Objectives Tillage methods affect soil health and crop nutritional quality. We compared the soil physio-chemical and microbial properties as affected by tillage methods, discussed the correlation of tillage methods with wheat grain quality.

Methods A field experiment was established in 2012 in Dezhou, Shandong Province, the main planting system was winter wheat–summer maize rotation. The four treatments were conventional tillage (CT), rotary tillage (RT), fallow tillage (FT) and no-tillage (NT). In 2020, after harvest of wheat, soil samples (0–20 cm deep) were collected to analyze physicochemical and microbiological properties, and wheat grain samples were collected for determination of nutritional quality.

Results NT, FT and RT treatments significantly increased contents of soil water, ammonium N, nitrate N, organic matter, total N, and available P compared with CT, while FT significantly increased soil bulk density and decreased soil porosity. NT, FT and RT treatments significantly increased soil microbial biomass C and N contents as well as the diversity index of soil bacterial community. FT and NT treatments increased the relative abundance of soil Firmicutes and Verrucomicrobia but decreased the relative abundance of Actinobacteria. In terms of nutritional quality, FT treatment significantly increased the content of protein, starch, and micronutrients in wheat grain. RT and NT treatments also significantly increased the protein content of wheat grain. Except for aspartic acid, other 16 amino acid compositions changed in a trend basically consistent with the total amino acids. Pearson correlation analysis and RDA results showed that the contents of starch, Fe, Zn, and Se in wheat grain were significantly and positively correlated with the contents of soil water, ammonium N, nitrate N, available P, microbial biomass C, and microbial biomass N. Ammonium N (F=25.7, P=0.002), microbial biomass C (F=4.9, P=0.008), total N (F=3.3, P=0.028), and soil pH (F=3.1, P=0.036) were the main environmental factors affecting wheat nutritional quality.

Conclusions Tillage method with minimum soil disturbance alters soil environmental factors and bacterial community structure to different degrees. Compared with RT and NT, FT can be more beneficial to the accumulation of protein, starch, microelements, amino acid composition and content in wheat grain, which is an effective tillage method to improve soil health and wheat nutritional quality.