Soil Fertility and Nutrient management (1+1)

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

1) SOIL TEST CROP RESPONSE (STCR)
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;
1. Nutrient requirement (NR) in kg/ quintal of the produce
2. Percentage contribution from soil available nutrients (SE)
3. Percentage contribution from added fertilizers towards making effective fertilizer prescriptions for specific yields.
    

    i)          Nutrient Requirement (NR)                                  =        Total nutrient uptake (grain+straw) kg/ha     
              (in kg for producing  1 Quintals of grain)                                         Yield of grain (q/ha)
   
ii)          Fertilizer Efficiency (FE in %)          =   Total nutrient uptake (kg/ha)-soil test value in treated Plot (kg/ha) X soil nutrient efficiency (%) X 100
                                                                                                                               Fertilizer dose applied (kg/ha)     
    
     iii)          Soil Efficiency (SE in %)                 =          Total nutrient uptake in control kg/ha X 100
                                                                                                      Soil test value in control kg/ha
With the help of above parameters, adjustment equations have been developed for a number of crops in various soils.
E.g.: 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.
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