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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Water Management and Conservation Research » Research » Publications at this Location » Publication #330620
Title: Active optical sensors in irrigated durum wheat: Nitrogen and water effects

Author
item Bronson, Kevin
item White, Jeffrey
item Conley, Matthew
item Hunsaker, Douglas - Doug
item Thorp, Kelly
item French, Andrew
item Mackey, Bruce
item HOLLAND, KYLE - Holland Scientific

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2017
Publication Date: 4/6/2017
Publication URL: https://handle.nal.usda.gov/10113/5700712
Citation: Bronson, K.F., White, J.W., Conley, M.M., Hunsaker, D.J., Thorp, K.R., French, A.N., Mackey, B.E., Holland, K.H. 2017. Active optical sensors in irrigated durum wheat: Nitrogen and water effects. Agronomy Journal. 109:1060-1071.

Interpretive Summary: The use of active optical sensors (AOS) for directing nitrogen (N) management of wheat (Triticum aestivum L.) has received much interest since the mid-1990s. Recently, AOS have been tested to assess water stress of crops in addition to plant N. Researchers have tried using vegetation indices (VIs) that employ red-edge reflectance, instead of the more usual visible and near infrared bands. Such an approach might assess N stress while minimizing effects of water stress. We conducted a 2-year study on a Casa Grande sandy loam soil in Maricopa, AZ with durum wheat (Triticum durum Desf) under an overhead sprinkler system. Uniquely, this study had 10 un-randomized levels of irrigation and five rates of N fertilizer. The objectives of the study were to compare 12 vegetation indices (VIs) for their ability to distinguish irrigation and N fertilizer effects, and to determine how well the VIs estimated biomass, plant N, grain yield, grain N, and yellow berry (yellow/low protein grains). Two Crop Circle 470 AOS with optical-band pass filters at 800, 730, 670, 590, and 530 nm were passed 1 m above the canopy, every 10 days during the growing season. The twelve vegetation indices calculated were NDVIA, NDVIR, NDVIG (amber, red, and green as the visible bands), and NDARE, NDRRE, NDRE, CCCI, DATT, PRI, CI, MTCI, and CIRE. Canopy temperature was also measured with infrared thermometers (IRTs). The three NDVIs showed very high N response in all four growth-stage-year combinations, and strong water response in three of four growth-stage years. The CCCI, DATT, and MTCI were the VIs with the best ability to assess N stress/effects with minimal effects of water.

Technical Abstract: Interest in the use of active optical sensors (AOS) for guiding nitrogen (N) management of crops like wheat (Triticum aestivum L.) has been strong since the mid-1990s. Recently, AOS have been used to assess water status of crops in addition to plant N status. Researchers have investigated vegetation indices (VIs) that employ red-edge reflectance, instead of relying solely on visible and near infrared bands that are used in the typical normalized difference vegetation index calculation. Specific VIs might assess N stress while minimizing water stress. We conducted a 2-year study on a Casa Grande sandy loam soil in Maricopa, AZ with durum wheat (Triticum durum Desf) under an overhead sprinkler system. Uniquely, this study had 10 un-randomized levels of irrigation and five rates of N fertilizer. The objectives were to compare 12 vegetation indices (VIs) for their ability to distinguish irrigation and N fertilizer effects and to determine how well the VIs estimated biomass, plant N, grain yield, grain N, and yellow berry. Two Crop Circle 470 AOS with optical-band pass filters at 800, 730, 670, 590, 550, and 530 nm were passed 1 m above the tallest plants in the field, every 7-10 days during the growing season. The twelve vegetation indices calculated were NDVIA, NDVIR, NDVIG (amber, red, and green as the visible bands), and NDARE, NDRRE, NDRE, CCCI, DATT, PRI, CI, MTCI, and CIRE. Canopy temperature was also measured with infrared thermometers (IRTs). In-season biomass at Zadoks 32 did not respond to N rate but did respond to irrigation level. Biomass at Zadoks 39 responded to N and water both years. Total N uptake was more affected by N than by water. The three NDVIs showed very high N response in all four growth-stage-year combinations, and high water response in three of four growth-stage-years. The CCCI, DATT, and MTCI were the most consistent VIs in responding to N, with minimal water effects. The CCCI at Zadoks 32 or 39 also showed the strongest potential among the VIs in estimating final grain N concentration. No VIs detected water stress with minimal N effect as well as IRTs.