Effects of Land Configuration and Wood-shavings Mulch on Pore Size Distribution and Water Retention Properties of an Ustipsamment in Northeast Nigeria

Abstract

Practices that alter the pore size distribution in favour of water retention micropores can increase the capacity of a coarse-textured soil to retain moisture. A four-year field experiment was initiated in1999 to study the effect of some land configuration practices with or without wood-shavings mulch on pore size distribution and water retention properties of a sandy loam soil in northeast Nigeria. The treatment combinations were: flat bed to serve as control (FB); open-ridge (OR); tied-ridge (TR); FB + mulch (FBM); OR + Mulch (ORM) and TR + mulch (TRM), each replicated four times in a randomized block design with sorghum grown each year under rainfed condition. Wood-shavings at the rate of 5t/ha was used in 1999 but this was increased to 10t/ha in subsequent years to ensure adequate soil coverage. At the end of the trial in 2002, pore size distribution and water retention properties from each of 0-7.5, 7.5-15 and 15-30cm depths were examined. The results indicate that after four years of annual application of wood-shavings mulch, the capillary pore space (diameter <36µm) in the top 0-7.5cm layer of the FBM, ORM and TRM treatments were 22.2, 15.4 and 11.7% higher, respectively, than the average for the bare (FB, OR, and TR) treatments. The corresponding increases in the capillary pore space due to the three mulch treatments relative to the bare treatments in the sub-surface 7.5-15cm layer were 12.1, 15.8 and 18.8%, respectively. On the other hand, the proportion of total pore space comprised by macro pore space (diameter >36µm) was little affected by tillage and residue management at all the depths investigated. Water content at saturation (SWC), water content at field capacity (FC), water content at wilting point (WP) and available water holding capacity (AWHC) were all higher in the mulch (FBM, ORM TRM) treatments than in the bare (FB, OR, TR) treatments in both 0-7.5 and 7.5-15cm soil layers. Comparing the three mulch treatments, FBM had the highest values of SWC, FC, WP and AWHC in the top 0-7.5cm layer and the least in the 7.5-15cm depth. The lower water retention exhibited by FBM treatment relative to the ORM and TRM treatments at the 7.5-15cm depth could be due to residue incorporation during construction of collapsed ridges and/or dikes in the ORM and TRM treatments. Among the bare treatments, SWC tended to be highest in the FB and least in the TR at both 0-7.5 and 7.5-15cm depths whereas the FC, WP and AWHC tended to be higher in ridged (OR and TR) treatments than in the FB treatment. In general, the soil water retention curves of FBM, ORM and TRM are always higher than the retention curves for the bare treatments across the range of measured pressure potentials.

Key words: Land configuration, wood-shavings, water retention, pore size, conservation, residue

Nigerian Journal of Soil Research Vol.5 2004: 14-22