Abstract
Soil water evaporation is an important parameter that needs to be accurately measured for the design of water-efficient agricultural systems. With this study, the abilities of the DFM capacitance probes and a neutron water meter (NWM) to measure evaporation from the soil surface were compared. Measured evaporation was compared to the control values measured with mini-lysimeters. Calibration of DFM capacitance probes and the NWM was done in the laboratory using the topsoil of a Bainsvlei soil form. Field measurements of soil water content were done on the same Bainsvlei soil. Calibration results indicated a good correspondence (r 2 = 0.99) between the measured values and known volumetric soil water contents. There was no significant difference ( p = 95%) between the DFM evaporation measurements and the control, whereas the NWM and control differed significantly. It was concluded that the DFM capacitance probe is a better tool than the NWM in measuring evaporation from the topsoil surface.
Highlights
In order to use the scarce water resource for agricultural production effectively, it is important that soil water content be measured as accurately as possible
Micro-lysimeter measured evaporation served as a control when comparing the evaporation measured by the DFM capacitance probe and neutron water meter (NWM) (Paruelo et al, 1991)
The coefficient of variation (CV) indicated there was much more variation in the readings taken for the dry soil compared to the wet soil
Summary
In order to use the scarce water resource for agricultural production effectively, it is important that soil water content be measured as accurately as possible. The amount of water in the soil determines how strongly water molecules are retained by the soil matrix. Soil water can range from thin hygroscopic films tightly held around soil particles to saturation, where all of the soil macro-pores are filled with water. The amount of soil water determines the forces that control its movement. These forces in turn determine the availability of soil water for plant use and processes of water movement like evaporation and drainage. Accurate measurement of soil water determines how accurately these components of the water balance can be quantified
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