Soil organic matter, biota and aggregation in temperate and tropical soils: effects of no-tillage

The long-term stabilization of soil organic matter (SOM) in tropical and temperate regions is mediated by soil biota (e.g. fungi, bacteria, roots and earthworms), soil structure (e.g. aggregation) and their interactions. On average, soil C turnover was twice as fast in tropical compared with temperate regions, but no major differences were observed in SOM quality between the two regions. Probably due to the soil mineralogy dominated by 1:1 clay minerals and oxides in tropical regions, we found a higher aggregate stability, but a lower correlation between C contents and aggregate stability in tropical soils. In addition, a smaller amount of C associated with clay and silt particles was observed in tropical versus temperate soils. In both tropical and temperate soils, a general increase in C levels ( $approx$ 325 $pm$ 113 kg C $cdot$ha $^{-1}cdot$yr -1) was observed under no-tillage compared with conventional tillage. On average, in temperate soils under no-tillage, compared with conventional tillage, CH 4 uptake ( $approx$ 0.42 $pm$ 0.10 kg C-CH $_4cdot$ha $^{-1}cdot$yr -1) increased and N 2O emissions increased ( $approx$ 1.95 $pm$ 0.45 kg N-N 2O $cdot$ha $^{-1}cdot$yr -1). These increased N 2O emissions lead to a negative global warming potential when expressed on a CO 2 equivalent basis.

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