Influence of some soil properties on Wimmera wheat yields

Abstract

In two experiments the growth and grain yield of wheat were compared on calcareous grey and brown clay soils, and related to seasonal changes in soil water, mineral nitrogen and labile (mineralizable) nitrogen. The soils occurred at the sites either as a mosaic (experiment 1) or as topographically distinct areas in the same paddock (experiment 2). Soil type did not affect grain yield in either experiment, although the more favourable seasonal conditions in 1971 (experiment 2) resulted in substantially higher yields. In experiment 2, grain protein content was highest on the grey clay, and was associated with a lower lability of organic nitrogen in the brown clay. In both experiments mineral nitrogen was predominantly nitrate. It declined during crop growth to very low levels by flowering; increases during grain ripening were small. The net decline in mineral nitrogen closely approximated plant uptake in both experiments. Losses due to leaching and denitrification appear to be small. Labile nitrogen increased during crop growth, probably as a result of the 'rhizosphere effect'. Soil type affected the depletion of soil water by the crop; consumption was higher in both grey clays, partly due to lower depletion from the subsoils of the brown clays. In experiment 2 this was associated with restricted root development in this zone. In both experiments the crops had depleted soil water to below the - 15 bar level by flowering; stress during grain filling was greatest in experiment 1, and higher on the brown clays.