Abstract
Conservation farming practices, such as no-tillage and crop residue retention, have been proposed as sustainable management practices. However, it remains unclear how different tillage practices and rice straw retention affect the soil bacterial community (SBC) and the soil C/N ratio in the long term. The objective of this study was to evaluate changes in SBC composition and abundance and soil properties (e.g., carbon (C), nitrogen (N)) and determine their relationship to the soil C/N ratio under long-term no-tillage and straw retention techniques. This study investigates the effect of a long-term field experiment begun in 2008 and continued until 2019 to measure the response of the SBC and soil properties and their relation to different tillage practices, including no-tillage (NT), no-tillage and straw mulching (NT-SM), conventional tillage (CT), conventional tillage and straw mulching (CT-SM), and conventional tillage and straw retention (CT-SR). Soil samples were collected at depths of 0–5 cm (A), 5–10 cm (B), and 10–20 cm (C) after rice harvesting in the early and late growing seasons in 2018–2019. The Illumina MiSeq sequencing and quantitative polymerase chain reaction (PCR) technology was used to analyze changes in SBC diversity in soil and determined the changes in the soil C/N ratio and their relationship with the SBC diversity. The results showed that the Proteobacteria, Acidobacteria, and Chloroflexi were the dominant phyla in the soil and accounted for 61.26%, 59.39%, and 55.62% of the total bacteria in the A, B, and C soil layers, respectively. The NT treatment increased SBC diversity, the number of operational taxonomic units (OTUs), and the proportion of Proteobacteria across the soil depths. Similarly, straw retention also significantly improved SBC diversity, soil organic C (SOC), total N (TN), soil C/N ratio, and the abundance of Proteobacteria and Acidobacteria in the soil layers A and B. The NT-SM treatment increased the SOC, TN, and soil C/N ratio by 30%, 21%, and 6% in 2018 and by 33, 25% and 7% in 2019, respectively, across the seasons and layers compared to the CT treatment. The NT-SM treatment had the highest soil bacterial diversity index, and the CT-SR treatment had the highest soil bacterial abundance and number of OTUs. The redundancy analysis showed that Acidobacteria were highly positively correlated with the soil C/N ratio. The results demonstrate that conservation tillage practices, i.e., no-tillage and straw retention, increase the SBC diversity and soil C/N ratio, thereby enhancing soil organic C and total N and changing soil microbial ecology. As a result, sustainable crop production and profitable agro-ecosystems are ensured.
Highlights
Soil microorganisms provide important ecosystem services, which are necessary to maintain agricultural productivity and ecosystem health [1,2]
Soil pH is the main soil indicator affecting the bacterial community, but in this study, we did not consider the soil pH and the correlation with the soil bacterial community (SBC). In this eleven-year field experiment, we observed that conservation tillage practices significantly affected the soil organic C (SOC), total N (TN), soil C/N ratio, and SBC
The soil C/N ratio, bacterial diversity, and richness index decreased with increasing soil depth
Summary
Soil microorganisms provide important ecosystem services, which are necessary to maintain agricultural productivity and ecosystem health [1,2]. Examples include the decomposition and synthesis of organic substances, which improve the soil structure due to the formation of organic matter [4]. The abundance and community structure of soil microorganisms, including bacteria, fungi, microbivores (protozoa and nematodes), and predators (nematodes) highly depend on soil management practices [5,6]. Changes in the soil bacterial community (SBC) can affect mineralization and decomposition of organic matter [7]. In-addition, the SBC plays a pivotal role in soil ecological processes, including the decomposition of organic matter and the formation of soil aggregates, thereby affecting soil fertility and improving soil ecosystems [10,11]
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