Net Aerial Primary Production of an Andropogon-Paspalum Grassland Ecosystem

Abstract

Changes in net aerial primary production as influenced by selected environmental parameters were evaluated in a grassland ecosystem for the 1973 and 1974 growing seasons. Biomass weight was estimated for phenologically determined harvest intervals. Efficiency of converting solar energy to chemical energy was determined. Between years, precipitation was the dominant environmental parameter associated with production. The quantity was not as critical as the date and the resultant effect on available soil water. Increments of production followed a monomodal pattern similar to yearly trends in soil temperature and solar radiation. Deviations in production from this monomodal pattern were related to available soil water and soil water deficit. Total production during 1973 (ca. 400 g m-2) was approximately 100 g m-2 higher than in 1974. This difference was due primarily to lower available soil water during early spring and a 4-week longer summer dry period in 1974. Based on measurements of photosynthetically active radiation, energy values, and production, the growing season conversion efficiencies were 0.34% in 1973 and 0.23% in 1974. The highest conversion efficiencies for a harvest interval occurred each year during June: 0.87% in 1973 and 0.59% in 1974.