Phosphorus Leaching in Soils Amended with Animal Manures Generated from Modified Diets

• Published in: Journal of environmental quality Vol. 45; no. 4; pp. 1385 - 1391
• Main Authors: Toor, Gurpal S., Sims, J. Thomas
• Format: Journal Article
• Language: English
• Published: United States The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc 01-07-2016
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2015.10.0542

New dietary modifications for dairy (reducing P content in feed) and poultry (addition of feed additives such as phytase) aim to reduce P excretion in manures. Our objective was to investigate if dietary changes were effective at reducing P leaching loss on land application of manures. We used 54 undisturbed lysimeters (30 cm diameter, 50 cm deep) collected from three typical mid‐Atlantic soils. Lysimeters received 85 kg total P ha−1 from fertilizer (superphosphate), dairy manures generated from low‐ or high‐P diets, or broiler litters generated from normal diet or reduced P‐ and phytase‐amended diets. Lysimeters were irrigated with 50 mm of water each week for 9 wk. The major forms of P in the leachate were dissolved (dissolved unreactive P > dissolved reactive P [DRP]) rather than particulate (total particulate P). The higher P solubility (100%) in superphosphate resulted in greater leaching of DRP, whereas the lower P solubility (<30%) in dairy manures or broiler litters resulted in lower DRP leaching from soils. Preferential flow in two soils caused greater DRP leaching; this effect was more pronounced in the superphosphate‐amended than in the manure/litter‐amended lysimeters. The dairy and poultry dietary modification was effective at reducing the amount of P in manures and litters. However, the application of treatments at similar P rate (85 kg ha−1) resulted in the addition of a higher amount of manure (54–66%) in lysimeters that received low‐P dairy manure–amended and phytase‐amended broiler litter, which then controlled P leaching from soils.
Core Ideas
Dissolved unreactive P was the major form leached from the mid‐Atlantic soils.
Existence of preferential flow pathways in soils caused greater P leaching.
Soil and manure characteristics controlled P leaching from soils.