Abstract
Soil moisture content (SMC) down to the root zone is a major factor for the efficient cultivation of agricultural crops, especially in arid and semi-arid regions. Precise SMC can maximize crop yields (both quality and quantity), prevent crop damage, and decrease irrigation expenses and water waste, among other benefits. This study focuses on the subsurface spatial electromagnetic mapping of physical properties, mainly moisture content, using a ground-penetrating radar (GPR). In the laboratory, GPR measurements were carried out using an 800 MHz central-frequency antenna and conducted in soil boxes with loess soil type (calcic haploxeralf) from the northern Negev, hamra soil type (typic rhodoxeralf) from the Sharon coastal plain, and grumusol soil type (typic chromoxerets) from the Jezreel valley, Israel. These measurements enabled highly accurate, close-to-real-time evaluations of physical soil qualities (i.e., wave velocity and dielectric constant) connected to SMC. A mixture model based mainly on soil texture, porosity, and effective dielectric constant (permittivity) was developed to measure the subsurface spatial volumetric soil moisture content (VSMC) for a wide range of moisture contents. The analysis of the travel times for GPR reflection and diffraction waves enabled calculating electromagnetic velocities, effective dielectric constants, and spatial SMC under laboratory conditions, where the required penetration depth is low (root zone). The average VSMC was determined with an average accuracy of ±1.5% and was correlated to a standard oven-drying method, making this spatial method useful for agricultural practice and for the design of irrigation plans for different interfaces.
Highlights
Monitoring soil moisture content (SMC, i.e., water content) is important for determining water-use efficiency and planning precision-agriculture programs
The ground-penetrating radar (GPR) signal reflection, using an 800 MHz antenna, from the metal bottom in the plastic 21 L soil boxes used for calibration, was identified on a single representative trace and by generic static section analysis (Figure 5)
The calibration experiment results showed that the GPR method slightly underestimated the moisture content in hamra soil by an average 1.9% with 2.3 SD and in loess soil by 4.6% with 3.4 SD compared to the standard method
Summary
Monitoring soil moisture content (SMC, i.e., water content) is important for determining water-use efficiency and planning precision-agriculture programs. Optimizing available water and land resources by adjusting the correct SMC to the specific agricultural crop will maximize crop yields and prevent damage. Optimization serves both the economy and the environment and will increase field productivity and decrease irrigation expenses, which can be enormous, especially in arid and semi-arid zones [1]. SMC is monitored by conservative local sampling and testing methods in the field and in the laboratory, which are time-consuming and expensive, making use of neutron gauges, various types of tensiometers, and time-domain reflectometry [3,4]
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