Agronomic traits of maize under different cropping systems
Maize crop exhibited higher yields in rotational cropping system as opposed to monocropping, regardless of maize species in most seasons, with the exception in 2013 and 2016 (Table 1). Short-term crop rotation did not show a significant effect on maize yield. The lowest yield of maize was observed in 2015 in both cropping systems. Maize yield was significantly affected by both cropping systems and the year of investigation (Table 1).
Table 1
Agronomic traits of maize with rotational cropping and monocropping systems
Year | Planting pattern | Maize yield (kg/hm2) | Plant height (cm) | Ear height (cm) | Ear length (cm) | Bald tip length (cm) | Ear diameter (cm) | No. of seed/ear | 100-weight (g) | Ears/row (10 m) |
2013 | monocrop | 10398 ± 803a | 318a | 126a | 20.4a | 0.99a | 5.13a | 623b | 37.5a | 44 ± 1a |
rotation | 10868 ± 882a | 280b | 93b | 21.0a | 0.60a | 5.10a | 699a | 35.1a | 44 ± 2a |
2014 | monocrop | 10244 ± 611a | 283a | 115a | 19.9b | 1.12a | 5.22a | 632a | 33.1a | 42 ± 3a |
rotation | 11696 ± 1024a | 285a | 109a | 21.6a | 1.80a | 5.11a | 616a | 31.4a | 44 ± 1a |
2015 | monocrop | 8496 ± 1413a | 254a | 112a | 19.2a | 1.25a | 5.32a | 579a | 35.3a | 30 ± 5a |
rotation | 9411 ± 907a | 249a | 104a | 18.1b | 0.85a | 5.26a | 546a | 36.7a | 37 ± 3a |
2016 | monocrop | 11417 ± 1497a | 282a | 113a | 21.9a | 0.63a | 4.75b | 641a | 33.4b | 40 ± 1a |
rotation | 11680 ± 1837a | 276a | 110a | 22.1a | 0.22a | 5.13a | 708a | 37.5a | 48 ± 7a |
2017 | monocrop | 9266 ± 746b | 255a | 108a | 20.7a | 1.53a | 4.89a | 614a | 38.8a | 35 ± 3a |
rotation | 11257 ± 516a | 253a | 106a | 20.8a | 1.21a | 4.94a | 666a | 42.8a | 38 ± 2a |
2018 | monocrop | 9559 ± 122b | 248a | 107a | 15.5a | 1.89a | 4.47b | 387a | 31.2a | 59 ± 2a |
rotation | 11999 ± 2007a | 242a | 101a | 19.0a | 1.78a | 4.57a | 415a | 32.2a | 60 ± 5a |
| ANOVA p-value |
Year | | 0.0379 | < 0.0001 | 0.4282 | 0.0134 | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 | 0.0089 |
Planting pattern | 0.0245 | 0.0002 | < 0.0001 | 0.2873 | 0.1841 | 0.0296 | 0.0017 | 0.0002 | 0.9152 |
Year * Planting pattern | 0.2060 | 0.2060 | 0.0008 | 0.5763 | 0.0768 | 0.0008 | 0.0029 | 0.0678 | 0.4691 |
Different letters indicate significant differences (P < 0.05) between monocrop and rotational cropping within each year within each column of the table. |
In 2013, no significant difference in most agronomic traits of maize was shown between monocropping and rotational cropping (P > 0.05), except in seed number per ear. The number of seed per ear in 2015, ears per hectare, and grain weight per ear in 2016 were significantly higher in rotational cropping than that in monocropping (P < 0.05). Ear length was higher in rotational cropping than in monocropping in 2015 and 2018 (P < 0.05). All agronomic traits of maize varied depending on the year, except for bald tip length. Rotational cropping significantly augmented ear length, seed count, ear quantity, and grain weight, which were all directly tied to maize yield.
Characteristics of soil properties with maize
Several soil parameters, including organic matter, total nitrogen, available nitrogen, available phosphorus, available potassium, and pH were determined (Table 2). Organic matter, available nitrogen, and pH were relatively higher in maize rotational cropping soil than in maize monocropping soil in 2014. Conversely, available phosphorus contents were relatively higher in monocropping soil than in rotational cropping soil. The content of available phosphorus and available potassium in 2014 significantly increased, compared to 2013. The content of available nitrogen, phosphorus, potassium, and pH values was statistically significant over the years. The pH value of the soil slowly decreased, which was in coincidence with Wang’s study (2018). The effect of cropping systems on the content of organic matter, total nitrogen, and available nitrogen was significant. The interactive effect was also significant between the year and cropping systems on available nitrogen, available phosphorus, and pH. Soil available nutrient contents significantly increased possibly linked to 2-year crop residue returns in 2014. No significant differences in the content of soil organic matter were detected from 2013 to 2018.The content of soil organic matter had a slightly decreasing trend over the years in the maize monocropping system, but maintained a stable level in maize rotational cropping.
Table 2
Physical and chemical properties of maize soils in monocropping and rotational cropping systems
Year | Cropping type | Organic matter (%) | Total nitrogen (g/kg) | Available nitrogen (mg/g) | Available phosphorus (mg/kg) | Available potassium (mg/kg) | pH |
2013 | monocrop | 2.73 | 1.10 | 68.9 | 6.85 | 68.0 | 5.57 |
rotation | 2.71 | 1.08 | 63.0 | 6.66 | 66.1 | 5.51 |
2014 | monocrop | 2.68 | 1.08 | 66.3 | 16.7 | 114 | 5.33 |
rotation | 2.80 | 1.28 | 73.2 | 15.5 | 134 | 5.42 |
2016 | monocrop | 2.55 | 1.47 | 69.1 | 26.6 | 116 | 5.26 |
rotation | 2.81 | 1.41 | 78.5 | 20.7 | 125 | 5.35 |
2018 | monocrop | 2.51 | 1.11 | 55.4 | 30.1 | 127 | 5.28 |
rotation | 2.80 | 1.23 | 57.5 | 21.2 | 130 | 5.31 |
Year | 0.0116 | 0.5504 | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 |
Planting pattern | 0.4630 | 0.0033 | 0.0358 | 0.0599 | 0.2824 | 0.4991 |
Year * Planting pattern | 0.6735 | 0.1310 | 0.0091 | 0.0367 | 0.8106 | 0.0477 |
Microbial community composition in different cropping systems
The effects of diversified rotations on crop productivity and stability are shown in long-term agriculture practice (Benitez et al. 2021). Therefore, 6th year soil samples were collected to analyze bacterial and fungal communities in rhizosphere soil through 16S rRNA gene and ITS1 amplicon sequencing. The richness and diversity of bacteria and fungi were different between monocropping and rational cropping (Fig. 1). The Chao1 index did not significantly differ between the two cropping systems, which was not affected by the type of crop (Fig. 1A, E). However, the change of fungal diversity index in rotational cropping system was significantly higher than that in monocropping soil (Fig. 1H, P < 0.05). Additionally, the fungi: bacteria ratio was significantly higher in the maize rational soil than that in maize monocropping soil (Table S2). These findings indicated that rotational cropping increased fungal diversity and no significant effect on the relative abundance of microbial population, compared to monocropping. At the genus level, the relative abundance of many fungi differed significantly between monocropping soil and rational soil. In the soybean and maize rotation system, the relative abundance of Trichoderma and Guehomyces significant decreased, while the relative abundance of Fusarium and leucoagaricus significant increased, compared with monocropping of maize
Relationships between microbial groups and soil physicochemical properties
We investigated the relationships between microbial communities and soil physicochemical properties using Spearman correlation, taking into account of organic matter, total nitrogen, available nitrogen, available phosphorus, available potassium, and pH (Fig. 4). pH values exhibited negative correlations with the relative abundances of Gemmatimonas, a prominent genus in soil bacteria. Conversely, it showed positive correlations between Pseudolabrys (bacteria) and Acremonium (fungi) (Fig. 4). Available potassium displayed positive correlations with bacterial Mucilaginibacter and fungal Penicillium and Trechispora. Available phosphorus exhibited sole negative correlations with Candidatus_and Solibacter. Available nitrogen demonstrated the negative correlations with Bryobacter and Rhodanobacter in bacteria community and with Humicola in fungal community. Total nitrogen was positive correlated with Fusarium (fungi) and Reyranella (bateria). Organic matter showed a close association with the relative abundance of fungi, displaying a positive correlation with Fusarium and negative correlation with Trichoderma, Guehomyces and Holtermanniella. Moreover, the abundance of some fungi closely related to organic matter content exhibits a significant difference between rotational cropping and monocropping with crop residues returned for each crop (Fig. 3).
Shift of soil bacterial and fungal co-occurrence pattern
The shift of the soil microbial co-occurrence pattern driven by cropping systems along with crop residue returns was explored by co-occurrence network analysis (Fig. 4, Table 3). The value of edges, average degree, and connection of bacteria and fungi in the monocropping was lower than those in the rotational cropping. Fungi were more responsive than bacteria to crop rotation. In the context of bacterial interactions, rotational cropping primarily led to an increase in positive edges. While in the fungal community, both positive and negative edges had notablely increased. These results collectively suggested that the microbial communities in monocropping exhibited less connectivity compared to those in the rotational cropping (Fig. 4, Table 3). Therefore, rotational cropping promoted interactions with bacterial and fungal communities, leading to a transformation in the relationship between various microbes.
Table 3
Network properties of maize soil bacterial and fungal communities
Microbial taxa | Cropping systems | Edges | Positive edges | Negative edges | Nodes | Connection index | Average degree | Average path length | Clustering coefficient | Centralization degree |
Bacteria | Monocropping | 63 | 30 | 33 | 19 | 0.3684 | 6.6316 | 1 | 1 | 0.1316 |
Rotation | 69 | 44 | 25 | 20 | 0.3632 | 6.9000 | 1 | 1 | 0.1105 |
Fungi | Monocropping | 63 | 29 | 34 | 20 | 0.3316 | 6.3000 | 1 | 1 | 0.0895 |
Rotation | 79 | 37 | 42 | 20 | 0.4158 | 7.9000 | 1 | 1 | 0.1632 |
For instance in bacterial communities, Gemmatimonas, a dominant bacterial genus, had positive interaction with Variibacter and Sphingomonas, and negative interaction with Haliangium in the monocropping. While Gemmatimonas had positive interaction with six genera including Dactylosporangium, Pseudolabrys, Rhodanobacter, Bryobacter, Variibacter and Candidatus_Solibacter in the rotational cropping. In fungal communities, Fusarium exhibited no interaction with Trichoderma in the monocropping, whereas a negative interaction was observed in the rotational cropping.
Diversity of functional microbiomes
Three types of trophic modes were analyzed, including symbiotrophs, saprotrophs, and pathotroth using the FUNGuild database to annotate fungi (Fig. 6A). The relative abundance of pathotroph-saprotroph-symbiotroph was slightly higher in rotational cropping compared to monocropping, while saprotroph was higher monocropping than in rotational cropping. However, none of trophic mode changes were significant (P > 0.05). Saprophytic fungi emerged as the predominant functional groups in the soil, reaffirming their importance in this study. The relative abundance of arbuscular mycorrhizal fungi (AMF) was promoted by crop rotation in contrast to monocropping (Fig. 6B).
The functional profiles of bacterial metabolism at the third level were predicted using PICRUSt and subsequently organized in hierarchical clustering (Fig. 6C). Various functional profiles exhibited modest increases in rotational cropping system, compared with monocropping. This included amino acids, bacterial chemotaxis, ABC transporters, xenobiotic degradation, and metabolisms of sulfur and nitrogen increased slightly, except for phosphorus metabolisms and carbon fixation.