Through land application multiple manure constituents are introduced to soil. These constituents include nutrients, organic matter, and contaminants such as antimicrobials and antimicrobial resistance genes (AMR genes). Many factors could affect the persistence and retention of these constituents in soil. Some manure constituents are more prone to degradation in soil than other constituents. Some constituents tend to accumulate in soil, while others tend to be removed from soil by runoff. The method of land application and the timing of land application in relation to rainfall events could also affect the persistence and retention of these constituents in soil. As a supplementary project to NPB 14-121, this project has two specific objectives: (1) determine how the method of manure land application affects the persistence and retention of multiple manure constituents, including nutrients, antimicrobials, and AMR genes, in soil; and (2) determine how the timing of manure land application in relation to rainfall events affects the persistence and retention of multiple manure constituents in soil. Swine manure slurry was land applied to plots in the field in the summer of 2014, and rainfall simulation tests were conducted 1 day (referred to as 0 week in this report), 1 week, 2 weeks, and 3 weeks after manure application.
Manure land application methods had noticeable impacts on the concentrations of nitrate and antimicrobials in soil, but not on the soil concentrations of ammonium, phosphorus, or AMR genes. Broadcast resulted in higher nitrate and antimicrobial concentrations in top soils than did injection. For plots receiving swine manure slurry through broadcast, the length of the time period between manure application and rainfall events had no impacts on nitrate, water soluble phosphorus, or Bray 1 phosphorus concentrations in top soils, while longer time period led to lower ammonium in top soils. Similarly, the length of the time period had no significant impacts on chlortetracycline or tiamulin concentration in top soil, while longer time period resulted in lower lincomycin concentrations in soil. Finally, three of the four AMR genes tested were not affected by the length of the time period between manure application and rainfall events, while the concentration of one AMR gene tet(Q) in top soils increased towards the end of the three week testing period.
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