Document: DAV-3-61-4

Primary production of summer-fallow winter wheat and native grasslands in the shortgrass steppe.

SMITH, D.P.*, W.K.LAUENROTH and I.C.BURKE

Colorado State University, Fort Collins, CO 80523 USA ¹

Abstract:
Landuse change has greatly affected the structure and function of grassland ecosystems. Approximately half of native perennial grasslands in the central grassland region of the United States have been converted to annual croplands. This study focused on shortgrass steppe ecosystems and their conversion to summer-fallow winter wheat. This conversion has affected net primary production and the dynamics of soil water. Our objectives for this study were to compare above and belowground net primary production and soil water dynamics among winter wheat, adjoining fallow strips and nearby native shortgrass steppe. Samples were collected from three wheat fields and three grassland sites, in Weld County, Colorado. Average aboveground primary production was 327 g/m2 ( 121 g/m²) for wheat sites and 126 g/m2 ( 51 g/m²) for native grassland sites. Aboveground primary production on the fallow phase of wheat was maintained at essentially zero for the purpose of water storage, as is the common cropping practice. Since half of the wheat acreage is fallow, system-level comparisons show an average of 130% higher net primary production in wheat sites than in grassland sites. Average belowground primary production was much lower in the wheat sites than in the grassland sites. Soil water dynamics differed only slightly among the three treatments. However, the wheat and adjoining fallow sites had higher volumetric soil water content than grassland sites. Additionally, wheat fallow sites had a more variable depth distribution of soil water, due to mixing caused by mechanical weed control. Results of this study lead to the conclusion that the conversion of shortgrass steppe ecosystems to summer-fallow winter wheat significantly affects net primary production and soil water dynamics.

Keywords: shortgrass steppe, winter wheat, net primary production, landuse

This abstract is being presented at: 3:30 PM in session:
AGROECOLOGY