In the upper Midwest along the Mississippi river, dairy is a major farming enterprise and as a result manure application to land is a common practice. In this region, the soils are relatively shallow and overlie the fractured dolomitic and calcitic bedrock. Over time the bedrock dissolves and leads to the formation of sinkholes. There is concern that nutrients from manure may be finding its way to the bedrock and then to the aquifer through the shallow overlying soil. One of the pathways suggested to the top of bed rock is through burrows formed by earthworms. This paper presents the results of a study at the University of Wisconsin, Southwest Agricultural Experiment Station at Lancaster, WI on the impacts of tillage and timing of manure application on nitrate losses through soil developed in loess overlying fractured limestone. Daily, scrape and haul dairy manure applied either in the fall (before snow) or winter (after snow) is compared to no manure under two tillage systems (no-till and fall chisel plowing). Corn is grown following corn. Nitrate concentration and water volume are determined from pan and wick samplers installed at 0.6 and 1.2 m depths. The data show that in general nitrate concentration in soil water are higher with fall and winter applied manure compared to no manure plots, higher under the chisel plow system compared to no-till conditions, and higher under fall applied compared to winter applied manure. The amount of water collected in pan samplers at 0.6 m depth varied from 4.5 to 6.9 cm for a cumulative rainfall of 17.4 cm during 1994. This suggest that substantial transport of water by earthworm burrows and decaying root channels. In this paper, we discuss the implications of our results especially the effects of manure application with and without snow cover on nitrate losses during the spring thaw period.
Satish C. Gupta, Professor Dept. of Soil, Water, and Climate 1991 Upper Buford Circle University of Minnesota St. Paul, MN 55108 TEL: (612) 625-1241 FAX: (612) 625-2208 e-mail: sgupta@soils.umn.edu