Irrigation management of soybean (Glycine max (L.) Merrill) in a semi-arid tropical environment. III Response to saturated soil culture

The response of soybeans to saturated soil culture (SSC), achieved through continuous furrow irrigation, was evaluated in two studies in the Ord Irrigation Area in north Western Australia. In the first study, the effect of SSC on 14 genotypes was compared with conventional irrigation after every 60 mm pan evaporation (CI60), in an early wet season sowing. Averaged across genotypes, seed yields with SSC were increased by 0.74 t ha-1 or 21% above the mean yield of 3.47 t ha-1 with the CI60 treatment. Among genotypes, the advantage with SSC ranged from 2 to 49%. In the second study, the effect of SSC on growth and yield of three cultivars of different maturity was evaluated in a late wet season sowing, where crop durations were shorter than in the first study. There was a strong interaction between irrigation method and cultivar. Average seed yields of the latest maturing cultivar Durack were 10% greater with SSC, average yields of the intermediate cultivar Ross were relatively unchanged, while average yields of the earliest cultivar Buchanan were reduced by 24% with SSC. In both studies, and regardless of time of application of the SSC treatment, a transient chlorotic phase developed which tended to be more severe when SSC was applied earlier in crop growth. Where the chlorosis had dissipated by flowering, and providing crop duration was sufficient to compensate for the initial depression in shoot growth, seed yields were promoted by SSC. Taken together, the two studies indicate that substantial yield increases are possible with SSC in this environment, with the extent of the increases depending on genotype, crop duration, and the timing of application of the treatment.