Improving Nitrogen Use Efficiency in Sustainable Corn Production Through Use of Remote Sensors to Direct Site-specific Nitrogen Application

Problem

Improving nutrient management on farms is a critical issue nationwide. Recent events demonstrate that nutrient management concerns are not going away. The Toledo, Ohio drinking water contamination and Des Moines, Iowa Water Works lawsuit against three counties for nitrate contamination are prime examples. In Nebraska, where groundwater contamination is the primary concern, some natural resource districts dictate when N is applied and require reporting. These events illustrate the need for farmers to actively pursue ways to improve their nutrient management. This is critical for preserving water as a vital natural resource and to demonstrate good stewardship to the general public.

Nitrogen fertilizer is applied to increase corn production, however inefficiencies in N fertilizer application are problematic. Applying a portion of N fertilizer during the growing season, alongside the growing corn crop is one way to improve nitrogen management. Sidedress N applications allow the availability of N fertilizer to more closely match the time when the crop is rapidly uptaking N. Additionally, waiting to apply a portion of the N during the growing season allows for management which is responsive to current growing season conditions. For example, higher than expected mineralization may result in more N being available to the crop. By waiting to apply a portion of the N during the growing season, farmers can be reactive to this decreased N fertilizer need and reduce applications accordingly. Conversely, heavy rainfall may lead to denitrification or leaching of N. By not applying all the fertilizer upfront, less N is lost and additional N fertilizer can be supplied to meet crop demand. Additionally, variable-rate N fertilizer applications have the ability to direct N applications according to spatial variations in the field, further improving N use efficiency. These strategies provide environmental and economic benefit, but are not widely utilized.

Solution

This project will promote adoption of in-season and variable-rate N management. The goal of this research project is to evaluate the use of a passive crop canopy sensor to direct variable-rate, in-season N fertilizer recommendation rates on corn. The sensor will calculate a normalized difference red edge index (NDRE) which is an established means of determining the N status of the crop. Compact, lightweight sensors have been produced, allowing them to be attached to an unmanned aerial vehicle (UAV) to rapidly and frequently monitor crop NDRE.

Research protocol:

The randomized, replicated on-farm research experiment will have three treatments:
1) traditional: static-rate, pre-plant N application at a rate normally used
2) sensor+algorithm: A sensor on a UAV will determine crop NDRE throughout the growing season. At each sensing, a virtual reference will be calculated (Holland and Schepers, 2013). This reference is comprised of the NDRE values of the top 5% “best-looking” corn in the field. When NDRE values of the sensor+algorithm treatment strip decline to 95% of the reference, a variable-rate application of N will be made using the Holland and Schepers sensor algorithm (Holland and Schepers, 2010) to determine the N rate.
3) sensor+Maize-N model: Same as the sensor+algorithm, but using the Maize-N model (Setiyono et al., 2011) instead of the Holland and Schepers algorithm.

For treatments two and three, 75 lb N/acre will be applied at planting. In season applications for treatments two and three will be made as described above, using aerial application of dry urea. Our hypothesis is that this tool will reduce over-application of nitrogen, reduce environmental contamination, and provide economic benefit for farmers due to more precise nitrogen management.

Research will be implemented in 2017 (one field) and 2018 (two fields).

1. Reduce environmental contamination by improving N management.
2. Increase farmer profitability by improving N efficiency.