Phosphorus Solubility in Poultry Litters and Granulates: Influence of Litter Treatments and Extraction Ratios

摘要

Phosphorus (P) loss from soils receiving manure has been strongly correlated to the water-extractable P (WEP) applied in the manure. Our main objective in this study was to assess the effects of different treatments (granulation alone and with urea, urea plus dicyandiamide, or hydrolyzed feathermeal) on WEP of poultry litter. We obtained poultry litters from two poultry farms located in the northwest Arkansas, and the selected litters were granulated in commercial granulating plants. During granulation, urea, urea plus dicyandiamide, and hydrolyzed feathermeal were added to poultry litters, which increased the total N:P ratio of litters up to 8.51. Results showed that granulated litters had greater amounts of WEP than raw and ground litters when measured at lower extraction ratio (1:100). However, the WEP was similar for all litters (raw, ground, heated, granulated) at 1:200 or 1:250 extraction ratios. This suggests that granulation of poultry litter does not influence the total amount of WEP in poultry litters. The extraction ratio had the greatest effect on WEP in the litter, while filter paper and method of P determination had minor effects on litter WEP. Of all water-extractable elements, Mg was most strongly correlated (R 2 0.75) with P in these poultry litters and granulates, suggesting that Mg-P minerals might control aqueous P concentrations in litter extracts. Based on these results, we recommend that WEP in poultry litter should be determined by using a 1:200 extraction ratio, followed by the use of Whatman No. 40 or 0.45 µ m filters, and the filtrates can be preferably analyzed using inductively coupled plasma - optical emission spectroscopy (ICP-OES). In conclusion, this study shows that (1) granulation of poultry litter does not increase WEP of the poultry litter as given by 1:200 or 1:250 extraction ratios, and (2) addition of urea during granulation made the poultry litter a balanced fertilizer (N:P = 8:1) compared with raw litter (N:P = 1.35:1), which would help decrease P surpluses in intensive animal production areas when litters are land applied