Analysis of Growth and Yield of Winter and Spring Wheats

In a field experiment to investigate the physiological causes of variation in yield between autumn- and spring-sown wheat and between old and new varieties, the grain yields of the winter wheats were 3-15 per cent, greater than of the spring ones and the new varieties Cappelle-Desprez and Jufy I yielded 40-70 per cent, more than Squarehead's Master and Atle. Nitrogen fertilizer increased the yields of Cappelle-Desprez and Jufy I more than of Atle, and decreased the yield of Squarehead's Master by making it lodge. Until ear emergence the winter varieties had greater leaf-area indices (L) and dry weights, but smaller net assimilation rates (E), than the spring varieties. Square-head's Master had greater L but smaller E, and similar dry weight to Cappelle-Desprez. Jufy I had similar E to Atlc, but greater L and dry weight. Nitrogen increased L and dry weight, but decreased E. All the differences in E between varieties and nitrogen treatments could be explained by the opposite effects on L, that is to say, the differences in E were caused by variation in mutual shading arising from the differences in L and not by changes in leaf physiology. L of winter wheat reached its maximum at the end of May, but L of spring wheat continued to increase until ear emergence. Afterwards Ldecreased more rapidly for winter than for spring wheat, so that eventually spring wheat had the greater L. These differences in the time changes of L partially compensated for the shorter growth period of spring wheat, and tended to equalize the grain yield from winter and spring sowings. After ear emergence total dry weight of winter varieties continued to be greater than of spring ones, but the difference in dry weight of ears was much smaller because ear: shoot dry-weight ratio was greater for the spring varieties. Total dry weight, ear dry weight and ear: shoot ratio were all greater in the new than in the old varieties. Leaf area duration (D) after ear emergence was slightly greater for the winter than for the spring varieties and similar for old and new. The apparent efficiency of this leaf area in grain production, measured by the grain leaf ratio (ratio of grain dry weight to D), was similar for winter and spring varieties but greater for new than for old. This suggests that Cappelle-Desprez and Jufy I have higher grain yields because their ears photosynthesize more than do the ears of Squarehead's Master and Atle. Before ear emergence winter varieties had more shoots than spring ones, and old varieties more than new. After ear emergence there were only small differences in numbers of ears; percentage survival was greater for spring than for winter and for new than for old varieties. Differences in dry weight between varieties were not caused by differences in nitrogen uptake.