Reaction of two spring wheat cultivars to nitrogen and sulphur fertilizer in the Swartland. II. Yield and baking quality. A decline in the average protein content of wheat has been experience in the Swartland area over the last decade despite increasing N applications. The importance of the correct N : S ratio raises the possibility that imbalances between Nand S can lead to poor N utilization at high levels of applied N in the Swartland. The spring wheat cultivars Palmiet and SST 66 were planted in a factorial trial on Langgewens Experimental Farm during the 1990 and 1991 seasons to study the combined effect of 0, 12.5,25 and 50 kg S ha-1 and 50, 100 and 150 kg N ha-1 on yield and baking quality. A urea ammonium nitrate mixture was used as a N source while sulphur was applied at sowing time as phospho-gypsum. At the lowest level all N was applied at sowing. At higher N levels the application was split between sowing time, the end of tillering and when in boot. Palmiet had a higher grain yield than SST 66. Almost all the yield components of Palmiet were higher than those of SST 66, except spikelets per ear. An increase in N resulted in more ears m-2 , more spikelets per ear, and a significant increase in the yield. The kernel mass was not influenced by any of the fertilizer treatments, but Palmiet produced larger kernels than SST 66. Seasonal variations, like the amount of rainfall during kernel filling, had a distinct affect on kernel weight. Favourable moisture conditions resulted in higher kernel mass. Sulphur had no affect on the yield or yield components, but in 1990 applications of 12.5 and 25 kg S ha-1 in combination with 150 kg N ha-1 resulted in significant yield increases. The baking quality of SST 66 was better than that of Palmiet. It also had a higher protein content. Increasing N levels resulted in higher protein content, but 150 kg N ha-1 was necessary to increase protein content significantly in 1991. The bread volume of SST 66 was improved by increasing the S from 0 to 25 kg S ha-1 , but above this amount it decreased. Sulphur had no effect on the bread volume of Palmiet. In general N levels of 150 kg N ha-1 increased the bread volume. The importance of having enough S in fertilizer programmes in areas with a high yield potential, and where high levels of N are applied, was shown by this study. The fact that only protein quantity, and not quality, is determined during the grading of wheat, was revealed as a shortcoming of currently used quality evaluation tests.
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