Saturday, 15 July 2006

Relationship between Nitrogen Use Efficiency and Response to Fertilizer in Winter Wheat.

D.B. Arnall, B. S. Tubana, K. Girma, W. R. Raun, K. W. Freeman, and R. K. Teal. Oklahoma State Univ, Ag. Hall, Stillwater, OK 74078

As the cost of Nitrogen (N) fertilizer increases and profit in wheat production is put at risk, scientists are challenged to develop N management strategies that guarantee increased N Use Efficiency (NUE). Under or over-fertilization will result in a loss of profit. Lower rates of N applied will result in reduced tillering, reduction in head size, poor grain fill, reduced yields, and low protein content. Alternatively, over application of nitrogen can result in reduced yield, higher input cost, and increased risk to the environment. Management zones, reference strips, and sensor based tools are emerging technologies that are keys to improve NUE. The Sensor Based Nitrogen Rate Calculator (SBNRC) developed at Oklahoma State University is showing increased NUE for many crops produced throughout the Midwest. The SBNRC technology works with the combination of sensor technology and a reference strip (N-rich Strip). Past research has shown the strong correlation of Normalized Difference Vegetative Index (NDVI) readings collected from remote sensors and plant biomass. With the calculation of biomass produced per day a potential yield is determined. The relationship between NDVI sensor readings from the N-Rich strip and the farmer practice is referred to as the Response Index (RI). This index is used as an indicator of that field's level of response to additional mid-season nitrogen. Potential yield and RI are used to calculate the rate of N needed to reach maximum yield for that crop season. This rate is multiplied by a theoretical NUE value to provide the applicator with the final N rate. Currently, N rates are determined without regard for a specific NUE, highly dependent upon temporal variability. This report reviews data from a long-term continuous wheat experiment in Lahoma Oklahoma, which was established in 1971. The results show a positive correlation between NUE and RI, and also between NUE and yield. With this information the precision at which topdress N rates are determined can be improved using an expected NUE. When the RI is determined from sensor readings the proper NUE for current season growing conditions can be input into the N-rate calculation.

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