Utilizing Crop Reflectance to Assess Spatial Variations of Corn (Zea mays L.) Nitrogen Status In the Mississippi Delta.

Spatial and temporal variations in soil N availability reduce the accuracy of uniform fertilizer N rate application. The objective of this study was to assess various spectral vegetative indices in their ability to detect the corn (Zea mays L.) variability of N status during early season. An on farm study was conducted during the 2010 and 2011 growing seasons near Yazoo City, MS. A 0.2 ha sampling grid was utilized to sample an 18 ha field. Eighty sample locations resulted lying across 15 transects traversing 6 soil mapping units. A total of 10 whole plant samples were collected at each sample location at the V5-V6 growth stage both years. Whole plant %N values ranged from 3.23 to 5.32% in 2010 and 2.62 to 4.11% during 2011. Ground-based crop reflectance was measured using a tractor mounted Yara N sensor at the V5 and V6 growth stages during 2010 and 2011, respectively. Reflectance measurements were acquired prior to N fertilization in 2010, but were acquired after the initial (50%) fertilizer N application in 2011. The Canopy Chlorophyll Content Index (CCCI) expressed the strongest relationships to plant %N and whole plant N uptake across both years compared to other indices examined. The CCCI coefficients of determination for plant %N were 0.51(V5) and 0.35(V6) in 2010 and 2011, respectively. Canopy CCI coefficients of determination for whole plant N uptake were 0.67(V5) in 2010 and 0.82(V6) in 2011. Generally, CCCI values as influenced by plant %N and whole plant N uptake were best described by linear equations except for whole plant N uptake in 2011, which was best described by a quadratic equation. These findings suggest that CCCI may be a valuable tool for assessing early season N status of corn in the Mississippi Delta.