Fertility Management Effects on Soil Physical and Chemical Properties Under Long - Term Maize Cropping in an Alfisol in Northern Guinea Savanna Zone

Long - term productivity and sustainability of agro-ecosystems has been of great concern in agriculture for decades, hence development of various new approaches designed to maintain and protect soil resources in the Nigeria Northern Guinea Savanna. Intensive cultivation of land requires continuous application of inorganic fertilizers, especially N fertilizers and organic amendments to maintain soil fertility and productivity. Effect of long-term management practices and input factors were evaluated in this study in an Alfisol at Samaru, Zaria. Changes in soil quality were assessed by measuring appropriate physical and chemical indicators from 2006 to 2008 Rain-fed cropping seasons. Soils were sampled at 0-10 cm (surface) and 10-30 cm (subsurface) and analyzed for chemical and physical properties. Data obtained were analyzed using the SAS statistical package for ANOVA and means were separated with DMRT at 5% level of probability. The study was established in 1997 and maintained till 2008. The treatments consisted of inorganic-N fertilizer (urea) and manure (cow dung) applied at 90 kg N ha-1 (sole or mixed-(45kg N inorganic-N + 45kg N manure).Results showed that application of manure in combination with sole inorganic-N fertilizer at the rate of 90 kg N ha-1 increased soil pH value by 1%, soil organic carbon by 68 %, total nitrogen by 51% and available phosphorus by 83 % at the surface compared to sole inorganic-N. Cation exchange capacity (CEC) was significantly improved by 28% at the surface and 67% at the subsurface levels. Furthermore, soil bulk density was significantly reduced by 12%, total porosity was increased by 6 %, available moisture contents at field capacity and permanent wilting point were increased by 60% and 25% respectively compared to sole inorganic-N fertilizer treatments. To sustain soil fertility for optimal crop yields, adoption of a balanced fertilization programme that combines inorganic-N fertilizer with manure is recommended.