PLANT-POPULATION STUDIES ON PEANUT (ARACHIS-HYPOGAEA L) IN SUBTROPICAL AUSTRALIA .1. GROWTH UNDER FULLY IRRIGATED CONDITIONS

Effects of plant density and spatial arrangement on growth and yield responses of 4 peanut cultivars were examined under fully irrigated conditions at Kingaroy, south-eastern Queensland (26-degrees-33'S., 151-degrees-50'E.). Cultivars represented either the Spanish or Virginia botanical type. Spanish cultivars had either very early (Chico) or early (McCubbin) maturity, while Virginia cultivars had either medium (Early Bunch) or very late (Mani Pintar) maturity. The interaction of plant density (44 000-376 000 plants/ha) with sowing date was assessed in 3 sowings in 1984-85 (S1, 1 November; S2, 5 December; S3, 15 January), with a further sowing in 1985-86 (S4, 21 November). The interaction of plant density and spatial arrangement was assessed in 1985-86. Total dry matter (TDM) and pod yields showed highly significant (P < 0.01) linear and quadratic responses to increasing plant density. Cultivars differed in their response to density. McCubbin, Early Bunch and Mani Pintar showed no responses to increased density above 88 000 plants/ha, while maximum TDM and pod yields of Chico were recorded at 352 000 plants/ha. Sowing date had no significant effect on the response of any cultivar to plant density. However, all cultivars except Chico produced significantly less TDM and pod yield in S3, due to cool temperatures and/or frosts terminating growth. A 1:1 (square) planting arrangement produced significantly greater pod yields and more TDM than the conventional commercial practice of rows 90 cm apart. Planting in a double-row arrangement (20 cm between 2 rows) based on 90 cm centres produced intermediate pod and TDM yields. A simple model was used to describe the effects of plant density and sowing date on yield, and proved useful for highlighting differences among cultivars and sowing dates. A limitation of the model was a tendency to overestimate pod yield at low plant density in Spanish cultivars, where the harvest index declined at very low plant densities.