Effects of Water and Nitrogen Additions to a Shortgrass Ecosystem (LT14)
Objective: The objective of this research is to evaluate the long-term response of shortgrass ecosystems to additional water and nitrogen inputs. An experiment was conducted during the IBP project (1970-1975) in which water and nitrogen were applied (Lauenroth et al. 1978, Dodd and Lauenroth 1979, Milchunas and Lauenroth 1995). While we gained an enormous increment in our knowledge about shortgrass ecosystems from this experiment it raised as many questions as it answered. One of the problems was that the treatments were very high levels of nitrogen (100-150kg/ha N) and water (600 mm/growing season) additions.
Methods: We will use a factorial combination of water and nitrogen additions. Our current plan is to have nitrogen additions in the range of 50 kg/ha N and water additions of about 350 mm/growing season. These represent our best estimates of conditions at the eastern extreme of the area in the Great Plains dominated by Bouteloua gracilis and Buchloe dactyloides. Our principal interest will be to assess effects on soil processes (nitrogen and carbon balance), plant population dynamics, plant community dynamics, and net primary production. The major disturbance to the plots besides the treatments will be the removal of soil cores. The maximum intensity of sampling would be 80 cores per treatment per year. This would only happen in a few years.
Study Area: We would like to use an area of approximately 2.25 ha (150 X 150 m; 5.5 acres) in section 21SE. The exact location is directly east of the east fence of the LTER headquarters exclosure. An important reason for choosing this location is that we need to be close to the irrigation well at the LTER headquarters. Initially we plan to use an electric fence to exclude cattle. Over time we will want to replace this with a permanent wire fence.
More on Methods and Experimental Design (pdf)
01/22/2008