Plant- and climate-based indicators for irrigation scheduling in mid-season peach cultivar under contrasting watering conditions.

摘要

Increasing water scarcity has changed the primary objective of farmers from seeking maximum yields to preservation of the agricultural system. Deficit irrigation may be used to reduce water use; however, the adoption of this technique requires precise knowledge of tree water status and the implementation of specific irrigation skills to reduce the impact of stress. The present work investigates the water status of peach in relation to water supply under high evaporative demand with the objective of developing practical methods for deficit irrigation scheduling. A field experiment was carried out in 2006 and 2008 at the research station of INAT-Mornag in northern Tunisia. Drip-irrigated mid-season cultivar Royal Glory grafted on GF677 was used. Total water applied during the dry season was in the range 50-100 mm in 2006 and 200-300 mm in 2008. Predawn ( Psi _PD), midday ( Psi _m), and stem ( Psi _stem) water potentials, weather factors, irrigation and soil moisture were monitored. Results show that ET_c was 524 and 603 mm for 2006 and 2008, respectively, under ET_o of 1171 and 1180 mm. With highly variable quantity and distribution of precipitation, the contribution of soil reservoir water is essential to regulate evapotranspiration of trees. In 2006, applied water covered 0.35-0.50 ET_c during the initial-mid season period and 0.60-0.65 ET_c in postharvest. Irrigation was adjusted in 2008 to cover 0.55-0.75 ET_c during vegetative and fruit growth and 0.50-0.65 ET_c during postharvest. Water supply indices were defined as ratios between cumulated water supply (I+P) and ET_o over different periods of time. Seasonal (K_s), 30-days (K₃₀), 15-days (K₁₅), and 7-days (K₇) were calculated over the cropping season starting in October. Tree water status and fraction of available water (FAW) was relatively high early in the season but declined to extremely low values during the high evaporative demand period and during the periods without irrigation. Extreme low values of -1.28, -2.13 and -2.51 MPa, respectively for Psi _PD, Psi _m and Psi _stem were observed during the high evaporative demand period. Relationships were significant between Psi _stem and Psi _PD and Psi _m. A good correlation was also observed between FAW and Psi _PD, Psi _m and Psi _stem. Analysis of the relationships between water supply indices (K₇, K₁₅, K₃₀ and K_s) and tree water potential shows a high correlation between Psi _stem and K_s. Upper and lower limits of 0.8 and 0.5 could be adopted for K_s in order to maintain water status of peach trees within acceptable level corresponding to moderate and severe water deficit.