Impact of soil and crop management practices on soil water and carbon dynamics

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    Sridhar Patra

    Sustainable, high-yield crop production is critical to maintaining food security, especially during a time of climate change. Long- term sustainability of high crop yields requires soil management practices that promote soil function, soil quality, and soil health. Against the background of an intensification of agriculture using the same land footprint to supply the rapidly growing demand for food, adaptive management as a preventative element of water and soil conservation are attracting increasing worldwide attention. Conservation agriculture (CA) practices have recently received much attention in this direction. CA is a system of agricultural practices that include reduced tillage (RT) or no-till (NT), permanent organic soil cover by retaining crop residues, and crop rotations, including cover crops. Together these practices aim to increase crop yields by enhancing several regulating and supporting ecosystem services. Though CA was originally introduced to regulate wind and water erosion (Baveye etal., 2011), it is now considered to deliver multiple ecosystem services such as climate regulation, soil carbon sequestration, in-situ water conservation, nutrients recycling etc.(Palm etal 2014). While CA was not initially conceived as a practice to sequester soil C, it is now considered as a potential technology to mitigate green-house gas emissions and has become a focus of CA research. Several reviews summarize the effects of the different component practices of CA on soil C stocks compared to conventional practices (Branca et al., 2011; Corsi et al., 2012; Gattinger et al., 2011; Govaerts et al., 2009; Grace et al., 2012; Lal, 2011; Luo et al., 2010).

    Strong change in soil hydrological regime has been reported in many studies following changes in climate, land cover, and soil management on soil water availability for plant growth; evapotranspiration components; seepage; groundwater recharge; runoff formation; and erosion risk (e.g. Krysanova et al., 2005, Hurkmans, et al., 2009). The permeability and water storage capacity of soils has been strongly related to soil structure (Assouline and Or, 2013). It is well-known that changes in management and land cover affect the soil structure and hence modify these soil properties (e.g. van Es et al., 1999; Horn and Baumgartl, 2002; Ahuja et al., 2006; Zimmermann et al., 2006; Peth et al., 2008; Roger-Estrade et al., 2009). Nevertheless, these alterations of soil properties are often not addressed in hydrological and biogeochemical modeling studies dealing with the impact of changes in land use, soil management and tillage practices (e.g. CA). An invariant soil pore system is often assumed when modeling the impact of land use change, agricultural management and tillage practices. A better understanding of dynamic changes in soil pore space is required as a basis to understand the changes in soil hydrology due to management, or climate change, or changes in ecosystems undergoing ecological succession (Jury et al 2011, Or, 2013).

    Soil moisture distribution in pore space also determines transformation of soil organic carbon, the decomposition of which produces carbon dioxide. Faulty management practices as well as land use change have adverse impacts on environment in terms of contributing greenhouse gas to the atmosphere. So it’s imperative to evaluate impact of agricultural management practices on production of greenhouse gases such as carbon dioxide. Spatial isolation of soil organic carbon (SOC) in different sized pores may be a mechanism by which otherwise labile carbon (C) could be protected in soils. When soil water content increases, the hydrologic connectivity of soil pores also increases, allowing greater transport of SOC and other resources from protected locations, to microbially colonized locations more favourable to decomposition (Jastrow et al., 2007).Literature review suggests that few studies have examined the combined impact of cropping systems and tillage management practices on temporal dynamics of soil pore systems and the consequent effect on soil hydrological (soil pore dynamics) and soil organic turnover processes. Moreover, though fragmented studies have been undertaken in the past on the effect of tillage practices on temporal and management induced changes of soil hydraulic properties, its short term and long-term effect on carbon turnover processes have not been investigated in detail. Models pertaining to hydrology and biogeochemistry have been separately tested for evaluating the impact of various cropping systems and tillage practices on soil water and carbon dynamics assuming an invariant pore system, while recent studies indicate strong temporal influence of agricultural management and tillage practices on soil pore system evolution. An integrated approach is needed to understand the interactions of temporal soil pore system evolution and soil organic carbon dynamics which will enhance the accuracy of assessment of impact of long-term climate and land use management strategies on soil health and its response on environment.