Exploring Phosphorus Dynamics in Mid-Atlantic Soils: A Multi-Scale Analysis Integrating Soil Fertility and Land Management for Environmental Sustainability

The legacy phosphorus (P) in the Eastern Shore of Virginia poses significant challenges for crop nutrition and water quality. Nutrient losses from row crop agriculture and poultry litter applications have potential to cause water quality impairments affecting the environment, aquaculture, and tourism industries. To address these concerns, this study investigated P management strategies across various scales. The first component of the study focused on optimizing edamame production in the context of high legacy soil P levels and harvest efficiency. Over three years, field experiments on Bojac sandy loam soil assessed the effects of different P fertilizer rates and legacy P levels on edamame yield, biomass, and P uptake. Results showed that short-season edamame in high legacy P soils had significantly more yield than long-season varieties. However, additional P fertilization was deemed unnecessary for soils with P concentrations above 21 kg P ha-1, as current edamame P recommendations exceed the crop's P removal needs. Moreover, mechanical harvesting efficiency was notably higher for short-statured edamame varieties (89.3%) compared to tall varieties, indicating their preference for improved harvesting. The second component examined the influence of agricultural lime on legacy P phases in the soil. Lime was applied at rates ranging from 0 to 2690 kg ha-1 to an acid sandy loam Ultisol (pH < 5.1). Using partial Hedley P fractionation, changes in water-soluble P, soil test P (Mehlich-1 extraction), and total soil P (nitric acid digest) were monitored. Although lime application significantly affected soil pH, calcium (Ca), and magnesium (Mg), it did not significantly alter the relative proportions of water-soluble and soil test P. This indicates that while lime can improve soil pH and nutrient availability, it does not substantially impact P phase distribution. The final study utilized historical water quality data from the Virginia Institute of Marine Sciences and GIS technology to analyze the impact of land use and land cover (LULC) on nitrogen (N) and P concentrations in 52 watersheds. Row crop LULC was significantly correlated with higher total nitrogen (TN) concentrations (p = 0.03), while forested LULC was linked to lower TN (p = 0.02) and nitrate-nitrite (NOx) concentrations (p = 0.05). Thirty-two out of 52 watersheds had mean total P concentrations exceeding 0.10 mg L-1, with stormflow conditions showing significantly higher total P concentrations and loadings compared to baseflow. Landscape-scale turbidity strongly correlated with elevated total P levels, emphasizing the role of particulate P transport. Baseflow samples also had higher ammonia (NH3) and NOx concentrations, but stormflow resulted in higher loadings. In conclusion, effective P management on the Eastern Shore requires a coordinated approach that addresses soil, crop, watershed, and landscape-scale factors in cooperation with multiple stakeholder groups. This study highlights the importance of optimizing agronomic practices and implementing targeted conservation strategies to mitigate nutrient and sediment losses, thereby improving both crop production and environmental quality.