Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2021
Publication Date: 3/19/2021
Citation: Bos, J.H., Williams, M.R., Smith, D.R., Armstrong, S., Harmel, R.D. 2021. Long-term effect of poultry litter application on phosphorus balances and runoff losses. Journal of Environmental Quality. 50(3):639-652. https://doi.org/10.1002/jeq2.20219.
Interpretive Summary: Assessing the impact of phosphorus (P) management strategies on P loss from fields and watersheds is needed to improve crop use efficiency and decrease nutrient loss to downstream water bodies. In this study, we used data collected from a long-term experiment (2001-2015) in Riesel, Texas to determine how poultry litter application influenced soil test P concentration and dissolved P loss in surface runoff from 9 fields and two watersheds. Phosphorus application rate in excess of crop requirements resulted in the build up of soil test P concentration and increased dissolved P loss in surface runoff. Despite having high rates of poultry litter applied to 12 to 30% of the watershed area, dissolved P concentration at the watershed outlet was not different from fields with a neutral P balance (i.e., inputs = outputs). Alternatively, dissolved P loading from the watersheds as a result of high poultry litter application depended on both source (P application rate and impacted area) and transport (connectivity) factors. This research shows the impact of long-term field management practices on both edge-of-field and watershed nutrient loss, and provides a framework for assessing the effect of conservation practices at the watershed scale.
Technical Abstract: Assessment of annual and cumulative impacts of phosphorus (P) management strategies at field and watershed scales is needed to improve crop use efficiency and reduce environmental losses. The objectives of this study were to assess relationships among agronomic P balance, soil test P (STP) concentration, and runoff dissolved reactive P (DRP) concentration from cultivated and pastures receiving different poultry litter application rates (0.0 to 13.4 Mg ha-1) and determine the effect of long-term poultry litter application on downstream DRP concentration and load using a paired, nested watershed approach. Nutrient management practices, crop yield, STP, and runoff P losses were assessed from nine fields and two watersheds from the USDA ARS Riesel Watersheds near Riesel, TX over a 15-year period (2001-2015). Field P balances were largely controlled by P application rate and had a positive relationship with STP and DRP flow-weighted mean concentration (FWMC) for both cultivated and pasture managed fields. Using paired, nested watersheds and a before-after control-impact design, results showed that DRP FWMC at the watershed outlets did not vary from a neutral P balance despite having high rates of poultry litter applied to 12 to 30% of the area. In contrast, watershed DRP loading varied from a neutral P balance according to both source (i.e., P application rate, impacted area) and transport (i.e., hydrological connectivity) factors. Findings highlight the impact of long-term field-scale P management strategies at both the edge-of-field and watershed outlet, and provide a paired, nested watershed framework for assessing watershed-scale conservation effects.