Crop response to thermal stress without yield loss in irrigated maize and soybean in Nebraska

Authors: BHATTI, SANDEEP - University Of Nebraska; HEEREN, DEREK - University Of Nebraska; Evett, Steven - Steve; O`Shaughnessy, Susan; RUDNICK, DARAN - University Of Nebraska; FRANZ, TRENTON - University Of Nebraska; GE, YUFENG - University Of Nebraska; NEALE, CHRISTOPHER - University Of Nebraska

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2022
Publication Date: 9/18/2022
Citation: Bhatti, S., Heeren, D.M., Evett, S.R., O'Shaughnessy, S.A., Rudnick, D.R., Franz, T.E., Ge, Y., Neale, C.M. 2022. Crop response to thermal stress without yield loss in irrigated maize and soybean in Nebraska. Agricultural Water Management. 274. Article 107946. https://doi.org/10.1016/j.agwat.2022.107946.
DOI: https://doi.org/10.1016/j.agwat.2022.107946

Interpretive Summary: Declining well yields in the U.S. Great Plains, California Central Valley, Mississippi Delta, and other regions of the country make effective irrigation scheduling crucial to maintaining crop yields and maximizing yield per unit of water used. But irrigators lack scheduling tools that are not labor intensive and expensive, while being readily available. In response to this problem, USDA-ARS scientists in Bushland, Texas, developed a patented automatic irrigation scheduling system using infrared thermometers (IRTs) to sense crop water stress and previously showed its effectiveness in maintaining yield per unit of water applied. However, a persistent question has remained: How can a crop yield be maintained when water stress is being detected? USDA scientists collaborating with a team at the University of Nebraska used this leaf canopy-based temperature sensor scheduling system to irrigate corn and soybean. They found there is a level of detectable crop water stress that occurs before yield loss begins which would allow timely irrigation to be scheduled. Therefore, irrigation scheduling techniques, like those patented by ARS-Bushland, can allow for some level of crop water stress without affecting crop yields, and promote maximum yields per unit of water applied. These results are of interest to irrigators and manufacturers of irrigation related equipment.

Technical Abstract: Crop water stress knowledge is crucial for irrigation scheduling and producing optimum yield. Thermal sensing provides rapid and accurate estimation of crop water stress through canopy temperature data. Canopy temperature is highly dependent on the transpiration rate of the leaves. It is usually assumed that any reduction in crop evapotranspiration (ET) leads to crop yield loss. As a result, an increase in canopy temperature due to a decrease in crop ET would indicate crop yield loss. This research was conducted to investigate whether crop water stress could be detected using canopy temperature measurements from infrared thermometers (IRTs) before incurring crop yield loss. It was hypothesized that this would be possible in a narrow range when the photosynthesis rate (and carbon assimilation) is limited by solar radiation instead of stomatal conductance. The response variables used in the analyses included integrated crop water stress index (iCWSI), ET, and crop yield for maize and soybean during the 2020 and 2021 growing seasons. The irrigation was applied at four different refill levels: rainfed (0%), deficit (50%), full (100%), and over (150%). The irrigation depth was prescribed using four different irrigation methods. The field was irrigated with a center pivot irrigation system, which was also used as a platform on which IRT sensors were mounted. The IRTs were also installed at two stationary locations with one IRT in each crop. The iCWSI thresholds for irrigation management were determined using the iCWSI dataset collected in 2020. The low, medium, and high iCWSI thresholds computed for triggering an irrigation event were 120, 150, and 180, respectively for maize and 110, 130, and 150, respectively for soybean. These thresholds could be used for triggering irrigation in a sub-humid location in the Central Great Plains. The iCWSI data for consecutive days after a wetting event were used to evaluate whether the thermal stress could be detected in the different irrigated treatments. The iCWSI and yield data for the fully watered plots indicated that the thermal stress was detected using the sensing system without incurring yield loss. The mean iCWSI values substantially increased with time from a wetting event for each level. The seasonal iCWSI for different levels were found to be negatively correlated with seasonal evapotranspiration for both years. The correlations between seasonal ET and crop yield were significant with the rainfed and deficit levels for maize (p-value < 0.001) and soybean (p-value = 0.04) in 2020. However, there were no correlations found between ET and crop yield with the full and over irrigation levels at a 5% significance level. Future studies should implement and evaluate the proposed iCWSI thresholds.