Dynamic variation of groundwater evaporation and soil temperature under plastic mulch with openings

Groundwater evaporation (GE) and soil temperature (ST) are important for field crops. The characteristics of GE and ST using non-weighing lysimeters were thus studied. The study consisted of five treatments: plastic mulch with a water table at 1.5 m but with five percentages of open areas (POs), that is 0.78%, 2.50%, 5.00%, 10.00% and 100% (CK). And the ST in the 5, 10, 15 and 20 cm layers were monitored. The results indicated that (1) The salt crusts formed around punched holes could inhibit GE and soil water lost, leading to a non-linear relationship between accumulated GE and opening area. The accumulated GE reduced by 73.77%, 69.07%, 60.17% and 66.63% for the design with PO of 0.78%, 2.50%, 5.00% and 10.00%, respectively, comparing with CK. (2) Modified Averiyanov and Ye equations had a high accuracy in calculating GE under plastic mulch with PO less than 10%. (3) In summer of experimental area, GE was larger at night than in daytime, and its major consumption periods were around 2:00~10:00 and 18:00~22:00. Further analyses showed that GE was significantly affected by topsoil temperature. This meant that it was restrained when ST decreased with increasing depth; conversely, it was enhanced when ST increased with increasing depth.