Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/15/2001
Publication Date: 11/15/2001
Citation: Bausch, W.C., Diker, K. 2001. Innovative remote sensing techniques to increase nitrogen use efficiency of corn. Communications in Soil Science and Plant Analysis. Interpretive Summary: A recent nutrient use survey showed that corn was the most fertilized crop with 97 % of the planted area fertilized with commercial sources of nitrogen (N). Managing N fertilizer so the crop uses as much of the applied nitrogen as possible each year is known as efficient N fertilizer management. To accomplish this, producers must be aware of the various sources of N available to the crop other than fertilizer and how to minimize N loss. The total amount of N required must be determined from reasonable estimates of yield, residual soil nitrate-nitrogen, and soil organic matter followed by an evaluation of N credit from other sources such as irrigation water, legumes, and manure. Since the plant is an integrator of its environment, it may be easier to allow the crop to indicate its N status rather than attempting to predict the N supply capability from these sources. Ground-based remote sensing was utilized in nthis study to assess the N status of an irrigated corn crop and to recommend when N applications should be applied during the growing season on an "as needed" basis. A wedge or pie-shaped area within a commercial center pivot sprinkler-irrigated field was used as a test area. Total N applied during the growing season to the pie-shaped area was reduced by 39.2 kg N/ha (35 lb N/ac) without reducing grain yield [13458 kg/ha (214 bu/ac) in the wedge as opposed to 12893 kg/ha (205 bu/ac) for the remainder of the field]. This reduction in applied N was equivalent to reducing input costs by $6.61/ac.
Technical Abstract: Nitrogen (N) fertilizer recommendations made without adequate knowledge of the N supply capability of a soil can lead to inefficient use of N. Proper crediting of N from manure and legumes as well as mineralization of N from organic matter is difficult. Remote sensing techniques that use the crop to indicate its N status show considerable promise for improving N management. Objectives of this paper were twofold: 1) to compare the N Reflectance Index (NRI) calculated from ground-based radiometer measurements acquired over irrigated corn (Zea mays L.) at a nadir view and an oblique view with measured plant N and 2) to evaluate the NRI obtained from both view angles for correcting in-season N deficiencies in a commercial corn field. The NRI calculated from canopy reflectance was not representative of plant N at the sixth leaf growth stage (V6) for either view angle because of the soil background influence on canopy reflectance. However, the oblique view NRI was a good predictor of plant N at V9 and V1 as was the nadir view NRI at V12. The nadir view NRI was not as sensitive as the oblique view NRI at the V9 growth stage because soil was still visible through the canopy. Consequently, the nadir view NRI provides a conservative estimate of plant N prior to complete canopy cover. Use of the nadir view NRI to detect in-season corn N deficiencies for the 1999 growing season reduced N application during the growing season by 39.2 kg N/ha without reducing grain yield. If the oblique view NRI would have been used to assess the plant N status, the first fertigation would not have been recommended which would have saved additional N.