Influence of Inorganic Fertilizer (NPK 15:15:15) and Cacao (Theobroma cacao L) Leaf Litter Application Rates on Cowpea (Vigna unguiculata L.) Performance in the Tropics

Abstract

Influence of inorganic fertilizer (NPK 15:15:15) and cacao (Theobroma cacao L.) leaf litter application rates on cowpea (Vigna unguiculata L.) performance in the tropics was studied for 24 months (January, 2017 – December, 2018) at Cocoa Research Institute of Nigeria (CRIN) Ibeku Sub-Station, Umuahia, Nigeria. Three 3 x 3 factorial experiments, each in a Randomized Complete Block Design (RCBD) with three replicates/blocks were used to study the responses of cowpea to three NPK 15:15:15 fertilizer rates 0 kg, 500 kg and 1000 kg ha-1 represented by (Factor F) F0, F1 and F2, respectively, and cocoa leaf litter rates 0 t, 10 t and 20 t ha-1 which were also represented by Lo, L1 and L2 (Factor L), respectively. The results obtained from the study show that the application of either 10 or 20 t ha-1 cocoa leaf litter alone or complementary application of either 10 or 20 t ha-1 cocoa leaf litter plus 500 or 1000 kg ha-1 NPK 15:15:15 fertilizer significantly increased the various cowpea growth and yield components than the fertilizer rates alone. The treatment without fertilizer and leaf litter, i.e. topsoil only (F0L0) gave significantly the least cowpea growth and yield components. The highest values were obtained with the application of 1000 kg ha-1 NPK 15:15:15 fertilizer with 20 t ha-1 cocoa leaf litter (F2L2). The cowpea crop performance in terms of growth, yield and yield components over the study periods, 2017 and 2018 were statistically similar. Therefore, the inclusion of leaf litter has greater potential for improving cowpea yield than when fertilizer was used alone. Leaves are potential sources of valuable nutrients providing a high quality of organic matter, which should be returned to the soil.