Cultivation of soils plays a crucial role in transferring carbon from terrestrial to atmospheric pools. A source of carbon comes from land use change from natural to agricultural conditions that implies the reduction of woody biomass and amount of residue returned to soil, as well as the increase of soil organic matter (SOM) mineralization. On the other hand, decreasing CO2 emissions from soil to atmosphere means to return the exceeding atmospheric C into the terrestrial pool, and sequestering carbon in soil turns soils from sources to sinks of carbon (Paustian et al. 2000).

C. Grignani (*) • F. Alluvione • C. Bertora • L. Zavattaro

Dipartimento di Agronomia, Selvicoltura e Gestione del Territorio, Universita di Torino, Turin, Italy e-mail: [email protected]

Dipartimento di Ingegneria Agraria e Agronomia del Territorio, Universita di Napoli Federico II, Naples, Italy

Dipartimento di Scienze dei Sistemi Colturali, Forestali e dell'Ambiente, University of Basilicata, Potenza, Italy

A. Piccolo (ed.), Carbon Sequestration in Agricultural Soils,

DOI 10.1007/978-3-642-23385-2_3, © Springer-Verlag Berlin Heidelberg 2012

SOM is recognized as the major factor controlling the capacity of soils to deliver agricultural and environmental services (Manlay et al. 2007). Therefore, it is evident that enlarging soil C stock has not only a pivotal function in reducing atmospheric CO2, but has several other positive advantages for agricultural systems, in terms of plant growth support, nutrients cycling, and water cycle regulation (Bauer and Black 1994; Mondini and Sequi 2008). SOM is indeed crucial for maintaining soil aggregation and aeration, hydraulic conductivity and water availability, cation exchange and buffer capacity, and supply of mineralizable nutrients (Khan et al. 2007).

Soil C content is the balance between C inputs and C outputs (Paustian et al. 1997; Lal 2004; Rees et al. 2005). Management practices aimed at enhancing soil C content can be addressed either to decrease C losses or to increase C supply.

In soils of southern Europe, SOM content is usually very small due to common synergy between natural and human-induced factors that induce SOM degradation (Zdruli et al. 2004). Southern Europe is mainly influenced by Mediterranean climatic conditions (i.e., cool humid winters and warm dry summers), which do not favor SOM accumulation. In hyperhumid regions, SOM accumulation is due to anaerobic conditions that reduce microbial activity (Satrio et al. 2009). Conversely, in temperate regions, SOM content generally increases with increasing rainfall, because larger soil moisture results in greater plant biomass that, in turn, provides more carbon residue and, thus, more potential food for soil biota. Moreover, high temperature and water availability accelerates SOM decomposition and finally result in low SOM content in such temperate conditions (Post et al. 1982).

In respect to human-induced factors, it is well known that land use change from natural to cultivated is one of the major causes of SOM degradation (Bruce et al. 1999; Guo and Gifford 2002; Celik 2005). In the Mediterranean basin, human pressure has been particularly high since at least 3,000 years. The needs of Mediterranean societies were satisfied by wide deforestation to allow intensive land management and exploitative agriculture (Blaikie and Brookfield 1987).

Soil tillage is the cultivation technique that exerts the major impact on SOM degradation due to inherent alteration of oxidative conditions, soil structure, and biodiversity (Fagnano and Quaglietta Chiaranda 2008). Conservation tillage techniques, minimizing soil inversion and soil structure disruption, have shown to increase SOM (Holland 2004). However, more complex strategies of conservation agriculture with integration of tillage and other practices are necessary to counteract soil degradation. As shown by long-term field experiments, the combined use of different techniques, such as long-time rotations (including permanent meadows which reduce tillage frequency), manuring, conservation tillage, and crop residue return to soils, led to a significant increase in SOM content (Reeves 1997).

Agronomic techniques employing secondary crops as cover crops, green manuring and live mulching, resulted particularly effective in limiting soil degradation (Wagger et al. 1998; Steenwerth and Belina 2008b). In addition, secondary crops strongly interact with the plant-soil nitrogen cycling and alter microbial activity in the rhizosphere (Steenwerth and Belina 2008a), thus also affecting SOM content in the long term. Similarly, soil mulching with crop residues proved to increase SOM content and soil fertility (Holland and Coleman 1987; Bot and Benites 2005).

Enhancing residues return to soils implies primary production growth, but also the increase of the nonharvested crop portions. Thus, the removal of crop residue for biofuels, devised as a possible plan for alternative energy production, creates a negative nutrient budget and can lead to soil degradation (Lal et al. 2004). Cropping systems and management practices which ensure large amounts of crop residue returned to soil are generally expected to cause a net build-up of SOC stock (Gregorich et al. 1996). Nevertheless, the addition of easily decomposable C compounds to soil may concomitantly induce an acceleration of mineralization processes by the priming effect and counterbalance the tendency in enriching the soil organic C pool (Kuzyakov et al. 2000).

Carbon is supplied to soil also via animal manure and compost. Both these practices imply the recycle of biomasses (from animal livestock, food industry, garden and urban wastes) and reduction of chemical fertilizers additions. Besides the contribution for carbon sequestration, the use of organic fertilizers enables the reduction of other greenhouse gases, thus diminishing both the energy required for unit of available nutrient and emissions of N2O after soil incorporation (Freibauer et al. 2004; Smith 2004; Alluvione et al. 2010).

Application of polymeric soil conditioners was applied in the past to attempt SOM stabilization (Wallace 1986) without much success. Recently, Piccolo and coworkers have introduced the concept of in situ photo-polymerization of SOM under the action of a biomimetic catalyst such as a synthetic Fe-porphyrin (Piccolo et al. 2005; Smejkalova and Piccolo 2005; Smejkalova et al. 2006). This innovative practice should enhance the molecular mass of humic molecules and, thus, their biochemical recalcitrance in soil (see Chaps. 1 and 4). The method has been tested in pot experiments (Piccolo et al. 2011) and microcosms (Gelsomino et al. 2010), and carbon sequestration in unplanted soils was successfully shown.

All agronomic practices which intend to promote soil C sequestration do strongly interfere with water balance and nutrient cycling in soil. Their impact on crop yield and SOM is potentially great, but actual effects are dependent on specific cropping systems and environmental conditions. It is therefore essential to study their efficacy in different conditions, since the application of practices developed in other climates can lead to unexpected results. For example, the beneficial effects of reduced tillage and cover crops are not obvious in Mediterranean climate zones, whereby a potential reduction of soil water content at crucial stages of crop growth, such as germination and grain filling, may severely affect crop production.

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