Lime and manure application to low-fertility tropical soils enhances phosphorus bioavailability for increased agronomic productivity

Liming and manuring to ameliorate soil acidity and enhance mineralization in acid tropical soils could promote their agronomic productivity. Synthetic lime and poultry-droppings manure’s effects in sandy-loam Ultisols were evaluated on soybean growth, exploring its relationships with soil pH, soil available P and plant P content. Lime was applied at 0, 2.5 and 5 t ha–1 equivalents and manure at 0, 25 and 50 t ha–1 equivalents to 2.5-kg potted soils. Crop growth was monitored and soil-plant analysis done during and after six weeks of growth, respectively. Treatment had more pronounced effects on plant height than leafiness of the soybean plants, being generally highest in the combination of lime at 2.5 t ha–1 and manure at 50 t ha–1 where the plants were about three times taller compared to unamended control. Soybean plants grew better due to 2.5 than 0 and 5 t ha–1 lime and to 50 than 0 and 25 t ha–1 manure. Plant height and leaf area depended on soil pH-influenced soil available P (R2 = 0.69**) and plant P content (R2 = 0.85**), respectively, while above-soil biomass depended on soil pH or plant height (R2 = 0.74**). Moderate synthetic liming (2.5 t ha–1) with ample poultry-droppings manuring (50 t ha–1) could enhance crop early-stage vegetative growth in low-fertility tropical soils, due largely to amelioration of soil acidity to enhance plant uptake of bioavailable P.