Repeated Application of Liquid Separated Dairy Manure as a Nutrient Source in a Sugarbeet Rotation

Study author(s): Melissa Wilson, University of Minnesota
Growing season(s): 2023, 2024, 2025
Minnesota location(s): Murdock, Nashua

Important: Reports are available for download below.

July 2024 Quarterly

WHAT IS THIS PROJECT ABOUT?

This project studies the impacts of applying liquid-separated dairy manure to fields in western Minnesota with a manure history. While large dairies now offer a reliable source of local manure, that was not always the case. Many regional fields do not have a long history of manure application, but will see more in the future. Because nutrient release rates vary based on soil types, weather, and manure history, it is difficult to predict when nitrogen (N) and phosphorus (P) become available to crops.

This study addresses the specific challenge sugarbeet growers face with late-season nitrogen. Excess nitrogen late in the growing season reduces the sugar content of sugarbeets, cutting crop quality and profitability. Manure provides a source of nitrogen that slowly releases over the growing season, which theoretically may cause issues. The research aims to determine where in a sugarbeet-soybean-corn rotation manure is best applied to maximize yields while minimizing the risk of reduced sugar content.

KEY PROJECT GOALS & FARMER BENEFITS

  1. Optimize Manure Placement: Identifies the safest, most beneficial crop in the rotation (corn, sugarbeets, or soybeans) to apply manure.
  2. Evaluate Sugarbeet Quality: Determine if the “slow release” nitrogen from manure causes issues with sugar content
  3. Reduce Fertilizer Costs: Provides clear recommendations on accounting for residual manure nutrients so farmers can safely cut back on commercial fertilizers.
  4. Local Data: Delivers targeted answers tailored to western Minnesota’s climate and soil types.

HOW THE STUDY WILL BE CONDUCTED

  • Field Plots & Crop Rotation: Testing takes place at field sites near Murdock and Nashua, MN using a 3-year crop rotation of sugarbeets, soybeans, and corn. All three crops are planted each year to observe every stage of the rotation simultaneously.
  • Application Rates: Researchers are testing three initial treatments: a high manure rate (~18,000 gallons/acre), a low manure rate (~14,000 gallons/acre), and a baseline using commercial fertilizer only.
  • Single Initial Application: Manure is applied only in the first year to track its lingering multi-year nutrient impacts throughout the rest of the 3-year rotation. Commercial fertilizer is supplemented in years two and three based on UMN recommendations and credit given for leftover manure fertility.
  • Soil & Crop Monitoring: Soil samples are taken before planting, during the season (around the V6 stage in corn to monitor nitrate and ammonium), and after harvest. Crops are harvested to measure yields, sugarbeet quality, and nutrient uptake.
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