Increased responsiveness of short oat cultivars to early sowing, nitrogen fertilizer and seed rate

Abstract

Oat cultivars of tall (West), intermediate (Mortlock) and dwarf height (Echidna) were compared for their response to sowing time, nitrogen fertilizer and seed rate. Experiments were carried out in the 500-800 mm average annual rainfall zone in Western Australia at nine sites. Cultivars were compared in experiments involving different times (3) of sowing, levels (5) of applied nitrogen and rates (5) of seed and in another experiment including all combinations of two levels of sowing time, nitrogen and seed. The optimum sowing times for the three cultivars were similar, but the yield advantage for Echidna over West was 0.63 t ha-1 for late May sowing but only 0.25 t ha-1 for sowing in late July. Yield responses to applied nitrogen were dependent on soil nitrogen status, seasonal rainfall, sowing date, cultivar and seed-rate. On average, Echidna was more responsive (0.42 t ha-1) to the initial 30 kg ha-1 of nitrogen than Mortlock (0.23 t ha-1). The optimum seed rate (where an increase of 1 kg of seed increased yield by 10 kg ha-1) was 77, 67 and 61 kg ha-1 for Echidna, Mortlock and West corresponding to 225, 185 and 160 plants m-2. The largest yielding combination of cultivar, time of sowing, nitrogen and seed rates increased yields by from 1.32 to 3.23 t ha-1 (51-220%) compared to the control or low input treatment. Biomass at heading increased linearly to about 6.5 t ha-1 with rainfall up to 200 mm. Rainfall to heading in excess of 200 mm appeared to be inefficiently used for biomass production. Grain yields also increased linearly up to about 4 t ha-1 with increasing biomass at heading and up to 6 t ha-l with the correct choice of cultivar, time of sowing, nitrogen and seed rates.