Influence of organic waste incorporation on changes in selected soilphysical properties during drying of a Nigerian alfisol

Changes in the physical properties during the drying of soil as affectedby incorporation of different levels of poultry waste were investigated on analfisol under fallow at the Teaching and Research Farm of Obafemi AwolowoUniversity, Ile-Ife, Nigeria. Bulk surface soil (0-150 mm depth) was air-driedand crushed to pass through a 4 mm mesh sieve, then moistened to 0.18 g g-1moisture before mixing with poultry waste at different rates of 0, 40 and 80 gkg-1. Pre-determined quantities of soil were packed in cylindrical cores 76 mmin height and 36 mm in diameter to achieve a pre-determined bulk density.Batches of the soil samples were prepared in replicates for each rate ofpoultry waste mixture and subjected to drying regimes in the laboratory. Atdifferent drying regimes, replicates of the soil samples were subjected to axialcompression at the strain rate of 2 mm min-1 until failure occurred. Theshrinkage index of the soil samples was also determined as the differencebetween the initial sample volume at preparation and the final sample volumeafter drying. The soil dry density (pd) increased gradually with degree ofdrying, attaining a maximum value within the moisture content range 0.14-0.10g g-1 and then subsequently decreased gradually. The porosity (n) of the soilexpectedly followed an inverse trend as pd. The rate of poultry wasteincorporation, however, had no significant effect on n and pd. Poultry wasteaddition increased the soil's unconfined compressive strength (UCS) implyingthat poultry waste enhances the integrity of soil aggregates when subjectedto stress. The soil's UCS also increased as the soil progressively dried out. Astrong positive correlation (r2 = 0.80) was obtained between soil moisturecontent and the shrinkage index. The strength of the relationship howeverdecreases with increased rate of poultry waste addition implying that poultrywaste reduces the dependence of moisture content. In general, the resultsindicate that poultry waste incorporation enhances the maintenance of theintegrity of soil aggregates under compressive loads thereby improving theworkability of the soil. Drying also increased the compressive strength of thesoil.