Variable Rate Fertigation: Opportunities and Investigations in West Central Nebraska.

Improving spatiotemporal correspondence between nitrogen application and crop nitrogen requirements can enhance both farm profitability and environmental stewardship. Many corn producers in west central Nebraska have adopted fertigation because it is a safe, timely, and cost-effective method of in-season nitrogen application. As the prevalence of variable rate irrigation systems, the availability of public and private spatial data, and the interest in site-specific management all continue to expand, variable rate fertigation is becoming feasible. Variable rate fertigation can adapt to differences in nitrogen losses and can tailor to variability in soil organic matter, residual nitrate, and yield goal. With such advantages, this emerging practice has the potential to reduce groundwater contamination and increase nitrogen use efficiency beyond what can be achieved with conventional flat-rate management. Irrigation and soil nutrient specialists in west central Nebraska are jointly researching variable rate fertigation. A center pivot equipped with sprinkler control capability was coupled with a fertigation pump that can maintain a constant ratio between fertilizer injection rate and center pivot flow rate. The nitrogen application accuracy of this and other variable rate fertigation systems is being evaluated. Also, tests are being conducted on the use of various canopy reflectance sensors for frequent spatial assessment of nitrogen sufficiency and on the use of a software tool for prescription map generation. Preliminary results will be presented.