2.2.3. Measurements
Two micro-lysimeters were installed in each plot (Experiment 1 only), to measure soil evaporation. Measurements of soil evaporation were made using micro-lysimeters containing undisturbed samples [10]. The micro-lysimeter casing and the pipe lining the holes, in which the micro-lysimeters were mounted, were both constructed from un-plasticized polyvinyl chloride (PVC) pipe. The dimension of the micro-lysimeters was 11 cm internal diameter and 15 cm in length. The liner tube was 12 cm internal diameter and 15 cm in length. The weight loss was recorded using an electronic scale (sensitivity is 0.01 g), and then put into the liner tube. Both tubes were put into the hole where undisturbed soil had been taken.Lysimeters with undisturbed soil were weighed each day at 8:00 a.m. To minimize the difference of soil core and its soil surrounding,an undisturbed soil core was renewed every four days under normal conditions, but it was immediately done after rainfall [4].Soil temperature was measured, using a geothermometer, from two locations in each plot (Experiment 1 only) at the 5, 10, 15 and 20 cm depths, starting from the original soil surface (0 cm) prior to adding mulch. Measurements were taken 3 times a year (May to September), within 10 consecutive days each time.Gravimetric soil water content was measured at 10 cm intervals in the top 40 cm of soil and at 20 cm intervals from the 40 to 160 cm depth, at four randomly selected locations in each plot, every 10 days between planting and harvesting. These samples were ovendried at 105 °C for 24 hours.We used a standard rain gauge to record the amount of rainfall.Evapotranspiration (ET) was determined using the following
formula: