Soil Test Calibration

• The objectives of this test are to determine the amount of nutrients that must be added to soil at different soil test levels of that nutrient to obtain maximum yield.
• After the analysis of soils, data are obtained and these data are grouped into different classes.
• This grouping is based on crop responses obtained in greenhouse studies (pot culture).
• The composite soil samples are obtained from the field for pot- culture plant studies to access the crop response to added fertilizers and calibrate response to soil-test value obtained.
• This classification indicates that very low and low classes of soil would markedly response to added fertilizer and the soil of high and very high would not respond to the fertilizer.

Interpretation of the result

• Quantitative associations between an absorbed nutrient and plant growth has been widely studied. However, the big problem is in interpreting the results in terms of fertilizer needed. The degree of accuracy depends on several factors like: (i) knowledge of soil (ii) yield level expected (iii) level of management (iv) weather etc.
• In a particular area, we simply want to know the critical level for a particular nutrient to be added.
• Sufficient amounts of that particular nutrient are added to bring yield to 95% or more of the maximum yield.
• While the concept fits a number of broad situations. It is applied where same pattern and rates of planting, same soil and seasonal conditions were prevailing. But for different condition, different yields may be obtained.
• Today, full ranges in concentration from deficiency to excessive amounts are considered for interpretation. Such interpretation data are obtained from response curve.