Effects of conservation tillage practices on soil carbon and nitrogen stocks in farmland under different climatic types and fertilization conditions

Objectives  Reduced tillage and straw mulching are regarded as alternatives to enhance soil organic carbon (SOC) and nitrogen sequestration and thus mitigate greenhouse gas emission. The paper investigated the differences of soil organic carbon and nitrogen stocks under different tillage practices in different soils, to providing reference for selecting efficient and practical soil managements.

Methods  The selected four typical long term tillage experiments located in Shouyang (SSY) and Linfen (SLF) of Shanxi Province, Langfang (HLF) of Hebei Province and Gongzhuling (GZL) of Jilin Province. The soil types in the above four bases were cinnamon soil, sandy soil, fluvo-aquic soil and balck soil in turn. The selected treatments included conventional tillage (CT), no-tillage with straw cover (NT) and shallow rotation tillage with straw covering (ST). The soil carbon and nitrogen concentrations in 0−100 cm depth were measured, and soil bulk densities were investigated.

Results  1) In comparison with CT, ST significantly reduced the bulk density of cinnamon soil, NT increased the bulk density of black soil (GZL), and both had little effect on sandy soil (SLF) and fluvo-aquic soil (HLF). 2) Conservation tillages affected the soil organic carbon stocks of 0−60 cm. Compared with CT, both NT and ST significantly increased the organic carbon contents in 0−60 cm of black soil (GZL). NT increased the organic carbon content of 0−50 cm in cinnamon soil (SSY). In sandy soil and fluvo-aquic soil, NT increased soil organic carbon content of 0−15 cm soil by surface straw mulching, but reduced soil carbon storage of 15−50 cm layer. In the 15−60 cm layer of fluvo-aquic soil, ST increased soil organic carbon storage, while NT did the opposite. 3) The soil nitrogen storage of NT in fluvo-aquic soil was 0.026 t/hm² more than that of CT, however, the increase was not significant. The nitrogen reserves of NT and ST in black soil were respectively 0.112 t/hm² and 0.207 t/hm² more than that of CT, and both the increases were significant. Conservation tillage reduced 1 m deep soil nitrogen storage in sandy and cinnamon soils. 4) Conservation tillage exacerbated the stratification of 0−20 cm soil nitrogen storage in sandy and fluvo-aquic soils, but had little effect on the interlayer distribution of soil carbon storage in black soil and cinnamon soil.

Conclusions  Tillage methods show effects on 0−60 cm soil organic carbon stocks. No-tillage could increase the carbon storage in cinnamon soil and nitrogen storage in fluvo-aquic soil, and conservation tillage could significantly increase the carbon and nitrogen reserves in black soil. Therefore, no tillage is suitable for cinnamon soil and fluvo-aquic soil, and conservation tillage is suitable for black soil, but both kinds of conservation tillage have not showed significant improvement effects in soil organic matter in sandy soil.