Monday, August 3, 2009 - 3:25 PM

SYMP 1-5: Trade-offs for sustainable agroecosystem management within the complex interactions between resources, soil biota, plants, soil structure, and C and N cycling

Johan Six, University of California, Davis


In managing the multiple ecosystem services provide by agroecosystems  in the long term and within a changing global environment, a trade-off between these services is often necessary because the complexity of interactions between different ecosystem variables, such as the soil microbial community, plant diversity, and soil properties, cause the different services to not always go hand in hand. Furthermore, to conduct an accurate trade-off analysis, services and controlling factors need to be understood and considered across a range of temporal and spatial scales. In this synthesis, I focus on how the interactions between resources, soil biota, plants, soil structure and carbon and nitrogen dynamics need to be managed to attain sustainable agriculture.


At the microscale, preferential C and N stabilization has been observed in specific soil microenvironments occurring more in alternative (e.g. organic, reduced tillage) than in conventional agricoecosystems. However, minimal differences in the microbial community within these microenvironments are observed and these microenvironments might be an ideal site for short-term N2O production. At the field scale, greater N2O fluxes concomitantly with greater soil C stabilization have been found, especially during the transition from conventional to alternative agroecosystems. Furthermore, the increased microbial abundance and activity in alternative agroecosystems does not necessarily translate in increased plant productivity but does improve the overall soil quality.  N additions are not only necessary for optimal plant growth, but they are often necessary to maintain increased C input that can be stabilized as soil C. Consequently, combining organic amendments with fertilizer additions might be warranted. Nevertheless, the benefits of this combining differ across soil textures and climates. Furthermore, balancing the short- versus long-term benefits of different qualities of organic amendments is necessary, i.e. residue quality affects short-term dynamics of C and N, but not long-term stabilization of soil C. In conclusion, trade-off analyses are needed, but complex, when managing for optimal provision of multiple agroecosystem services.