Energy balance and partitioning in partial plastic mulched and non-mulched maize fields on the Loess Plateau of China

Energy and water exchange processes between the land surface and atmosphere drive photosynthesis, evapotranspiration, sensible heat flux, energy storage in vegetation, and heating of the soil. Thus, understanding of energy exchange and partitioning is of importance for crop model development and water use efficiency improvement in raifed agro-ecosystems. The present study investigated the energy exchange and partitioning over rainfed maize croplands under two cultivation methods-conventional flat planting without mulching (CK) and a furrow-ridge system with plastic film partially mulching (MFR) for two growing seasons through synchronous measurements of eddy covariance system with multi micro-lysimeters on the eastern Loess Plateau of China, the effects of rainfall on the energy partitioning were also discussed. The results indicated that average energy balance closure were 0.89 and 0.84 for CK and MFR at half-hourly, 0.91 and 0.93 at daily interval, respectively. Each energy flux component presented typical diurnal variations during the entire growing stage, which was a single-peak curve. Latent heat flux (LE) showed typical seasonal variation that it increased during May to June, and reach a high value in July, then decreased gradually. However, compared to LE, sensible heat flux (H) and Bowen ratio showed a similar opposite trends, LE became the main consumer of available energy after maize plants grown quickly. LE of spring maize was the main component of net radiation (Rn), followed by H and soil heat flux (G), which accounted for 64.3%, 28.6%, and −0.2% for CK and 68.5%, 29.7%, and 0.1% for MFR in 2011, 56.8%, 20.1%, and 2.8% for CK and 58.0%, 25.5%, and 8.6% for MFR in 2012, respectively. Transpiration was the main component of LE, which accounted for 54.3%-76.6% of LE for the both treatments. Compared to the energy fluxes before rainfall, LE increased significantly while H and G decreased after rainfall in development stage, however in late stage, the changes in soil water content resulted by rainfall didn't increase LE significantly for the both treatments due to the high canopy cover and senescent maize plants.