Assays involving six soil heating treatments were performed during the summers of 2004 and 2005: 1) no solar treatment (control), 2) solarization using a 50 μmthick transparent polyethylene sheet (solarization), 3) soil heating using water warmed by flat plate solar collectors
with a single glass cover (single collectors), 4) soil heating using water warmed by flat plate solar collectors with two glass covers (double or insulated collectors), 5) soil heating using water warmed by parabolic trough concentrators with a non-insulated heat-pipe absorber (non-insulated concentrators), and 6) soil heating using water warmed by parabolic trough concentrators with an insulated heat-pipe absorber (insulated concentrators).