Nitrogen nutrition of cereals in a short-term rotation. II. Stem nitrate as an indicator of nitrogen availability

Abstract

The effect of cultural treatments and fertilizer nitrogen on nitrate nitrogen concentration of cereal steins and the relation between nitrate nitrogen and cereal production were examined in a three-year experiment. Five cultural treatments in the first year were medic or subterranean clover pasture, field beans, oats or bare fallow. These were oversown in the second year with barley, wheat and triticale, with 0, 30, 60 or 90 kg ha-1 of fertilizer nitrogen. Wheat was sown over the whole area in the third season. There were marked differences in nitrate nitrogen concentrations in the second year cereals as a result of the previous cultural treatments and the current application of fertilizer nitrogen. For cultural treatments the concentrations were highest after fallow, intermediate after legumes, and lowest after oats. There was an asymptotic increase in nitrate nitrogen as fertilizer nitrogen increased. The second year had low rainfall, and there was little correlation between nitrate nitrogen concentration and production, but measurements of nitrate nitrogen clearly indicated relative availability of nitrogen. In the third season's wheat crop the residual effects of first year subterranean clover gave highest nitrate nitrogen, but effects of fallow were almost as high. Second year fertilizer had less effect than first year cultural treatments. Grain yield of wheat in the third year was closely related to nitrate nitrogen concentration during early growth stages. This was a year with good rainfall. Measurement of nitrate concentration in plant stems could be useful for determining the need for fertilizer nitrogen.