Soil fertility indices of tropical loamy sand as influenced by bambara groundnut variety, plant spacing and fertilizer type

Abstract

Agricultural sustainability ensues when cultivation of field crops and associated techniques improve not just crop yields but also management-responsive soil properties. Bambara groundnut as an underutilized crop lacks research-based information on its agronomic requirements. This paper reports the key fertility indices of a loamy-sand soil in southeastern Nigeria as influenced by soil and agronomic management practices involving factorial combinations of two bambara groundnut varieties (Caro and Olokoro), two plant spacings (30 cm × 75 cm and 45 cm × 75 cm) and four organic/inorganic fertilizer options. These fertilizer options were NPK 15-15-15 (NPK), single super phosphate (SSP), poultry manure (PM) and Control. The plots under Caro variety spaced 30 cm × 75 cm and grown with NPK or SSP fertilizer showed the highest CEC (8.40 cmol kg^–1) and exchangeable K (0.15 cmol kg^–1), respectively. Olokoro variety spaced 45 cm × 75 cm and grown with PM or SSP gave the highest total nitrogen (0.14%), soil pH_water (6.35), available phosphorus (107.60 mg kg^-1) and exchangeable Ca (3.70 cmol kg^-1). The interactions plant spacing × fertilizer type and crop variety × fertilizer type affected all the soil fertility indices studied, while crop variety × plant spacing affected soil pH_water, available phosphorus, CEC and exchangeable Ca and Mg. Generally, as main factors, Olokoro variety, NPK and 45 cm × 75 cm improved soil properties better than their counterparts.