The effects of soil amendments and mulch on emergence, pod development and yield of bambara groundnut (Vigna subterranea L.) in a hard-setting soil

Abstract

Poor crop establishment is a common problem in the soils of semi-arid areas of South Africa and is often one of the main factors limiting crop yields. Hard-setting Hutton soils (Chromic Luvisol) expose shoots of emerging crop seedlings to high soil strength, which is detrimental to growth and. early establishment. The effects of surface application of 3.0 t ha−1 gypsum, 1.0 t ha−1 polymer gel, 3.0 t ha−1 grass mulch, 5.0 t ha−1 cattle manure and an untreated control on the establishment and yield of bambara groundnut were investigated in a hard- setting soil at Mafikeng in the North West Province. Soil amendments and mulch significantly improved (P<0.05) seedling emergence (75.2, 87.9 vs 64.8%), pegging (71.3, 78.9 vs 58.7%), podding (70.2, 78.6 vs 60.0%), pod yield (1440.0, 1846.1 vs 807.3 kg ha−1) and grain yield (896.3, 1115.0 vs 603 kg ha−1) of bambara groundnuts over the control. The improvements in amended soils were associated with increased moisture contents and reduced penetrometer resistance compared with un-amended soils. Differences within the amendments were consistently in the order mulch>manure>gypsum=polymer gel>control. The results indicate that the application of amendments to hard-setting soil can significantly improve the establishment and yield of bambara groundnut under local conditions. Further testing of mulches and other locally available materials for use as soil amendments is recommended, especially for smallholder farmers.