Impacts of long-term organic manure inputs on cultivated soils with various degradation degrees

With an increasing concern of soil health and sustainable development, organic manure application has been readdressed in recent years. In Northeast China, the agricultural industry is highly developed and organic manure resources are abundant, but soil degradation is serious due to extensive expansion of cultivation. Currently, limited information is available on how soils with various degradation degrees respond to long-term manure fertilization. Given that, a comparative study was conducted based on soil functional assessment of croplands with over 35 years of manure fertilization (maize straw compost, SA; cattle manure, CA) and various degradation degrees (none, light, moderate, and heavy). Soils in these croplands were loess-derived Mollisols and concentrated on a gentle to flat slope. Except for the difference in manure fertilization (SA and CA), similar field managements were adopted for these croplands during the past 35 years. Results showed that the impacts of erosion degradation and manure fertilization on soil physical structure lasted across the whole profile (0 ∼ 120 cm), while their impacts on soil nutrient properties were concentrated in shallow layers (<50 cm). Meanwhile, erosion degradation dominated 17.9% of the variance of soil physical structure, and soil profile depth contributed to 15.9% of soil nutrient variation. According to field validation regarding soil erosion modulus and crop yield, principal component analysis (PCA) with a nonlinear scoring method showed a good performance on the integrated soil functional index (ISI) assessment in this study area. The ISI of these croplands was found to be minimally characterized by BD, SOC, TN, AK, sand content, and CEC (R2 >0.64, p < 0.001). In addition, manure fertilization could significantly improve the ISI and maize yield for degraded soils, but had a slight impact on these two indicators for non-degraded soils. In terms of contribution to ISI improvement, SA (1.79% ∼ 283.73%) generally outperformed CA (4.53% ∼ 212.83%), while the latter was more effective in altering soil structure in deep layers (>70 cm). Generally, the ISI and maize yield were more susceptible to erosion degradation than manure fertilization. The obtained results provide useful information for a better cropland management in Northeast China.