Understanding the environmental impact of phosphorus in acidic soils receiving repeated poultry litter applications

With rising global demand of poultry products, a surge in poultry production would warrant safe disposal of waste byproducts such as poultry litter (PL). A dilemma exists over environmental phosphorus (P) loss risk and agronomic utilization of PL in highly weathered soils with high P fixation capacity. The objective of this study was to determine P forms and their distribution in highly weathered Piedmont soils located in high density poultry operation (HDPO) areas and evaluate environmental P loss risk using soil P storage capacity (SPSC) approach. Soil samples from agricultural fields with 10 +/- 2 years PL application history were collected from surface (0-15 cm) and subsurface (15-30 cm) depths. Approximately 64 +/- 11% of total P was in non-reactive P (NRP) form, 35 +/- 19% in moderately reactive P (MRP) forms, and < 1% in highly reactive P (HRP) form. Phosphorus sorption index (PSI) was higher in subsurface (316 L kg(-1)) compared to surface soils (150 L kg(-1)). The SPSC calculated based on a distinct soil threshold P saturation ratio (PSR; ratio of P/[Al + Fe], all elements expressed in moles) was higher in subsurface (17 mg kg(-1)) than surface (-150mg kg(-1)) soils. Repeated application of PL resulted in P saturation of surface soils (SPSC<0) and represents a source of P to the environment. The NRP form decreased, and MRP forms increased when a) soil test P (STP) rating transitioned from low to extremely high, and b) SPSC changed from positive to negative. Results indicate that P release in soil solution is predominantly controlled by buffering action of MRP forms since HRP was minimal and NRP is mostly unavailable in highly weathered soils. A holistic approach that includes STP for maintaining agronomic productivity along with SPSC to minimize environmental P loss risk will be desirable for sustainable management of PL in HDPO. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The study highlights the risk of environmental phosphorus loss associated with the reutilization of poultry litter in highly weathered soils in areas with high-density poultry operations. The decrease in non-reactive phosphorus and increase in moderately reactive phosphorus forms led to P saturation in surface soils and subsequent release of phosphorus into the environment.