Inoculation of arbuscular mycorrhizal fungi with plastic mulching in rainfed wheat: A promising farming strategy

Inoculation of arbuscular mycorrhizal fungi (AMF) is an environment-friendly solution to improve field productivity and agro-ecosystem sustainability in semiarid rainfed agricultural areas. Yet, whether it can be incorporated into plastic-film mulching farming systems is an unanswered fundamental question. In 2014 and 2015, two relatively independent but closely related field trials were conducted to evaluate the inoculation effects of AMF species on grain yield, biomass accumulation, water use efficiency (WUE), soil organic carbon and economic profitability in field-grown wheat under plastic film mulching in a typical semiarid site of northwest China. Trial 1 included two treatments: traditional flat planting (CK-1) and plastic film mulching (PFM); while Trial 2 consisted of PFM treatment inoculated with three AMF species (Acaulospora laevis, Glomus monosporum, and Glomus intraradices) alone or in combination, or without inoculation as the control (CK-2). PFM resulted in significant increases in grain yield and WUE due to improved hydro-thermal balance in both growing seasons. Importantly, across all the species under PFM, the AMF inoculation increased grain yield and aboveground biomass by 46.6% and 56.5%, respectively, in wet year 2014, and 16.6% and 27.4%, respectively, in warm dry year 2015, comparing with the non-inoculation treatment. AMF symbiosis also significantly enhanced harvest index and population fitness, and higher inoculation rates generally led to greater increases in yield, biomass and WUE. We also quantitatively estimated the economic benefits among various treatments, and found that compared with CK-1, PFM significantly increased net economic income by 35.8% in 2014 and 245.0% in 2015, while AMF inoculation further promoted average net income by 72.9% in 2014 and 21.7% in 2015 compared with CK-2. Meanwhile, the output to input ratio in PFM or PFM-mulching treatment was generally boosted or remained unchanged in comparison with that of control groups over two growing seasons. Principal component analysis (PCA) demonstrated that hydrothermal balance (PFM and precipitation) acted as the major factors to determine the grouping pattern from group I into group II, and all AMF treatment clusters into group III. Critically, PFM led to small increases in soil organic carbon (SOC) content in both growing seasons, and AMF inoculation further significantly increased the SOC by 16.5% in 2014 and 1.9% in 2015. The AMF diversity in the rhizosphere was re-tested and identified, providing evidence that three exotic AMF species had been established efficiently in rhizosphere soil and become dominant species. For the first time, we found that an integrated AMF-mulching farming system improved field productivity, economic benefit and soil organic carbon, thereby providing as environment-friendly and high-yielding management solution for wheat production and ecosystem sustainability in dryland agriculture.