Global emphasis on food security and soil health should consider rehabilitation of degraded lands, especially where oil contamination limits the use of such lands. Three legume plants (Gliricidia sepium, Leucaena leucocephala and Calapoconium caerulean) alone or along with 0.5% (w/w) (equivalent of 10 tons ha -1 ) poultry manure, were used to treat the soil, in which the oil residuals were monitored for three years. Results showed that significantly high levels of residual total petroleum hydrocarbon content (RTPHs) persisted in the non-amended soil after 36 months. At 3 months, 43% of RTPHs was removed by Gliricidia sepium and Leucaena luecocephala along with poultry manure. Net loss of RTPHs after 12 months was 69% for Gliricidia sepium and Leucaena luecocephala combined with poultry manure and only 38% for A 5 , explaining that, degradation of petroleum hydrocarbon by indigenous soil micro-organisms was very low. At 18 months when additional load of oil was applied, the degradation rate increased from 71.7 mg kg -1 day -1 to 142 mg kg day -1 within 6 months for all the legume plants along with poultry manure. This explained increased in number of hydrocarbon-degrading micro-organisms due to increase in oil load. The oil inhibited germination and yield of maize crop completely. Treatments with legume plant along with poultry manure significantly (p < 0.05) increased both germination and yield of maize crop. The effects of legume plants combined with poultry manure were the better treatment than legume or poultry manure alone in improving the soil properties for growth and performance of maize crop.
Information on hydraulic conductivity and macro-and micro-aggregate stability is needed for evaluating the ease with which soils slake and erode when in contact with water. In fine-textured soils, it will provide information on ponding of water and decrease in hydraulic gradient with wetting. This study was conducted to determine changes in hydraulic conductivity and macro-and micro-aggregate stability of a fine-textured submerged soil under intense cattle grazing for 15 years. Hydraulic conductivity of the cattle grazing soil ranged from very slow (0.46 cm hr -1 ) to slow (19.56 cm hr -1 ) in the top 0-25 cm depth, and attained near zero permeability (0.15 cm hr -1 ) before 75 cm depth. Permeability was rapid (21.1 to 30.06 cm hr -1 ) throughout the profile in the non-cattle grazing soil. Organic residues from cattle grazing activities raised the soil total organic carbon to as high as 72 g kg -1 in the top 0-25 cm depth. Wet trampling of organic residues from cattle excreta induced greater soil swelling and loss of soil strength resulting in low aggregated silt and clay (ASC) and clay flocculation index (CFI) within the 25-75 cm depth. Clay dispersion index (CDI) showed significant negative (P < 0.05) relationships with mean weight diameter (MWD) of water stable aggregates and saturated hydraulic conductivity (r = -0.631 and -0.596 respectively). Soil parameters controlling water storage and infiltration in such soils need to be increasingly studied to increase the area of land available for crop production and reduce soil erosion since such soils usually have high chemical fertility status.
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