Improvement in wheat yields in northern India since 1965: measured and simulated trends

This paper describes results of a three-year field experiment and a simulation study to quantify the magnitude of improvement in yield potential at different levels of management and climatic variability. In two crop seasons for crops planted on time, there was a significant increase of 1.0-1.3% per year in yield of cultivars but it was negligible in the third season when March was relatively warmer. In late plantings done in one season, the rate of improvement in yield varied between -0.16 and 0.57% per year. This indicates that in warm conditions, particularly during grain-filling period, there was only a negligible difference among the cultivars. It suggests that new cultivars yield more than the older ones only when the temperatures are favorable for growth and development. The trends in simulated yields were similar in direction but lower in magnitude compared to the trends in observed yields in field experiments. The simulated rate of change in yield was always greater in the potential production conditions compared to the modest level of management as is practiced today. Simulation always showed a negative trend in yielding ability of cultivars in seasons when grain-filling duration was less than 29 days. When the grain-filling duration exceeded 29 days, the trend in most cases was positive varying up to +0.67% per year. The late-released cultivars used in this study have long vegetative duration that extends grain-filling to high temperatures. Crop seasons that favored long vegetative duration or had high March temperatures that shorten grain-filling showed a negative trend in yield improvement whereas seasons with cool March showed a positive improvement. Conclusions based on limited experimentation in field studies, therefore, can be biased depending upon the agro-environment experienced by the cultivars. Simulation studies can supplement such field studies and assist in reducing this bias