Soil profile dismantlement by land levelling and deep tillage damages soil functioning but not quality

Abstract

We investigated the effects of land levelling followed by deep tillage, thus inducing a drastic dismantlement of soil profile, on both soil functioning and quality by monitoring various bioindicators (microbial biomass and community structure, basal respiration, enzyme activities) expressed on either whole soil and TOC mass units, respectively. As expected, in disturbed soils all measured properties had much higher coefficients of variation (CVs), regardless of either whole soil or TOC mass basis, due to the induced spatial variability. The amount of total organic C in the first cubic meter of soil profile was of one order of magnitude greater in undisturbed soils compared to disturbed ones. Soil bioindicators monitored on whole soil mass basis appeared greatly worsened while unchanged or even improved under TOC mass basis. This was essentially due to a couple of reasons: (1) soil bioindicators are constitutively dependent on soil TOC content; (2) soil spatial rearrangement may have made some organic C available to microbial biomass, otherwise unreachable when allocated throughout the undisturbed soil profile. Concluding, our work highlighted the need of expressing soil biondicators on soil mass basis when the response of the whole agrosystem to soil deep spatial rearrangement has to be assessed, while on TOC mass basis if the soil biological features are the major concerns.