Symbiotic activities in soybean and yield validation with apsim under tillage and mulching practices

Abstract

Smallholder farmers are usually confronted with severe climatic conditions during summer growing seasons on production fields that are generally characterized by poor soil fertility and consequent low crop yields. Conservation agriculture could be a feasible local practice under such conditions to ensure a more sustainable and environmentally friendly system for cultivating crops. A rainfed field experiment was conducted at two diverse agroecological sites, Syferkuil and Ofcolaco during 2017 growing season in the Limpopo Province of South Africa to evaluate production, and symbiotic activities in soybean (Glycine max (L.) Merrill) and also to validate the performance of the Agricultural Production System Simulator (APSIM) model in simulating soybean biomass accumulation and grain yield under tillage and mulch practices. The experiment was established as a randomized complete block design in a split-plot arrangement with tillage (till and no-till) as the main plot treatment and four rates of grass mulch (0, 3, 6 and 9 tons ha-1) as the sub-plots treatment. The APSIMSoybean model was used to validate the result for simulated biomass and grain yield for the tillage practices at different mulching rates. A greenhouse experiment was also conducted during the 2017/2018 growing season to enhance the understanding of undulation potential in the selected soybean cultivar together with other cultivars. The greenhouse experiment was laid out in a randomized complete block design (RCBD) with four replications. Three soybean cultivars, commercial cultivar Donmario 8.6IRR (sourced from Agricol), Dundee commercial cultivar and Ibis 2000 (both sourced from Agricultural Research Council) were evaluated for their growth, phenological development, and symbiotic activities. Soybean growth was significantly (p≤0.001) affected by tillage at Syferkuil but not at Ofcolaco with the tilled soil having more pronounced growth than no-till at the former. Addition of mulch resulted in improved soybean growth relative to the control at both localities. Tillage and mulch as well as their interactive effects on soil moisture was significant at Syferkuil. Across tillage practices mulch application exhibited the highest moisture content than the control plots. At Ofcolaco tillage and mulch significantly (p≤0.001) affected soil water content but not the interaction effect, with more moisture recorded under the no-tilled condition and mulch application rate of 9 t ha-1 Soybean shoot and root nitrogen content was not influenced by tillage but was responsive (p≤0.001) to mulch application at both sites. The application of 9 t ha-1 mulch increased the shoot nitrogen content compared to the control plants at both locations. Soybean biomass and grain yield were also significantly influenced by tillage and mulch at Syferkuil but not at Ofcolaco (p≤0.001). A significant interaction effect of tillage and mulch (p≤0.001) on biomass and grain yield was also observed at Syferkuil but not Ofcolaco. At Syferkuil, higher biomass and grain yield was observed under the tilled condition when mulch at the rates of 6 and 9 tons were applied whereas, at Ofcolaco, soybean biomass and grain yield was higher under mulch application than the control with mulch application of 9 tons ha-1 at this location having the highest biomass and grain yield. The results of the APSIM model simulation showed the simulated biomass and grain yield to have a positive relationship. Hence, APSIM model can be used to guide alternate management practices to improve soybean production in the Limpopo Province. Findings from the greenhouse trial revealed that soybean cultivars significantly (p≤0.001) vary in symbiotic activities, growth, and physiological development. Across the cultivars, Ibis 2000 was superior in all studied parameters whereas Donmario, the cultivar used in the field trial was generally inferior among the three.

KEYWORDS: Cultivars, Grain yield, Soybean,