Irrigation management of soybean (Glycine max (L.) Merrill) in a semi-arid tropical environment. I. Effect of irrigation frequency on growth, development and yield

The effect of frequency of irrigation on the growth, development and yield of soybeans was studied in two experiments at the Irrigation Research Station, Ord Irrigation Area (15' 39'S., 128' 43' E.), Western Australia. Irrigation frequencies were based on Class A pan evaporation and involved irrigation after every 30, 60, 120 or 240 mm of cumulative pan evaporation. An additional treatment, saturated soil culture (SSC) or continuous furrow irrigation (analogous to 0 mm pan evaporation), was included in one of the experiments. Seed yields increased linearly with increasing irrigation frequency with the highest yields being obtained with SSC. Increasing the frequency of irrigation increased seed yields through the promotion and prolongation of crop growth. Growth rates of all plant components, viz. vegetative, reproductive, roots and nodules 'were enhanced by more frequent irrigation, senescence was delayed, and leaf area retained later in the growing period. Greater yields were reflected mainly in larger seed. The physiological basis for the observed responses is discussed.