Document: DAV-3-89-3

Spatial heterogeneity in vegetation light use efficiency over an agricultural landscape in central Illinois.

TURNER, D.P.* ¹, S.T.GOWER ², W.B.COHEN ³, M.GREGORY ¹ and T.K.MAIERSPERGER ¹

Oregon State University, Corvallis OR 97331 USA ¹
University of Wisconsin, Madison WN 53706 USA ²
USDA PNW Research Station, Corvallis OR 97331 USA ³

Abstract:
Light use efficiency (LUE) algorithms are likely to be the most effective means of monitoring global NPP using satellite-borne sensors such as MODIS. These algorithms rely on an estimate of absorbed photosynthetically active radiation (APAR) from satellite imagery and theoretical or empirical LUEs (gC/MJ) to estimate NPP. C₃ and C₄ crop species are believed to vary considerable in LUE, yet they often grow in close proximity, notably the large areas of corn and soybeans in the American Midwest. The significance of this heterogeneity to satellite-based NPP estimates has not been investigated. In this study we examined LUE in adjacent corn (C₄) and soybean (C₃) fields and the spatial distribution (30 m resolution) of the two crop types over a 25 km² area in northern Illinois. Biomass production was estimated from periodic harvesting and APAR was derived from measurements of incident PAR and the fraction of PAR absorbed by the vegetation. The objective was to provide a basis for comparisons with LUE-based NPP algorithms using generalized LUE factors and operating at relatively coarse spatial resolutions. Results suggest that parameterization of coarse resolution LUE algorithms for this area may need to accommodate the large difference in LUE between the crop types and the fine scale heterogeneity of the crop type distributions.

Keywords: net primary production, light use efficiency

This abstract is being presented at: 10:30 AM in session:
REMOTE SENSING