Wednesday, November 4, 2009: 11:15 AM
Convention Center, Room 301-302, Third Floor
To remain economically viable, many dairy farms are increasing herd size and importing more feed nutrients on the same land base creating nutrient management issues. Current cropping systems based on corn and alfalfa use manure nutrients inefficiently. At two locations in southern Wisconsin, a field study was established in 2004 and 2005 to compare a grass ley system to that of continuous corn silage. Using a factorial design, two 4-yr rotations were compared: 1) a short cycle heavily-manured grass ley (GL); and 2) continuous corn for silage (CS): Each system was compared with two fertilizer strategies: 1) manure (M) or 2) commercial fertilizer (F). In 2007 and 2008, after termination of the 3rd yr, corn was planted across the entire trial with no additional N inputs and yields were measured. Soil test phosphorus (STP) and potassium (STK) were also monitored over time and slopes (change in soil test levels) were compared. After the 4-yr rotations, soil fertility was highest under GL+M in which STK increased at a rate of 17 ppm/yr across locations while STP increased by only 4 ppm/yr vs. no change for CS+M with slurry (p<0.0001; p<0.0006) and a decline in OG+F and CS+F. In accord with the soil fertility differences, corn silage yields (on a dry matter basis) were highest under GL+M averaging 9.2 tons/a and lowest for CS+F at 6.0 tons/a across locations. Across species, M out yielded the F treatment by 1.4 tons/a (p<0.0007) and across fertility strategies, GL yielded over 2.0 tons/a higher than CS (p<0.0002). The GL+F yielded as well as CS+M showing that N credits from the grass biomass was similar to 3-yrs of annual manure application (or 84 lbs/a/yr). The GL+M system opened up in-season manure spreading windows while enriching the soil for efficient crop production the following year.