Fate and transformations of dissolved phosphorus forms in runoff: Effect of poultry litter and products extracted with variable water extraction ratios

In many intensive animal production areas, the over-application of manure has resulted in a build-up of soil phosphorus (P) and the creation of legacy P soils that threaten water quality. We investigated dissolved P forms losses in runoff using simulated rainfall in packed soil boxes amended with three poultry litter and products, including raw (unprocessed) litter, granulated litter with the addition of urea, and heated raw litter. These were applied at 3 kg water-extractable P (WEP) ha-1 as determined with three litter-to-water extraction ratios (1:10, 1:100, and 1:200). Over three simulated rainfall events, the amount of dissolved reactive P (DRP) lost was significantly greater in runoff from soils amended with granulated litter (1.09 +/- 0.02 kg ha-1) than raw (0.81 kg ha-1) and heated (0.58 kg ha-1) litters. No significant differences in the amount of dissolved unreactive P (DUP) in runoff (0.38 +/- 0.07 kg ha-1) were observed among three litter amended soils. The soil test P (i.e., Mehlich 3-P) increased from 6.9 mg kg-1 in control to 10.4-11.6 mg kg-1 in litter amended soils, whereas the total WEP (0.26 +/- 0.03 mg kg -1) in soils was similar after three rainfall simulation events. We conclude that (1) an accurate litter-to-water extraction ratio (>1:200) is critical to determine the amount of WEP in manure as it will ensure similar amounts of soluble P application and will result in identical runoff losses of dissolved P, and (2) the granulation and heating of litter created a product that could enhance the use of poultry litter, especially in non-agricultural markets, resulting in sustainably using manure and reducing the risk of P loss to water bodies.

Automated summary

In many intensive animal production areas, the excessive use of manure can lead to the accumulation of phosphorus in the soil and the formation of legacy P soils, resulting in a threat to water quality. This study investigated the loss of dissolved P forms in runoff from packed soil boxes amended with different types of poultry litter products. The results showed that granulated litter amendments significantly increased the loss of dissolved reactive phosphorus in runoff compared to raw and heated litter amendments. The loss of dissolved unreactive phosphorus in runoff did not differ significantly among the different litter amendments.