Canopy Temperature for Optimal Deficit Irrigation Scheduling.

Canopy temperature (C_T) is a good indicator of plant water stress and has been applied to irrigation scheduling in different systems using a derived Stress Time Threshold (STT) as a trigger. SST triggers for full irrigation may not be optimal especially for deficit furrow irrigation thus limiting C_T use in deficit irrigation. To extend its application to deficit irrigation in cotton (Gossypium hirsutum L.), a modified STT based on relationships of leaf water potential (Ψ_l) and soil water deficit to C_T was used to test the feasibility of C_T-based scheduling  with traditional (fixed soil water deficits) irrigation scheduling. Crop development, C_T, Ψ_l and soil moisture were monitored from first-square to boll opening. Pre-irrigation Ψ_l was not significantly different but was slightly higher in C_T (-1.8 ±0.1 MPa) than traditional (-1.6 ±0.1 MPa). No difference in plant height, biomass harvest, vertical and horizontal boll distribution, and yield (P<0.05) was observed  although mean modified STT between irrigations was 2.9h more in C_T than traditional schedule. C_T crops matured slightly earlier with 86 (±14) open bolls/m² at 176 days after sowing compared to 68 (±4) in the traditional. These findings show the applicability of C_T in deficit irrigation scheduling and suggest that it can be used to optimise yield by avoiding water stress, and to manipulate crop maturity.