • I) Use of inorganic fertilizers:
    • They are very important for sustaining and increasing food production. Different kinds of fertilizers are commercially available in the market for all the major and micronutrients. However, they are costly inputs and their excessive use may deteriorate the soil quality and food quality. Hence, there is a need to improve their use efficiency through efficient and balanced fertilizer management and essentially follow the four R’s formula for judicious and effective nutrient/fertilizer management. They are
      • Ø Right Type of fertilizers.
      • Ø Right Dose of fertilizers.
      • Ø Right Method of application.
      • Ø Right Time of application.
  • II. Use of organic manures/ materials:
    • Due to intensive cultivation of soil and less organic manure application, the soils are low in organic matter status. A decrease in soil organic matter results in compact soil, poor aeration and low infiltration and water holding capacity and also low fertility status. The organic matter status in soils can be improved and maintained by constant addition of organic manures such as FYM. compost, green manures, poultry manures, vermicompost, oilcakes etc., Organic matter is good source of macro and micro nutrients, and more over improves physical, chemical and biological properties soil.
  • III. Use of biological sources/biofertilizers:
    • Biofertilizers are cultures of micro organisms (bacteria, fungi, algae). Their use benefits the soil and plants growth by providing N & P and also brings about the rapid mineralization of organic materials in soils. They are capable fixing N, solubilizing and mobilizing the phosphorus and mineralizing organic matter in soil. Their incorporation improves the physical and biological properties of soils.
  • IV. Maintaining the physical properties of soil:
    • Physical properties such as soil aggregation, soil texture, structure, aeration, water holding capacity (WHC), infiltration rate, etc., should be maintained regularly through better cultivation practices and organic manure applications to maintain soil fertility & nutrient availability.
  • V. Management of problematic soils:
    • Problematic soils such as acid soils, saline and alkaline soils, water logged soils are known to decrease the productivity of the soil. Acid soil having the problems like toxicities of Iron, Mn, Al, deficiency of P & Mo. Similarly, saline and alkali soils showing the deficiency of Fe, Mn, Zn and Cu and also toxicities of Mo. These soils should be regularly managed and reclaimed through the application of soil amendments such as lime for acid soil, gypsum for alkali soils and other organic and inorganic materials based on soil test results. It helps to improve soil fertility and productivity and sustain the yield.
  • VI. Better/Judicious water management practices:
    • Plants absorb the nutrients from the soil only in a dissolved state and sufficient moisture is therefore required for utilizing the nutrients of the soil. Management of moisture in the soil by improved and modern irrigation techniques like drip or sprinkler or basin where the rainfall is low and draining the soil where it is subjected to stagnation of water helps to increase water and nutrient availability to the crops.


This is all from a free online study from India. It can all be found here:
Last edited:


Mixing light is fun!
Mar 3, 2017
Reaction score


son of soil
Oct 11, 2013
Reaction score
wow! quite the read, I'll have to come back to this, a few times! Having built my soil from silt and compost there is a lot here I'm familiar with, but mostly overwhelmed by how much info is here