Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 15, 1995
Publication Date: N/A
Interpretive Summary: Aerial photographs are a relatively inexpensive way to visually evaluate spatial variability in crop growth. Irrigated corn was grown at five different rates of nitrogen (N) fertilizer to generate a range of canopy colors. A color aerial photograph of the corn canopy in the mid-grain fill period was digitized and the color or each pixel was separated into its three primary components (i.e., red, green, and blue). The intensity of each color component was compared with grain yield. The intensity of both the red (~650 nm) and green (~550 nm) colors correlated well with corn yield. A digitized black-and-white aerial photograph taken through a lens filtered at 536 nm also produced data that was highly correlated with corn yield. This technology permits the use of low cost aerial photographs to characterize variability in crop N status throughout a field. Producers and consultants can use such aerial photographs to improve N management practices.
Technical Abstract: Spatial variability of soil parameters with fields complicates N fertilizer recommendations for corn production. Thus, the ability to identify differences in crop N status with corn fields could lead to efficiencies in N fertilizer application and decreased ground water pollution. In this study, we digitized aerial color photographic transparencies using an eight-bit system to generate digital counts for the red, green, and blue primary colors in photographs taken at the R5 growth stage and related them to yield. Digital count responses were relative to the N treatment in which grain yield plateaued. Experiments were conducted in 1992 and 1993 using four irrigated corn hybrids with five fertilizer N rates on a 6-ha field near Shelton, Nebraska. Red and green digital counts relative to those for the high N treatment provided better prediction of yield response than relative blue counts in both years. Black-and-white photographs, also obtained in 1993, that were exposed to light centered around 536 nm also predicted yield response to N well (r2=0.93). These findings permit the use of low cost aerial photographs to characterize variability in crop N status throughout entire fields.