Extraneous factors affecting cumulative yields in long-term fertilizer experiments

In the long-term experiments the yield of any crop in the system is a function of both controllable and uncontrollable factors and is also related to the yield of the preceding crop, plotwise residuals and magnitude of the available soil nutrients. Under such situations analysis of covariance technique can play a vital role in identifying various factors influencing the current crop yields. The technique was applied on the data of each crop in the cropping systems at Ludhiana(1981–96) and Bangalore (1987–97) centres under the Long-Term Fertilizer Experiments project of ICAR taking plotwise preceding crop yields/residuals or available soil nutrients as covariates. The linear, quadratic, logarithmic and reciprocal relationships of soil parameters and combinations thereof as co-variates were also considered. The results revealed that plotwise residuals at Ludhiana and residuals as well as different relationships of available soli nutrients at Bangalore influenced the succeeding crops of wheat and ragi respectively by considerably reducing the coefficient of variation in different years at these places.