Radiation interception and the accumulation of biomass and nitrogen by soybean and three tropical annual forage legumes

Abstract

Field experiments were conducted at Gatton and Dalby in southeastern Queensland to determine parameters associated with radiation interception and biomass and nitrogen (N) accumulation for the ley legume species, phasey bean ( Macroptilum lathyroides (L.) Urban) and vigna, ( Vigna trilobata (L.) Verdc.). Sesbania ( Sesbania cannabina Retz.), a native legume species, and soybean ( Glycine max (L.) Merrill)) were included in the study for comparison. The most important differences between species related to differences in radiation interception, radiation-use efficiency (RUE), N-accumulation efficiency and the partitioning of N to plant parts. During early growth, soybean intercepted more radiation than the other species, primarily because of its greater leaf area index (LAI). Sesbania had the highest RUE (1.08 g MJ −1) followed by phasey bean (0.94 g MJ −1), soybean (0.89 g MJ −1) and vigna (0.77 g MJ −1). The efficiency of N-accumulation was greater in soybean (0.028 g N g −1) and phasey bean (0.030 g N g −1) than in vigna (0.022 g N g −1) and sesbania (0.021 g N g −1). In all species, the proportion of N allocated to leaves declined throughout the experimental period, being more rapid in soybean than in sesbania and phasey bean. Despite this decline in total N partitioned to the leaves, both soybean and phasey bean maintained a relatively stable specific leaf nitrogen (SPLN) throughout the experimental periods although sesbania and vigna displayed rapid decreases in SPLN. The large variation between species in RUE and N-accumulation efficiency indicates that the development of ley legume cultivars with a combination of traits for more efficient legume production, water use and soil N-accumulation in the water-limited environments of the grain belt of eastern Australia may be possible. The sensitivity of forage production, water use and soil N-accumulation to variation in RUE and N-accumulation efficiency needs to be quantified using modeling techniques prior to embarking on screening programs to select appropriate germplasm for evaluation studies.