Agronomic studies on soybean (Glycine max (L.) Merrill) in the dry seasons of the tropics. I. Limits to yield imposed by phenology

Abstract

An analysis was undertaken of the development, growth and seed yield of irrigated soybean crops grown during the dry season of the semi-arid tropics in north-western Australia, to establish yield potentials and identify major climatic or physiological constraints. Ten tropically adapted genotypes were grown at three sowing times, using agronomic management practices designed to maximize productivity and minimize constraints due to water supply, fertility, weeds and insects. In addition to phenology, seed yield, dry matter (DM) accumulation, and seed and plant morphological traits, measurements were made at the beginning and end of flowering of DM accumulation, leaf area development and interception of photosynthetically active radiation (PAR). Harvest indices were generally large, but maximum seed yields were only c. 3 t ha-1, apparently because of inadequate biomass production. The analysis of growth and development suggested that DM accumulation during the vegetative phase was limited primarily by cumulative PAR interception by the crop canopy rather than the efficiency of conversion of intercepted PAR. In turn, both cumulative PAR interception, and canopy leaf area development, were constrained by precocious flowering, induced by the comparatively short-day/warm temperature conditions of the dry season. It was concluded that yield improvement strategies for the dry season will need to be based on agronomic and/or breeding strategies to enhance canopy development and improve biomass production.