Submitted to: Plant Biosystems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/4/2012
Publication Date: 1/1/2013
Citation: Baker, J.T., Gitz, D.C., Lascano, R.J., Mahan, J.R., Eprath, J.E. 2013. Comparison of deficit irrigation scheduling methods that use canopy temperature measurements. Plant Biosystems. 147(1):40-49. Interpretive Summary: Plants that suffer from water stress can’t release enough water from their leaves to cool themselves. This causes water stressed plants to heat up during the day. Plant temperatures can be automatically measured with devices called infrared thermometers. In this experiment we compared two different methods of using plant temperatures to assess the amount of plant water stress and schedule irrigations. The first method applied more water early in the season compared with the second method. We conclude that both methods can suggest when to apply irrigation water but neither of these methods can determine how much water to apply. Further research will be needed to answer this last question.
Technical Abstract: Canopy temperature (Tc) provides an easy to acquire indication of crop water deficit that has been used in irrigation scheduling systems, but interpretation of this measurement has proven difficult. We compared the timing of irrigation application of the Stress Time (ST) method of irrigation scheduling with the Stress Degree Hours (SDH) method on deficit irrigated cotton (Gossypium hirsutum L.) where each irrigation event delivered 5 mm of water through subsurface drip tape. A well watered (WW) control and a dry land (DL) treatment were also part of the experimental design. We used data collected from the WW and DL treatments to develop upper and lower baselines for the Crop Water Stress Index (CWSI) appropriate for cotton grown at our location here in West Texas. The ST method detected drought stress earlier in the growing season when both the SDH and CWSI indicated very little drought stress. The SDH method applied irrigations relatively later in the growing season when the CWSI also detected higher levels of drought stress. These results suggest that the adding certain micrometeorological variables to simple Tc methods of deficit irrigation scheduling may improve the ability to detect and quantify the degree of crop drought stress. As expected, cotton lint yields increased with applied water.