Effects of Plastic Film Mulching on Soil Carbon Fixation Capacity and Fertility Level in Eastern Qinghai

[Objectives] To explore the effects of single application of chemical fertilizers on soil carbon fixation capacity and soil fertility under plastic film mulching conditions in eastern Qinghai, and to provide a theoretical basis for realizing the sustainable development of film mulching planting methods in this area. [Methods] The effects of single application of chemical fertilizer cultivation mode under film mulching conditions on the soil organic carbon (SOC), labile organic carbon (LOC), carbon management index (CMI), extractable humus carbon (CHE), humic acid carbon (CHA), and fulvic acid carbon (CFA) in the cultivated layer (0-20 cm) were studied through three consecutive years of field experiments on dryland maize farmland in the eastern Qinghai. [Results] Under the film mulching condition, the SOC, LOC and CMI of the single application of chemical fertilizer cultivation mode were lower than the open field control. CHE, CHA and CFA increased with the increase of planting years, but the degree of increase was generally less than that of the open field control. With the increase of planting years, by 2020, the soil LOC/SOC value of film mulching decreased by 4.97% compared with before the start of the experiment, while the open field control increased by 1.11%; the organic carbon oxidation stability coefficient (KOS) of the film mulching was higher than that of the open field control; the soil CHA/CFA value and PQ value were higher than that of the open field control. [Conclusions] Under the condition of single application of chemical fertilizers, the continuous film mulching cultivation mode reduces the soil carbon fixation capacity, and soil organic carbon tends to be stable, which is not conducive to biological utilization and could reduce the soil fertility and degrade the soil quality, causing adverse effects on the stability of crop yield and sustainable production in the long run.