Differential Effects of Biomass Removal and Soil Test K (STK) Level On Over-Winter Changes in STK On Five Wisconsin Soils.

Past research has shown a wide range in response of soil test K (STK) levels to environmental conditions. To reduce the impact of environmental conditions on nutrient recommendations, it is generally suggested that soil sampling occur at the same time of year. However, it is not always possible to follow this suggestion. The objective of this research was to assess the effects of corn silage vs grain removal and different STK levels on over-winter changes in STK. This three-year study was conducted on five pedogenically unique and agriculturally important soils in Wisconsin. The experimental design consisted of a split plot design with corn harvest management system (HMS, grain vs. silage) as the main plot with 2006 spring preplant K application rate as the subplot. Soil test K was monitored during the three crop years. Yield and K uptake were measured. At the Arlington and Marshfield locations, STK generally increased over-winter for the lower K testing plots and decreased for the high K testing plots. Arlington was the only location where over-winter change in STK was significantly greater for the grain HMS compared to the silage HMS in 2006-2007 and was related to greater K uptake and redistribution of K in the top of the soil profile. STK at Hancock consistently increased 10-25 mg kg^-1 STK over-winter even though this soil has a low cation exchange capacity. STK at Lancaster and Fond du Lac mostly increased in the 2006-2007 over-winter period, but decreased for some higher testing plots in the 2007-2008 over-winter period. Although some generalizations can be made regarding over-winter changes in STK levels, the results of this study also suggest that it is not entirely consistent from year to year at a given location; thus, if possible, soil should be sampled consistently at the same time of the year.