Quantitative Assessment of Agricultural Practices on Farmland Evapotranspiration Using EddyCovariance Method and Numerical Modelling

Abstract

While low cost eddy covariance (EC) techniques based on the open-path laser analyzers have been widely used, they are not very accurate and are restricted to use in non-rainy days. As an alternative, and relevant to promoting precision agriculture where water availability is proving key, the application of the EC technique based on closed-path QCLAS-EC Analyzer is described, in a study of cabbage farmland evapotranspiration (ET). This study uses the advantages of the closed-path EC method to quantitatively assess the impact of agricultural activities on farmland ET and compared with RZWQM2 (Root Zone Water Quality Model) model. The cumulative ET is shown to have increased by 1.5–3.6 mm over ten-days after planting, and decreased by 3.5–8.1 mm over 10 days, following harvesting. While irrigation contributed to ET, the cumulative ten-day ET increase is between 0.6–2.3 mm which is significantly lower than the effects due to planting and harvesting. The RZWQM2 model was used to quantify the effects of four agricultural practices. Simulation of ET attained R2 and RMSE as 0.79 and 0.013 mm/d, respectively. In addition, the RZWQM2 model successfully simulated groundwater levels, Leaf area index, and crop height (R2 values of 0.71, 0.98 and 0.97, respectively). The RZWQM2 model simulates the effects of planting, harvesting, and irrigation on ET, indicating the same directional changes of magnitude with measured data. The results provide a comprehensive and direct study based on the closed-path EC method and RZWQM2 model to assess the impact of multiple agricultural activities on farmland ET and to improve precision agriculture.