Strategies for management of high phosphorus agricultural soils on the Delmarva Peninsula
Date
2017
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Publisher
University of Delaware
Abstract
Historical application of poultry litter to Delmarva agricultural soils at nitrogen (N)-based rates resulted in build-up of soil test phosphorus (P) above agronomic optimum levels. These high P “legacy” soils have an increased risk of dissolved P losses in runoff or leachate. Phosphorus losses from these legacy P soils are a concern for water quality in sensitive water bodies. Unfortunately, most of traditional best management practices (BMPs) focus only on controlling particulate P losses or dissolved P losses related to current P applications and are not effective at controlling dissolved P losses from the soil itself. New and innovative BMPs are urgently needed to specifically address the issue of dissolved P losses from legacy soils. The objectives of this paper are to: 1) evaluate changes in P distribution among soil P fractions and P sorption characteristics of agricultural soils following long-term applications of poultry litter and commercial fertilizers; 2) determine the mechanisms of P removal by P sorbing materials (PSMs) used in stormwater P filtrations structures; and 3) evaluate fall silicon (Si) fertilization to enhance soil P availability and uptake by winter wheat from legacy P soils. ☐ We found that long-term application of poultry litter or inorganic fertilizer at above crop removal rates can significantly increase soil test P levels, and build up P concentrations in both labile (extracted by H2O and NaHCO3) and recalcitrant soil P pools (extracted by NaOH and HCl; Objective 1). The increase in labile soil P will immediately increase the dissolved P losses from legacy sites while the increase in recalcitrant soil P pool will act as a long-term P source to slowly release P over the time. ☐ Stormwater filtration structures are one of a few existing BMPs that can effectively reduce dissolved P in runoff water. Using synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy technique, we identified various calcium-, iron-, and/or aluminum-associated phosphate in reacted PSMs (Objective 2). Knowing the P speciation of different PSMs enable us to select appropriate materials for efficient P removal in stormwater filtration structures, as well as determine the potential disposal options for spent materials. ☐ We also found that Si fertilization is a promising BMP that can improve early-season soil P availability and reduce the use of starter fertilizer for the growth of winter wheat on high P legacy soils in Delmarva Peninsula (Objective 3). Specifically, the applied Si can compete with phosphate for soil sorption sites and thus increase the solubility of bonded P. However, more research is needed to identify commercially-available Si sources that can be easily accessible by farmers.
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Keywords
Biological sciences, Filtration structure, Manure-amended soil, Non-point P pollution, P sorbing material, Si fertilization, X-ray near-edge absorption spectroscopy