LAUSR

Land application of manure, while beneficial to soil health and plant growth, can lead to an over-abundance of nutrients and introduction of emerging contaminants into agricultural fields. Compared to surface application of manure, subsurface injection has been shown to reduce nutrients and antibiotics in surface runoff. However, less is known about the influence of subsurface injection on the transport and persistence of antibiotic resistant microorganisms. We simulated rainfall to field plots, at two sites (Virginia and Pennsylvania, U.S.), 1 or 7 days after liquid dairy manure surface and subsurface application (56 Mg ha-1 ) and monitored the abundance of culturable antibiotic resistant fecal coliform bacteria (ARFCB) in surface runoff and soils for 45 days. We performed these tests at both sites in spring 2018 and repeated the test at the Virginia site in fall 2019. Manure subsurface injection, compared to surface application, resulted in less ARFCB in surface runoff and this reduction was greater during the 1st day after application compared to the 7th day. The reductions of ARFCB in surface runoff because of manure subsurface injection were 2.5-593x at the Virginia site in spring 2018 and fall 2019 and 4-5x reductions at the Pennsylvania site in spring 2018. The ARFCB were only detectable in 0-5 cm soil depth within 14 days of manure surface application but remained detectable in the injection slits of manure subsurface injected plots even at the 45th day. This study demonstrated that subsurface injection can significantly reduce surface runoff of ARFCB from manure-applied fields. This article is protected by copyright. All rights reserved.