Abstract
Phosphorus (P) is one of the most abundant and essential nutrient elements for crop growth; however, it is often not available to plants in sufficient quantity. Organic amendment can enhance its availability in acid tropical soils. In this study, we investigated the effects of manure type on the pattern of P release in highly weathered tropical soils of contrasting lithology and mineralogy. Two fallow-land soils from Isinyi-Nando and UNN-Nsukka in southeastern Nigeria with antecedent Bray-2 available P of 3.73 and 20.83 mg kg‒1, respectively, were amended with poultry droppings, pig slurry and cattle dung at soil-manure mass ratio of 100:6 and incubated. They were sub-sampled at 0, 1, 2, 4, 8, 16 and 28 weeks of incubation. In the two soil types, the highest increases in soil pH and available P always occurred with poultry droppings, with P release peaking at 16 weeks. Manure-induced increases in available P were greater in the less oxide-rich Isinyi-Nando soil compared with the more oxide-rich UNN-Nsukka soil over the incubation duration, with lower values in the former than the latter without amendment (5.79 and 23.57 mg kg‒1, respectively) and across treatments (40.59 and 45.16 mg kg‒1, respectively). The P release patterns were defined more by increases and decreases in soil pH and organic carbon with incubation time, respectively, and less by soil aggregation. Poultry droppings could enhance P release around 16 weeks post-amendment of these soils. Further studies are needed on its synchronized bioavailability and the prospects of slow-mineralizing cattle dung beyond 28 weeks
