Long-Term Ditch-Buried Straw Return Increases Functionality Of Soil Microbial Communities

Ditch-buried straw return (DB-SR) is a novel soil fertility building method by combing straw incorporation and tillage rotation in rice-wheat annual double cropping system. Several benefits of DB-SR have been shown, e.g. improving carbon sequestration, nitrogen retention and soil aggregation. However, how long-term DB-SR affecting the metabolic activity and diversity of soil microbial communities is still unclear. In this study, we investigated the effects of DB-SR application after 5 years (rice season) and 5.5 years (wheat season) on functional patterns, including the overall functional activity, reflected by fluorescein diacetate hydrolase (FDA) activity, the overall growth activity, reflected by soil respiration rate, extracellular element-cycling enzyme activity, glomalin content and metabolic diversity in different soil layers. Our results first showed that DB-SR significantly increased the overall functional activity (FDA hydrolase) and growth activity (respiration rate) in 10-20 cm and 20-30 cm soils. Second, beta-glucosidase, lipase, acid phosphatase and arylsulphatase activities were significantly increased by DB-SR in different soil layers. However, urease activity was only increased by DB-SR in wheat soils, but reduced in the 0-10 cm and 20-30 cm soils after growing rice. In addition, DB-SR significantly increased the content of total glomalin and easily extracted glomalin. Finally, DB-SR significantly increased microbial metabolic diversity of carbon substrates in different soil layers. Overall, the metabolic activity and diversity of microbial communities were shown with a larger increase in 10-20 cm (above the straw layer) than 0-10 cm and 20-30 cm soil layers; and tended to increase with straw burial duration. These findings suggest that the long-term application of DB-SR is helpful to drive material transformation and nutrient supply, which can further benefit crop production in rice-wheat rotation systems.