[Effects of sand-covering on apple trees transpiration and fruit quality in dry land orchards of Longdong, Gansu].

Aiming at the seasonal drought in the dry land orchards of Longdong, Gansu Province, a sand-covering experiment was conducted with 15-year-old Nagafu No. 2 apple trees, with the soil water content, temperature, stem sap flow velocity, leaf stomatal conductance, and fruit quality measured. In the orchard covered with 5-cm-thick riversand, the increment of soil temperature in February-April was lower than 1 degrees C, while in June-July, it was 2.44 degrees C and 2.61 degrees C on sunny and cloudy days, respectively. The soil water content was over 60% of field capacity throughout the growing season. On sunny days with high soil water content (H season), the stem sap flow curve presented a wide peak. Under sand- covering, the sap flow started 0.6 h earlier, and the maximum sap flow velocity was 25.5% higher than the control. On cloudy days of H season, the maximum sap flow velocity was 165.6% higher than the control. On sunny days with low soil water content (L season), the sap flow curve had a single peak, and under sand covering, the sap flow started 0.5-1 h earlier than the control on sunny days. The maximum sap flow velocity was 794 g x h(-1). On cloudy days of L season, the sap flow started 1 h earlier, and the maximum sap flow velocity was 311.0% higher than the control. The evaporation of the control was 156.0% higher than that of sand-covering from March to July, suggesting that excessive ground water evaporation was the main reason to cause soil drought. Under sand-covering, single fruit mass was improved obviously whereas fruit firmness was reduced slightly, and soluble solids, vitamin C, total sugar, and organic acid contents were somewhat promoted.