Effects of bush clearing and tillage methods on some soil chemical properties in Epemakinde, southwestern Nigeria

The effects of bush clearing and tillage methods and their interactions on soil organic matter and macronutrients were investigated for three cropping cycles (1995/96 to 1997/98) on a primary forest area of Southwestern Nigeria. The bush clearing methods were: Bulldozed and windrowed (BW), Bulldozed not windrowed (BNW) and Clear-fell, slashed and burned (CSB), while Conventional (CT), Minimum (MT), Traditional (TT) and Zero (ZT) were the tillage methods. Adjoining natural forest was also incorporated as a treatment to serve as a control. The bush clearing and tillage methods, which were randomly distributed within the main- and sub-plots, constituted main-and sub-treatments. Results revealed a greater decline in the soil organic matter, macro-nutrients, cation exchange capacity and base saturation in BW plots than in BNW and CSB plots throughout the investigation period. The CSB conserved 22, 23, 15, 21, 5 and 11% more soil organic matter, to tal N available P, K, Ca and Mg (0 - 15 cm soil depth) respectively than BW after the first cropping cycle. Similar trends were maintained in subsequent years. Among the tillage methods, ZT conserved soil organic matter and macro-nutrients more than other tillage methods. The ZT indicated 9 - 14% and 16 - 32% more total N and organic matter in 1995/96; 11-26% and 14-38% in 1996/97; and 7 - 21% and 6 - 34% in 1997/98 (0 - 15 cm soil depth) than other tillage methods. The available P, Mg, K, cation exchange capacity and base saturation followed the same trend. The interactive effects of bush clearing and tillage methods were significant on the chemical properties. The CSB + ZT or TT combination conserved soil nutrients the most. The CSB being slow inefficient and laborious and would hardly fit in soil improvement program. The adoption of BNW + MT combination would therefore be more appropriate in primary forests of the humid tropics.