Soybean ( Glycine max L. Merr) productivity in varying agro-ecological zones

Abstract

Soybean (Glycine Max L. Merr) is one of the most important food crops in the daily diets of humans and animals, as it provides essential proteins and other nutrients. The crop is not only a source of food, but is also beneficial to the soil, as the crop has a symbiotic relationship with Rhizobium bacteria, which is capable of fixing atmospheric nitrogen in the soil, resulting in no need to apply nitrogen to the crop. Although soybean is a crop grown world-wide, individual cultivars often demonstrate a limited adaptation to specific agro-ecological conditions, since the growing season must be long enough and soybeans are also photoperiod sensitive. During the growing season, daylength is therefore one of the most important factors to take into consideration for cultivar choice. The aim of this study was to determine the growth, development and yield response of soybean cultivars of different maturity groups when planted in varying agro-ecological zones. Field experiments were conducted at Pretoria, South Africa, and at two locations in Swaziland, Malkerns and Nhlangano. Six soybean cultivars of different maturity groups and different growth habits (determinate and indeterminate) were planted at these sites. Plant growth analyses were carried out every two weeks, from plant establishment until physiological maturity. Thermal time requirements to reach different growth stages were calculated and final grain yield was determined at harvest and also during growth analysis. The growing degree day requirement from planting to crop emergence ranged from 45 to 62 d°C for all six cultivars. Thermal time requirement for completion of the vegetative stage ranged from 530 to 900 d°C, with the early maturing cultivar LS 6162 having the lowest requirement of 530 d°C, while the late maturing cultivars PAN 737 and LS 6164 required 890 and 900 d°C. The different cultivars also showed distinct differences in growth during the season. Grain yields obtained from the different cultivars from the three locations ranged from 0.9 t ha-1 (LS 6162) to 3.4 t ha-1 (PAN 737). The indeterminate cultivar (LS 6150) gave significantly higher yields compared to the other cultivars at Malkerns (1.3 t ha-1) and Nhlangano (1.9 t ha-1). Cultivar PAN 737 gave higher yields than all the cultivars at Pretoria (3.4 t ha-1) The six soybean cultivars that were evaluated in these experiments have demonstrated substantial differences in growth, development and yield potential. Cultivar specific model growth parameters were calculated. The Soil Water Balance model was then calibrated and used to simulate growth and yields of each cultivar. The simulations were acceptable for all the cultivars, which will in future enable us to forecast how cultivars of different maturity groups will perform in different environments.