Integrated Isotopic Approaches for an Area-wide Precision Conservation to Control the Impacts of Agricultural Practices on Land Degradation and Soil Erosion

Current concerns to enhance food security for the ever growing world population and arrest widespread land degradation have highlighted the importance of agricultural land use and management on soil erosion losses and related impacts on the farmers’ environments. Both of them represent a serious threat to intensification of agricultural production and environmental sustainability in many regions of the world. Moreover, these impacts are likely to increase further with additional pressures resulting from climate change and variability. Scientists and conservation practitioners will have to work together with farmers across a wide range of soil and climatic conditions to meet the increasing demands of food and biofuel production, while maximizing the conservation of the soil resources. New technologies will need to be developed and applied to better understand and manage natural and agricultural resources in agro-ecosystems to meet this dual goal of sustainable agricultural production and agro-environmental sustainability. Precision Conservation is a rapidly developing key science integrating geospatial techniques, models and other tools that are applied to better understand the spatial variability of erosion across the landscape connecting farm to natural surrounding areas and to identify hot spots on the farm and throughout the agricultural land on an area-wide assessment basis. This integrated approach provides better informed decisions on critically-degraded areas (i.e., risk areas) and assists land resource managers/farmers to target soil conservation measures and appropriate land uses to these site-specific hot spots. This will ultimately result in higher efficiency of resource management, economical returns and environmental sustainability.

In this CRP, two main complementary approaches based on the combination of fallout radionuclide (FRN) and compound specific stable isotopes (CSSI) techniques have been identified for further study and development to support the implementation of Precision Conservation. The use of FRN such as Pb-210 excess, Cs-137 and Be-7 are useful in discriminating source types such as sheet erosion and gully erosion and will provide information on soil erosion rates (as successfully done with previous CRPs D1.50.10 and D1.50.08) but also on the distribution patterns and soil deposition-remobilisation rates in the studied areas on an area-wide basis.
Previous CRPs (D1.50.10 and D1.50.08) using FRN have focussed only on the plot and field scales and on soil erosion rates. At a larger scale on an area-wide basis, it is important to quantify not only soil erosion rates but also deposition and remobilization rates for estimating amounts of soil losses/deposits in different sink-source areas. This requires a new approach involving not only FRN but also up-scaling soil sampling strategy, geostatistics and modelling.
The use of compound specific stable isotope (CSSI) techniques based on the measurements of 13C and 15N natural abundance signatures of specific organic compounds (e.g., 13C values in fatty acids extracted from soil) of plant and animal origins in the soil profile (surface soil and subsoil) is useful not only to identify soil sources but also to apportion their relative contribution from different land uses in catchments including a range of farming systems (e.g., areas under different crops or from cultivated land, pasture and agro-forestry) and environments worldwide in order to produce standardized tools to support better land management decisions on an area-wide basis. Recently it has been demonstrated that isotopic composition of the individual organic carbon does not change significantly with time (Boyd et al., 2006), making it a valuable tool in source fingerprinting (e.g., Chikaraishi and Naraoka, 2003; Gibbs, 2008).