Impact of plastic mulch on the surface soil heat flux estimation over cotton in northwest China

Surface soil heat flux (G0) is an indispensable component of the surface energy balance (SEB) and is important for estimating instantaneous surface evapotranspiration (ET). The plastic mulch is laid on the cotton field for reducing soil evaporation and economizing water resource in arid area in Xinjiang Autonomous Prefecture of northwest China. The mulch affects soil thermal conduction, which has an important impact on G0 estimation. In the present study the G0 under mulch and bare soil between two mulches were calculated by the thermal conduction equation, respectively. The results show that the hourly G0 under mulch is smaller than G0 for bare soil both in daytime and nighttime. The mulch not only hinders energy into soil in daytime but also reduces soil heat loss in night. G0 under mulch decreases quickly since July, while G0 over bare soil decreases slowly. That's because the drip irrigation under mulch makes soil moisture increasing and the shallow soil temperature varies slowly since July, which decrease the soil thermal conduction. The mulch has little effect on daily G0, as G0 under mulch are nearly same as that for bare soil.