Assessing the Implications of Chloride from Land Application of Manure for Minnesota Waterways

Abstract

Chloride concentration in the environment is a growing concern for ground and surface water quality in many regions in the northern United States. While the land application of manure is an important strategy for agricultural producers to fertilize croplands, it could be a source of chloride, and it is unclear how manure and soil characteristics interact to affect chloride leaching into groundwater, which makes understanding manure’s role in groundwater contamination difficult. We conducted a series of large intact column (0.3 m depth × 0.3 m diameter) leaching studies to evaluate manure and soil type interactions on chloride leaching potential after manure application. Four soil types (sandy loam, silt loam, silty clay loam, and clay loam) around Minnesota were chosen for this study. Columns were surface applied with four treatments (swine manure, turkey litter, KCl, or control) before carrying out three 5-cm irrigation events on day 4, 11, and 18 of the study following treatment application. We measured chloride concentration of leachate after each irrigation event, the percentage of chloride leached relative to amount of chloride applied, and the percent change in soil chloride storage from the beginning to the end of the experiment. Our results showed that surface treatment and soil type interacted to affect chloride concentration in leachate, and that chloride concentrations varied through time. While soil type did not affect the percentage of chloride lost to groundwater, surface treatment type did, with swine manure leaching 87% of chloride applied compared to turkey litter and KCl treatment which leached 57% and 49% of chloride applied respectively. These results are likely due to swine manure’s low dry matter content which allowed it to be flushed out of the soil more rapidly compared to other treatments. Before data can be used at a field scale, future studies should evaluate chloride leaching potential at a longer timescale with additional irrigation events, as well as from a wider variety of manure types and application methods.