Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/23/2008
Publication Date: 7/23/2008
Citation: Hatfield, J.L. 2008. Seasonal patterns of vegetative indices over cropping systems [CD-ROM]. In: International Conference on Precision Agriculture Abstracts & Proceedings, July 20-23, 2008, Denver, CO.
Technical Abstract: Remote sensing of reflectance in the visible and near-infrared portions of the spectrum has been used for agronomic applications for a number of years. The combination of different wavelengths into vegetative indices have proven useful for a variety of applications that range from biomass, leaf area, leaf chlorophyll, yield, crop residue, and crop damage. To help refine our understanding of vegetative indices studies were conducted on corn (Zea mays L.), soybean (Glycine max (L.) Merr.), wheat (Triticum aestivum L.), and canola (Brassica juncea var. juncea) canopies grown under different tillage systems and nitrogen rates to determine the temporal patterns of reflectance and vegetative indices. Additional studies were conducted on eight corn hybrids and eight soybean cultivars to determine if there were detectable differences among genetic material. Reflectance observations were made throughout the year on clear days to determine the reflectance patterns over bare soil and then over the crop canopies through the complete growing season. These observations were made with the four-band Exotech radiometer and the eight-band CropScan radiometer. The same locations were measured in each plot over the period from 2000 through 2007 with five subsamples within each plot. Reflectance over bare soil changed slightly as the soil surface was wet with rainfall and after tillage but the different indices showed little variation within treatments. There was no significant difference among treatments during the offseason. During the season the greatest difference occurred and the visible wavelengths showed little variation within the season with the greatest change in the near-infrared wavelengths. Variation in vegetative indices changed during the season and most showed the largest standard deviation during the vegetative period of development with the least variation during the grain fill period. The patterns changed with the vegetative index being used and this information will guide decisions for precision agriculture.