CDR LTER

Water and nitrogen are two potentially major limiting resources in prairie grasslands of the region, and thus might be added to restored high-diversity grasslands used for biofuel production. In this full-factorial experiment, 36 high-diversity 9 m x 9 m plots that were planted with 32 species in 1994 were randomly assigned to one of six treatments. Treatments were all combination of a water treatment (ambient rainfall or ambient rainfall plus ~ 2 cm/week of irrigation) and of a nitrogen treatment (annual nitrogen addition of 0, 7, or 14 grams of N - as ammonium nitrate - per square meter). Aboveground biomass is harvested each fall in each plot, dried, and weighed. These treatments are determining the importance of both water and N limitation in high-diversity restored prairie grassland, their interactive effects, and the year-to-year variation in yields and treatment effects. They are also determining the potential sustainability of such yields and the effects of the various treatments on plant diversity.