Effects of Integrated Use of Organic and Inorganic Fertilizer on Soil Chemical Properties in the Guinea Savannah Zone of Ghana
A two-year field experiment was conducted at Nyankpala, near Tamale during the 2014 cropping season and continued in 2015, to evaluate the effects of indigenous organic materials on soil chemical properties in the Guinea savannah zone of Ghana. The treatments included 4 organic materials (Biochar, Groundnut shells, Rice husk and Rice straw) applied at 3 rates (viz. 2.5, 5.0 and 7.5 t/ha on dry matter basis) and 3 fertilizer N rates using NPK (0,45-30-30, and 90-60-60 kg/ha) in 2014 and sulfan N (0,45 and 90 kg/ha) in 2015. The plots dimensions were 5m × 5m with maize planted at 40cm × 80cm to maturity stages in both years. The results after the second year revealed that the application rate of 2.5 t/ha groundnut shells without inorganic N supplement was superior in improving soil C, N, P and K but with addition of inorganic fertilizer the same soil nutrients increased most in biochar treated soils. Rice straw without fertilizer N improved the soil pH and Ca levels. The superior effects of groundnut shells and biochar were more pronounced at the application rate of 5 t/ha with or without sulfan N. Similarly, at 7.5 t/ha application of organic materials with or without fertilizer, groundnut shells and biochar enhanced the soil nutrients than the rice materials. The rice materials were found to affect more of soil pH and exchangeable Ca but for soil Mg, biochar appeared the most influential material. We conclude that, application of either groundnut shells or biochar could improve the soil nutrients of the savanna agroecology for crop production whilst with acidic soils and/or Ca deficient soils, rice materials are recommended for use.