|Scharf, Peter -|
|Palm, Harlan -|
|Roberts, Darrin -|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2009
Publication Date: November 13, 2009
Citation: Kitchen, N.R., Sudduth, K.A., Drummond, S.T., Scharf, P.C., Palm, H.L., Roberts, D.F., Vories, E.D. 2010. Ground-Based Canopy Reflectance Sensing for Variable-Rate Nitrogen Corn Fertilization. Agronomy Journal. 102:71-84. Interpretive Summary: With increasing costs for crop inputs, corn farmers are interested in better methods to help them precisely apply the rate of nitrogen (N) fertilizer that will give them optimal profit. Additionally, environmental concerns continue because a large amount of N from agricultural fields moves into streams, rivers, and oceans. Since more N fertilizer in the U.S. is applied to corn than any other crop, interest is high for exploring new technologies for improved corn N management. In recent years, light reflectance sensors have been proposed as a technology on which to base side-dress variable-rate N applications. This research was conducted to assess the utility of these sensors for determining the most profitable N rates in corn. Findings over three diverse Missouri soil types demonstrate sensor-based variable-rate N fertilizer applications could generate an increase in returns ranging from $10 to $20 per acre. As fertilizer cost increases relative to the price of corn grain, the value of using canopy sensors for N management improves. Differences were also observed when comparing soil types. River bottom soils appeared to be especially well-suited for this technology. The results of this study are being used to develop procedures and decision rules for how much N to apply in corn. Farmers will benefit because they can reduce excess N applications, which with increasing N fertilizer cost, should save them money. If fertilizer can be better matched with crop need, N loss to lakes and streams will be reduced and the environment will be improved.
Technical Abstract: Nitrogen (N) available to support corn (Zea mays L.) production can be highly variable within fields. Canopy reflectance sensing for assessing crop N health has been proposed as a technology to base top-dress variable-rate N application. Objectives of this research were to evaluate the use of active-light crop-canopy reflectance sensors for assessing corn N need, and derive the N fertilizer rate that would return the maximum profit relative to a single producer-selected N application rate. A total of 16 field-scale experiments were conducted over four seasons (2004-2007) in three major soil areas. Multiple blocks of randomized N rate response plots traversed the length of the field. Each block consisted of 8 treatments from 0 to 235 kg N/ ha on 34 kg N/ha increments, top-dressed between V7-V11 vegetative growth stages. Canopy sensor measurements were obtained from these blocks and adjacent N-rich reference strips at the time of top-dressing. Within fields, the range of optimal N rate varied by more than 100 kg N/ha in 13 of 16 fields. A sufficiency index calculated from the sensor readings correlated with optimal N rate, but only in 50% of the fields. As fertilizer cost increased relative to grain price, so did the value of using canopy sensors for N management. While soil type, fertilizer cost, and corn price all affected our analysis, a modest ($25 to $50/ha) profit using canopy sensing was found. These results affirm using crop-canopy reflectance sensors for detecting corn N fertilizer needs that vary spatially within fields.