2Plant-based techniques to measure crop water status offer advantages over soil-based methods. 3 The objective of this study was to quantify the relationship between leaf thickness 4 measurements, as a promising plant-based technique, with leaf relative water content (RWC) and 5 assess the model across different species and leaf positions. The relationship between RWC and 6 relative thickness (RT) was determined on corn (Zea mays L.), sorghum (Sorghum bicolor (L.) 7 Moench), soybean (Glycine max (L.) Merr.), and fava bean (Vicia faba L.). RWC was calculated 8 as measured leaf water content/leaf water content at full turgor, and RT as measured leaf 9 thickness/leaf thickness at full turgor. Two leaves from the top, middle, and bottom of five plants 10 of each species were collected at 60 days of age. Leaf samples brought to full turgor were left to 11 dehydrate in a lab. Leaf thickness was measured using a magnetic field sensor and water content 12 using weight loss. The RWC-RT relationship showed a distinct breakpoint, which we 13 hypothesize coincides with the turgor loss point. Linear piecewise modelling was used to regress 14 RWC versus RT, resulted in models explaining 86-97% of the variations. The precision was 15 improved by including leaf position on the plant in the model. The piecewise model parameters 16 were related to salt tolerance of the species, which is also an indicator of drought resistance.
17Generally, the species with greater drought and salinity tolerance had a larger RT at the 18 breakpoint.
19Keywords: leaf thickness sensor; water stress; plant water status; drought tolerance; leaf 20 structure; piecewise model. 21 22 5early or late irrigation, which may lead to water or yield loss. Ideally continuous measurements 6 of plant water status would be the optimum means to determine the best irrigation timing.
7Common methods of plant water status estimation for practical applications tend to range from 8 the simple visual wilting approach to measurement intensive evapotranspiration models, or soil 9 moisture measurements (Jones, 2004). Irrigation scheduling based on plant measurements merits 10 consideration as an alternative to soil measurements and/or water balance computations. There 11 are plant-based alternatives for estimating plant water needs, such as pressure chamber, 12 psychrometer, thermal sensing, and sap-flow sensors (Jones, 2004). We propose a simple 13 measurement method based on leaf thickness as suggested by Seelig, Stoner, and Linden (2011).Instead of improving soil moisture measurement methods or evapotranspiration models, we 1 suggest it may be better if the critical water stress points at which irrigation should start could be 2 directly measured on the crops grown. Plant-based approaches may offer a more reliable plant 3 water status estimation by reducing the need for complex calculations and data sets associated 4 with soil-plant-atmosphere water relationship (Jones, 2004; Kramer & Boyer, 1995). In this 5 study, we set out to determine if leaf thickness could be a...
