Abstract: The objective of this study was to investigate the effect of different tillage and mulching methods on soil nutrients, soil bulk density, enzyme activity and microbial populations in the tillage layer in arid croplands of eastern Gansu Province, China. The experiments included a no-tillage treatment with residues of film (T) and a double ridge plastic film mulching treatment (CK) and used a randomized block design. Soil nutrient levels, hydrolase enzyme activities (sucrose, urease, phosphatase, catalase), and microorganism abundance (bacteria, actinomycetes, fungi) were compared in the two treatments. It was found that compared with CK, the T treatment significantly increased the soil organic matter by 7.8%, total phosphorus by 11.3%, total potassium by 3.7%, available phosphorus by 12.7% and available potassium by 6.1% in the 0-10 cm soil layer at crop harvest. These indicators decreased with increase in soil depth. The alkali nitrogen content of the T treatment in the 0-20 cm soil layer was lower than in the CK treatment. However, in the 20-40 cm soil layer, the alkaline nitrogen content was high in the T treatment. The T treatment significantly increased the bulk density by 7.1%-12.4% in the 0-30 cm soil layer. In the 0-40 cm soil layer, the most abundant microorganisms were bacteria, followed by actinomycetes, with fungi the least abundant. The tillage treatments affected soil microbial populations differently at different crop growth stages. For a given crop growth stage, the soil microbial abundance decreased with increase in soil depth, especially in the T treatment. Compared with CK, the T treatment increased bacterial abundance by 23.7%, 64.5%, 7.6%, 44.0%, 5.6% at the seedling, jointing, flowering, grain filling and harvesting growth stages, respectively. The T treatment also increased fungal abundance by 31.1%, 91.7%, 85.7%, 10.5%, 33.3%, respectively, at the same five growth stages, and increased actinomycete abundance by 79.8%, 15.1% and 17.6% at seedling, jointing, and harvesting growth stages, respectively, and decreased actinomycete abundance by 17.2% at flowering and 33.2% at the grain fill growth stage. The tillage method also had a significant impact on soil enzyme activity in different soil layers. At any given crop growth stage, the soil enzyme activity decreased with increase in soil depth, and this pattern was more pronounced in the T treatment. The activities of sucrase, urease, phosphatase and catalase were increased in the T treatment by 4.7%-126.1%, 9.8%-47.0%, 5.4%-33.7% and 2.3%-43.2%, respectively, compared to the CK treatment, over the crop development cycle. Significant positive correlations were found among the activity values of the various enzymes, and also between enzyme activities and numbers of microorganisms. Hence, these results indicate that soil enzyme activities and microorganism abundance could be considered good indicators of soil fertility level. In summary, no-tillage with residues of film and stubble was beneficial to improve the soil nutrient content, microbial abundance and enzyme activity in dryland cropping fields.

Key words: no-tillage with residues of film and stubble, dryland, soil enzyme activity, soil nutriment, soil microbial quantity