Assessment of Phosphorous Release from Bat Guano with Respect to Their use as Organic Fertilizers in Crop Production

Bat guano from Kisarawe cave A (BGK-A), Kisarawe cave B (BGK-B) and Sukumawera cave (BGS) in Tanzania were studied in a laboratory incubation experiment for 112 days to assess the phosphorus release patterns and establish the pick periods of P mineralization. Total P contents from BGK-A, BGK-B and BGS were 8.55, 7.03 and 3.45 % respectively. Bat guano from each deposit mixed with soil at varying rates of 0, 10, 20, 40 and 80 mg P 200 g-1 soil. The experiment was arranged in 3×5 factorial experiment in randomized complete design (RCD) with three replications. Results showed a gradual increase of P availability from 28 days to 84 days of incubation; followed by a slow decrease up to the 112th day of incubation. P release (availability) from the studied guano was in the order of BGK-B < BGS < BGK-A. BGK-A indicated higher potential as an alternative P source for agricultural application. P-source and application rate had a significant interaction effect (P < 0.05) on P release at all incubation intervals when P was applied at 80 mg kg-1 soil.  The soil pH showed very strong negative correlation (r > 0.8) with P released in the soil throughout incubation period. It was concluded that P release from the three bat guano deposits in soils is gradual and reaches the pick in almost three months after application. Thus, it should be applied at least two months before planting for more effectiveness of P release