Legacy effects of fertilizing with alum-treated poultry litter on phosphorus runoff

Authors: Moore Jr, Philip

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/15/2022
Publication Date: 9/12/2022
Citation: Moore Jr, P.A. 2022. Legacy effects of fertilizing with alum-treated poultry litter on phosphorus runoff. Abstract.

Interpretive Summary:

Technical Abstract: Treating poultry litter with alum (Al2(SO4)3.14H2O) is a best management practice (BMP) that greatly reduces ammonia (NH3) volatilization, as well as phosphorus (P) runoff and leaching. Lower ammonia levels in poultry houses treated with alum result in faster growing birds with better feed conversion, lower mortality and results in much less propane being used during cooler months (which lowers carbon dioxide emissions) because of lower ventilation requirements due to less ammonia. Currently 40% of the broiler chickens in the USA (~3.4 billion chickens per year) are grown with alum, mainly due to improved poultry production and lower propane use because of lower NH3 levels in rearing facilities, although our original goal for developing this BMP was to reduce non-point source P pollution. The objectives of this study were to evaluate the long-term effects of alum-treated poultry litter and untreated litter on soil test P and P runoff from pastures being fertilized for 20 years and to evaluate the legacy effects after fertilization was ended. Litter (5.6 Mg/ha) was applied to paired watersheds each year in spring. During the period when the fields were fertilized, the average P runoff from untreated litter (1.96 kg P/ha) was 231% higher than alum-treated litter (0.85 kg P/ha). Mehlich III P (0-10 cm) values in soil after 20 years of application were higher where alum-treated had been used (468 mg P/kg) than with untreated litter (388 mg P/kg), due to less leaching and runoff. However, water extractable P (WEP) in soil was 159% higher where untreated litter had been applied (49.1 versus 30.9 mg P/kg), indicating the use of alum-treated lowered soluble P in soil. Phosphorus concentrations and loads in runoff decreased dramatically after fertilization ended, even though Mehlich III soil test P levels were still high, indicating that poultry litter had been the dominant source of P in runoff while litter was being applied. During the six-year period after fertilization ended total P loads in runoff from the field which had been fertilized with untreated litter (0.71 kg P/ha) was 203% higher than P loads from the field that had been fertilized with alum-treated litter (0.35 kg P/ha). This study provides further evidence that treating poultry litter with alum is a sustainable BMP that provides both short-term and long-term improvements in water quality.