## 1 Introduction  
Previous studies have used the particle size fractionation for obtaining information about the influence of land use and depth on the distribution of soil organic carbon (SOC) [1, 2]. The various soil fractions can differently immobilize organic carbon (OC) through the formation of organo-mineral complexes [3, 4]. In particular, quartz particles exhibit only weak bonding affinities to organic matter (OM), while clay size particles (i.e., sesquioxides and phyllosilicates) have a large surface area and numerous sorption sites [3, 4]. The physical protection of OM through its occlusion within clay minerals limits its microbial decomposition, which reduces the C mineralization [5]. Therefore, the sand related OM represents the active pool of soil organic matter (SOM), the OM linked to the silt size fraction is the intermediate pool, and the clay related OM represents the passive and the older SOM pool [4]. The microaggregates, composed mainly of clay minerals, represents the most efficient way to stabilize the SOM [6, 7] by forming bridges between the exchangeable cations of layer silicates and functional groups of organic compounds [8]. The formation of macroaggregates is favored by the decomposition of fresh plant residues and fungal hyphae [9]. The SOM in the macroaggregates is available for microbial utilization while the protected microaggregates form a long-term reserve of mineral-associated C that is not \"humified\" and can be attacked by microorganisms once exposed [9].  
It is known that chemical fertilizers can modify soil physical, chemical, and biological properties with clear consequences on soil aggregates [10]. A different development of the root system, stimulated by fertilization, influences the production and release of root exudates, directly involved in the formation of aggregates [11]. In addition, a greater growth of the root system following the fertilization increases the SOM [11]. Several previous studies have demonstrated that tillage practices influence the content and the dynamic of SOM [7; 12; 13; 14]. Soil tillage increases the turnover of macroaggregates by inhibiting the formation of microaggregates within macroaggregates and, thus, reducing the sites where the OM is stabilized [5].  
In order to identify the minerals and their changes among the different soil fractions, the diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been utilized. This technique can be considered rapid, inexpensive, and precise, and can be applied to estimate the water-bearing minerals, such as clay minerals together to other sheet silicates as muscovite, illite, smectite, kaolinite, and chlorite [15], and the presence of organic matter [16]. DRIFT spectroscopy allows us to analyze the matrices without pressing them by avoiding the error due to scattering [17], and to have a band intensity four times greater than that of IR spectroscopy due to the non-mixing of the soil sample with KBr [18].  
The objective of this study was to investigate the effects of different soil managements on the quantity of SOC associated with several soil-size fractions. In addition, with DRIFT analysis, we tried to better understand the OM interaction with the mineral parts of the different soil fractions.