| http://www.w3.org/ns/prov#value | - Apparatus for maintaining a plot of soil at a predetermined moisture level, comprising:a) a corrosion-resistant sensor adapted to be embedded in said soil, said sensor including:i) a radiation source; ii) a radiation receiver; iii) a transparent body forming a radiation path from said source to said receiver; iv) said body including at least one surface disposed in said path and arranged to reflec
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