Evaluation of row spacing and population density effects on grain sorghum over a range of northern Australian environments

Abstract

Fifteen experiments were conducted between 1976 and 1978 to determine the response of grain sorghum to row spacing and population density over a range of soil types, planting dates and seasonal conditions. One experiment was at Kununurra, Western Australia, and the rest were in southern and central Queensland. The trials virtually covered the full range of growing conditions likely to be experienced in the sorghum growing area. Narrow and standard single rows (0.33 m to 1.07 m spacings) yielded as well as or better than more widely spaced (1.50 to 4.27 m) single or twin rows (0.33 or 0.36 m apart) at equivalent population densities over a wide range of yield levels. Only at yield levels below 900 kg ha-l was there a trend for 2.00 or 2.13 m twin rows to outyield the 0.33 or 0.36 m single row spacing. Significant yield reductions resulted in a number of trials, at yield levels above 1600 kg ha-l, from the use of wide row spacings. Where there was severe water stress, grain yields were also reduced by high population densities (>150,000 plants ha-l), particularly at the 0.33 or 0.36 m row spacing. There was no evidence that response to row spacing differed between cultivars. In the one experiment where it was studied, root pruning had no effect on grain yield under conditions of ample moisture supply, but yield was reduced by root pruning of wide row sorghum (1.8 m spacing) under conditions of moisture stress.