The effect of farm liquid waste application on receiving water quality - Final report

Twelve manure spreading events were monitored in 1989 and 1990 in order to further understand how soil properties, soil type, and rate of manure application effect tile drain water quality. Farm operators and custom applicators involved in this study were asked to spread their liquid manure as they would normally and the investigators monitored changes in bacteria and chemicals in the soil and tile drain water. Application rates varied from 36,000 L ha-1 to 159,000 L ha -1. The bacteria tested for in the soil and water included the indigenous fecal coliform (FC), fecal streptococcus (FS), and Escherichia coli (EC). In addition, the biotracers nalidixic acid resistant Escherichia coli (EC(NA)) and rifampicin resistant Strep. faecalis (FS(RIF)) were used. The chemical parameters tested for in the tile drain water included: biochemical oxygen demand, various forms of nitrogen and phosphorous, pH, chloride, conductivity and potassium. Magnesium, nitrate, organic matter, pH, phosphorus, and potassium were tested for in the soil in 1989. In 1990 soil sample analysis also included also calcium and cation exchange capacity. Subsurface tile drains became contaminated shortly following manure application for nine of the 12 manure spreading events monitored. It appears as though flow in the tile drains is required for contamination to occur at the time of manure application. Tile flow was absent for two of the spreading events and minimal contamination resulted when tile flow resumed. An acceptable rate of application may be dependent on whether or not there is tile flow when the manure is applied. For the third spreading event, where there was little contamination, the field had been tilled just prior to manure application. The tillage may have sheared the soil macropores at the soil surface impeding flow of the manure components to the tile drains. For three of the 12 manure spreading events it was possible to calculate the loads of bacteria and nutrients discharged from tile drains in the first 24 hours following manure application. In addition, the percent loads of bacteria and nutrients were calculated based on the portion of the initial loadings from the manure application compared to the loads of bacteria and nutrients discharged from the tile drains. The percent of FC in the applied manure that reached the tile drains averaged for the three events was 0.57%. The actual load of FC averaged for the three events was 1.04 X 1010 FC ha-1 for the first 24 hours following manure application. Expressed as a percent of the applied manure, 0.04%, 0.04% and 0.0005% of the N, P, and K respectively reached the tile drains. That represented 0.052 kg ha-1, 0.0006 kg ha-1, and 0.024 kg ha-1 for N, P, and K respectively. These results only represent three of the 12 spreading events therefore other similar loading calculations should be made before definite conclusions may be drawn.