DETERMINATION OF SOIL AND CROP WATER STATUS FOR IRRIGATION SCHEDULING IN A HUMID ENVIRONMENT

Authors: Sassenrath, Gretchen; PRINGLE, H. - DREC; ALARCON-CALDERON, V - MSU

Submitted to: American Society of Agronomy Branch Meeting
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2003
Publication Date: 2/2/2003
Citation: SASSENRATH COLE, G.F., PRINGLE, H.C., ALARCON-CALDERON, V.J. DETERMINATION OF SOIL AND CROP WATER STATUS FOR IRRIGATION SCHEDULING IN A HUMID ENVIRONMENT. SOUTHERN BRANCH OF AMERICAN SOCIETY OF AGRONOMY ABSTRACTS. 2003. Session 4: 11:45, p. 17.

Interpretive Summary: Increased dependence on irrigation to insure adequate crop production has increased the need to reliable, accurate irrigation scheduling. In arid environments, irrigation scheduling methods have been developed that rely on remote sensing of crop and soil moisture status for information on supplemental water needs. In humid growing environments, environmental conditions complicate the detection of crop and soil moisture status due to interference from humidity in the atmosphere. This study explores the potential of remote sensing methods, including spectral reflectance in the visible region, and thermal emissivity, to detect the onset of crop water stress. We have developed a method of analyzing spectra that retains all of the information in the spectra, by performing a Fourier transformation of the spectral information. These transformed spectra can then be mathematically manipulated to develop synthetic images. The individual components contributing to the canopy image can then be isolated and examined individually as to their impact in the canopy spectral image. The synthetic images generated in this fashion are true to the actual canopy spectra.

Technical Abstract: Producers in the Mid-South have adopted no standard method to monitor soil moisture or crop water stress for irrigation purposes. To increase implementation of automated irrigation scheduling, we need rapid detection methods for determination of crop water status. We are exploring visible and thermal remote imagery for its potential in estimating available soil water and detecting crop water status. While the water potential of the soil and individual leaves or plants can be measured with a fair degree of accuracy, extrapolation from these well-defined measures in a small portion of a field to an estimate of whole field canopy water status is error-prone. Changes in canopy structure and leaf angle alter the reflectance and introduce deviations in the recorded spectra due to increases in reflectance from the soil and lower canopy layers. These factors, together with atmospheric distortions, change the reflectance spectra of a crop canopy from that recorded for individual leaves or plants within that canopy. This study explores the feasibility of remote sensing in the thermal and visible regions for detecting the onset of water stress in cotton canopies under the humid growing conditions of the Mid-South. Soil water availability was altered in research plots through changes in tillage and irrigation. Concurrent measurements of insolation, air temperature and spatial position were taken with various sensors mounted on a boom for rapid scanning of test plots. The measured individual leaf spectral characteristics were then approximated by Fourier transformations, and then randomly mixed and visualized using an imaging software package. The resultant synthetic spectra were remarkably similar to remote images of crop fields obtained from aerial sources.