Changes of soil organic matter, nitrogen and phosphorus contents in the process of pear branch decomposition

Abstract:【Objective】The experiment was to investigate the changes of soil organic matter, N and P contents in the process of Kuerlexiangli pear branch decomposition by indoor mixed culture. In order to improve the soil and increase the yield of Kuerlexiangli pear, the period with the highest nutrient content was found within 150 days.【Methods】This experiment was to collect 5 and 10 years old branches from Awati farm in Korla city. After the original soil in the pear orchard was collected and brought back to the laboratory, indoor mixed culture was conducted for 150 days. The method for collecting the branches was to randomly select robust 5- year- old and 10- year- old pear trees in three Kuerlexiangli pear orchards. For each individual tree, plant samples were collected from the upper, middle and lower parts of the canopy in four different directions of east, west, south and north according to different levels and orientations. Healthy and disease-free branches were selected and cut into a length of ＜1 cm, and then the samples in different directions were mixed uniformly in proportion to obtain mixed samples. The soil samples in three orchards were randomly selected according to the“S”curve to collect from 40-60 cm soil drills at 5 locations, and the soil samples were brought back to the laboratory for mixing and then the roots and debris were selected. Before each measurement, it should go through the following nine steps:“air drying - sorting - de-impurity - grinding - sieving - mixing - bottling - storage - registration”. The shoot samples should be washed with distilled water, wiped and weighed, dried in a 70 ℃ incubator, and crushed through a 60-mesh sieve for later use.【Results】There were differences in the effects on soil nutrient content during the simulated return of Kuerlexiangli pear branches with different tree ages. Compared with CK in the same period, all the treatments reached the significant level (p ＜0.05). The average value of soil organic matter in Treatment 1 and Treatment 2 increased by 2.16 and 1.93 times, respectively, compared with CK. The maximum organic matter content of Treatment 1 was 62.43 g · kg- 1 on the 60th day after decomposition in the soil, which was 2.71 times more than that of CK. The maximum organic content of Treatment 2 was 67.90 g · kg^-1 on the 45th day after decomposition in the soil, which was 2.93 times more than that of CK. Compared with CK, the average soil total nitrogen with Treatment 1 and Treatment 2 increased by 61% and 59%, respectively. The best improvement effect was achieved on the 30th day after decomposition in the soil. The total nitrogen content of Treatments 1 and 2 reached 0.11 g · kg^-1 and 0.09 g · kg^-1 , which were 2.92 times and 2.24 times more than that of CK in the same period. The soil total nitrogen of the two treatments increased significantly compared with CK in the same period. Compared with CK, Treatment 1 and Treatment 2 showed the same improvement performance, and Treatment 2 had the best effect. The improved effect reached the maximum value of 7.39 mg·kg-1 and 9.38 mg·kg^-1 in Treatment 1 and 2, which were 0.56 times and 0.98 times more than that of CK in the same period. Compared with CK, the average value of soil total P with Treatments 1 and 2 increased but not significantly. Treatment 2 increased total phosphorus content and reached the maximum value of 0.71 g·kg^-1 on the 75th day, which was 0.12 times more than that of CK at the same time and there was significant difference (p ＜0.05). Compared with CK, the average soil available P in Treatment 1 and Treatment 2 increased, which was 5.88 and 6.88 times more than that of CK, respectively. The best improvement effect was achieved on the 90th day after decomposition in the soil, and the available phosphorus content of Treatment 1 and Treatment 2 was 6.91 mg · kg^-1 and 7.24 mg·kg^-1 , 44.78 and 46.96 times more than that of CK in the same period.【Conclusion】During the decomposition of pear branches, the contents of soil organic matter, nitrogen and phosphorus increased, and the overall performance of the improvement effect was that the branches from 10- year- old trees were better than those from 5-year-old ones. Returning of pruned branches to the field provides a reliable theoretical basis for solving the bottleneck problem of organic manure shortage in orchards, and ensures technical support for improving soil fertility and the rhizosphere micro-environment of pear trees.