In situ and modelled soil moisture determination and upscaling from point-based to field scale
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Date
2015, 2015
Authors
Ojo, Emmanuel Rotimi
Journal Title
Journal ISSN
Volume Title
Publisher
Soil Science Society of America
Soil Science Society of America
Soil Science Society of America
Abstract
The relevance, value and multi-dimensional application of soil moisture in many areas such as hydrological, meteorological and agricultural sciences have increased the focus on this important part of the ecosystem. However, due to its spatial and temporal variability, accurate soil moisture determination is an ongoing challenge. In the fall of 2013 and spring of 2014, the accuracy of five soil moisture instruments was tested in heavy clay soils and the Root Mean Squared Error (RMSE) values of the default calibration ranged from 0.027 and 0.129 m3 m-3. However, after calibration, the range was improved to 0.014 – 0.040 m3 m-3. The need for calibration has led to the development of generic calibration procedures such as soil texture-based calibrations. As a result of the differences in soil minerology, especially in clay soils, the texture-based calibrations often yield very high RMSE. A novel approach that uses the Cation Exchange Capacity (CEC) grouping was independently tested at three sites and out of seven different calibration equations tested; the CEC-based calibration was the second best behind in situ derived calibration.
The high cost of installing and maintaining a network of soil moisture instruments to obtain measurements at limited points has influenced the development of models that can estimate soil moisture. The Versatile Soil Moisture Budget (VSMB) is one of such models and was used in this study. The comparison of the VSMB modelled output to the observed soil moisture data from a single, temporally continuous, in-field calibrated Hydra probe gave mean RMSE values of 0.052 m3 m-3 at the eight site-years in coarse textured soils and 0.059 m3 m-3 at the six site-years in fine textured soils. At field-scale level, the representativeness of an arbitrarily placed soil moisture station was compared to the mean of 48 data samples collected across the field. The single location underestimated soil moisture at 3 of 4 coarse textured fields with an average RMSE of 0.038 m3 m-3 and at only one of the four fine textured sites monitored with an average RMSE of 0.059 m3 m-3.
Description
Keywords
Soil moisture, Calibration, VSMB model, Upscaling
Citation
SSSAJ
VZJ
VZJ