Green manuring legume pasture for aerial-sown rice

Abstract

The potential for suppling a portion of the required nitrogen (N) for aerial-sown rice crops by green manuring legume pasture was investigated in southern New South Wales. Green pasture material could be the source of up to 300 kg N/ha in the southern New South Wales ricegrowing systems. Three experiments were conducted over 2 seasons. Each included 3 land preparation treatments (fallow, pasture removed, pasture incorporated) split for 5 rates of N (0, 40, 80, 120, 160 kg N/ha) applied as urea immediately before flooding for aerial sowing. In all experiments fallow resulted in lower anaerobic incubation soil ammonium levels at flooding than the pasture-incorporated treatment. When the fallow was extended, N losses led to a decrease in grain yield. The incorporation of green manure resulted in an increase in grain yield at the nil N rate in experiment 1, where soil N levels were comparatively low and seasonal temperatures average. In experiment 2, where soil N levels were high and the temperatures before panicle initiation below average, the incorporation of green manure reduced total dry matter and increased per cent unfilled grain. Land preparation treatments did not affect total dry matter or grain yield in experiment 3, where a short season variety was grown and all treatments lodged severely. Grain yields in all experiments were affected by a season x soil fertility x variety interaction.