Off-Season Heavy Application of Poultry Manure to Droughty-Acid Soils under Heavily Protective Organic Mulch Later Burnt to Ash Improves Their Productivity

Abstract

The effects of poultry-droppings manure at high rates (up to and > 50 t/ha), termed heavy application, on soil productivity indices of sandy-loam Ultisols were evaluated on okra, under conditions of heavily protecting the amended soil with dry-grass mulch and subsequent burning of same. The plots, prepared in dry season, were saturated weekly by manual irrigation. Two months after manuring, the protective surface mulch was completely burnt to ash. Weekly irrigation continued till the rains stabilized in the next rainy season, 7 months later, okra was sown. The soil was sampled before sowing and after harvest of okra, in- between which gravimetric water content was determined twice some 5-9 h after rain events ≥ 30 mm. Just before cropping, soil organic matter steadily increased while soil bulk density decreased with increasing manure rate. Total porosity, aggregate stability indices and saturated hydraulic conductivity of the soil all showed higher values in 75 t/ha than the rest at both sampling periods. Macro- and microporosity tended to decrease and increase, respectively with manure rate. Soil water content was not affected during okra growth, but treatment enhanced post-cropping microporosity. Treatment optimally enhanced pre-cropping soil pH and available phosphorus including okra vegetative growth at 50 t/ha, and pre-cropping total nitrogen and cation xchange properties including okra fruiting at 25 t/ha. Adding poultry manure at ≥ 25 t/ha to droughty-acid tropical soils with a heap of protective organic mulch to be ashed later can improve their productivity in the following rainy season, most likely due to enhanced pre-cropping soil pH and phosphorus fertility and postcropping water availability relative to no-manure soil.