Clipped Cowpea (Vigna unguiculata (L.) Walp) Fodder Management: A Potential for Soil Organic Matter Enrichment in Degraded Savannah Soils of Nigeria

Severe nutrient depletion of the soils of the savannah tropics of Africa over the years has made it difficult to improve the productivity of varieties of crops using cultural practices alone. But interestingly, it has been observed that when a cowpea (Vigna unguiculata (L.) Walp) crop is cut (clipped) before senescence; it can regenerate after defoliation (provided there is enough soil moisture). And when the clipped organic fodder is added and/or ploughed back into the soil, it enriches the soil organic matter (SOM) content that in turn enhances crop productivity. Thus, this study was carried out with the objective of determining the influence of intra-row spacing, clipping height and time on the productivity of cowpea and SOM; at the Institute for Agricultural Research, Ahmadu Bello University, Samaru, Zaria, Nigeria; during the 2002-2005 wet seasons. The experimental lay out was a Randomized Complete Block Design (RCBD), replicated three times. The collected data was analyzed statistically using the analysis of variance test (ANOVA); and the means separation was done using the Duncan Multiple Range Test (DMRT). Results showed that the textural class of the experimental site soil was loam silt; with a conducive pH of (6.6 in 2002 and 5.5 in 2005), for crop growth. The soil organic carbon content (SOC), nitrogen (N) and cation exchange capacity (CEC) were very low (0.30 g kg-1, 0.88 g kg-1 and 4.90 respectively) in 2002. These increased to 10.37 g kg-1, 2.2 g kg-1 and 11.10 respectively in 2005. Total rainfall in 2002 was 1007.9mm and 871.5mm in 2005. Mean air temperature, relative humidity and sunshine hours in 2002 ranged between 21.0-31.5 °C, 16.0-90.6 and 4.5-8.5 respectively; while mean air temperature and relative humidity ranged between 24.7-32.0 °C and 40.5-85.3% respectively in 2005. Total harvested clipped fodder yield was 15t ha-1; and this was added to the soil; and it effectively increased SOM content by about 42%. Consequently, it was concluded that the adoption of this innovative clipping management technology, holds great potential of improving soil pH, increasing soil CEC, SOM and crop productivity generally, for the low technology, resource poor, and subsistence farmers in the region. Without doubt, overcoming SOM decline is a major component in the development of more sustainable agro-systems.