Purpose
Previous research conducted in western Washington State has demonstrated that when manure N is applied at rates greater than needed for grass uptake, excess N in soil in the form of nitrate-N can leach to shallow groundwater during the months of high rainfall. In a prior study, it was evident that tillage and reseeding of the cropland was a contributor to loss of nitrate–N from soil to underlying groundwater. The objective of this study was to characterize the effect of re-seeding of cropland using minimum tillage and conventional tillage methods on crop uptake of nitrogen, soil nitrate-N concentration, nitrate concentration in shallow ground water underlying the field, and the relationships between these matrices.
What did we do?
A two- year study was initiated in 2009 to study the fate and transport of nitrogen from dairy manure when applied to cropland that was reseeded to grass for silage production. One-half of a 22- acre grass field was prepared with conventional tillage, and one-half was prepared with minimum tillage in May of 2009. In 2009, after the grass was reseeded, the conventional till grass was harvested 2 times, and the minimum till grass was harvested 3 times. Due to poor stand establishment, the minimum till area received minimum till treatment again in 2010. In 2010, the conventional till grass was harvested 4 times, and the minimum till grass was harvested twice.
What we have learned?
Total nitrogen harvested for minimum till and conventional till respectively, were: 310 and 298 lbs/acre (2009), and 425 and 477 lbs/acre (2010). Total nitrogen applied for minimum till and conventional till, respectively, were: 523 and 440 lbs/acre (2009), and 697 and 697 lbs/acre (2010). Soil nitrate-N for the minimum till plot remained below 30 ppm in 2009 except on one occasion. Soil nitrate for the minimum till plot was observed to increase to 40 and 60 ppm in 2010. Soil nitrate-N for the conventional till plot increased to 60 ppm in 2009, and 35 ppm in 2010. There was no evidence of a difference in groundwater nitrate-N due to the type of tillage treatment. Groundwater nitrate-N concentrations on the whole were higher in monitoring wells after both tillage methods were applied. Results from this case study indicated that the type of tillage had an impact on the timing of increases in soil nitrate. However, variability in denitrification conditions in monitoring wells did not allow a determination of whether one method had more of an impact on groundwater nitrate than the other. (See Figures 1 and 2.)
Authors
Joe Harrison*, Professor and Nutrient Management Specialist, Washington State University, jhharrison@wsu.edu
Barb Carey, Environmental Assessment Program Washington Department of Ecology; and Lynn VanWieringen, Research Associate, Washington State University.
*presenter
Future plans
A study has been proposed to characterize the effect of converting the grass field to corn silage and determine uptake of nitrogen, soil nitrate-N concentrations, nitrate concentrations in shallow ground water underlying the field, and the relationships between these matrices.
Additional information
Joe Harrison jhharrison@wsu.edu Joe Harrison, jhharrison, 253-445-4638, Washington State University
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