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Can no-tillage stimulate carbon sequestration in agricultural soils? A meta-analysis of paired experiments

Luo, Zhongkui, Wang, Enli, Sun, Osbert J.
Agriculture, ecosystems & environment 2010 v.139 no.1-2 pp. 224-231
agricultural land, agricultural soils, carbon sequestration, no-tillage, meta-analysis, environmental factors, land management, soil organic matter, tillage, soil depth, spatial distribution, double cropping, crop rotation, agroecosystems, air temperature, rain, nitrogen fertilizers, cropping systems, biodegradation
Adopting no-tillage in agro-ecosystems has been widely recommended as a means of enhancing carbon (C) sequestration in soils. However, study results are inconsistent and varying from significant increase to significant decrease. It is unclear whether this variability is caused by environmental, or management factors or by sampling errors and analysis methodology. Using meta-analysis, we assessed the response of soil organic carbon (SOC) to conversion of management practice from conventional tillage (CT) to no-tillage (NT) based on global data from 69 paired-experiments, where soil sampling extended deeper than 40cm. We found that cultivation of natural soils for more than 5 years, on average, resulted in soil C loss of more than 20tha⁻¹, with no significant difference between CT and NT. Conversion from CT to NT changed distribution of C in the soil profile significantly, but did not increase the total SOC except in double cropping systems. After adopting NT, soil C increased by 3.15±2.42tha⁻¹ (mean±95% confidence interval) in the surface 10cm of soil, but declined by 3.30±1.61tha⁻¹ in the 20-40cm soil layer. Overall, adopting NT did not enhance soil total C stock down to 40cm. Increased number of crop species in rotation resulted in less C accumulation in the surface soil and greater C loss in deeper layer. Increased crop frequency seemed to have the opposite effect and significantly increased soil C by 11% in the 0-60cm soil. Neither mean annual temperature and mean annual rainfall nor nitrogen fertilization and duration of adopting NT affected the response of soil C stock to the adoption of NT. Our results highlight that the role of adopting NT in sequestrating C is greatly regulated by cropping systems. Increasing cropping frequency might be a more efficient strategy to sequester C in agro-ecosystems. More information on the effects of increasing crop species and frequency on soil C input and decomposition processes is needed to further our understanding on the potential ability of C sequestration in agricultural soils.