Shallow-buried drip irrigation promoted the enrichment of beneficial microorganisms in surface soil

Abstract

The Xiliao River plain is situated in the “Golden Belt of maize production worldwide” and it is one of the few high-yield areas of well-irrigated maize in China. Drip irrigation is recognized as one of the most water-efficient techniques for farmland irrigation. However, because of the flawed recovery mechanism of plastic film, many years of continuous accumulation of plastic film mulch have resulted in a considerable amount of plastic film residue in the soil, extensively harming the soil environment. This study aimed to investigate the effects of two primary irrigation methods, shallow-buried drip irrigation and under-mulch drip irrigation, with varying levels of irrigation on soil microbial diversity in the Xiliao River plain. A split-plot experiment was conducted, and the amount of irrigation was sub-treated at three levels: 40% (1440 m3 ha−1), 50% (1800 m3 ha−1), and 60% (2160 m3 ha−1) of that used for traditional irrigation. We studied the effects of water saving on soil bacteria and fungi using high-throughput sequencing. The results showed that in the 0–20 cm soil layer, with the same irrigation, the operational taxonomic unit number of bacteria in shallow-buried drip irrigation was greater than that of the under-mulch drip irrigation. In the 20–40 cm soil layer, as irrigation decreased, the operational taxonomic unit numbers of bacteria and fungi in both drip irrigation methods decreased. There was a significant difference in the relative abundance of microorganisms between the two drip irrigation methods with 50% irrigation. Compared with film drip irrigation, shallow-buried drip irrigation increased the relative abundance of Proteobacteria, Bacteroidetes, Firmicutes, and Acidobacteria in the 0–20 cm soil layer and increased the relative abundance of Proteobacteria and decreased the relative abundance of Firmicutes in the 20–40 cm soil layer. With reduced shallow-buried drip irrigation, the relative abundance of Pseudomonas initially decreased and then increased, whereas the abundance of other genus pairs remained stable. Under-mulch drip irrigation reduced the stability of the soil microbial network in the topsoil. With decreasing irrigation, the relative abundance of Zygomycota, Glomeromycota, and Chytridiomycota increased in the 0–40 cm soil layer when using shallow-buried drip irrigation, whereas the relative abundance of Zygomycota and Chytridiomycota decreased when using under-mulch drip irrigation. Shallow-buried drip irrigation enriched microbial communities, which were significantly positively correlated with organic matter and available nutrient content, including Holophagae, which prefers a dominant plant rhizosphere soil, Thermoanaerobaculaceae, which plays an important role in nitrogen transformation, and Microtrichales, which is crucial for the hydrolysis and utilization of complex organic matter. The microplastic-degrading Nocardioidaceae was enriched in the soil of under-mulch drip irrigation, and Propionibacteriales, which maintained a high proportion of species under high salinity, were enriched in the soil of under-mulch drip irrigation.