Partial root-zone drying in field-grown papaya: Gas exchange, yield, and water use efficiency

Partial rootzone drying (PRD) is an irrigation technique that usually applies less water (than well-watered control treatments) to only part of the rootzone (the irrigated side) and alternates the irrigated and non-irrigated sides. However, an incomplete understanding of the effects of its components (decreased water application versus frequency of alternating the irrigated side) on physiological responses of fruit crops such as papaya, is considered to be a constraint for its adoption under semiarid conditions. Therefore, a study was performed to determine effects of PRD on soil water dynamics, leaf gas exchange, yield, water use efficiency and water footprint in field grown papaya. Yields and physiological measurements were evaluated under control (Full Irrigation FI) and restricted (50 % and 35 % reduction in irrigation water depth IWD) irrigation with the irrigated side alternated every 0, 7, 14 and 21 days. A drip irrigation system with three emitters on each side of the plant was used to apply surface drip irrigation as needed to supplement natural rainfall during the study period. Physiological functions, including stomatal conductance (gs), transpiration (E) and net photosynthesis (A) did not differ among treatments, but resultant differences in plant height and diameter growth rates were found to be significantly and positively related to yield. Decreasing the irrigation applied at moderate alternate frequency (PRD7 35 % and PRD14 35 %) increased agronomic water use efficiency of papaya (AWUE) without compromising its yield and gas exchange. Therefore, PRD strategy with irrigated side alternation frequency of every 7-14 days with a 35 % reduction in the irrigation depth could become a viable technique to reduce the water footprint of papaya, thus increasing the effective use of water under semiarid conditions.