Abstract. Plastic film mulching (PFM) has been widely used for saving water and improving yield around the world, particularly in arid areas. However, the effect of PFM in agriculture on soil respiration is still unclear, and this effect may be confounded with irrigation and precipitation. To detect the effects of PFM, irrigation and precipitation on the temporal and spatial variations in soil respiration, plastic mulched and non-mulched drip irrigation contrast experiments were conducted in the arid area of the Xinjiang Uygur Autonomous Region, Northwest China. PFM generated more complicated spatial heterogeneity in the microclimate with increased albedo, improved soil temperature, soil moisture and crop growth, and led to the stronger spatial heterogeneity of the soil respiration. The soil respiration in the plant holes was larger than in the furrows, and plastic mulch itself can emit up to 2.75 μmol m−2 s−1 CO2, which indicates that furrows, plant holes and plastic mulch were the important pathways for CO2 emissions in the mulched field. Frequent irrigation and precipitation made the soil respiration much more dynamic and fluctuated. The sensitivity of the soil respiration to soil temperature was weakened by extreme variations in the soil moisture with lower correlation and Q10 values. In the wetting-drying cycle, both irrigation and precipitation restrained the soil respiration at a high soil water content (SWC) with a threshold of 60 % water-filled pore space (WFP) in the furrows and 50 % WFP in the ridges, and the restrain effect decreased gradually with the depleting of soil moisture. The accumulated soil respiration calculated from the area ratio of the different parts in the furrows and ridges in the mulched field were both larger than in the non-mulched field during the growing season. However, this magnitude decreased with increasing precipitation over three experimental years. It was speculated that the effect of drip irrigation on the soil respiration was primarily on the ridges while the effect of precipitation mostly concentrated in the furrows and ridges in the non-mulched field because of the mulch barrier. Therefore, the precipitation accelerated more respiration in the mulched than in the non-mulched field. The difference in soil respiration between the mulched and non-mulched fields was observed to have a positive correlation with precipitation per the findings of other studies. In a humid climate with much more precipitation, soil respiration in the non-mulched field can also exceed that of the mulched field and explains why certain studies concluded that plastic mulch decreased soil respiration. The above results indicate that both irrigation and precipitation alter soil respiration and this effect can be modified by plastic mulch. Therefore, whether the PFM increases soil respiration compared to a non-mulched field largely depends on precipitation in the field.
Effect of mulching, row direction and spacing on microclimate and wheat yield at Ludhiana
