Characterizing ecosystem water-use efficiency of croplands with eddy covariance measurements and MODIS products

摘要

How to quantify the variability in ecosystem water use efficiency (WUE) of croplands is of vital importance. Especially in the context of changing hydrologic environment, much attention need to be paid on how to use limited water to improve crop yield. However, the biophysical performances of environmental/biological controls, crop types, and effects of diverse farming practices on WUE remain unclear. Therefore, this study aims to address these questions through tower-based measurements from eddy covariance and satellite-based estimates from MODIS GPP and ET products at the two annual soybean/corn rotation fields. The results exhibited that temperature and solar radiation are the most important meteorological factors. MODIS WUE estimates captured the broad trend of 8-day tower-based observations. However, ecosystem WUE was overpredicted at the seedling stage and after harvest, and was severely underestimated at the peak periods of maize, which was mainly ascribed to the uncertainties in MODIS GPP. Finally, we evaluated the effects of two farming practices (conventional vs alternative) on WUE and carbon sequence (NEE). On annual time scale, WUE of both soybean and maize are improved obviously under the alternative management whereas contrasting effects are observed on NEE. But the overall carbon balance for both treatments is nearly identical over 2-year rotation. (C) 2015 Elsevier B.V. All rights reserved.