The Effect of Nitrogen Addition and Irrigation in High Diversity Prairies
Experiment Id

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.