Nitrogen nutrition of cereals in a short-term rotation. I. Single season treatments as a source of nitrogen for subsequent cereal crops

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Abstract
The residual effects of one season of five cultural treatments common in southern Australian dryland farming were examined with respect to soil water and nitrogen, and the production of cereals in the next two years. The initial treatments were medic or subterranean clover pasture, faba beans, oats or bare fallow. In the second year barley, wheat and triticale were grown on the same plots, with 0,30,60 or 90 kg ha-1 of fertilizer nitrogen. Wheat was sown over the whole area for the third season. The medic and subterranean clover pastures contributed approximately 100 kg ha-1 of nitrogen in top growth, but this remained on the surface until cultivation. Oats and fallow plots declined in total soil nitrogen by about 70 kg ha-1. The nitrogen content of the faba bean stubble showed that this crop has the potential of providing equivalent nitrogen to a good legume pasture. At the beginning of the second season the previous plots of fallow, beans, subterranean clover and medic had 36,27, 14 and 12 mm more water in the top metre of soil than oat plots. Cereals after oats apparently did not respond to fertilizer nitrogen because of the dry conditions, but on other plots the yield response was not proportional to the additional water. Although first year treatments affected growth of the three cereals in the second season, the new cereal, triticale, showed no evidence of different adaptation to growing conditions than wheat or barley. The effects of first and second year treatments carried through to the wheat crop in the third season. There were marked differences in nitrogen availability, but evidence that the second crop was depleting soil nitrogen reserves. Nitrogen from first year legume residues was available earlier in the season than second year fertilizer nitrogen which had been leached from the surface soil.

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