Effects of continuous deficit irrigation and partial root-zone irrigation on root growth of young apple tree

A study was conducted to evaluate the effects of different irrigation patterns on root growth in 2-year-old apple trees (Malus pumila Mill. cv. Changfu No. 2). In the traditional pot experiments, the 2-year-old apple trees were subjected to conventional irrigation (CI; i.e., irrigation amount is 100% evaporation, measured with 120 mm diameter pans, on both sides of the root system), continuous deficit irrigation (CDI; i.e., irrigation amount is 50% CI on both sides of the root system), and partial root-zone irrigation (PRI; i.e., irrigation amount is 50% CI alternatively on one side of the root system) in Experimental Orchard of Fruit Research Institute, Yantai Academy of Agricultural Sciences in May to October of 2007. The results show that root length under PRI treatment is longer than that under CI treatment. Apple root length is shortest under CDI treatment. PRI treatment significantly promotes growth of absorbing roots with diameters less than 2 mm without obvious increase in total root dry weight. Curves of root biomass accumulation in young apple trees follow a typical sigmoid curve, corresponding to the three irrigation treatments. It is noted that high apple root growth rate and maximum root weight coincide with extremely high root vitality under PRI treatment. This is attributed to the good soil aeration, resulting from suitable soil moisture conditions. Compared with PRI, slower root growth rate and lower root vitality are observed under CI treatment due to beyond suitable soil water content. This coincides with lower root biomass, ranging between the other two treatments. Both root activity and root weight are the lowest under CDI treatment, probably due to persistent dry soils. For the three irrigation treatments, root-shoot ratios decline with increasing treatment time. Root-shoot ratio is highest under PRI treatment and lowest under CI treatment. PRI is most beneficial to root growth in young apple trees under 50% reduction in water supply.