Healthy soils are vital for food production as 95% of global food production directly or indirectly depends on soils. To ensure the food security of the burgeoning world population, it is necessary to evaluate soil health (SH) with a potential soil health index (SHI). Although there are several reputable methods for SH assessment at present, the connotations of and evaluation methods for SH are still unclear and such indexes are targeted at specific stakeholders or problems. In this study, we reviewed the fundamental steps in current attempts to develop SHIs, SH assessment methods and proposed a unified SHI based on the priorities of stakeholders. The proposed approach was designed as “three sets of dual index systems”, including the soil function (i), nutrition (j), and output (k) index systems, as well as the current (C) and expected (E) values of the respective index systems. The indicators included in index-i, index-j, and index-k reflect the soil regulatory functions, nutrient status, and quality and quantity of the output, respectively. The E values are used as a reference for the C values, and the health status is obtained, by using the ratio (R) of C to E for the respective index systems and their degree of deviation from “1” (R-1). For any evaluated soil, the farther the number of attributes and their ratios deviate from “1”, the unhealthier it is. This approach can provide a unified and comprehensive SH assessment method by diagnosing the most significant, healthy as well as unhealthy indicators. This method can be applied easily, not only by scholars but also by farmers and land managers.

The assessment of soil health through a robust index system having a sufficient number of indicators is an important step toward sustainable crop production. The present study aimed at establishing a minimum data set (MDS) from soil functional and nutritional attributes using a dual index system to evaluate the soil health of farmlands under wheat (Triticum aestivum)–maize (Zea mays) crop rotation in Yanting County, Sichuan, China. Farms from 10 villages in the study area were selected, out of which three sites were considered healthy/ideal sites and used as a reference for the remaining seven targeted sites, and soil samples were collected at depth of 20 cm from these farms. The MDS indicators were selected by using principal component analysis (PCA) followed by Pearson’s correlation on 25 attributes. Based on significant values, eight attributes were retained in the final MDS, including the sucrase level, pH, wilting coefficient, water holding capacity, organic matter, NK ratio, total potassium, and available phosphorus. Based on the results, most of the farmland soils in Yanting County were in a healthy condition, accounting for 61.71% of the surveyed samples, followed by sub-healthy, degraded, and weak soils, accounting for 19.64%, 9.71%, and 8.93%, respectively. The values of most of the indicators at the targeted sites were significantly lower than those at ideal sites. Thus, specific steps should be taken by adding soil organic matter, combined with other fertilizers, to enhance the microbial biomass, enzymatic activities, and other biological activities in the soil.

Molybdenum (Mo) is an important trace nutrient element in the soil and plays a significant role in maintaining plant growth. However, there are scarce studies on soil Mo content change and its driving factors based on historical soil samples. This paper studied the characteristics of Mo content in three different parent rock types (PRTs) and different eras. The findings indicated that the available Mo (AMo) and total Mo (TMo) in the purple soil were 0.087–0.131 mg/kg and 0.488–0.903 mg/kg, respectively, which were considered deficient. The TMo of J₃p was higher than those of J₂s and K₂j, but the AMo was slightly lower than those of K₂j and J₂s. Compared with the old samples, the AMo of K₂j, J₂s and J₃p has increased by 35.58%, 120% and 30.86%, respectively, and their TMo has increased by 29.37%, 25.21% and 11.97%, respectively. Our studies showed that PRTs directly impacted AMo, and indirectly influenced TMo and AMo through soil pH and organic matter. Organic matter and pH positively affected TMo, while pH negatively affected AMo. Overall, soil molybdenum content in the study area was generally insufficient, and local governments should comprehensively consider the molybdenum content and its main constraints for scientific fertilisation.

Nitrogen application significantly affects microorganisms in agricultural ecosystems. However, it is still unclear how nitrogen application affects soil chemical properties and microbial communities in purple mudstone weathering products. In this study, a field soil column experiment was conducted in a typical purple soil area with four nitrogen fertilizer application gradients of 0 [CK], 280 [N1], 560 [N2], and 840 [N3] N kg ha⁻¹. Nitrogen addition decreased the bacterial chao1 value and increased the bacterial evenness index. For both α- and β-diversity, the effect of nitrogen addition on bacteria was much greater than that on fungi. Nitrogen addition significantly increased the relative abundance of Proteobacteria, Gemmatimonadetes, Bacteroidetes, and Ascomycota and decreased the relative abundance of Actinobacteria, Cyanobacteria, and Basidiomycota. Both pH and TC are the most important soil chemical properties influencing the bacterial and fungal communities. With the increases in the nitrogen application rate, the co-occurrence network complexity increased and then decreased. In summary, nitrogen fertilizer application could significantly change the soil chemical properties, microbial community diversity, composition, and co-occurrence network of purple mudstone weathering products. Among them, the N2 treatment (560 N kg∙ha⁻¹) can more effectively stimulate the soil nutrients, enhance microbial network complexity, and promote further weathering of purple mudstone.