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Title: TILLAGE AND NUTRIENT SOURCE IMPACTS ON WATER QUALITY FROM A FLAT LANDSCAPE 1631

Author
item Thoma, David
item GUPTA, S.
item STROCK, J.
item MONCRIEF, J.

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2005
Publication Date: 5/11/2005
Citation: Thoma, D., Gupta, S., Strock, J., Moncrief, J. 2005. Tillage and nutrient source impacts on water quality from a flat landscape. Journal of Environmental Quality. 34(1102-1111).

Interpretive Summary: Leaving crop residue on the soil surface after harvest is a good way to minimize soil erosion from steep lands. For this reason regulatory agencies often recommend farmers use conservation tillage practices that leave greater than 30% crop residue on the soil surface after harvest. Because few studies have been made to determine the effectiveness of conservation tillage on flat lands, an experiment was conducted to determine the effect of conventional versus conservation tillage as well as nutrient source effects on water quality leaving flat agricultural plots in Minnesota. Results showed that there was no decrease in erosion from flat lands associated with using conservation tillage compared with conventional tillage practices used in the experiment. The only important reduction in nutrient pollution was observed for plots treated with manure which lost less nitrogen than plots treated with commercial fertilizer. Results from this study will be used to re-evaluate the recommendation that conservation tillage be used on flat landscapes expressly for the purpose of reducing erosion

Technical Abstract: Beneficial outcomes of conservation tillage practices that leave residue at the soil surface are well documented for steep lands. However, the same can not be said for poorly drained flat lands that are drained with pattern tile and surface inlets. This study was conducted to quantify the effects of tillage, fall chisel plowing (45% residue cover after tillage and 23% after planting) vs. fall moldboard plowing (11% residue cover after tillage and 7% after planting), and nutrient source, injected liquid hog manure vs. surface applied urea, on tile line and runoff water quality as well as continuous corn yield from a relatively flat land (<3%) in the Minnesota River Basin. The experiment was established on a Webster Clay Loam soil (Fine-loamy, mixed, mesic Typic Haplaquolls) at Lamberton, MN. Runoff was analyzed for flow, total solids, NO3-N, NH4-N, dissolved P and total P. Tile line effluent was analyzed for flow, NO3-N and NH4-N. In four years of rainstorm and snowmelt runoff events there were relatively few significant differences (p<0.10) in water quality between corresponding treatments. The results showed that on flat lands small benefits of residue cover in chisel plowed plots are counter balanced by increased water storage capacity in moldboard plowed plots. Furthermore, the effectiveness of residue cover during snowmelt is somewhat minimal. Conversely, there was a slight decrease (p=0.025) in corn grain yield from chisel plowed plots (9.7 Mg/ha) compared to moldboard plow plots (10.1 Mg/ha). There were some beneficial effects of reduced mineral N losses via surface runoff from manure vs. urea treatments. We conclude that chisel plowing (~30% residue cover) is not enough to reduce non-point source pollution from these poorly drained flat lands especially to the extent (40% reduction) desired by the regulatory agencies.