GROUNDNUT GROWTH AND DEVELOPMENT IN CONTRASTING ENVIRONMENTS. 1. GROWTH AND PLANT DENSITY RESPONSES

Data from studies of growth and development, and response to plant density in common groundnut (Arachis hypogaea) cultivars were examined from published studies. Data were available from the humid tropics of Indonesia, the semi-arid tropics of north-west Australia and the humid coastal and inland elevated areas of north-east Australia. Temperature and irradiance played a major role in determining crop duration, individual plant size and partitioning of dry matter to pods across environments, and these plant characteristics provided the major determinants of pod yield and response to plant density. Crop duration was shortest in humid tropical and subtropical environments, with both high and low temperatures apparently delaying crop maturity. A relatively small individual plant size in humid tropical environments was due to a combination of low incident irradiance and short duration, with very high plant densities needed to maximize dry matter production. The progressive decline in harvest indices in more tropical environments was due to a decline in pod numbers per plant. Although increased plant density resulted in greater numbers of pod initials in the humid tropics, a high proportion of these pods did not contain developed seeds and pod yield at high densities remained relatively low at ≤2.5 t ha−1.