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AICRP on Soil Test Crop Response

Target Yield Equation

Research & Development


Targeted Yield Concept

Liebig’s law of minimum states that the growth of plants is limited by the plant nutrient element present in the smallest amount, all others being in adequate quantities. From this, it follows that a given amount of a soil nutrient is sufficient for any one yield of a given percentage nutrient composition. Taking a cue from Truog regarding the basis for fertilizer application for targeted yields, Ramamoorthy and co workers in 1967 established the theoretical basis and experimental proof for the fact that Liebig’s law of the minimum operates equally well for N, P and K. Among the various methods of fertilizer recommendation, the one based on yield targeting is unique in the sense that this method not only indicates soil test based fertilizer dose but also the level of yield the farmer can hope to achieve if good agronomic practices are followed in raising the crop. The essential basic data required for formulating fertilizer recommendation for targeted yield are (i) nutrient requirement in kg q-1 of produce, grain or other economic produce (ii) the per cent contribution from the soil available nutrients (iii) the per cent contribution from the applied fertilizer nutrients.

The above mentioned three parameters are calculated as follows:

Nutrient requirement of N, P and K for grain production:

kg of nutrient/q of grain =

Total uptake in control plot (kgha-1)

Contribution of nutrient from soil (CS%)=Soil test values of nutrient in control plot (kgha-1)× 100

Contribution of nutrient from fertilizer (CF)

=Total uptake of nutrients in treated plots – (Soil test value of nutrients in fertilizer treated plots × CS%)

Contribution from Fertilizer (CF %) =  × 100

Calculation of fertilizer dose:

The above basic data are transformed into workable prescription equation as follows:

Fertilizer dose = × 100 × T – × soil test value

= a constant × yield target (q/ha) – b constant × soil test value (kg/ha)

Targeted yield concept strikes a balance between fertilizing the crop and fertilizing the soil. The procedure provides a scientific basis for balanced fertilization and balance between applied nutrients and soil available nutrients. In the targeted yield approach, it is assumed that there is a linear relationship between grain yield and nutrient uptake by the crop and for obtaining a particular yield, a definite amount of nutrients are taken up by the plant. Once this requirement is known for a given yield level, the fertilizer needed can be estimated taking into consideration the contribution from soil available nutrients.

Use of Targeted Yield Equation and Development of Prediction Equation for Cropping Sequence

Nutrient availability in the soil after the harvest of a crop is much influenced by the initial soil nutrient status, the amount of fertilizer nutrients added and the nature of the crop raised. But recently, the monoculture is replaced by cropping sequence approach. To apply soil test based fertilizer recommendations, the soils are to be tested after each crop, which is not practicable. Hence it has become necessary to predict the soil test values after the harvest of the crop. It is done by developing post-harvest soil test value prediction equations making use of the initial soil test values, applied fertilizer doses and the yields obtained or uptake of nutrients following the methodology outline by Ramamoorthy and coworkers in 1971. The post-harvest soil test values were taken as dependent variable and a function of the pre-sowing soil test values and the related parameters as yield/uptake and fertilizer nutrient doses. The functional relationship is as follows:

Prediction Equations for Cropping Sequences:

The method of calculation for prediction of post-harvest soil test values for cropping sequences is given below for use by each center:

YP/H = f (F, IS, yield/nutrient uptake)

Where,YP/H is the post-harvest soil test value, F is the applied fertilizer nutrient and IS is the initial soil test value. The mathematical form is

YP/H = a + b1F + b2 IS + b3 yield/uptake

Where, a is the absolute constant and b1, b2 and b3 are the respective regression coefficients. Prediction equations for post-harvest soil test values were developed from initial soil test values, fertilizer doses applied and yield of crops/uptake of nutrients to obtain a basis for prescribing the fertilizer amounts for the crops succeeding the first crop in the cropping sequence.



All the seventeen cooperating centers viz. Barrackpore (West Bengal), Bengaluru (Karnataka), Bhubaneswar (Odisha), Bikaner (Rajasthan), Coimbatore (Tamil Nadu), Hisar (Haryana), Hyderabad (Telangana), Jabalpur (Madhya Pradesh), Kalyani (West Bengal), Ludhiana (Punjab), New Delhi (Delhi), Palampur (Himachal Pradesh), Pantnagar (Uttarakhand), Pusa (Bihar), Rahuri (Maharashtra), Raipur (Chhattisgarh) and Vellanikkara (Kerala), have generated technologies for integrated supply of plant nutrients involving fertilizers, organic manures and biofertilizers. In this technology, the fertilizer nutrient doses are adjusted not only to that contributed from soil but also from various organic sources like FYM, green manure, compost crop residues and bio-fertilizers like azospirillum and phosphobacteria. As the present requirement of chemical fertilizers is 32 million tonnes and only 22 million tonnes of chemical fertilizers are being used, a shortage of 10 million tonnes is occurring and hence combined use of chemical fertilizers along with organics becomes inevitable. In addition to this, application of organics will help in sustaining the soil productivity and maintaining the soil health by way of improvement of soil physical, chemical and biological properties. The work done by various centers for development of IPNS targeted yield equations has been detailed as given below:

Methodology of IPNS using STCR Calibration

As in the regular STCR studies, the field experiment consisted of two parts- first, creating artificially a large variation in fertility status by applying three graded dose of N, P and K fertilizers to three strips and by growing a gradient crop to stabilize the treatments. The levels of P and K were fixed based on P and K fixing capacities of soils. Secondly, test crops were grown following fractional factorial design with treatments consisting of varying levels of N, P, K; two to three levels of organic manures and absolute controls.

The test crops were grown up to maturity and harvested. The yields of economic produce were recorded. The available NPK before initiation of the experiment and the concentrations of NPK in the plant samples collected at harvest were chemically analyzed. Using the concentrations and yield data, the total uptake of NPK by the test crops were calculated.

Basic Parameters

Making use of the data generated in the test crop experiments, the nutrient requirement (NR) in kg q-1 of economic produce, per cent availability of soil available nutrients (CS) as measured by soil tests, per cent availability of the fertilizer nutrients (CF) and per cent availability of organic nutrients (CO) were computed. The methods of calculation of basic data are furnished below:

Kg N / P2O5/ K2O required per 100 kg of economic produce (NR) = Total uptake of N/ P2O5/ K2O (grain +straw) in kgha-1
Yield of economic produce in 100 kgha-1


Contribution of N / P2O5/ K2O from soil (CS) =  

Total uptake of N / P2O5/ K2O (grain + straw) in kg ha-1 in control plots

STV of available N or P x 2.29 or K x 1.21 kg ha-1 in control plots



Contribution of N / P2O5/ K2O from Fertilizer   (CF) = Total uptake of N / P2O5/ K2O in fertilized plots in kg ha-1 STV of N or P x 2.29 or K x 1.21 in fertilized plots in kg ha-1 x mean CS of N / P2O5/ K2O
Fertilizer  N / P2O5/ K2O applied in kg ha-1


Contribution of N / P2O5/ K2O from Organics (CO) =


Total uptake of N / P2O5/ K2O in organic plots in kg ha-1 STV of N or P x 2.29 or K x 1.21 in organic plots in kg/ha x mean CS of N / P2O5/ K2O
Amount of N / P2O5/ K2O added as organics in kg ha-1

The above-calculated parameters are transformed into the fertilizer prescription equation as given below.

F = T x NR/ CF – CS x STV/ CF – CO x M/ CF



F = Fertilizer dose of N, P2O5 or K2O in kg ha

T = Yield target in q ha-1

NR = Nutrient requirement of N, P2O5 (P x 2.29) or K2O (K x 1.21) for 100 kg economic produce.

CS = Contribution from soil nutrients in fraction

CF = Contribution from fertilizer nutrients in fraction

CO = Contribution from organic nutrients in fraction

STV = Soil available nutrients N, P2O5 (P x 2.29) or K2O (K x 1.21) determined through soil analysis

M = Nutrient content in organic matter N, P2O5 (P x 2.29) or K2O (K x 1.21) determined through organic matter analysis FYM




The STCR project is expected to provide a scientific back-up for the state soil testing laboratories either to replace or modify the existing methods for determination of N, P and K nutrient status and suggest new approach or method of refining or fine-tuning the fertilizer recommendations on the basis of the results of the research conducted by different centers.

Soil testing is the best means to know the nutrient status of soils and assess the fertilizer requirements for a crop or cropping system. Soil test crop response project employs targeted yield concept to work out fertilizer nutrient requirements to obtain a desired yield. Fertilizer prescription equations were generated incorporating nutrient requirement of crop and fraction of soil and fertilizer nutrients utilized. These targeted yield equations were tested in follow-up trials and frontline demonstrations on farmers’ fields. In this section numerous examples where balanced fertilizer use based on targeted yield approach helped to produce higher crop yields and obtain higher benefit: cost ratios have been presented. These follow-up trials also revealed that soil test based recommendations help to efficiently use available resources, maintain soil fertility and practice integrated plan nutrient supply to crops.


The extent of any crop responses to any particular nutrient depends not only upon the particular nutrient status but also upon the deficiency or sufficiency status of other essential plant nutrient in soils. So the real crop response to N, P and K cannot be realized if any one of the essential plant nutrients is in short supply. Furthermore, the magnitude of response of crops to applied nutrients is largely controlled by the extent/emergence of constraint of one or more nutrients during the crop growth as a result of their continuous depletion by heavy crop harvest; or their imbalance/suboptimal or no use. The response (kg grain per kg-applied nutrient) to fertilizer nutrient has been decreasing with time and it is more so during 1980’s after the decontrol of fertilizers. Soil Test Crop Response Correlation Project has generated targeted yield equations and calibration charts for targeting higher yield and recommending fertilizers on the basis of soil tests.


Schedule Tribe Component (erstwhile Tribal Sub Plan, TSP) is a programme funded by Government of India to uplift the economic condition of tribal farmers. It was first started in the 5th Five Year Plan to have a focused emphasis on the integrated development of the tribal areas and the communities. With the fast developing world, tribals required specific attention not only with monetary allocation but along with special interventions for their rapid socio-economic development. It required an integrated approach of all departments in a united manner and not works in isolation. The Schedule Tribe Component envisages reducing gaps between the tribal and non-tribal in health, education, communication and other areas of basic amenities of life by providing legal and administrative support. The Sub-Plan also implements income-generating schemes to boost the income of the tribals on a sustainable basis by taking into account their aptitude and skill. All India Coordinated Research Project on Soil Test Crop Response (AICRP on STCR) has implemented TSP across the country in various tribal belts since 2012-13.