|Jabro, Jalal "jay"|
Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2003
Publication Date: 10/10/2005
Citation: Leib, B.G., Casperi, H.W., Redulla, C.A., Andrews, P.K., Jabro, J.D. 2005. Partial rootzone drying and deficit irrigation of Fuji apples in a semi-arid climate. Irrigation Science. 24:85-99.
Interpretive Summary: ‘Fuji’ apple trees grown in deep soils with high water holding capacity showed no statistically significant differences in yield, fruit size, and crop yield among Control (CI), Deficit Irrigation (DI) or Partial Rootzone Drying (PRD) treatments in 2001. However, yield was significantly reduced by DI compared to CI in 2002, while PRD did not differ significantly from CI or DI. Further, the concentration of soluble solids tended to be higher in PRD and DI than CI. These differences to CI were significant in both years for DI, and in the second year only for PRD. Treatment effects on titratable acidity were inconclusive, being significantly lower in DI and PRD than CI in one year, and significantly higher in the second year. Fruit from PRD and DI tended to be firmer than CI fruit in both years. Irrigation volumes applied in CI were only 70-75% of the modeled ETc from PAWS weather data in both years when excluding the excessive late-season irrigation in 2002. The soil-water content in CI was kept near field capacity throughout both seasons. Thus, basing irrigation decisions on soil-water monitoring rather than modeled ETc resulted in significant water conservation. A further 40-45% of irrigation water was conserved with DI and PRD with no negative impacts on yield and fruit size with PRD in both years. However, yield was reduced with DI compared to CI in the second year. Our results indicate the potential of DI and PRD strategies for large water savings with no or small impacts on yield and fruit size. They also confirm that deficit irrigation strategies can be used to alter fruit quality. However, further work is required to fine-tune these irrigation strategies so that reductions in yield and fruit size can be avoided. Also, further experiments comparing PRD and DI are required to determine if placement and/or volume determine apple tree responses to soil water deficit.
Technical Abstract: The effects of Deficit Irrigation (DI) and Partial Rootzone Drying (PRD) on apple (Malus domestica Borkh. Cv. Fuji) yield, fruit size and quality were evaluated during the 2001 and 2002 growing seasons in the semi-arid climate of Washington State. Apple trees were irrigated using three different regimes: a control (CI) where micro-sprinklers on both sides of a tree were operated to maintain soil water content near field capacity, DI where both micro-sprinklers were operated at half the time as the CI, and PRD where only one microsprinkler alternately wetted half the rootzone with half the water as the CI. Irrigation amounts applied were 538 mm and 670 mm in the CI; 302 mm and 434 mm in the DI; and 272 mm and 389 mm in the PRD for the 2001 and 2002 seasons, respectively. No significant differences were found in yield and fruit size among treatments in 2001. In 2002, DI had significantly lower yield than CI, while the yield of PRD did not differ from CI and DI. No significant differences were found with respect to average fruit weight and crop load. Fruit from DI and PRD were firmer and had higher concentrations of soluble solids than CI fruit, both at harvest and following short-term storage at 20 C. Treatment effects on fruit titratable acidity were inconsistent. Additional water was preserved in the soil profile under PRD compared to DI in 2001, but no statistical differences were found between PRD and DI in 2002. Our results demonstrated that approximately 45-50% of irrigation water was saved by implementing newly developed DI and PRD irrigation strategies without any significant impact on fruit yield and size with the PRD regime in both 2001 and 2002. However, apple yield was reduced with the DI compared to the CI regime in the second year.