Nitrogen Management in No-till Winter Wheat Production Systems
Gaidos, Joan Marie
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Determining optimum N fertilization rate and timing is critical to improve yields and economic sustainability for no-till winter wheat (Triticum aestivum L.) in the Virginia Coastal Plain. Little data are available evaluating N management strategies, optimum N rate prediction methods, or potential NO3 leaching under no-till wheat in soils and climate similar to the mid-Atlantic region. The objectives of our research were: (1) to determine economic optimum N fertilization rates and timings; (2) evaluate selected methods for predicting optimum N rates at GS 25 and GS 30; and (3) measure NO3 leaching loss under selected N management strategies. Eleven experiments over three years evaluated N rates at GS 25 and GS 30. Six experiments over two years evaluated pre-plant and December or GS 25 N rates under no-till winter wheat in farm fields of the Coastal Plain region of Virginia. Nitrate leaching was measured under selected pre-plant and December or GS 25 N application rates. All sites represented common Coastal Plain soil types and cultural practices for no-till wheat production. Yield data were used to calculate economic optimum N rates for a range of combinations of N management strategies. Optimum N rates were regressed against tiller density at GS 25, and wheat tissue N content and SPAD chlorophyll meter readings at GS 30, to determine their effectiveness as predictors of the optimum N rate at GS 25 or GS 30. Tiller density was an effective predictor of optimum GS 25 N rate in these split application management strategies. However, wheat tissue N contents and SPAD chlorophyll meter readings were not effective predictors of optimum N application at GS 30. Yields across all experimental designs were affected by planting date. Timely planted no-till wheat consistently produced higher yields compared to late planted. Sites under continuous no-till production for 8 years or more also produced higher yields than sites under continuous no-till production for less than 8 years. Including an additional December N application with the more traditional N management strategy of pre-plant, GS 25 and GS 30 N applications improved yields. Nitrate leaching loss at selected pre-plant and December or GS 25 N rates was not higher than background check plot levels under timely planted no-till wheat. Additionally, economic optimum N application rates and timings at these sites did not produce NO3 leaching losses above background levels under timely or late planted wheat, except at one late planted site. These data indicate N application rates and timings in no-till wheat can be managed for improved economic sustainability and reduced environmental impact.
- Doctoral Dissertations