Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2010
Publication Date: 3/5/2010
Citation: Hatfield, J.L., Prueger, J.H. 2010. Value of Using Different Vegetative Indices to Quantify Agricultural Crop Characteristics at Different Growth Stages under Varying Management Practices. Remote Sensing. 2:562-578.
Interpretive Summary: Observations of plant canopies have been made possible through sensors which measure the reflectance in different wavelengths. These wavelengths have been arranged into combinations of different vegetative indices which have been related to various canopy parameters like amount of biomass, leaf area, greenness of the leaves, and even crop yield. Many of the studies have used single observations during the growing season to assess plant canopies. This study was conducted across multiple years with the same sensors to observe the changes in reflectance over different cropping systems. Observations were collected as many as 40 times during the year over these systems for the purpose of evaluating the changes in the vegetative indices over time and to determine when these indices provided the most reliable information about plant canopies. An examination of the individual wavelengths showed the rapid increase in the near-infrared reflectance as the canopy developed and a decrease in the visible reflectance. There was little variation among the wavelengths when the soil was not covered with growing plants. The changes in the variation of the different indices reveal information about the capability of the vegetative index to detect changes. This information provides insights into how remote sensing information can be used by consultants and producers to evaluate field variation patterns.
Technical Abstract: Combination of different wavelengths into vegetative indices has proven useful for a variety of applications that range from biomass, leaf area, leaf chlorophyll, yield, crop residue, and crop damage. To determine the temporal patterns of reflectance and vegetative indices, reflectances were obtained from a four-band Exotech and an eight-band CropScan radiometer from corn (Zea mays L.), soybean (Glycine max (L.) Merr.), wheat (Triticum aestivum L.), and canola (Brassica juncea var. juncea) canopies grown under different tillage practices and nitrogen rates. Reflectance from 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. 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.