Reducing Manure and N Fertilizer Inputs in Alfalfa-Corn Rotations

View the project final report

Commodities

• Agronomic: corn, hay
• Animal Products: dairy

Practices

• Animal Production: feed/forage
• Crop Production: conservation tillage, crop rotation, no-till, nutrient cycling
• Education and Training: on-farm/ranch research
• Soil Management: nutrient mineralization, soil analysis

Reports from farm surveys suggest that many farmers do not trust current estimates of legume N credits. Applying excessive manure or N fertilizer to first-year corn after alfalfa decreases profit, wastes resources, and increases the risk of environmental damage. This proposed research project will expand current on-farm research on alfalfa N credits to corn by directly comparing farmer practices (N fertilizer or manure application) to current recommendations when alfalfa is terminated with intensive tillage, and by determining the N credit in no-till or minimum-tilled systems. This project also will determine the validity of using the presidedress nitrate test (PSNT) in first-year corn after alfalfa as a way to verify N supply. Thirty conventional and organic farmers with suitable fields representing two categories of tillage practices, no-/minimum-tillage and conventional tillage, will be chosen to cooperate in locating and staking plots, implementing tillage and applying N input treatments, and organizing Field Days. Manure and N fertilizer applications will be tested against un-treated controls in conventional tillage to evaluate whether corn grain yield responds to additional N inputs. In no-/minimum-tillage plots, a range of N fertilizer rates will be applied to determine the optimum rate. The results should help farmers: i) adopt N credits to increase sustainability ii) conserve manure for use in areas that are nutrient deficient, to market to other farmers, or for potential use in anaerobic digesters iii) reduce fossil fuel inputs and save money by applying no or less N fertilizer to corn following alfalfa (iv) determine validity of PSNT in first-year corn after alfalfa (v) reduce nitrate leaching.

This research is aimed at helping farmers become aware of and gain trust in the N credit from alfalfa to first-year corn. It also will provide knowledge for farmers to use when considering tillage in alfalfa-corn rotations. This research will help farmers become aware of the potential for using the presidedress nitrate test (PSNT) to predict corn N requirements in early growth stages.

This awareness should motivate and prompt farmers to reduce the amount of manure and N fertilizer applied to terminated alfalfa in order to:
(i) utilize N credits from alfalfa to increase sustainability
(ii) conserve manure for use in areas that are nutrient deficient, market to other farmers, or for potential use in anaerobic digesters
(iii) reduce fossil fuel inputs by applying no or less N fertilizer to corn following alfalfa
(iv) determine validity of PSNT in first-year corn after alfalfa
(v) reduce nitrate leaching

This project will begin in spring and summer of 2010 with finalizing cooperators and alfalfa fields. Cooperators will be chosen in Minnesota and Wisconsin to represent three categories: no-/minimum-tillage, conventional tillage with manure application, and conventional tillage with fertilizer application. Potential fields will be topsoil sampled to determine phosphorus (P) and potassium (K) fertility to assure they are not limiting. In September, plots will be staked within a planned thirty organic and conventional final-year alfalfa fields rotating to corn in 2011 (10 farm “replicates” for each category).

Alfalfa fields that have adequate and uniform stands of four or more plants/square foot and that are three to five years old will be chosen in order to supply the full 150 lb/acre N credit and reduce variability across sites. Age of alfalfa stands and amount of alfalfa regrowth will be considered when performing statistical analysis. In each conventionally tilled field, 8 to 12 plots will be selected to represent 4 to 6 replications of N input (manure or fertilizer) versus no N input in order to test the response of corn grain yield. The no-/minimum-tillage plots will be 4 to 6 replications of farmer’s treatments versus six N fertilizer rates (0, 20, 40, 60, 80, 160 lb N/acre) in order to determine the optimum N rate under reduced tillage.

At sites where manure is applied, several manure subsamples will be taken, combined, and analyzed to determine C and N concentrations and calculate N inputs. PSNT samples will be taken in the spring of 2011 from each plot and a comparison between treated and untreated plots will determine if there would have been a response to additional N.

University of Minnesota Extension will be involved in organizing field days in the summer of 2011 at two or more research sites where at least 20 neighboring farmers, consultants, and Extension educators will be invited to participate. Corn grain will be harvested in the fall of 2011 at each site. Stover samples will be taken at silage corn sites. Corn ear samples will be shelled, weighed, and measured to calculate grain yield (and stover where appropriate) and adjusted for moisture in each plot. The results will be analyzed and summarized during November and December of 2011. The overall report will be presented to each farmer, along with the individual results from their farm.