Environmental Challenges (Dec 2021)
Stratification of soil phosphorus forms from long-term repeated poultry litter applications and its environmental implication
Abstract
Increasing demand for poultry products has led to an intensification of concentrated poultry feeding operations resulting in the generation of enormous amounts of poultry litter (PL). For example, in 2017 the southeastern U.S. alone generated 9.35 million U.S. tons of broiler litter. Repeated applications of PL along with no-till practices in agricultural fields located in high-density poultry operation regions often result in buildup of soil phosphorus (P) and raise environmental concerns. Less is known about how P forms such as highly reactive P (HRP), moderately reactive P (MRP), and non-reactive P (NRP) are stratified in soil layers and their potential environmental P loss risk in no-till agricultural lands that have a long-term history of PL applications. The objectives of this study were 1) to quantify the vertically distributed P forms in distinct soil depths; 2) identify the relationship between P forms and extractable P, and 3) understand the relationship between different P forms and the P saturation ratio (PSR) in PL impacted soils. Soil samples from the Madison series (Fine, kaolinitic, thermic Typic Kanhapludults) with an average 10-year PL application history on no-till agricultural fields were collected from four depths (0–5, 5–15, 15–30, and 30–45 cm) and P forms were determined using Hedley fractionation procedure. The P forms were found highly stratified within the soil layers, where the surface soils (0–5 cm) had an average of 20% of total P present in HRP, 50% in MRP, and 30% in NRP. The percentages of HRP and MRP forms decreased significantly and NRP became the dominant P form down the soil depth (15–30 and 30–45 cm). Multiple regression analysis indicated oxalate extractable P (Ox-P) represented all the three P forms (HRP, MRP, and NRP) and can be used as an index of long-term P availability. The PSR decreased down the soil profile and was linearly associated with HRP and MRP but not with NRP. Subsurface application of PL in regions where repeated loadings cannot be avoided would require careful evaluation of distinct P forms (reactive vs. non-reactive) along with the determination of soil PSR for the subsurface soil depths.
