Effect of plant density and spatial arrangement on the yield of Leucaena leucocephala cv. Peru in subcoastal south-eastern Queensland

Abstract

Leucaena (Leucaena leucocephala cv. Peru) was sown at 5 plant densities with 2 spatial arrangements at Brian Pastures Pasture Research Station, Gayndah, to determine the effects of these factors on leucaena and inter-row grass dry matter yield. During the 2 year establishment phase, yields of edible leucaena (leaves, pods, flowers and stems to a diameter of 5 mm) averaged 4400 and 2440 kg/ha respectively. Yields in subsequent years stabilised to an overall mean of 1360 kg/ha, with the amount of edible leucaena increasing with increasing leucaena plant density from 640 to 2260 kg/ha at 6000 and 62 500 leucaena plants/ha respectively. Edible leucaena yield for the mean of the 5 plant densities was increased by 38% when row spacing was doubled. Yields of both total and senesced leucaena were directly related to the annual rainfall. At the end of each growing season in May, edible leucaena yield remained stable between rainfall extremes of 492 and 878 mm while the amount of senesced leucaena litter increased. Edible leucaena yield was directly related to leucaena plant density (R2= 0.86). Annual total leucaena yield (edible leucaena yield plus leucaena litter) was best related to the plant parameters leucaena plant volume (R2 = 0.92), leucaena stem numbers (R2 = 0.90) and leucaena stem diameter (R2 = 0.90). Number of green panic (Panicum maximum var, trichoglume) shoots showed a marked increase at the 3 higher leucaena densities (mean of 28 shoots/m2) compared with the 2 lower leucaena densities (mean of 7 shoots/m2). Total soil nitrogen also increased at the 3 higher leucaena densities (mean of 0.186%) relative to the 2 lower leucaena densities (mean of 0.170%). Inter-row grass and grass litter yields both declined from 4640 and 4010 kg/ha to 31 10 and 2420 kg/ha respectively with increasing leucaena density. Maximum yields of edible leucaena were obtained when leucaena was grown at a density of 62 500 plants per ha in rows 0.8 m apart.