Project Number:
DNR-080
Other Project Number:
WR90R003
Funding Year:
1990
Contract Period:
07/01/1990 - 12/31/1992
Funding Source:
DNR
Investigator(s) and affiliations:
Gary Bubenzer, University of Wisconsin–Madison;
Frederick William Madison, University of Wisconsin–Madison
Abstract:
A large-plot crop rotation study was initiated at two locations in southern Wisconsin in 1990 to compare the productivity, profitability, and environmental impact of contrasting cropping systems. Three studies were conducted from 1990 to 1992 to monitor the environmental impact of different cropping systems.
Study 1. Leaching of agricultural chemicals to ground water is a function of the amount and type of chemicals used and the amount of water percolating through the soil profile. Field testing with a bromide (Br) tracer indicated that breakthrough times to a shallow (1 m) groundwater table took less than one growing season, regardless of the cropping system. The rapidity of Br leaching and inability to identify a leaching front with repeated soil sampling indicated that preferential flow dominated piston flow under natural rainfall conditions under all the rotations on this prairie-derived silt loam soil.
Study 2. Fall soil nitrate (NO3–) levels are a measurement of synchrony between nitrogen availability and uptake by the crop. Excess NO3–in the fall in the upper midwest is liable to leaching below the root zone prior to the next cropping season. Pre-planned contrasts and combined analysis across years (1991 and 1992) and locations indicated that fall NO3– under the corn phase of the rotations were significantly greater than the pure legume phases. Legume phases had significantly greater fall NO3– than the intercrop (soybean/wheat, wheat/red clover, oats/alfalfa) phases. Also, the addition of wheat after soybean significantly reduced fall NO3– levels compared to no fall seeding after soybean harvest.
Study 3. An important component of long-term agricultural stability is the maintenance of soil fertility. Neither buildup nor continual draw-down are acceptable. Nutrient budgets for phosphorus (P) and potassium (K) were constructed a for six rotations. Due to high initial fertility, no P or K fertilizers were used. Nutrient balance after three cropping seasons indicated a deficit of P in the cash grain rotations and a large deficit of K in the forage rotations. Soil testing in the fall of the third cropping season indicated a consistent drop in available P and exchangeable K to a depth of 90 cm.