Influence of Poultry Manure Incorporation on Changes in Selected Physical Properties of an Alfisol during Drying

Abstract

Changes in the physical properties during the drying of soil as affected by incorporation of different levels of poultry waste were investigated on an alfisol under fallow at the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, South-Western Nigeria. Bulk surface soil (0 – 15 cm depth) was air-dried and crushed to pass through a 4 mm mesh sieve, then moistened to 0.18 g g-1 moisture before mixing with poultry waste at different rates of 0, 40 and 80 g kg-1. Pre-determined quantities of soil were packed in cylindrical cores 76 mm in height and 36 mm in diameter to achieve a pre-determined dry density of 1.93 g cm-3. Batches of the soil samples were prepared in replicates for each rate of poultry waste mixture and subjected to drying regimes in the laboratory. At different drying regimes, replicates of the soil samples were subjected to axial compression at the strain rate of 2 mm min-1 until failure occurred. The shrinkage index (ΔV) of the soil samples was also determined as the difference between the initial sample volume at preparation and the final sample volume after drying. The soil dry density (d) increased gradually with degree of drying, attaining a maximum value within the decreasing moisture content range 0.14 – 0.10 g g-1 and then subsequently decreasing gradually. The porosity (n) of the soil expectedly followed an inverse trend as d. The rate of poultry waste incorporation, however, had no significant effect on n and d. Poultry waste addition increased the soil’s unconfined compressive strength (UCS) implying that poultry waste enhances the integrity of soil aggregates when subjected to stress. The soil’s UCS also increased as the soil progressively dried out. A strong negative relationship (0.83 ≤ r2 ≤ 0.98) was obtained between soil moisture content and the shrinkage index (ΔV). The strength of the relationship however decreases with increased rate of poultry waste addition implying that poultry waste reduces the dependence of ΔV on moisture content. In general, the results indicate that poultry waste incorporation enhances the maintenance of the integrity of soil aggregates under compressive loads thereby improving the workability of the soil. Drying also increased the compressive strength of the soil.