New Approach to Improve the Soil Water Balance Method for Evapotranspiration Estimation

Ali Rashid Niaghi,Xinhua Jia

doi:10.3390/w11122478

Abstract

As an important component of the water budget, quantifying actual crop evapotranspiration (ET) will enable better planning, management, and allocation of the water resources. However, accurate ET measurement has always been a challenging task in agricultural water management. In the upper Midwest, where subsurface drainage is a common practice due to the shallow ground water depth and heavy clayey soil, ET measurement using traditional ground-based methods is more difficult. In this study, ET was measured using the eddy covariance (EC), Bowen ratio-energy balance (BREB), and soil water balance (SWB) methods during the 2018 corn growing season, and the results of the three methods were compared. To close the energy balance for the EC system, the residual method was used. For the SWB method, capillary rise was included in the ET estimation and was calculated using the measured soil water potential. The change of soil water content for ET estimation using the SWB method was calculated in four different ways, including daily average, 24:00–2:00 average, 24:00–4:00 average, and 4:00 measurement. Through the growing season, six observation periods (OPs) with no rainfall or minimal rainfall events were selected for comparisons among the three methods. The estimated latent heat flux (LE) by the EC system using the residual method showed a 29% overestimation compared to LE determined by the BREB system for the entire growing season. After excluding data taken in May and October, LE determined by the EC system was only 10% higher, indicating that the main difference between the two systems occurred during the early and late of the growing season. By considering all six OPs, a 6%–22% LE difference between the EC and the BREB systems was observed. Except during the early growing and late harvest seasons, both systems agreed well in LE estimation. The SWB method using the average soil water contents between 24:00 and 2:00 time period to calculate the daily capillary rise produced the best statistical fit when compared to the ET estimated by the BREB, with a root-mean-square error of 1.15. Therefore, measuring ET using the capillary rise from a shallow water table between 24:00 and 2:00 could improve the performance of the SWB methodology for ET measurement.

Highlights

Precise estimates of actual crop evapotranspiration (ET) are crucial for the understanding of land and atmosphere energy exchange, especially for agricultural production
The results from the eddy covariance (EC) and the Bowen ratio-energy balance (BREB) methods may be used to improve the accuracy of the soil water balance (SWB) method in the Red River Valley (RRV) region with a shallow water table and heavy clayey soil
In the current study, latent heat flux (LE) determined by the BREB method was compared with LE determined by the EC method, and the results revealed that the EC method is as accurate as the BREB method when crop

Summary

Introduction

Precise estimates of actual crop evapotranspiration (ET) are crucial for the understanding of land and atmosphere energy exchange, especially for agricultural production. Knowledge about measurement techniques and their related errors is essential for agricultural water management. Development of instrumentation, data acquisition systems, and remote sensing have enhanced the ability of ET measurement over large areas and have significantly intensified the knowledge of ET measurement [1]. Numerous methods and techniques are being used either remotely [2] or in situ (e.g., eddy covariance, Bowen ratio, soil water balance, and lysimeter) [3,4,5] for ET estimations. Despite the development of many methods and equations through past decades, accurate ET estimation is still a challenging task [7], and more efforts is required to increase our knowledge and the benefits of the available methods, while limiting their drawbacks

Results

Discussion

Conclusion