Sensor- and Evapo-Transpiration-Based Irrigation for Plant Process Quantification for Drought.

Quantitative information on soil moisture-dependent plant processes is vital for crop management and modeling, particularly with projected shrinking and uneven distribution of rainfall and irrigation water supplies due to climate change. Several experiments were conducted in sunlit growth chambers to determine the growth, physiology, biomass, and yield responses of sweetpotato and cotton under evapotranspiration (ET)-based irrigation treatments of 100, 60, 40, and 20% ET imposed at specific crop growth stages. During these experiments, measurements were made of leaf water potentials (LWP) at midday, soil moisture, plant gas exchange and several growth and developmental parameters. The midday LWP was strongly and linearly correlated with soil moisture content showing the interplay between these two processes. Net photosynthesis (Pn), stomatal conductance, and transpiration rates (Tr) declined while photosynthetic water-use efficiency (Pn/Tr) increased with decreasing LWP. Both total chlorophyll content and cell membrane thermostability decreased linearly as midday LWP decreased. Stem/vine length, leaf area, and node number per plant decreased linearly as soil moisture content decreased in both the crops. Seed cotton, individual seed weight, boll number, and total biomass were reduced significantly under severe water deficit treatments, reflecting declining trends in photosynthesis. Cotton fiber length, strength, and uniformity declined linearly with decrease in LWP; whereas, fiber micronaire increased. Changes in LWP had a large effect on fiber strength, followed by micronaire, length, and uniformity. Immature fiber content increased and fiber maturity ratio decreased with diminishing LWP. In sweetpotato, vine length, leaf area, and node number per plant decreased linearly by approximately 3.2 cm, 96.6 cm², and 0.39 no. plant^-1, respectively, per unit change in ET-based irrigation. The optimum soil moisture treatments for total plant and storage root dry weight were 100 and 72% of ET, respectively. Biomass partitioning to storage roots declined linearly and leaf and stem portioning increased with increases in irrigation. Outcomes of this research will enable producers to schedule irrigation to optimize yield and researchers to develop process-based models for various crops.