Effects of Maize-Crop Rotation on Soil Physicochemical Properties, Enzyme Activities, Microbial Biomass and Microbial Community Structure in Southwest China

Abstract

Introducing cover crops into maize rotation systems is widely practiced to increase crop productivity and achieve sustainable agricultural development, yet the potential for crop rotational diversity to contribute to environmental benefits in soils remains uncertain. Here, we investigated the effects of different crop rotation patterns on the physicochemical properties, enzyme activities, microbial biomass and microbial communities in soils from field experiments. Crop rotation patterns included (i) pure maize monoculture (CC), (ii) maize-garlic (CG), (iii) maize-rape (CR) and (iv) maize-annual ryegrass for one year (Cir1), two years (Cir2) and three years (Cir3). Our results showed that soil physicochemical properties varied in all rotation patterns, with higher total and available phosphorus concentrations in CG and CR and lower soil organic carbon and total nitrogen concentrations in the maize-ryegrass rotations compared to CC. Specifically, soil fertility was ranked as CG > Cir2 > CR > Cir3 > CC > Cir1. CG decreased enzyme activities but enhanced microbial biomass. Cir2 decreased carbon (C) and nitrogen (N) acquiring enzyme activities and soil microbial C and N concentrations, but increased phosphorus (P) acquiring enzyme activities and microbial biomass P concentrations compared to CC. Soil bacterial and fungal diversity (Shannon index) were lower in CG and Cir2 compared to CC, while the richness (Chao1 index) was lower in CG, CR, Cir1 and Cir2. Most maize rotations notably augmented the relative abundance of soil bacteria, including Chloroflexi, Gemmatimonadetes and Rokubacteria, while not necessarily decreasing the abundance of soil fungi like Basidiomycota, Mortierellomycota and Anthophyta. Redundancy analysis indicated that nitrate-N, ammonium-N and microbial biomass N concentrations had a large impact on soil bacterial communities, whereas nitrate-N and ammonium-N, available P, soil organic C and microbial biomass C concentrations had a greater effect on soil fungal communities. In conclusion, maize rotations with garlic, rape and ryegrass distinctly modify soil properties and microbial compositions. Thus, we advocate for garlic and annual ryegrass as maize cover crops and recommend a two-year rotation for perennial ryegrass in Southwest China.

Keywords: enzyme activity; microbial biomass; microbial communities; physicochemical properties; rotation patterns.

Figure 1

Location and basic information on experiment sites in this study.

Figure 2

Soil enzyme activity of BG and NAG (a), NOS and GS (b), nitrogenase and LAP (c) and ACP (d) for the six cropping patterns. Note: pure maize monoculture (CC), maize–garlic rotation (CG), maize–rape rotation (CR) and maize–annual ryegrass of one-year crop rotation (Cir1), two-year crop rotation (Cir2) and three-year crop rotation (Cir3). BG: β-1,4-glucosidase; NAG: β-N-acetylglucosaminidase; NOS: nitric oxide synthase; GS: glutamine synthetase; LAP: leucine aminopeptidase; ACP: acid phosphatase. Values are the means ± standard errors. * Indicates a significant difference at 0.05 level. ** Indicates a significant difference at 0.01 level.

Figure 3

Soil MBC (a), MBN (b) and MBP (c) for the six cropping patterns. Note: pure maize monoculture (CC), maize–garlic rotation (CG), maize–rape rotation (CR) and maize–annual ryegrass of one-year crop rotation (Cir1), two-year crop rotation (Cir2) and three-year crop rotation (Cir3). MBC: microbial biomass carbon. MBN: microbial biomass nitrogen. MBP: microbial biomass phosphorus. Values are the means ± standard errors. Different letters within a figure show significant differences (p < 0.05) based on analysis of variance and Tukey’s test for pairwise comparisons. The red rhombus is discrete point.

Figure 4

Relative abundance (%) of major soil bacterial phyla under six rotation cropping patterns (relative abundance ≥ 1% in at least one sample). Note: pure maize monoculture (CC), maize–garlic rotation (CG), maize–rape rotation (CR) and maize–annual ryegrass of one-year crop rotation (Cir1), two-year crop rotation (Cir2) and three-year crop rotation (Cir3). The vertical axis represents the respective phyla, the column length represents the average relative abundance of the corresponding phylum in each sample group and the different colors represent different cropping patterns. The numbers on the right-hand side are the p values. * Indicates a significant difference between the cropping patterns at 0.05 level. ** Indicates a significant difference at 0.01 level.

Figure 5

Relative abundance (%) of major soil fungal phyla under six rotation cropping patterns (relative abundance ≥ 1% in at least one sample). Note: pure maize monoculture (CC), maize–garlic rotation (CG), maize–rape rotation (CR) and maize–annual ryegrass of one-year crop rotation (Cir1), two-year crop rotation (Cir2) and three-year crop rotation (Cir3). The vertical axis represents the phylum, the column length represents the average relative abundance of the corresponding phylum in each sample group and the different colors represent different cropping patterns. The numbers at the right-hand side are the p values. * Indicates a significant difference between cropping patterns at 0.05 level. ** Indicates a significant difference at 0.01 level.

Figure 6

Redundancy of bacterial (a) and fungal (b) communities at phylum level and soil properties for six cropping patterns. The red arrows represent the different soil physical and chemical properties and the blue arrows represent the top ten bacterial (a) or fungal (b) phyla in terms of abundance.