Project Number: 3640-12210-001-01
Project Type: Reimbursable

Start Date: Apr 01, 2008
End Date: Mar 31, 2011

Objective:
The goal of this on-farm research is to determine optimal rates of K topdressing for the last production year of alfalfa, in terms of the response of alfalfa and the following first corn crop. The objectives are to: 1) determine alfalfa yield, forage quality, and final plant population in response to topdressed K applied in spring of the last production year; 2) determine the fertilizer N requirement for corn after alfalfa that received different K rates; 3) determine the apparent fertilizer K carryover for corn when K is topdressed on alfalfa; and 4) calculate the net marginal economic returns for topdressing K on alfalfa during its last production year.

Approach:
Research will be conducted on 12 Minnesota farms during a 3-year period. In each of the first 2 years, we will identify six established alfalfa fields that have had no recent manure applications and have differing soil test K (STK) levels. Based on the STK in each field, rates of K will be applied that are likely to provide data for response curves. For each field, we will determine the optimum K rate for alfalfa yield, quality, market value (based on local hay auction prices), and final plant population. We will directly compare the optimum K rates from these curves with the current University of Minnesota Extension recommendation. To assess carryover K, we will determine the STK in each previous K plot in spring of the corn year. We will measure fertilizer N response by applying five rates of N to subplots within each of the previous topdressed K rates (a split-plot design). We will apply dry N fertilizer to individual plots near the time of corn planting at rates of 0 to 160 lb N/a. We will include a second 80 lb N/a plot that also receives K in the corn year based on current Extension recommendations for corn. Grain and stover yields will be determined by hand harvesting ears from 20 to 40 feet of row in each plot. All treatments will be replicated four times at each site. We will collect prior field history, crop management, alfalfa variety and corn hybrid identification, and other pertinent data from each cooperating farmer. Data will be analyzed using ANOVA and non-linear (quadratic-plateau model) regression.