Effects of different application rates of organic fertilizers derived from soybean residue and pig manure on yield, quality of pear and soil fertility

Abstract:【Objective】Effects of application of different organic fertilizers partially replacing chemical fertilizer on the yield and quality of pear fruit as well as soil fertility in southern pear orchards were investigated. The optimal dosages of two kinds of organic fertilizer were explored to provide a basis for reasonable fertilization in southern pear orchards.【Methods】A field experiment was conducted from 2019 to 2020 in Anji county, Zhejiang province. Seven fertilization treatments were set including chemical fertilizer (CF) and the combinations of 7.5, 15.0 and 22.5 t· hm- 2 soybean residue organic fertilizer with chemical fertilizer (DZ1, DZ2 and DZ3), 7.5, 15.0 and 22.5 t · hm^-2 pig manure organic fertilizer with chemical fertilizer (ZF1, ZF2 and ZF3). All treatments had the same nitrogen input. The organic fertilizer nutrients were calculated according to the annual mineralization rate of 50% and the nutrient deficiency part of organic fertilizer treatments was supplemented by chemical fertilizer. The yields and qualities of Cuiyu pear were analyzed as well as the soil physicochemical and microbial properties. Subsequently, the quality of pear fruits and soil physicochemical properties of pear orchard were compre-hensively evaluated using the integrated score model of principal component analysis.【Results】Compared with the chemical fertilizer (CF) treatment, the pear yields with the soybean residue fertilizer treatments and pig manure fertilizer treatments increased by 29.4%-46.7% and 30.3%-55.7%, respectively. ZF3 showed the highest yield. The application of the two organic fertilizers could improve the quality of pear fruits. The total soluble sugar and organic acid content, sugar-acid ratio and single fruit weight significantly increased by organic fertilizer application. There was no significant difference in the soluble solids and vitamin C contents between two organic fertilizer treatments and chemical treatment. However, the effects of organic fertilizer on pear quality varied with the type and dosage of the organic fertilizers. The application of organic fertilizer significantly improved the accumulation of medium and trace elements in pear fruits. More calcium was accumulated in pears with the application soybean residue fertilizer, whereas more copper, manganese and magnesium were accumulated in pears with the application of manure fertilizer. Besides, compared with chemical fertilizer treatment, the combined application of organic fertilizer with chemical fertilizer effectively alleviated the acidification of the soil in the pear orchards, and increased the available nutrients in the orchard soils in some cases. Meanwhile, the application of the two kinds of organic fertilizers significantly increased soil microbial Shannon indexes as the increase of the application rate. ZF3 treatment had the highest value. Moreover, the application of organic fertilizers significantly improved soil microbial Pielou evenness index. According to the comprehensive evaluation by principal component analysis, five principal components with eigenvalues over 1 were extracted. The contribution rates of the principal components 1, 2, 3, 4 and 5 were 24.51%, 20.64%, 14.42%, 10.34% and 8.18%, respectively. The cumulative variance of the five principal components reached 78.08%, and the five principal components could reflect the information provided by 13 indicators. The comprehensive scores of principal component analysis of fruit quality and soil physico chemical properties were in the order of DZ3＞DZ2＞ZF1＞ZF2＞DZ1＞ZF3＞CF.【Conclusion】The application of the soybean residue based and pig manure based organic fertilizers could increase the yield and quality of pear fruits and improve the orchard soil fertility. The improvement effect of the soybean residue fertilizer application was better than that of pig manure fertilizer. The optimal application rate of the soybean residue organic fertilizer was 15.0 t · hm- 2 with the nitrogen replacement rate of 35.8%. The optimal application rate of pig manure organic fertilizer was 7.5 t·hm-2 with the nitrogen replacement rate of 13.0%.