Short-Term Effects of Tillage on N Mineralzation from Farm Yard Manure in Semi-Arid Tropical Vertisol

Tillage may have different effects on physical protection of organic matter during decomposition process. Short-term effects of tillage on N release from Farmyard manure (FYM) was studied during August to October (2005) in the Experimental Research Farm, Faculty of Agriculture, University of Khartoum, Shambat, Sudan. The manure was either disc ploughed (DP), disc harrowed (DH) or applied on the surface (S) and compared with control plots. Plots were irrigated weekly in absence of plants and mineral (NH4+-N + NO3--N), pH and soil moisture content of the topsoil (0-30 cm) were monitored every two weeks for 12 weeks. Results showed that content of total mineral nitrogen (NH4+ -N and NO -N) determined in surface application of all sampling weeks was significantly (P < 0.005 - 0.02) higher than that obtained under both disc harrow or disc plow. Disc ploughing farm yard manure enhanced down wards movement of NO -- N thereby, decreasing availability in the 0-30cm soil depth. However, disc harrowing seemed to decrease release of mineral N due to enhanced physical protection. All methods of manure management did not cause N immobilization during mineralization and consequently crops might not be faced with N starvation. Soil moisture content and pH were not generally affected by tillage.