The Influence of Lablab Purpureus Growth on Nitrogen Availability and Mineral Composition Concentration in Nutrient Poor Savanna Soils

Abstract

Low soil fertility in savanna soils has been linked to low crop yields, with nitrogen being the most limiting factor in crop yield. Soil used in this pot experiment was obtained from Motshephiri village with low total N, low NO3− and high NH4+. A pot experiment was conducted in a greenhouse laid in a Randomized Complete Block Design with four treatments (1) control, (2) Bradyrhizobium japonicum inoculant, (3) superphosphate and (4) Bradyrhizobium japonicum inoculant + superphosphate). The superphosphate was applied at three different levels (45, 60 and 75 kg/ha). Lablab was cultivated in each treatment and the results of the study indicated that lablab growth significantly increased total N and NO3−, and reduced concentration NH4+ relative to the original soil herein referred to as pre-lablab growth. However, the N forms (total N, NO3− and NH4+) did not differ significantly amongst different levels of superphosphate with or without Bradyrhizobium japonicum inoculant. Lablab growth, proved to have a significant impact on both the soil macro (P, K, Ca, Mg, and Na) and micronutrient level (Fe, Mn, Cu, B and Cl) with the exception of Zn. This study suggests that lablab’s ability to rapidly boost soil N content, overall soil fertility in a short period of time without the use of superphosphate fertilizers or Bradyrhizobium japonicum inoculants makes it ideal for intercropping or rotating with non-leguminous crops that have a short growing season.