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 simulat ion study to quantify the magnitude of improvement in yield potential at di fferent 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 indi cates that in warm conditions, particularly during grain-filling period, th ere 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 obser ved yields in field experiments. The simulated rate of change in yield was always greater in the potential production conditions compared to the modes t level of management as is practiced today. Simulation always showed a neg ative 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 duratio n that extends grain-filling to high temperatures. Crop seasons that favore d long vegetative duration or had high March temperatures that shorten grai n-filling showed a negative trend in yield improvement whereas seasons with cool March showed a positive improvement. Conclusions based on limited exp erimentation in field studies, therefore, can be biased depending upon the agro-environment experienced by the cultivars. Simulation studies can suppl ement such field studies and assist in reducing this bias. (C) 2000 Elsevie r Science B.V. All rights reserved.