Distribution of soil water-stable aggregates and organic carbon content affected by tillage systems: a meta-analysis

A better understanding of soil carbon( C) distribution within aggregate fractions is essential to evaluating the potential of no-till for sustaining productivity and protecting the environment. A metaanalysis on 744 comparisons from 34 studies was conducted to determine the effects of three different tillage treatments( conventional mouldbould ploughing tillage( CT),reduced tillage( RT) and no tillage( NT)) on water-stable aggregate size distribution,soil C concentration in aggregate fractions.The meta-analysis indicates that compared with CT treatment, NT/RT significantly( P < 0. 05)increases macro-aggregate above 20 cm by 20. 9%-82. 2%( > 2. 00 mm) and 5. 9%-19. 1%( 0. 25-2.00 mm),whereas NT/RT significantly reduces micro-aggregate and silt clay fractions above 20 cm.NT/RT significantly( P < 0. 05) increases the SOC in macro-aggregate( > 0. 25 mm) and microaggregate( <0. 25 mm) size classes above 20 cm soil depth compared with CT. The results suggest that soil sampling depth should be considered to evaluate the influence of tillage systems on the distribution of soil aggregate,and the content of aggregate-associated C content.