In 1994 a study was established in a poorly-drained flat soil on the eastern portion of the Elwell Agroecology Farm (EAF) to evaluate tillage systems (chisel plowing vs. ridge tillage) and nutrient sources (urea vs. solid beef manure) effects on water quantity and quality leaving the landscape via surface tile inlets and subsurface tile drains. The study was modified in 1998 with tillage comparisons between moldboard plowing and chisel plowing, and nutrient source comparisons between urea vs. injected liquid hog manure. Four-year results show that except for nitrate-N losses in tile drainage there was no effect of tillage on non-point source pollutant (sediment, total and soluble P) losses from these relatively flat lands (3% slope). Higher nitrate-N losses via tile drainage from moldboard plowed plots only occurred during the snowmelt period possibly due to greater fall mineralization of soil organic matter. Sediment losses were about one-tenth of the soil tolerance value for the Webster clay loam soil. It appears that the small benefits (less soil detachment) from the presence of residue cover in chisel plowed systems are counter balanced by increased water storage capacity of moldboard plow systems on these relatively flat lands.

Over the four-year period, average grain yield was about 6 bushel/acre less with the chisel plow system. However, this decrease in corn yield will be compensated for with less fuel use in chisel plowing compared to moldboard plowing.

The beneficial effect of manure as opposed to urea application was a decrease in NO3+NH4-N losses via surface runoff in at least in one year. This suggests slow but continuous release of manure organic N that is taken up by the crop more efficiently. Another beneficial effect of manure application was increased corn grain yield even though it occurred only for one year.

The implications of the above results are that chisel plowing (30% residue cover) although beneficial in many ways will have none to minimal effect on Minnesota River water quality.

In fall 2003, we modified the study to evaluate the role of surface inlets in nutrient losses from flat lands in the Minnesota River Basin. From half of the plots, we removed surface inlets and for the other half we kept the surface inlets. Therefore the two comparisons are: (1) tile lines without surface inlets, and (2) tile lines with surface inlets. The hypothesis we are testing is: whether an absence of surface inlet will cause more water to percolate through soil thus carrying more nitrate through the tile line. In other words, are we trading increased nitrate losses via leaching to no sediment and phosphorus losses via surface runoff if the surface inlets were not present in these flat landscapes? We will be doing this quantification for two nutrient sources (liquid hog manure vs. urea) both during the snowmelt and the rainfall periods. All plots will be chisel plowed in the fall. The details of the above research are available from Satish Gupta in the dept. of Soil, Water, & Climate; University of Minnesota, St. Paul, 55108: 612-625-1241.

Researchers:

Satish Gupta, University of Minnesota Department of Soil, Water and Climate