Several studies have reported how tillage and cropping systems affect quantity, quality, and distribution of soil organic matter (SOM) along the profile. However, the effect of soil management on the chemical structure of SOM and on its hydrophobic and hydrophilic components has been little investigated. In this work, the long-term (19 years) effects of two cropping systems (wheat monoculture and wheat/faba bean rotation) and three tillage managements (conventional, reduced, and no tillage) on some chemical characteristics of SOM and their relationships with labile carbon (C) pools were evaluated. Soil samples were taken from the topsoil (0-15 cm) of a Chromic Haploxerert (central Sicily, Italy). After 19 years of different tillage and cropping systems management, total organic C significantly differed among treatments with the labile organic C pools showing the greater amount in no till and in wheat/faba bean plots. Hydrophobic and hydrophilic components of SOM, determined by diffuse reflectance infrared Fourier transform spectroscopy, were mainly affected by cropping system, whereas aromatic components of SOM by tillage. Soil organic matter components and characteristics showed significant correlations with the soil biochemical parameters, confirming the expected synergism between chemical and biochemical properties. This study demonstrated that (i) no tillage and crop rotation improve the chemical and biochemical properties of SOM of Vertisols under semiarid environment; and (ii) tillage management and cropping systems have affected, after 19 years, more the chemical and biochemical properties of SOM than its quantity.

Organic amendment and tillage reduction are two common practices to contrast soil organic matter decline, thus promoting sustainable cropping and carbon sequestration. In a horticultural land use system under Mediterranean climate, we\ud evaluated the 9-year effects of two compost inputs (15 and 30 t ha−1 y−1, low and high input, respectively) and two tillage intensities (intensive and reduced) on soil macronutrients concentration, microbial biomass and activity. Total organic C, total N and POlsen were smaller in plots amended at low input, whilst intensive tillage decreased them at both compost inputs. These decreases in intensively tilled plots was ascribed to the disruption of soil aggregates, with consequent microbial degradation of the physically protected organic matter by oxidative processes. On the contrary, reduced tillage increased the extractable C, likely due to a higher protection of the most labile soil C fraction from the mineralization. Similarly, microbial biomass C and N increased following both doubling compost input and reducing tillage intensity, with a greater effect by the first factor. The higher values of cumulative 10-day basal and 20-h glucose-induced respiration,\ud and metabolic quotient in intensively tilled plots suggested that high tillage favoured soil aggregate disruption and C accessibility. This was also confirmed by higher values of dehydrogenase activity/total organic C in those plots. Intensive tillage caused a higher soil aeration and organic substrates accessibility to microflora, thus undoing the fertility benefittillage s provided by the high compost input. However, also a low compost input coupled to reduced seemed to accomplish soil sustainability needs

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