Abstract

Nutrient leaching limits sustainable fertility management of tropical sandy soils. Therefore, phosphate leached from NPK 15:15:15 (NPK), sole compost (SC), phospho-compost (PC), poultry manure (PM), fresh Gliricidia sepium leaves (GL) and integrated (INTG) fertilizers applied at 40 kgP2O5 ha-1 and an unamended soil (AC) in leaching columns containing 2.5 kg soil were studied. Each soil was simulated for leaching at 2, 4, 6, 8, 10 and 12 weeks after cowpea seed sowing. Fertilizer application significantly reduced total leachate volume (TLV) over AC in the order of AC > SC > NPK > INTG > PC > GL > PM. Total phosphate leached (TPL) was  the highest (1505.3 mg l-1) in GL followed by 436.5, 229.7, 69.0, 33.4, 30.5 and 0.0 mg l-1 from NPK, INTG, AC, PM, SC and PC, respectively. The PC, PM and INTG produced significantly higher dry shoot (DSW) and root (DRW) weights, N and P uptake. Cowpea grain weight (CGW) was significantly higher (2.42 g plant-1) in INTG over AC (0.99 g plant-1). Significant negative correlation was between TLV and DSW, CGW, N and P uptake and between TPL and soil available P, N and P uptake. Stabilized organic (PC and SC) and integrated fertilizers (INTG) are therefore suitable for reduced phosphate leaching in sandy soil.

Key words: Chemical fertilizers, Leaching column, NPK 15:15:15, phospho-compost, phosphate leachate losses, soil nutrient leaching.