Effect of continuous application of pruning compost on the growth anddistribution of pear roots

Abstract:【Objective】Annual pruning in pear orchards leaded to a large number of branches which con⁃tain abundant mineral nutrients. Traditionally, pruned branches are stacked optionally, or burned as fuel,and both methods lead to loss of nutrients. It is important to use these solid waste resources and recycletheir nutrients. Composting is a way to turn the wasted prunings to a useful organic fertilizer. Long-termapplications of organic fertilizer had profound effects on soil physical, chemical and biological properties.Moreover, the application of organic fertilizer also promotes the growth of plant roots, affecting the yieldand quality. However, it is not clear about application of pruning compost into pear orchard. The aim ofthis experiment was to study the effects of pruning compost on soil properties, root growth and distribution,yield and quality in pear.【Methods】The experiment was conducted on 10-year-old‘Zaosu’pear treesfor 4 consecutive years. Based on the equal mineral nutrients and organic matter, the treatments includedpruning compost (PC), sheep manure (SM) used as traditional organic fertilizer, and chemical fertilizer setas the control (CF). Randomized block design was used for this experiment, with three replicates in eachtreatment. At the harvest in 2015, a soil excavating method was used to sample roots, and nine trees withaverage vigor were selected from each treatment for root sampling. Root images were obtained by root scan⁃ner, and root feature parameters such as root length, root surface area, root volume were analyzed. Further⁃more, the experiment also studied effects on yield and quality of pear.【Results】(1) PC significantly in⁃creased the contents of alkali-hydrolysable nitrogen in the soil, which was 1.44 times of the control. Soilorganic matter, available P and available K contents were increased by 25.7%, 30.3% and 7.5% in PCtreatment compared with the control, respectively. (2) PC and SM significantly increased the total rootlength, total root surface area and the number of root tips. These root feature parameters were in the orderof SM>PC>CF. In horizontal direction, total root length in the range of 0-40 cm under PC treatment was1.77 times of the control (P < 0.05). Organic fertilizer treatments significantly increased total root lengthand total root surface area in the ranges of 120-160 cm and 160-200 cm, and root distribution densitywas in the order of PC>SM>CF. Compared with CF, SM increased total root length, total root surface areaand total root volume in the range of 80-120 cm although only the increase in total root surface area wassignificant. The coarse root was most significantly increased by 90.8%. There were no significant differences among root length, root surface area, root volume of absorbing roots and coarse roots under different fer⁃tilization treatments. In vertical direction, applications of PC and SM increased the length of absorbingroots, root surface area and volume in 0-30 cm and 30-60 cm soil layers, and coarse root length was alsosignificantly increased by PC treatment. In 30-60 cm layer, SM increased coarse root length to 0.11 mm·cm-3which was 2.14 times of CF. Meanwhile, total root surface area of SM was significantly increased by71.4% compared with CF. Coarse root surface area under SM treatment was increased by 90.8%, and absorbing root surface area was 2.01 times that of the control. Additionally, the absorbing root volume in SMand PC treatments were 0.39 mm3·cm-3 and 0.41 mm³·cm^-3 in 30-60 cm soil layer, respectively, whichwere both significantly increased compared with the control. Absorbing root volume in 30-60 cm soil layer in SM treatment was 0.38 mm3·cm-3, while in PC treatment it was 0.41 mm3·cm-3, and both were significantly higher than the control. Although SM significantly increased total root surface area in 90-120 cmsoil layer, the increases in surface area of absorbing root and coarse root were not significant. Results alsoshowed that root composition was changed by applying organic fertilizers. The relative length of absorbingroots in PC was 96.5%, significantly increased by 1.71%. The two organic fertilization treatments signifi⁃cantly alerted absorbing root surface areas and absorbing root relative volume, which were in the order of PC>SM>CF. In addition, very fine roots were most affected by organic fertilization. There were no significant differences between fine root relative length and surface area among treatments, except for fine rootrelative volume which was significantly increased under PC treatment. On the contrary, CF treatment resulted in highest coarse root relative length, surface area and volume, followed by SM treatment. (3) Application of PC had a significant effect on weight of single fruit, which was 20.7% higher than that of the control. The yield of pear under PC treatment was 1.36 times that of the control. PC significantly increasedthe content of soluble solids in the fruit, and the ratio of sugar to acid was 1.23 times of the control. SM significantly decreased soluble solids in the fruit.【Conclusion】Application of PC for 4 consecutive years im⁃proved the soil nutrient contents, enlarged the distribution of roots in soil, and promoted the growth of pearroots especially the absorbing roots. Furthermore, PC increased single fruit weight and yield and improvedfruit quality.