Syswerda, S. P. 2009. Ecosystem services from agriculture across a management intensity gradient in Southwest Michigan. Dissertation, Michigan State University, East Lansing, MI, USA.
I investigated how agricultural systems can be managed to minimize the environmental impact of agriculture without sacrificing productivity—or, conversely, to maximize the ecosystem services provided by agriculture, including productivity. Agricultural systems have a large impact on nutrient cycling, climate regulation, and fresh water and food provisioning, and I have used nitrate leaching, drainage, carbon sequestration, soil inorganic nitrogen, greenhouse gas fluxes, annual net primary productivity, and agronomic yield across a management intensity gradient as a measure of the provision of these services.
Research was conducted at Kellogg Biological Station’s Long-Term Ecological Research site in southwest Michigan. Treatments included four annual maize-soybean-wheat rotations with conventional, no-till, reduced-input, and organic management; three perennial systems in alfalfa, poplar, and conifer crops; and four native successional systems ranging from early successional (~20 years since abandonment from agriculture) systems to old growth forest. All systems were replicated in the landscape on the same soil series.
Nitrate leaching over an 11 year period ranged from less than 1 kg NO3—N ha-1y-1 in poplars to 62 kg NO3—N ha-1y-1 in the conventional row-crop system. The no-till, reduced input, and organic systems leached 34%, 61%, and 68% less nitrogen, respectively, than did the conventional system. The alfalfa and conifer stands leached nitrogen at rates similar to the organic system. The successional and poplar systems leached the least amount of nitrogen. Drainage levels were highest in the no-till annual system and deciduous forest. Our findings show that long-term water quality is substantially affected by crops and management practices.
Soil carbon levels 11 years post-establishment differed substantially among systems in the surface soil, where carbon contents were significantly greater than the conventional system in the no-till, organic, alfalfa, poplar, conifer, early successional, never tilled mid-successional, and deciduous forest systems. However, soil carbon levels in the deeper portions of the soil profile were more variable, and showed very few significant differences among treatments. Subsequently soil carbon levels in the total profile to 1 meter differed little among treatments, with only the early successional and never-tilled mid-successional systems containing more soil carbon than the conventional system. Deeper soil carbon was much more variable than carbon in upper soil layers, which suggests that finding differences among treatments when including deeper soils will be more difficult. Results demonstrate the importance of measuring carbon to depth but also the need for more intensive sampling than has been undertaken to date.
The additional measured ecosystem services also differed by management system. Yield was highest in the no-till system, and the lowest in the organic system. The reduced input and conventional treatments had similar yields, despite differences in management. Nitrous oxide production was highest in the alfalfa and annual cropping systems, and lowest in the poplar system. Nitrous oxide fluxes were tightly linked to soil nitrate levels. Soil methane oxidation was highest in deciduous forest system, and lowest in the conventional system. Net primary productivity was highest in the reduced input system, and lowest in the poplar system. Soil inorganic nitrogen levels were highest in the alfalfa and early successional system, and lowest in the reduced-input, conventional, and poplar systems. As systems were managed more intensely, soil carbon levels decreased, nitrate leaching increased, methane oxidation decreased, and nitrous oxide production increased. Trade-off curves and flower diagrams provide a means to display these alternative services and their effects.
Analyses of multiple ecosystem services are a first step towards better understanding the large scale trade-offs that occur with land management decisions. Trade-offs in multiple ecosystem services can be used to help develop models incorporating the complexity of the different components of the ecosystem. Future research might focus on using such models to predict the outcome of individual management decisions on the services delivered by managed systems.
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