Soil texture and mineralogy influence on the productivity of selected tropical legumes

Abstract

Cowpea (Vigna unguiculata) and tepary bean (Phaseolus acutifolius) are essential legumes which provide food for many people in South Africa. However, the productivity of these major tropical legumes in Limpopo Province is low partly because of poor soil fertility and soil degradation. This study aimed to determine the productivity of tropical legumes (cowpea and tepary bean) in different soils in Limpopo Province. Two pot experiments were conducted at the University of Venda experimental farm. The experimental design was a Completely Randomized Design (CRD) arranged in a 2 × 4 factorial treatment structure replicated three times. The aim of the first experiment was to determine the effect of soil types on nodule dry weight (NDW), root dry weight (RDW) and above-ground biomass (ADB) of the legumes. Modified plastic pots (2.0 L) were used for planting the legumes. The second experiment was aimed at determining the effect of soil types on productivity variables including the number of branches per plant (NB), plant height (PHT), plant vigour (PV), number of pods per plant (NPP), number of seeds per pod (NSP), pod length (PL), pod weight per plant (PWT) and seed weight per plant (SWTP) of the two legume species. Similarly, 5.0 L plastic pots were filled with soil (4.5 kg) and used for sowing the seed of legumes. Soil type had highly significant (P≤0.001) effects on NDW, ADB and RDW of legume species. The highest NDW (0.2133 g), ADB (3.6767 g) and RDW (2.1067 g) of cowpea was observed on the Leptsols. There were no nodules in tepary bean. For tepary bean, the highest ADB (1.6933 g) was observed in Leptsols whereas, the highest RDW (0.7433 g) was observed in Luvisols. In the second experiment, the results showed highly significant (P≤0.001) effects of Luvisols, Leptsols, Ferralsols and Fluvisols on PHT, NB, NPP, PWT, SWTP and PV. However, soil type had no significant (P >0.05) effects on PL and NSP. Leptsols was the most productive soil type for cowpea in all the measured parameters when compared to other soil types. The results in both experiments could be attributed due to variations in soil properties. It was concluded that Leptsols is the most productive soil for cowpea. However, field experiments are recommended to validate the results.