Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2011
Publication Date: 7/21/2011
Citation: O'Shaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2011. Using radiation thermography and thermometry to evaluate crop water stress in soybean and cotton. Agricultural Water Management. 98(10):1523-1535.
Interpretive Summary: Cropped fields are often variable in terms of topography and soil type or because of disease or non-uniform plant growth. This variability can lead to decreased crop yields if irrigation is applied uniformly. The use of remote sensors to measure crop canopy temperature is one useful method of providing information to a farmer with large or multiple fields. By mounting sensors on a moving sprinkler system and capturing data daily, timely information can be provided to a farmer. This information can help improve crop productivity and decrease time investment in overseeing irrigation delivery. In this study, temperatures from thermal images and infrared thermometers were used to calculate an empirical crop water stress index. This index was used because of its simplicity and requirement for few additional inputs. Results showed that the stress index is strongly related to in-situ stress indicators, plant water use efficiency, and crop yield. Also, temperature data from infrared thermometers mounted on a moving pivot can be used to provide the spatial location of stressed crops on a frequent basis which may aid in irrigation scheduling.
Technical Abstract: The use of digital infrared thermography and thermometry to investigate unapparent but important field conditions (poor drainage, non-uniform irrigation, soil variability, or biotic infestations) offers a producer improved management tools to avoid yield declines or to deal with variability in crop status. This study investigated historical spatial and temporal crop water stress based on crop canopy temperature extracted from remote thermal images and infrared thermometry from soybean (Glycine max L.) and cotton (Gossypium hirsutum L.) crops cultivated under a center pivot using manual and automatic irrigation control. Canopy temperature data from infrared thermography was used to benchmark the relationship between an empirical crop water stress index (CWSIe) and leaf water potential across a block of eight treatment plots (of two replications) receiving irrigation levels of 100, 67, 33, and 0% of full replenishment of soil water to field capacity in the top 1.5 m. There was a significant negative linear correlation between midday leaf water potential measurements and the CWSIe after irrigation treatments were well established and during the absence of heavy rainfall. Average seasonal CWSIe values calculated from canopy temperature measured with infrared thermometer thermocouples mounted on a center pivot lateral were significantly related to crop water use with r**2 values greater than 0.89 and 0.55 for soybean and cotton, respectively. Crop yields from the differentially irrigated treatment plots were negatively correlated to the CWSIe, with r**2 values ranging from 0.88 to 0.83 for soybean grown in 2004 and 2005, and from 0.85 to 0.74 for cotton in 2007. The correlation was not significant in 2008 for cotton. The spatial and temporal CWSIe contour maps indicated that differences in water stress were detectable two weeks after irrigation treatments were applied.