Tillage and poultry manure effects on soil fertility and sorghum yield in southwestern Nigeria

The data on tillage methods, mulching and manuring are needed to identify strategies for sustainable management of soils and for improving agronomic productivity. Hence, three field experiments were carried out at two locations in late-season 2004, early 2005 and late-season 2006, respectively, on Alfisol (Oxic Tropuldalf) at Owo in the forest-savanna transition zone of southwest Nigeria to evaluate the effects of different tillage methods and poultry manure on soil fertility and sorghum grain yields. The treatments consisted of five tillage methods (zero tillage with mulch, zero tillage without mulch, ploughing, ploughing plus harrowing and ploughing plus harrowing twice), and two rates of poultry manure at 0 and 7.5 Mg ha(-1). These were factorially combined and arranged in a randomized complete block design and replicated three times. The surface soils (0-15 cm) were analysed for chemical properties before and after second and third experiments. There was a percentage decrease of soil organic C, total N, available P, exchangeable K, Ca, and Mg concentrations in ascending order for zero tillage with mulch, zero tillage without mulch, ploughing, ploughing plus harrowing and ploughing plus harrowing twice while percentage increases were recorded in a descending order for all the various combinations of tillage with poultry manure in that order. Zero tillage with mulch, zero tillage without mulch, ploughing, and ploughing plus harrowing out-yielded ploughing plus harrowing twice by 33.7, 30.5, 18.9 and 17.9%, respectively. Poultry manure application in combination with tillage increased grain yield by 39.5% compared with tillage only. The manure-zero tillage methods increased grain yields by 15% compared with manure-mechanized tillage methods. The study indicates that sorghum can be grown sustainably in the forest-savanna transition zone of southwest Nigeria by employing zero tillage with mulch and zero tillage without mulch in combination with 7.5 Mg ha(-1) poultry manure. (C) 2008 Elsevier B.V. All rights reserved.