The influence of annual and perennial irrigated pastures on soil fertility as shown by the yield and quality of a subsequent wheat crop

Abstract

Three annual and three perennial pastures produced on a red-brown earth and consisting respectively of a legume, a grass, and the same grass supplied with fertilizer nitrogen were ploughed up and sown to wheat. The physical properties of the various pasture soils after cultivation were similar. After perennial pastures the yields of wheat were greater than after annual pastures. Nitrogen applied to the wheat crop at the rate of 112 kg/ha cancelled the differences in grain yields, which indicated that differential mineralization of nitrogen following annual and perennial pastures caused the yield differences. The observed differences in yield were unrelated or poorly related to simple chemical estimates of available nitrogen. The amounts of nitrate present after 2 weeks' incubation of the soils collected at sowing were greater after perennial pastures, and were related to the vegetative yields, the number of fertile tillers, grain yields, and the nitrogen uptake of the wheat crop. At all levels of available nitrogen, there was a 2 : 1 ratio between nitrogen in the grain and in straw plus chaff. Grain protein and gluten protein contents increased with nitrogen uptake and were inversely related to the extent of mottling.