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 pHwater (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 pHwater, 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.
The soils were characterized with regards to their macro morphology, physicochemical properties and heavy metal contents. This is to infer their pedogenesis and propose agrotechnology transfers as well as management considerations necessary for sustainable cultivation. A reconnaissance survey was used for initial soil identification. Two categories of the flood plain soils were identified viz. the levee and the back-swamp. Three profile pits were dug on each identified category. The results showed that the soils on the back-swamps were poorly drained and the soils on the levee were well-drained. Their colours varied from dull yellow (2.5 YR 6/5) to light grey (7.5YR 8/2) on the levee and dull reddish-brown (5YR 6/3) to pale reddish-orange (7.5YR 8/3) on the back-swamp. Mottling was observed in all the pits, indicating redoximorphism. Clay content was low to high and ranged from 4 to 30 %. It showed illuviation in the back-swamp. The soil pH was slightly acid. It has low exchangeable acidity of 0.2 to 5.83 cmol/kg and low cation exchange capacity ranging from 1.82 to 7.61cmol/kg. The low CEC values imply that the clay mineral dominant in the soils is non-expansible. The soils were not sodic as the mean values for the exchangeable sodium percentage was <6 %. Prevailing pedogenic processes identified in the area, were eluviation, illuviation, gleization, pedoturbation, beautification, and leaching. The soils were classified as Entisols, suborder Psamment and inceptisols, suborder Ustepts and correlated in FAO/WRB as Fluvisols (Dystric fluvisols) and Gleysols. Management practices like drainage practices, use of organic manure to enhance the soil conditions were recommended.
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