Spatial relationship between root system and soil properties of mature and densely planted Kuerlexiangli pear under long-term strip fertilization

【Objective】Kuerlexiangli pear (Pyrus sinkiangensis Yü et Lu.) is the main cultivar in Southern Xinjiang. In recent years, the main trunk dense planting pear orchard has developed rapidly and entered the peak fruiting period. With the increase of tree age, problems such as poor resistance, death vulnerability, and unstable yield have become prominent in dense planting pear orchard. Fertilization methods affect the distribution of the roots of the fruit tree and nutrient utilization, and are closely related to tree resistance and yield. Fertilization in mature and densely planted pear orchards is often carried out atthe edge of the tree crown, about 1 meter away from the main trunk, by opening a strip-shaped ditch for fertilization. As the tree ages, further research is needed to determine whether this fertilization method is reasonable under dense planting conditions. The study aimed to survey the spatial characteristics of the root system and soil physicochemical properties of the densely planted mature Korla pears under long-term strip fertilization in order to provide a basis for scientific and efficient water and fertilizer management in the densely planted pear orchards.【Methods】Using the profile excavation method and WinRHIZO root analysis system, the root morphology of 11 year old Kuerlexiangli pear with Pyrus betulifolia Bunge as rootstock was analyzed at a distance of 50-200 cm between the rows and tree trunks, and at a depth of 10-110 cm. The soil organic matter, available nutrients, soil bulk density, porosity, saturated water content, field water holding capacity and other soil physical and chemical properties were measured.【Results】The results showed that the length and surface area of the pear roots were mainly dominated by the absorbing roots, accounting for 92.57% and 62.62%, respectively; The root volume was mainly composed of the conducting roots, accounting for 52.98%. In the horizontal direction, the root length and root surface area density were the highest near the fertilization ditch, accounting for 32.32% and 27.06% respectively; The proportion of the root length and root surface area in the soil layer at a depth of 30-50 cm in the vertical direction was the highest, accounting for 26.30% and 25.99%, respectively. The average root length density in the area with a depth of 10-90 cm and a horizontal distance of 140 cm was 0.62 mm·cm-3 , accounting for 75.56% of the total root length in the sampling area. It was the densely distributed area of pear root system. There were differences in the enrichment areas of the different nutrients in long-term strip fertilization orchard. The organic matter and available phosphorus accumulated at a distance of 1 meter from the main stem in the fertilization ditch, and exhibit layered distribution characteristics. The content of the organic matter and available phosphorus contents at a depth of 10-30 cm were 2.62 times and 16.28 times higher than those at a depth of 90-110 cm, respectively. The content of the alkaline nitrogen and available potassium in the soil at 50-80 cm were 1.35 times and 1.21 times higher than those at 140-170 cm, respectively; The alkaline hydrolyzable nitrogen content at depths of 90-110 cm was 2.28 times higher than that at depths of 10-30 cm. There was a significant difference in the physical properties of the soil between the fertilization ditches and rows at a depth of 10-50 cm. Compared with the fertilization ditches, the soil bulk density significantly increased while the porosity, saturated water holding capacity, and field water holding capacity decreased in the distance of 150 cm away from the main stem due to the mechanical compaction for a long time. The nutrient content of the roots and soil was closely related to spatial location. The correlation coefficients between the V and Ⅵ grade roots and soil depth were 0.45 and 0.62, respectively. The correlation coefficients between the Ⅰ and Ⅳ grade roots and horizontal distance were -0.55 and -0.45, respectively; The correlation coefficients between the organic matter and available phosphorus and soil depth were -0.73 and -0.74, respectively. The correlation coefficient between the alkaline nitrogen and soil depth is 0.55. The correlation coefficient between the available potassium content and horizontal distance was -0.66. There was a highly significant and positive correlation between the grade Ⅰ-Ⅱ root systems and available phosphorus (r= 0.70 and 0.64, respectively).【Conclusion】In summary, under long-term strip fertilization, the organic matter and phosphorus nutrients in the densely planted Kuerlexiangli pear orchard accumulated in and near the fertilization ditch, and the soil porosity and water holding capacity in the soil between the rows decreased. The spatial differences in the distribution of the organic matter and available nutrients, as well as the differences in the soil physical properties between the fertilization ditch and mechanical compaction site would be unfavorable factors for the rootextension and growth of mature densely planted Kuerlexiangli pear orchards.