One of the challenges in utilization of solid manure sources is deciding on the optimum amount of soil tillage to incorporate manure for enhanced nutrient value but leave enough crop residues for reduction of erosive losses. Soil test P levels are high near the soil surface when tillage for incorporation is reduced. This study was conducted to evaluate the impact of tillage system in combination with a one time application of solid beef manure on annual runoff and sediment loss from 1992 to 1994 at Morris, MN. The treatments were fall moldboard plowing followed by spring field cultivation (MP) and ridge till (RT, two row cultivations) with or without manure (56 Mg manure ha-1 with 161 kg P ha-1 in the Spring of 1992) . The crop was continuous corn (Zea mays L.). Surface runoff and the associated sediment as well as total P (TP), particulate P (PP), and dissolved molybdate reactive P (DMRP) were measured from runoff plots on an annual basis. The soil was a complex of a Udic Argiboroll and Typic Calciboroll (Foreman-Buse loam) with a uniform 12 % slope and easterly aspect. The manure application resulted in an increase in soil test P of 10 to 17 and 16 to 25 mg P kg-1 for the MP and RT treatments respectively. For the RT plots, the main source of annual runoff was snow melt, whereas in the MP plots it was rainfall. There was 2-6 times more runoff from snow melt on RT plots compared to MP plots. Snow melt runoff was the main source of annual TP, PP, and DMRP in RT plots whereas in the PL plots it was rainfall runoff. Laboratory extraction studies with corn residue and nylon bag studies in the field suggests that 74% of the snow melt P losses with the RT treatment were leached from corn stover. On an annual basis TP was still 2-7 times higher with the MP compared to the RT system. The PP was 4-8 times higher and DMRP losses were similar. Manure application reduced annual runoff and sediment loss 50 and 71 %, respectively. Sediment loss in snow melt runoff was very small compared to the loss in rainfall runoff. The effects of manure were more frequently significant with rainfall runoff compared to snow melt runoff. Manure application resulted in lower seasonal rainfall runoff volume and sediment loss for both tillage systems. Manure in MP plots (residue cover less than 5 percent) reduced runoff with moderate rain but was overwhelmed with catastrophic events. In RT plots (residue cover 48 percent) runoff was much lower and reduced by manure even for catastrophic events.
John F. Moncrief, Professor and Extension Soil Specialist Department of Soil, Water, and Climate College of Agricultural, Food, and Environmental Sciences University of Minnesota St. Paul, MN 55108 phone: 612-625-2771 FAX: 612-625-2208 E-mail: moncrief@soils.umn.edu or West Central Experiment Station PO Box 471, State Hwy 329 Morris, MN 56267 phone: 320-589-1711 FAX: 320-589-4870