AVAILABLE P ENHANCEMENT IN ROCK PHOSPHATE AND AN ANDISOL AMENDED WITH POULTRY MANURE

Background: Poultry manure (PM) is a source macro and micro nutrients for plant growth. PM applied to soil enhances soil properties and increases the crop yield. As an important strategy to decrease the amount of inorganic phosphorus (P) fertilizers, the combined use of rock phosphate (RP) with PM has been found to be more advantageous for sustainable agriculture than their single use. The objective was to assess PM dose effect on RP dissolution and the PM effect on P availability in an Andisol.

Methods: Composted PM was chemically analyzed according to Sadzawka et al. (2006). Additionally, it was fractionated according to a modified sequential Hedley P methodology. Then, we performed two incubation experiments. The first incubation was done by mixing PM and RP at two different rates: 50:50 and 70:30 during 30 days. In the second experiment, an Andisol was incubated with PM at the dose of 100, 200 and 300 mg P kg^-1 and soil subsamples were taken at 1, 3, 5, 7, 10 days of incubation. P availability was determined according to Olsen and Summers (1982) based on an extraction with a solution of 0.5 M sodium bicarbonate at pH 8.5, using molybdate colorimetry of Murphy and Riley (1962).

Results and Conclusions: Combined use of PM and RP at 70:30 rate resulted in the greatest increase of available P released from RP during PM decomposition. The Andisol amended with the highest PM dose (300 mg P kg^-1) showed the highest P availability at the third incubation day. Then, at the fifth incubation day, both PM doses (200 and 300 mg P kg^-1) resulted in similar increases. We therefore conclude that poultry manure addition may mobilize protected soil P. Long-term results will be necessary to analyze the combined effect of PM and RP in pasture growth.