A METHOD FOR CALCULATING THE POPULATION YIELD RELATIONS OF GROUNDNUT (ARACHIS-HYPOGAEA) IN SEMIARID CLIMATES

Between 1980 and 1986, six field experiments were conducted to investi gate the relations between planting density, total dry matter and pod yield of groundnut (Arachis hypogaea L. cv. TMV2) grown at different l evels of irrigation and rainfall at two sites in central India. In gen eral, the relationship between total dry matter and planting density f or most treatments was well described by the function: 1/W = 1/w(m)P 1/W(m) where W is the crop dry weight per unit ground area, w(m) is t he maximum weight per plant, W(m) is the maximum crop weight per unit ground area and P is the plant population. Because the harvest index, h, was constant for each treatment irrespective of plant population, a similar equation described the relationship between pod yield and pla nting density. When nine of the eleven treatments planted in a square (i.e. 1: 1) arrangement were compared, the asymptotic value W(m) varie d between treatments depending on available soil water and atmospheric demand. To quantify the effects of plant and environmental factors on crop productivity, a 'transpiration equivalent' (OMEGA(w); (g/kg)/kPa ), i.e. the product of the dry matter/water ratio and mean seasonal sa turation deficit D, was used as a crop constant to calculate productiv ity at each site or season from a knowledge of seasonal rainfall and/o r irrigation and soil water-holding capacity. Thus, total crop product ivity, W(s)', was calculated using the equation W(s)' = OMEGA(w) S/D w here S (mm) is a soil supply term dependent on soil water-holding capa city and monthly values of rainfall and/or irrigation. When values for W(m) and W(s)' were plotted against each other, a linear regression w as obtained with a slope = 1.02 (R2 = 0.78). The mean harvest index of 0-38 was used to predict pod yield from a knowledge of W(s)'. It was concluded that of all the climatic. soil and management factors that i nfluence crop growth in semi-arid situations, it is the interaction be tween the supply of and demand for water that ultimately determines to tal productivity, pod yield and optimum plant population.