Abstract
Proximal gamma-ray spectroscopy is a consolidated technology for a continuous and real-time tracing of soil water content at field scale. New developments have shown that this method can also act as an unbiased tool for remotely distinguishing rainwater from irrigation without any meteorological support information. Given a single detector, the simultaneous observation in a gamma spectrum of a transient increase in the 214Pb signal, coupled with a decrease in the 40K signal, acts as an effective proxy for rainfall. A decrease in both 214Pb and 40K signals is, instead, a reliable fingerprint for irrigation. We successfully proved this rationale in two data-taking campaigns performed on an agricultural test field with different crop types (tomato and maize). The soil moisture levels were assessed via the 40K gamma signal on the basis of a one-time setup calibration. The validation against a set of gravimetric measurements showed excellent results on both bare and vegetated soil conditions. Simultaneously, the observed rain-induced increase in the 214Pb signal permitted to identify accurately the rain and irrigation events occurred in the 8852 h of data taking.
Highlights
Due to continuing human population growth and the consequent increasing demand for available water, the management of water resources has become a pressing issue for governments and international organizations
The time evolution of the SWCγ values recorded during the two data-taking periods (Figure 3) highlighted the ability of the PGRS technique to reliably follow the phases of dampening and subsequent drying following rain and irrigation events, both in bare and vegetated soil
The sensor response to water precipitation was immediate: the SWCγ increased as soon as water fell on the ground and decreased with a week-long timescale immediately after water stopped precipitating
Summary
Due to continuing human population growth and the consequent increasing demand for available water, the management of water resources has become a pressing issue for governments and international organizations. A concrete solution for an adequate irrigation schedule is the use of a decision support system based on novel technologies for a non-invasive and smart monitoring of soil water content (SWC) [3,4]. PGRS [7,11] is, together with cosmic-ray neutron sensing (CRNS) [12,13,14], a field scale non-invasive technique that fills the aforementioned scale gap. CRNS is based on the measurement of cosmic-ray neutrons that scatter on hydrogen atoms in the ground. These atoms mainly come from the water in the soil, so the CRNS technique can infer the SWC level by studying the scattered neutron flux. PGRS is sensitive to the gamma radiation produced by the nuclear decays of 40 K and of radionuclides belonging to 232 Th and 238 U chains, which are naturally present in the soil
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