|Todd, Richard - Rick|
Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2012
Publication Date: N/A
Interpretive Summary: Nitrogen (N) is a plant fertilizer, but too much N can damage N-sensitive ecosystems like shortgrass prairie found on the Southern High Plains. Part of a native shortgrass prairie pasture closest to and downwind from a beef cattle feedyard in the Texas Panhandle turned to mostly weeds during thirty years. We used historical documents and published studies to determine what the pasture was like before the feedyard operated. Then, we sampled plants and soil to determine the current state of the pasture. Undesirable weeds were most plentiful within 150 meters of the feedyard; nitrogen and phosphorus (P) in the soil were also highest there. Both the plant composition and soil N and P were at expected levels more than 500 meters from the feedyard. Using collected dust samples and changes in soil N and P, we concluded that the extra N and P blown in from the feedyard began the negative ecological changes in the pasture, but that the damage was limited to less than 500 meters from the feedyard.
Technical Abstract: Excessive reactive nitrogen negatively impacts N-sensitive ecosystems when invasive nitrophilic species outcompete native species adapted to low N. Part of a shortgrass prairie pasture directly downwind from a cattle feedyard in the Texas Panhandle degraded to annual weeds during thirty years of feedyard operation. Published studies from 1966-1972 and anecdotal observations and photos from the 1940s were used as benchmarks to compare historic plant composition with contemporary (2000) plant composition. Soil N and P and dust deposition gradients with distance downwind from the feedyard were also measured during 2000 and 2004. Annual weeds dominated within 150 m of the feedyard, with almost total exclusion of desirable native perennials. Manure dust deposition and soil N and P were greatest within 150 m, decreasing with distance from the feedyard. Evidence indicated that N enrichment initiated a cascade of negative ecological change, with effects limited to less than 500 m from the feedyard.