Growth and productivity of irrigated Sorghum bicolor (L. Moench) in northern Australia. I. Plant density and arrangement effects on light interception and distribution, and grain yield, in the hybrid Texas 610SR in low and medium latitudes

Abstract

The influence of plant arrangement and density on yield of the grain sorghum hybrid Texas 610SR grown as an irrigated dry season crop in the Ord Irrigation Area (lat. 16¦S) was determined. Neither the rate of dry matter production nor the pattern of partitioning of dry matter during grain-filling varied between treatments, and grain yield was unresponsive to row spacings below 75 cm and densities above 267000 plants ha-1. The results were analysed by considering the effect of radiation interception and distribution in the canopy on dry matter production. The opportunity was then taken to compare this trial, and two others conducted at the same low latitude where grain yield was unresponsive to density, with four trials conducted at higher latitudes (27¦S.) where Texas 610SR was very responsive to density. The effect is shown to be associated with radiation penetration into canopies. In the low latitude trials the poorer penetration of photosynthetically active radiation (PAR) into high density stands could have resulted from lack of structural adjustment of the canopy, in contrast to the experience at medium latitude. Equally, there may have been an effect of lower solar angles at low latitude, resulting in the poorer PAR distribution. The consequence was a failure of response of dry matter production to increasing density, reflected in grain yield.