Comprehensive assessment methodology of characteristics of soil fertility under different fertilization regimes in North China

Abstract: Soil fertility is a typical index to evaluate the soil ability of supplying the proper conditions for plant growth. This study focused on the differences among soil physical, chemical, and biological properties under different long-term fertilization strategies and the results of those properties were analyzed synthetically to establish the suitable fertilization strategy to improve soil fertility. A 26 years long-term experiment was conducted in the Dezhou station of Chinese Academy of Agriculture Sciences. Six treatments included no fertilizer and manure (CK), half conventional dosage of organic manure and half of chemical fertilizer (MF), conventional dosage of organic manure (CM), conventional dosage of chemical fertilizer (CF), and high dosage of organic manure (HM) and high dosage of chemical fertilizer (HF). The indicators of soil physical, chemical and biological characteristics under the different fertilization treatments were determined to clarify the effects of fertilization on soil fertility. Principal component and cluster analyses were applied to get a comprehensive assessment on the effects of different fertilization strategies on soil fertility. The results showed that: 1) The significant differences of soil properties were found among the fertilization treatments. Compared with chemical fertilizer, long-term application of organic manure or combination of organic and inorganic fertilizers reduced soil bulk density by 5.0% - 11.0%, and increased soil total porosity by 4.1% - 9.9%，increased soil organic carbon, total nitrogen, available phosphorus and available potassium by 95% - 136%, 69% - 137%, 500%, and 81% - 103%，respectively. In addition, the soil pH in the treatments of organic manure or combination of organic and inorganic fertilizer was lower than that of chemical fertilizer treatments by 0.15-0.47. 2) According to principal component analysis, soil fertility indexes could be classified into two principal components. The first component (PC1) consisted of soil organic carbon (C), total nitrogen (N), organic N, microbial biomass N, microbial biomass C, total phosphorus (P), available P, available potassium (K), organic P, soil bulk density, and total porosity and pH, which had high loadings about 83.73%. In the second component (PC2), however, soil total K had high minus loadings, and the proportion of total K in the component was only 8.49%. 3) Cluster analysis classified the indexes into 4 classes of CM and MF, CF and HF, CK, and HM. Based on the analyses above, we concluded that the high application rate of organic manure could lead to the best impacts on the soil fertility. The effects of all fertilization strategies on soil fertility presented the descent orders as: HM > CM > MF > HF > CF > CK. Thus, the contents of soil nutrients increased more effectively under the treatments with organic manure or combination of organic and chemical fertilizer than chemical fertilizer. Moreover, the treatments with organic manure or combination of organic manure and chemical fertilizer could also alter the balance of soil nutrients, enhance soil fertility comprehensively in the aspects of soil physical, chemical and biological fertilities, and improve the supply ability of soil nutrients.