Document: SAR-3-59-19

The relative role of water and nitrogen in regulating productivity in tallgrass prairie.

BEHRENS, S.L.*, S.HARPER, L.JOHNSON, J.KOELLIKER, T.BENNETT and A.KNAPP

Kansas State University, Manhattan, KS 66506 USA ¹

Abstract:
Water limitation is a defining characteristic of tallgrass prairie. However, the degree to which nitrogen co-limits productivity is not clear. Irrigation to eliminate water limitation, combined with N additions, assesses the relative role of water and N in controlling productivity and identifies water by N interactions. The experimental design is comprised of 3 levels of water (85, 50, 0% of maximum irrigation, 300mm/season =100% supplementation) combined factorially with 4 levels of N (0, 2.5, 5.0, and 10 gN/m²/season). Our objectives were to determine: 1) the relative importance of water and N in limiting productivity in uplands and lowlands; 2) thresholds of response to water and N; and 3) functional group response. We hypothesized: 1) a strong and synergistic water x N interaction; 2) that uplands will show a greater response to water than N, and lowlands will respond just the opposite; and 3) forbs will respond more strongly than grasses to water and N. First year results indicated that only grasses responded to water and N. Grasses in uplands responded primarily to water and in lowlands to N. A productivity response was detected only at 10gN/m² or 85% water. Contrary to hypotheses, we did not detect water x N interactions in either upland or lowland, indicating no synergistic effect on productivity.

Keywords: prairie, nitrogen limitation, productivity, water

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.