The influence of sowing date on the yield of grain sorghum in a short summer rainfall environment

Abstract

Sowings of Hegari grain sorghum were made during the rainy season at Katherine (14.3�S, 132.3�E), for 78 consecutive days beginning on December 7, and at a second site for 41 consecutive days beginning on December 16. In the following season 16 sowings were made approximately twice a week. The experiments were conducted under natural rainfall. The yields for December sowings were higher than for January sowings, and there was a steady decline with February sowings. There were marked fluctuations in yield with sowing date. Internode numbers were higher with December than January sowings and presumably influenced the size of head initiated. The decline in daylength could account for the difference between December and January sowings. The fall-off in yield with February sowings was due mainly to diminishing soil moisture supply. There was a negative correlation between saturation deficit about 12 days after anthesis and grain yield, and the evidence strongly suggests that atmospheric dryness during grain development might have appreciable influence on grain yield. There was a strong association between total grain number and yield. In the sowings up to the end of January more than 50 per cent of the grain was large, but with February sowing the proportion of smaller grain increased.