Managing Temporal Variability in Nitrogen Recommendation Using Nitrogen Rich and Ramped Nitrogen Reference Strips.
Kefyalew Girma, Clinton Mack, Brian Arnall, and william Raun. Oklahoma State Univ, 368 Ag Hall, Stillwater, OK 74078
Methods that increase nitrogen use efficiency, farmer profitability and reduced environmental impact are no longer simply commendable, but required. This review assesses the temporal variability in winter wheat with respect to N nutrition and presents some approaches, including calibration stamp, N-rich and ramped N-reference strips and sensor based N rate calculator to over come this variability. The N-rich strip Program has been validated in several farmers’ field across Oklahoma in US since 2004. The N-rich strip program contains a few simple steps. Farmers need to set up 4-5 strips in the field each receiving different N rate applied pre-plant or soon after planting. Then, the farmer waits until the winter wheat crop reaches Feekes growth stage 5-6 or between Feb. and March and subsequently evaluates either visually or using Hand-Held Sensor if any of those strips are different from the entire field in greenness. In the former case just apply the lowest rate where the difference was apparent. In the latter, the N recommendation is based on in-season predicted yield potential and response index of the field. In 2005 alone, 10 N-rich strip trials were conducted and the results suggested an improvement in both NUE and profit of $25 per hectare to farmers. The Ramped N-reference strip gives farmers the opportunity to include more rates in the strip so that it could be possible for them to determine the actual N rate required to top-dress in the field. Like the N-rich Strip, this method can also be used either as a visual tool or along with the Hand-Held Sensor. These simple temporal variability based N recommendation tools avoid the need to run soil analysis and accounts for any in-season N available from rainfall, mineralization, legume rotation, and manure application.