Environmental Science & Technology
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Item Hotspots of Legacy Phosphorus in Agricultural Landscapes: Revisiting Water-Extractable Phosphorus Pools in Soils(MDPI, 2021-04-07) Roswall, Taylor; Lucas, Emileigh; Yang, Yun-Ya; Burgis, Charles; Scott, Isis S.P.C.; Toor, Gurpal S.Controlling phosphorus (P) losses from intensive agricultural areas to water bodies is an ongoing challenge. A critical component of mitigating P losses lies in accurately predicting dissolved P loss from soils, which often includes estimating the amount of soluble P extracted with a laboratory-based extraction, i.e., water-extractable P (WEP). A standard extraction method to determine the WEP pool in soils is critical to accurately quantify and assess the risk of P loss from soils to receiving waters. We hypothesized that narrower soil-to-water ratios (1:10 or 1:20) used in current methods underestimate the pool of WEP in high or legacy P soils due to the equilibrium constraints that limit the further release of P from the solid-to-solution phase. To investigate P release and develop a more exhaustive and robust method for measuring WEP, soils from eight legacy P fields (Mehlich 3–P of 502 to 1127 mg kg−1; total P of 692 to 2235 mg kg−1) were used for WEP extractions by varying soil-to-water ratios from 1:10 to 1:100 (weight:volume) and in eight sequential extractions (equivalent to 1:800 soil-to-water ratio). Extracts were analyzed for total (WEPt) and inorganic (WEPi) pools, and organic (WEPo) pool was calculated. As the ratios widened, mean WEPi increased from 23.7 mg kg−1 (at 1:10) to 58.5 mg kg−1 (at 1:100). Further, WEPi became the dominant form, encompassing 92.9% of WEPt at 1:100 in comparison to 79.0% of WEPt at 1:10. Four of the eight selected soils were extracted using a 1:100 ratio in eight sequential extractions to fully exhaust WEP, which removed a cumulative WEPt of 125 to 549 mg kg−1, equivalent to 276–416% increase from the first 1:100 extraction. Although WEP concentrations significantly declined after the first sequential extraction, WEP was not exhausted during the subsequent extractions, indicating a sizeable pool of soluble P in legacy P soils. We conclude that (i) legacy P soils are long-term sources of soluble P in agricultural landscapes and (ii) the use of a 1:100 soil-to-water ratio can improve quantification and risk assessment of WEP loss in legacy P soils.Item EVALUATION OF BASE LINERS TO REDUCE NITROGEN AND SALT LEACHING FROM POULTRY LITTER STORAGE STOCKPILES TO THE UNDERLYING SOIL - A FIELD COLUMN STUDY(2011) Baranyai, Vitalia; McGrath, Joshua M; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agriculture has been linked to the eutrophication of the Chesapeake Bay. The Delmarva Peninsula is an intensive poultry producing region, where poultry litter (PL, mix of manure and bedding material) is often stored in outdoor stockpiles. Continued development of management practices is required to achieve environmentally sound PL storage. This study evaluates base liners placed between the bottom of the pile and the soil to reduce nitrogen (N), potassium (K) and sodium (Na) movement from PL stockpiles after 15 and 91 days of storage. Six conically shaped stockpiles were established with five PVC pipe columns placed in the soil under each pile. The soil surface in each column was covered with one of five treatments: alum, gypsum, lime, plastic, or control (no material). Nitrogen, K and Na concentrations increased between 15 and 91 days of storage. Ammonium losses under alum and lime treatment were not different from the control. Alum created adverse conditions by dropping the pH to 3.8. After 91 days of storage, the surface 10 cm of the soil was severely salt affected: under alum, gypsum, lime and control the conditions became moderately to strongly saline. Plastic was most effective in preventing N, K and Na leaching to the soil.