UNCORRECTED PROOF Development of crop water stress index of wheat crop for scheduling irrigation using infrared thermometry N.K. Gontia a , K.N. Tiwari b, * a College of Agricultural Engineering and Technology, Junagadh Agricultural University, Junagadh 362001, Q1 Gujarat, India b Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur 721302, West Bengal, India 1. Introduction The globally growing demand for water has ushered the need for its efficient and judicial utilizations in all fields, and agriculture in particular being a single largest consumer of water. The majority of irrigation projects in India perform at a very low efficiency, which calls for application of efficient water management technologies for meeting the increasing water demands. Estimation of soil moisture or crop evapo- transpiration from climatic parameters provides objective criteria for irrigation management. Methods to estimate evapotranspiration require huge climatic data, which are seldom available and not applied by common crop growers. Estimation of crop water requirement through soil moisture requires soil moisture measurement at several locations, which is time consuming exercise and may not give proper assessment of crop water need. However, the plant based indicator approach considers the plant water status for scheduling irrigation. This might be considered as the ideal criterion because the plant water is a good integrator of the soil, water and climatic parameters. When plants are under water stress causes stomatal closure, which interrupt in energy dissipation and result in rise of leaf temperature. The leaf or canopy temperature is agricultural water management xxx (2008) xxx–xxx 1 2 3 4 5 6 7 8 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 24 24 25 26 27 28 29 30 31 32 33 34 35 36 article info Article history: Received 7 July 2007 Accepted 26 April 2008 Keywords: Canopy–air temperature difference Infrared thermometry Crop water stress index (CWSI) Irrigation scheduling abstract This study was conducted to develop the relationship between canopy–air temperature difference and vapour pressure deficit for no stress condition of wheat crop (baseline equations), which was used to quantify crop water stress index (CWSI) to schedule irrigation in winter wheat crop (Triticum aestivum L.). The randomized block design (RBD) was used to design the experimental layout with five levels of irrigation treatments based on the percentage depletion of available soil water (ASW) in the root zone. The maximum allowable depletion (MAD) of the available soil water (ASW) of 10, 40 and 60 per cent, fully wetted (no stress) and no irrigation (fully stressed) were maintained in the crop experiments. The lower (non-stressed) and upper (fully stressed) baselines were determined empirically from the canopy and ambient air temperature data obtained using infrared thermometry and vapour pressure deficit (VPD) under fully watered and maximum water stress crop, respectively. The canopy–air temperature difference and VPD resulted linear relationships and the slope (m) and intercept (c) for lower baseline of pre-heading and post-heading stages of wheat crop were found m = 1.7466, c = 1.2646 and m = 1.1141, c = 2.0827, respectively. The CWSI was determined by using the developed empirical equations for three irrigation schedules of different MAD of ASW. The established CWSI values can be used for monitoring plant water status and planning irrigation scheduling for wheat crop. # 2008 Published by Elsevier B.V. * Corresponding author. Tel.: +91 3222 283150; fax: +91 3222 255303. E-mail addresses: kamlesh@iitkgp.ac.in, kamlesh_iitkgp@yahoo.co.in (K.N. Tiwari). AGWAT 2615 1–9 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/agwat 0378-3774/$ – see front matter # 2008 Published by Elsevier B.V. doi:10.1016/j.agwat.2008.04.017 Please cite this article in press as: Gontia, N.K., Tiwari, K.N., Development of crop water stress index of wheat crop for scheduling irrigation using infrared thermometry, Agric. Water Manage. (2008), doi:10.1016/j.agwat.2008.04.017