Remote Sensing for Crop Management

Scientists with the Agricultural Research Service (ARS) and various government agencies and private institutions have provided a great deal of fundamental information relating spectral reflectance and thermal emittance properties of soils and crops to their agronomic and biophysical characteristics. This knowledge has facilitated the development and use of various remote sensing methods for non-destructive monitoring of plant growth and development and for the detection of many environmental stresses which limit plant productivity. Coupled with rapid advances in computing and positionlocating technologies, remote sensing from ground-, air-, and space-based platforms is now capable of providing detailed spatial and temporal information on plant response to their local environment that is needed for site specific agricultural management approaches. This manuscript, which emphasizes contributions by ARS researchers, reviews the biophysical basis of remote sensing; examines approaches that have been developed, refined, and tested for management of water, nutrients, and pests in agricultural crops; and assesses the role of remote sensing in yield prediction. It concludes with a discussion of challenges facing remote sensing in the future. Introduction Agricultural production strategies have changed dramatically over the past decade. Many of these changes have been driven by economic decisions to reduce inputs and maximize profits and by environmental guidelines mandating more efficient and safer use of agricultural chemicals. However, growers now have a heightened sensitivity to concerns over the quality, nutritional value, and safety of agricultural products. They are selecting cultivars and adjusting planting dates to accommodate anticipated patterns in weather, e.g., El Niño or La Niña events (Jones et al., 2000). They are also relying on biotechnological innovations for suppressing pests, e.g., insect protected (Bt) and Roundup® ready crops (Monsanto Company, 2003). The possibility for selling carbon credits to industry is breathing new life into on-farm conservation tillage practices that enhance carbon sequestration (Robert, 2001). Perhaps the most significant change in agriculture during the past ten years is the shift towards precision, or sitespecific, crop management (National Research Council, 1997). Growers have long recognized within-field variability in potential productivity. Now, at the beginning of the 21st Century, they are seeking new ways to exploit that variability. In the process, they are discovering they need more information on soil and plant conditions than was required a decade ago. Not only does this information need to be accurate and consistent across their farm and from year to year, it must also be available at temporal and spatial scales that match rapidly evolving capabilities to vary cultural procedures, irrigations, and agrochemical inputs. A very large body of research spanning almost four decades has demonstrated that much of this required information is available remotely, via aircraftand satellitebased sensor systems. When combined with remarkable advances in Global Positioning System (GPS) receivers, microcomputers, geographic information systems (GIS), yield monitors, and enhanced crop simulation models, remote sensing technology has the potential to transform the ways that growers manage their lands and implement precision farming techniques. The objective of this paper is to review progress that has been made in remote sensing applications for crop management and, in particular, highlight the role that the USDA and its primary research agency, the Agricultural Research Service (ARS), has had in the movement. Of course, these advances have not been a singular effort by ARS (Pinter et al., 2003; p. 615 this issue). They have resulted from long-standing cooperation among a number of different agencies and institutions, all in pursuit of expanding remote sensing’s role in providing information for crop management. We will begin with some fundamental relationships between the electromagnetic spectrum and basic agronomic conditions and biophysical plant processes, and then present specific examples of remote sensing P H O T O G R A M M E T R I C E N G I N E E R I N G & R E M O T E S E N S I N G Photogrammetric Engineering & Remote Sensing Vol. 69, No. 6, June 2003, pp. 647–664. 0099-1112/03/6906–647$3.00/0 © 2003 American Society for Photogrammetry and Remote Sensing P.J. Pinter, Jr., is with the USDA, ARS, U.S. Water Conservation Laboratory, 4331 E. Broadway Rd., Phoenix, AZ 85040-8807 (ppinter@uswcl.ars.ag.gov). J.L. Hatfield is with the USDA, ARS, National Soil Tilth Research Laboratory, 2150 Pammel Dr., Ames/Ankeny, IA 50011-3120 (hatfield@nstl.gov). J.S. Schepers is with the USDA, ARS, Soil and Water Conservation Research Laboratory, 120 Keim Hall on the University of Nebraska E. Campus, Lincoln, NE 68583-0934 (jschepers1@unl.edu). E. M. Barnes was with the USDA, ARS, U.S. Water Conservation Laboratory, 4331 E. Broadway Rd., Phoenix, AZ 85040-8807; he is currently with Cotton Inc., 6399 Weston Parkway, Cary, NC 27513 (Ebarnes@cottoninc.com). M.S. Moran is with the USDA, ARS, Southwest Watershed Research Center, 200 E. Allen Rd., Tucson, AZ 85719-1596 (smoran@tucson.ars.ag.gov). C.S.T. Daughtry is with the USDA, ARS, Hydrology and Remote Sensing Laboratory, Bldg. 007, BARC-West, 10300 Baltimore Blvd., Beltsville, MD 20705-2350 (cdaughtry@ hydrolab.arsusda.gov). D.R. Upchurch is with the USDA, ARS, Cropping Systems Research Laboratory, 3810 4th Street, Lubbock, TX 79415 (dupchurch@lbk.ars.usda.gov). IPC_Grams_03-904 4/12/03 7:40 AM Page 1