Abstract
Manure effects on soil organic matter (SOM) and related physicochemical fertility indices wane rather fast in the tropics due mainly to the prevailing high temperatures. In texturally similar soils, SOM-mediated aggregation controls hydraulic properties including rainfall-to-field-capacity time (FCtime) and field capacity water content (FCwater) that relate to water/nutrients availability to crops. This study assessed the residual effects of poultry-droppings manure at 25, 50 and 75 t/ha on SOM and aggregation, P-fertility and hydraulic properties of sandy-loam Ultisols in southeastern Nigeria. Mulch-protected treatment plots were water-saturated weekly during the dry season. Sampling for immediate effects was done one month after treatment; that for residual effects in the subsequent rainy season, 7-8 months after treatment, when FCtime/FCwater was monitored at 3-24 h intervals after three rainfall events each ≥ 30 mm. A given monitoring time was designated FCtime if the corresponding FCwater was similar to that of the succeeding one. Immediate effects showed higher soil pH, SOM, aggregates’ mean-weight diameter and available P in 50 and 75 t/ha than unamended control, but similar sand-corrected water-stable aggregates and permeability indices among treatments. Residual effects toed similar trends except that aggregates’ mean-weight diameter was unaffected, while soil bulk density was lower and microporosity higher in 75 t/ha than the rest. Across the three sampling periods, FCtime averaged 42 and 26 h, respectively at ≤ 25 and ≥ 50 t/ha, while FCwater increased steadily (0.08-0.22 g/g) with manure rate. Beyond the season of application to droughty Ultisols, poultry-droppings manure at heavy rates (50-75 t/ha) can still be promoting their SOM and P-fertility but not macro-aggregation. Up to 75 t/ha of the manure may be required for similar residual effects on soil hydraulic properties (including FCtime and FCwater), with FCtime seemingly varying not just with SOM but also the associated rainfall’s characteristics.
Published Version
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