The C cycle contributed to the soil acidification mainly via the removal of alkaline products from the field, through the harvest of maize grain, which was higher in leguminous-based cropping systems and in N-fertilised soils.
According to the model, alkalinisation occurred in soils where organic carbon stocks decreased (negative values in Table 3), mainly in the F/M system, while acidification occurred in soils where the stocks increased.
The effect of C cycle (removal of alkaline products from field plus the effect of changes in soil carbon stocks considered in this study) on soil acidification resulted in contrasting contributions to the total acidification.
The acidification due to the N cycle (nitrate leaching), which was obtained by difference between the total acidification and the sum of the other factors of soil acidification, ranged from null in soil under L + M 0 and 180 N to about 1.
Observing the effect of leguminous crops in absence of N fertilisation (0 N), the inclusion of vetch to the O/M system increased the relative acidification due to C cycle from 25.
As the acidification due to nitrate leaching in N cycle is obtained by difference, this approach assumes that all acidification that is not accounted for by other processes was due to nitrate leaching.
Because some soil layers achieved relatively low pH values, it is probable that the weathering of alumino-silicate minerals prevented a further decrease in soil pH, and it should be considered in the assessment of the net acidification found.
Soil acidification was intensified by leguminous species in notill cropping systems and by N fertilisation, associated to a decrease in pH values and base saturation and an increase in exchangeable A1 and A1 saturation in soil.
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