LTER Interaction Sites

The KBS LTER Interactions Experiment is a long-term study established in 1985 to provide an experimental context for examining interactions between tillage and fertilizer. The experimental site contains two areas that differ in land use history: one historically tilled and the other never tilled. On historically tilled land, the experiment originally consisted of two tillage treatments (conventional and no tillage) and two nitrogen fertilizer treatments (with and without N); each combination replicated in four 27 x 40 m plots for a total of 16 plots planted to continuous corn. Four in ground monolith lysimeters were installed in 1990. Around 2005 crops planted followed that of the Main Cropping System Experiment (MCSE; corn-soybean-wheat rotation). In spring 2016 all plots were planted to switchgrass (Cave-in-rock). Since switchgrass is a perennial crop, the conventional tillage plots are no longer tilled, however the fertilized and not fertilized treatments persist in all plots. In 2018, additional buried mesocosms were installed in the no till, no fertilizer plots for associative nitrogen fixation (ANF) experiments. Rainout shelters manipulate soil wetting/drying regimes to examine the relationship between ANF and switchgrass phenology, diazotroph communities, and nifH expression.

On never-tilled land, the original experimental design remains. Four no tillage, not fertilized plots (15 x 40 m) still follow the MCSE crop rotation and serve as a tillage reference. In addition, four plots maintained in early successional vegetation (Ref) are also the MCSE Treatment 8 mown grassland, and provide reference for an undisturbed and uncropped soil profile. These plots have been mown annually in the fall to inhibit tree growth since the site was deforested ca. 1960.

The four monolith lysimeters (each 1.2 m x 2.2 m x 2.2 m deep) are located in historically tilled plots; one in each of 2 replicate plots of the no tillage, not fertilized and the recent tillage, not fertilized treatments.



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