Effects of root restriction on canopy characteristics and fruit quality of greenhouse-grown nectarine in non-arable land

Abstract：【Objective】The shortage of arable land resource is a serious situation in China. The Gobi arealocated in Hexi Corridor of Gansu Province, has suitable natural conditions for fruit development such aslight density and light period. However, Gobi is covered by coarse sands and gravels, which form a hardtop soil layer in the desert terrain. Therefore, cultivating nectarines in the non-arable lands of Gobi needsto remove 80 cm deep gravel, then backfill soils from arable lands which are limited in Hexi Corridor.Such a practice seriously affects the quality of farmland and causes serious damage to the fragile ecologi⁃cal environment. Nectarine trees grow vigorously in greenhouses, which substantially affect photosynthesisand growth of the trees and the quality of the fruit. Branch pruning for controlling canopy is nutrition-con⁃suming and costly and causes physiological diseases. Root restriction can save water and fertilizer in Gobinon-arable lands. It is good for high-density, high-yielding and high-efficiency cultivation through con⁃trolling vegetative growth. Soil volume in root restriction influences tree growth, canopy characters andeconomic characters. Suitable tree canopy characteristics are the basis for high yield. Studying the effectsof root restriction on nectarine tree canopy characteristics can provide a theoretical basis and practical ex⁃perience for nectarine cultivation in non-arable lands in greenhouse.【Methods】The field experiment wasconducted to examine the effects of soil volume in root restriction on the vegetative growth, yield, fruitquality and canopy characteristics of greenhouse-grown nectarine‘Zhongnong Jinhui’in non-arableland. The experiment included four treatments, where the dimensions of the root restriction containers(Length × width × depth) were 0.9 m × 0.5 m × 0.3 m (135 L)，0.9 m ×0.5 m × 0.5 m (225 L)，0.9 m ×0.8m × 0.5 m (360 L) and 0.9 m ×0.8 m × 0.8 m (576 L), and root restriction material was geotechnical cloth.The local traditional cultivation method was adopted as the control, where backfilling soil was conductedafter removing 80 cm of the original Gobi surface soil (control, 1 440 L). Randomized block design wasused for this experiment, with three replicates in each treatment. The plant and row space was 0.9 m × 2m, and the whole experimental area was 150 m2. Canopy images were collected by a CI-110 canopy ana⁃lyzer. After zenith angle (140°-170°) and azimuth angle (45°-135° and 225°-315°) were removed using aplant canopy analysis system V6.0, leaf area index (LAI) and transmission coefficient for diffuse penetra⁃tion (TCDP) were calculated with the CI-110 canopy analyzer software. Sugar content and soluble solidcontent (SSC), single fruit weight, fruit number per tree and yield were collected to evaluate the economiccharacters, and trunk diameter 10 cm above graft joint was used to evaluate plant growth.【Results】Rootrestriction had significant inhibitory effect on vegetative growth of the greenhouse-grown nectarine treesin non-arable land, which was shown by the impact on the stem diameter. The stem diameter in L135treatment was 21.7 mm, which was 49.7% that of the control. The treatments of L225 and L360 caused20% reduction in stem diameter compared to the control. The treatment of L135 reduced the average fruitweight and yield but increased SSC significantly (P<0.05). The treatment of L225 had significant differ⁃ences from the control in average fruit weight, however its production had no significant differences. Theresults showed that leaf area coefficient was in the range of 1.81-2.90. Different soil volumes had signifi⁃cant influence on LAI. The LAI in the treatment of L135 was 1.81, which was significantly lower than thatin L225 (2.02) and L360 (2.21) treatments, which equaled to 63%, 70% and 77% that of the control, re⁃spectively. There was no difference between L576 (2.87) and control (L1440) in LAI. Root restriction limit⁃ed the branch and leaf growth. As a result, TCDP increased. In 135 L treatment, the TCDP increased to0.34, which was three times that of the control, indicating serious light-leaking. The TCDP in the L225 and L360 treatments was 0.30 and 0.25, respectively, which were also significantly higher than that of thecontrol. TCDP of treatment of L576 was slightly higher than the control, but no significant difference wasobserved.【Conclusion】LAI is an important parameter of canopy structure character. The highest LAI mea⁃sured by CI-110 was 2.90, which was smaller than the results from direct measuring method and othermethods. Quantitative analysis and measurement by CI-110 needs correction on the top of direct measuring method. Although the canopy analyzer method was not very accurate, it is still a fast and efficient cano⁃py analysis method. The results showed that root restriction volume of L135 increased SSC but decreasedyield and fruit weight. Therefore, it is not suitable for greenhouse-grown nectarine in non-arable lands.Light loss in root restriction treatment with soil volumes of L225 and L360 was higher than in the control.The L225 and L360 treatments could be used for growing nectarine in non-arable land greenhouse, pro⁃vided high planting density is adopted. These two treatments need only 15.6% and 25% of the soil volumein the control. According to the comparison and analysis of the three methods of images processing, removing zenith angle (from 140° to 170°) and azimuth angle (from 45° to 135° and from 225° to 315°) could reduce the experiment error caused by the surrounding environment. This images processing method couldreveal the actual differences between experimental treatments.