Impact of Soil and Climate On Long-Term Yield Trends of Rice-Rice System In India.

Rice-Rice system (4.67 mha) is second major cereal-based cropping system of India after rice-wheat (9.18 mha) and dominates southern and eastern part of India.  Based on time trends analysis of yield at long term experiments, several studies have reported stagnation or decline in the yield of rice crop, mainly due to nutrients deletion in soil or change in climatic conditions. However, nobody in India has reported a comprehensive study on yield trends in rice-rice system and its relationship to change in soil and climate. The objectives of this study, therefore, were to test the hypothesis that (1) a declining trend of grain yield in rice-rice system in 0NPK (no fertilizer) and NPK (recommended fertilizer dose) treatments and NPK+FYM (50% NPK+50% NPK from farm yard manure) treatment slows down the declining yield trend, and (2) to assess the impact of change in soil and climate on grain yield of rice crop. We have analyzed yield time trends (18-25 years) of 0NPK, NPK and NPK+FYM treatments of long term experiments of eight locations using least square linear regression and SAS Meta analysis. In site-wise analysis, we found that yield trends were varying from negative to positive with majority of sites showing significantly positive trends in NPK and NPK+FYM treatments. Overall, the yield trends remained neutral in 0NPK and significantly positive in NPK (r²=0.51**) and NPK+FYM ((r²=0.55**) treatments. There was no significant effect of treatments (especially NPK+FYM) on status of organic carbon, P and K in soil. Though, an increase in yield is witnessed after 6-8 years of continuous application of FYM with NPK.  Site wise regression analysis of soil nutrients (OC, P and K) and system yields showed a overall negative trend in all treatments. Significant decrease in wind speed over the years had significant positive impact on yield of rice at 6 sites (out of 8) in wet and dry seasons.