Bc. Pengelly et al., Radiation interception and the accumulation of biomass and nitrogen by soybean and three tropical annual forage legumes, FIELD CR RE, 63(2), 1999, pp. 99-112
Field experiments were conducted at Gatton and Dalby in southeastern Queens
land to determine parameters associated with radiation interception and bio
mass 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 soybe
an (Glycine max (L.) Merrill)) were included in the study for comparison. T
he most important differences between species related to differences in rad
iation interception, radiation-use efficiency (RUE), N-accumulation efficie
ncy 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 vign
a (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 (0.0122 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 m
ore rapid in soybean than in sesbania and phasey bean. Despite this decline
in total N partitioned to the leaves, both soybean and phasey bean maintai
ned a relatively stable specific leaf nitrogen (SPLN) throughout the experi
mental periods although sesbania and vigna displayed rapid decreases in SPL
N. 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-accum
ulation in the water-limited environments of the grain belt of eastern Aust
ralia 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. (C) 1999
Elsevier Science B.V. All rights reserved.