Effects of organic fertilizer of pig manure on yield and quality of Red Fuji apple

Abstract：【Objective】Luochuan county, Shaanxi province is an agricultural area featuring apples as the leading industry, and due to its natural geographical resource advantages, it has become a typical location on the world's best apple growing belt. Most of the Luochuan apples were built in the 1990s of last century, and improving the quality and efficiency of the old orchards is the main task of the local apple industry. In addition, Luochuan’s history has frequent natural disasters such as drought, little rain, soil erosion and low soil organic matter content in Luochuan orchards, fruit farmers have long emphasized the application of chemical fertilizers, and soil impoverishment has seriously affected the yield and quality of apples and even caused great harm to the soil environment, becoming an obstacle factor in the sustainable development of Luochuan apple industry. In order to prolong the fruiting life of the old orchard, improve the production efficiency of the old orchard and change the current situation of insufficient organic fertilizer in the sustainable development of Luochuan apple industry, this study explored the effects of different application levels of organic fertilizer (pig manure) on the quality and yield of Red Fuji apple and soil fertility of orchards at peak fruiting period by adopting the ecological model of fruit and animal combination, and determines the optimal application amount of organic fertilizer, so as to provide a basis for scientific and reasonable fertilization of apple orchards at full fruit stage.【Meth-ods】Taking the 27-year-old Changfu 2 apple as the research material, a one-year experiment on the application of pig manure was carried out in a grower’s orchard in Luochuan county, Shaanxi province. In the experiment, a total of 5 organic fertilizer application levels were set as below: 0, 5, 10, 15 and 20 kg ·tree^-1 (control, T1, T2, T3, T4), respectively, the leaf area, leaf thickness, weight per 100 leaves and leaf SPAD values were determined at the young, swelling and ripening stages of fruit trees, photosynthetic indexes were measured at the fruit swell stage, fruit weight, longitudinal and transverse longitude, soluble solids content, titratable acid content, fruit parenchymal structure, peel color and other indicators were collected at the fruit ripening stage, and 0-20 cm soils were collected in the orchard after fruit harvest. The soil organic matter content, total nitrogen content, available nitrogen content, available phosphorus content, available potassium content and pH values were determined in 20-40 cm and 40- 60 cm soil samples, and the measured indexes of different treatments were comprehensively evaluated by the principal component analysis.【Results】Compared with control treatment, soil nutrient content significantly increased by the application of organic fertilizer, and the soil organic matter content, available nitrogen content and available potassium content increased most significantly under 0-20 cm soil layer, increasing by 2.60%-17.67%, 9.16%-31.88% and 0.30%-38.92%, respectively. The total nitrogen content and available phosphorus content increased very significantly under the 40-60 cm soil layer, increasing by 10.84%-27.71% and 26.77%-80.84%, respectively. Compared with control treatment, the application of organic fertilizer increased apple leaf area, leaf thickness, weight per 100 leaves and relative chlorophyll content at the young fruit stage, swelling stage and ripening stage. In the fruit swelling stage, the application of organic fertilizer increased the net photosynthetic rate, transpiration rate and stomatal conductance of leaves, and decreased the intercellular CO2 concentration of leaves, all of which reached the highest value in T3 treatment. Compared with other organic fertilizer treatments, T3 treatment was beneficial to leaf growth, which was conducive to increasing the photosynthetic rate of leaves and promoting the accumulation and transformation of dry matter in leaves. Compared with control treatment, the organic fertilizer application treatment could increase the fruit yield by 3.79%- 19.49%, and the T3 treatment could fully improve the income increase effect of the orchard in the test area. With this treatment, the single fruit weight, longitudinal and transverse warp rates, peel redness a^* , peel hardness, pulp brittleness and soluble solids content increased the most obviously, and the peel yellowness b^* and titratable acid content were effectively reduced with this treatment, all of which were significantly different from control treatment. T2 treatment had significant effects on peel brightness L^* , peel ductility and pulp hardness. A total of four principal components were extracted by the principal component analysis method, and the characteristic values of each principal component were 15.559, 4.932, 3.169 and 2.34, the total variance contribution rates of the 1st, 2nd, 3rd and 4th principal components were 59.841%, 18.971%, 12.187% and 9.001%, respectively, and the cumulative contribution rate was 100%. The results of principal component analysis showed that the increased application of organic fertilizer had a good effect on the leaf growth, fruit quality, yield and soil fertility of Fuji apple, and especially T3 treatment was relatively optimal. The comprehensive scores of organic fertilizer application treatment from different pig manure sources were as follows: T3＞T2＞T1＞T4＞control.【Conclusion】Under the conditions of this experiment, the application of 15 kg · plant- 1 of pig manure can improve the soil fertility of orchards and achieve the effect of improving fruit quality and increasing yield in orchards, which is the optimal amount of organic fertilizer in apple orchards at peak fruiting stage, and can be promoted in actual production.