Fig. 2. Plateau regression applied to the relationship between the normalized transpiration ratio (NTR) and relative soil water content (RSWC) for two entries (Haskell and G2120) in a single replication. Data for which NTR < 0.1 (horizontal dashed line) were not included in the regression. The critical relative soil water content (RSWC_c) is the RSWC where NTR is estimated to begin to decline; above RSWC_c, NTR is assumed to be 1.0. The RSWC at which NTR = 0.1 (RSWC₁₀) was estimated by interpolation from the regression. This value was used to calculate the critical fraction of transpirable soil water (FTSW_C) from RSWC_C as described in the text.