Next Article in Journal
Modeling the Water and Nitrogen Management Practices in Paddy Fields with HYDRUS-1D
Previous Article in Journal
Adverse Effects of Long-Term Continuous Girdling of Jujube Tree on the Quality of Jujube Fruit and Tree Health
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agriculture
Volume 12
Issue 7
10.3390/agriculture12070923
agriculture-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effects of Continuous Ridge Tillage at Two Fertilizer Depths on Microbial Community Structure and Rice Yield

by
Lihua Liu
,
Shize Cui
,
Meng Qin
,
Liqiang Chen
,
Dawei Yin
,
Xiaohong Guo
,
Hongyu Li
and
Guiping Zheng
*
Heilongjiang Provincial Key Laboratory of Modern Agricultural Cultivation and Crop Germplasm, College of Agriculture, Heilongjiang Bayi Agricultural University, Daqing 163319, China
*
Author to whom correspondence should be addressed.
Agriculture 2022, 12(7), 923; https://doi.org/10.3390/agriculture12070923
Submission received: 30 May 2022 / Revised: 21 June 2022 / Accepted: 23 June 2022 / Published: 25 June 2022
(This article belongs to the Section Agricultural Soils)
Browse Figures
Review Reports Versions Notes

Abstract

:
Ridge tillage at two fertilizer depths is a new type of conservation tillage method that was previously shown to substantially improve rice yield. This study aimed to compare the effects of continuous ridge tillage at two fertilizer depths (L treatment) with those of conventional cultivation (P treatment) on bacterial and fungal diversity in the rice root zone and study the correlation between microorganisms and yield components. At the mature stage, the yield and yield components of rice plants were compared. Test soil (0–20 cm) with continuous tillage for 3 years was used for high-throughput sequencing to analyze the microbial community structure in the root–soil of the two treatments. We found that the L treatment increased soil nutrient content and improved soil physical properties, which altered the composition of the microbial community. The bacterial ACE and Chao indices in the L treatment increased by 1.46% and 1.83%, respectively, and the fungal ACE and Chao indices increased by 5.25% and 5.49%, compared with the P treatment, respectively. The average theoretical yield under the L treatment was 9781.51 kg/ha, which was 19.23% higher than that under the P treatment. Continuous ridge tillage at two fertilizer depths can provide a better soil environment for rice growth and increase the yield.

1. Introduction

Rice (Oryza Sativa L.), is one of the main grain crops in the world and plays an important role in ensuring national food security. Rice yield is the primary focus of agricultural scientists. Presently, widely adopted methods such as whole-layer soil fertilization and agitation have resulted in high soil compaction and poor air permeability, consequently restricting overall rice yield [1].
Due to serious problems such as dense physical structure and poor nutritional composition, improving rice yield and ensuring food security is of strategic significance. Soil microorganisms, especially rhizosphere microorganisms, play active roles in decomposing organic matter by releasing and storing nutrients in plant rhizosphere nutrition. Soil microorganisms are an important part of farmland ecosystems and are sensitive to rapid long-term fertilizer accumulation [2]. Microorganisms are an important index of soil quality, soil fertility, and crop productivity [3,4,5]. They can enrich soil nutrients and improve soil productivity by forming humus, transforming nutrients, and promoting the circulation of nutrient elements such as carbon, nitrogen, and phosphorus. Soil diversity and structure continue to be used as important indicators to evaluate soil health [6,7]. Changes in root–soil physical characteristics and organic matter directly determine microbial diversity and community structure [8,9]. Various studies have shown that conservation tillage and appropriate fertilization can increase soil organic matter, enhance soil water absorption and conservation, improve soil chemical and physical properties, and considerably affect soil microbial community structure [10,11,12,13,14,15,16]. Conservation tillage has been reported to be an effective measure for balancing the relationship between agricultural production and soil ecological protection, and it has an impact on soil aggregates and organic matter in rice cropping systems [11,12,17,18]. Several researchers have reported that conservation tillage can increase crop yield [19,20]. Many studies have demonstrated a significant benefit to rice yield under ridge cropping over conventional flat cropping, with an average yield increase of 14.60% [21,22,23,24].
Good tillage and fertilization can improve the soil, water, air, and heat conditions of the plow layer. Ridge cultivation and fertilization have been found to increase yield, which manifested as an increased number of ears and seed setting rates [25,26,27]. However, ridge cultivation and ladder cultivation methods have been formulated for rice cultivation in the south of China; only a few of these were found to be suitable for rice cultivated in the northern colder regions of China [28,29]. There are fewer studies on soil bacterial abundance and rice yield under continuous ridge tillage. A new conservation tillage model—ridge tillage at two fertilizer depths—for rice was proposed in 2014 (Figure 1) [30]. A deep-sided fertilizer transplanter can perform lower layer fertilization during ridge formation; that is, the fertilizer can be placed 6–8 cm deep in the middle of the ridge and applied to the upper layer at the same time to form two shallow fertilizer belts, 3 cm from the side of the seedling belt and 2–3 cm deep. Compared with conventional full-layer slurry fertilization, it can protect soil structure and improve the fertilizer utilization rate of rice. In this study, we aimed to examine the effects of ridge tillage at two fertilizer depths on soil microbial abundance and rice yield in cold areas of northern China over 3 years.

2. Materials and Methods

2.1. Test Site

The experiment was performed at 46.59 °N, 125.16 °E at the Daqing Campus of Heilongjiang Bayi Agricultural University between 2016 and 2018. The annual sunshine duration was 2726 h, and the frost-free period was 143 days, with an annual average temperature of 4.2 °C, annual precipitation of 427 mm, and annual evaporation of 1635 mm.

2.2. Test Materials

The rice variety used was Kenjing 5, which was provided by the Rice Center of Heilongjiang Bayi Agricultural University. The employed fertilizer was a compound slow-release fertilizer from Sinochem (21.0% N, the slow-release nitrogen content of which was 7.0%; P, 3.27%; and K, 6.64%). Ridge tillage at two fertilizer depths was applied twice for the upper and lower layers, and the control flat cropping treatment was the conventional full layer fertilization. The amount of fertilizer used is shown in Table 1.

2.3. Test Design

The trial was repeated from 2016 to 2018 with the same design. The seedlings were planted in May and harvested in September, and the land was fallowed for the rest of the year. A single-factor, randomized block experiment design was used, with a plot area of 200 m2, two randomized treatments, and three replicates for each treatment. Different plots were separated by ridges of the earth. Ridge tillage at two fertilizer depths (L treatment) involved dry leveling, artificial ridging using hoes and shovels (bottom ridge width 60 cm, ridge width 40 cm, and ridge depth 20 cm), artificial strip fertilization, and double rows on the ridge; the technical specification is shown in Figure 1. The control group (P treatment) used conventional flat cropping. Field management was identical in both treatments, except for fertilization tillage. Each hill (30 cm × 12 cm) had five transplanted seedlings. A water layer of 5 cm was maintained for 5–7 days during the transplanting period. The soil moisture was allowed to dry naturally, and the soil maintained a 3–5 cm layer of water until late maturity (when the water surface evaporates below 3 cm, the water was made up to 3–5 cm through irrigation). When the rice plants turned yellow, the soil was drained of water. Table 2 shows the basic physical and chemical properties of the test soil.

2.4. Measurement Index and Method

2.4.1. Soil Sampling and Analysis

After the rice was harvested (20 September 2018), the nutrient contents and physical properties of soil samples from five sampling points in P- and L-treated plots, respectively, were analyzed. Each sample had at least three biological replicates.
The soil was collected using a ring knife at four soil depths (0~5 cm, 5~10 cm, 10~15 cm, and 15~20 cm) for the mensuration of the total porosity and bulk density. The soil samples were kept in their original structure and natural humidity and were immediately sent to the laboratory for determination. At the same time, 1000 g soil samples were taken from 0~10 cm and 10~20 cm soil depth, respectively, and were screened with a 2 mm sieve. The impurities larger than 8 mm were extracted and air-dried, waiting for the mensuration of soil total aggregates.
Rice rhizosphere soil at the depth of 0–20 cm was collected at the rice maturity stage with a stainless steel soil drill with a diameter of 2 cm, and 15 sampling points were randomly selected from each treatment. After removing the roots, weeds, soil animals, and other impurities, they were mixed and used as replicate samples for the same treatment. The soil sample was put into a sterile sealed bag and temporarily stored in a low-temperature ice box and was taken back to the laboratory. The soil sample was divided into two parts after being screened by a 2 mm sieve. A portion of the soil samples was frozen at −40 ℃ for analysis of microbial bacteria (16S rRNA) and fungal (18S rRNA) communities, while the other soil samples were air-dried for the analysis of the chemical properties of the soil.

2.4.2. Soil Physical Properties Analysis

The weights of the soil sample and ring knife were recorded as W0. The soil sample and ring knife were then placed in a basin for overnight wetting, and the weight of saturated water was recorded as W1. After natural drying (without water leaking from the pot bottom), the soil sample and ring knife were then dried at 105 °C for 24 h, and the weight of the soil and ring knife was recorded as W2. The total porosity and bulk density of soil samples were calculated by the following equations [31]:
Soil total porosity = (W1 − W2)/V × 100%
Soil bulk density = (W2 − W0)/V × 100%
where V refers to the volume of the ring knife.
The soil total aggregates were graded using a soil aggregate tester (2000 µm,250 µm, and 53 µm), and 50 g of air-dried soil was placed on a 2000 um sieve and immersed in distilled water for 10 min before the soil aggregate tester was turned on. The sieve vibrated for 10 min at 30 r/min. The aggregates and solutions were collected and transferred into aluminum boxes and were dried in a 65 °C oven for 24 h. The aluminum boxes were weighed after drying. Soil total aggregates were calculated by the following equation [32]:
Soil total aggregates = The sum of drying quality of all levels/Dry soil sample quality × 100%
Then, 10 g of air-dried soil was screened with a 2 mm sieve and placed in a 50 mL conical flask. Afterward, 25 mL distilled water was added, and the flask was shaken for 30 min at 200 r/min. Soil pH was determined using a pH meter.
Soil organic matter content was determined via the potassium dichromate method; total nitrogen content was determined using the Kjeldahl method, and soil total phosphorus content was determined with the sodium-hydroxide-melting molybdenum–antimony anti-colorimetric method. The contents of total potassium and available potassium in soil were determined via an atomic absorption spectrophotometer, the contents of alkali-hydrolyzed nitrogen in soil were determined using the diffusion method, and the contents of available phosphorus in soil were determined using the sodium-bicarbonate-extracted molybdenum–antimony anti-colorimetric method.
All chemical indices were determined according to Soil Agrochemical Analysis, which was published by China Agriculture Press [33].

2.4.3. Microbial Community Structure Analysis

After 3 years of continuous farming, soil samples (0–20 cm) were collected using an auger from the two test plots, and three replicates were taken for each test plot in 2018. Each soil sample weighed 0.5 g, and deoxyribonucleic acid (DNA) was extracted using a TGuide S96 Magnetic Soil/Stool DNA Kit (Tiangen Biotech Co., Ltd., Beijing, China), following the manufacturer’s instructions. The 338F: 5′-ACTCCTACGGGAGGCAGCA-3′ and 806R: 5′-GGACTACHVGGGTWTCTAAT-3′ universal primer set was used to amplify the V3–V4 region of the 16S rRNA gene from each sample. The reaction volume for polymerase chain reaction (PCR) amplification was 50 µL. An initial denaturation at 95 °C for 5 min was followed by 25 cycles of denaturation at 95 °C for 30 s, annealing at 50 °C for 30 s, extension at 72 °C for 40 s, and a final step at 72 °C for 7 min. Bioinformatics analysis for this study was performed using the BMK Cloud (Biomarker Technologies Co., Ltd., Beijing, China).
Alpha diversity is a measure of richness and diversity in a single sample. There are many measures of alpha diversity: Chao, Ace, Shannon, and Simpson. The Chao and Ace indices measure species abundance or the number of species. The Shannon and Simpson indices are used to measure species diversity and are influenced by species abundance and evenness in a sample community. Under the same species abundance, a greater evenness of the species equates to a greater diversity of the community. The higher the Shannon index, the lower the Simpson index. This indicates a higher species diversity of the samples. Samples’ alpha diversity indices were evaluated using the Mothur (Beijing, China) (version v.1.30) software.

2.4.4. Rice Theoretical Output and Output Composition

A total of 3 samples per treatment, with 10 technical replicates within each sample, were taken for rice plants to calculate the mean number of single-point stems and the number of panicles per unit area. Two representative hills were sampled at each point. Each treatment consisted of six representative hills. At maturity, the grains were air-dried and threshed by hand. The seed setting rate (100 × filled spikelets/total spikelets), 1000-grain weight (1000 × filled spikelet weight/filled spikelets), and spikelets per panicle (total spikelets per hill/panicles per hill) were calculated and used to calculate the theoretical yield.

2.5. Data Processing and Analysis

Histograms and Venn plots of species composition and relative abundance were drawn using Excel and R language tools. SPSS 22.0 (IBM Corp., Armonk, NY, USA) was used for variance analysis and comparison. A significant difference between the means was assessed at p < 0.05.

3. Results

3.1. Effects of Continuous Tillage at Two Fertilizer Depths on Soil Nutrient Content and Physical Properties

As shown in Table 3, compared with P treatment, the pH of L treatment samples was 7.81. The soil organic matter content during rice ripening was 8.39% greater than that for P treatment. The content of alkali-hydrolyzed nitrogen increased significantly in L treatment samples, by 6.07%. The content of available phosphorus was 20.67% greater than that for P treatment. The total nitrogen content increased significantly, by 10.69%, the total phosphorus content increased by 9.30%, and the content of total potassium increased by 1.60% in the L treatment samples.
As shown in Table 4, compared with conventional treatments, the soil bulk density of continuous tillage at two fertilizer depths decreased significantly, by 11.85% and 10.42%, in 0–5 cm and 5–10 cm, respectively; the soil total porosity of 0–5 cm and 5–10 cm increased significantly, by 31.68% and 27.67%, while the other depths had no significant difference in the L treatment. The total aggregates of continuous tillage at two fertilizer depths were significantly higher, by 13.78% and 17.96%, at 0–10 cm and 10–20 cm, respectively.

3.2. Analysis of Soil Microbial Operational Taxonomic Units (OTUs)

Table 5 shows that bacterial OTUs increased in the L treatment compared with the P treatment. The numbers of bacterial OTU units in the L and P treatments were 1549 and 1465, respectively, a relative increase of 5.73%. The numbers of fungal OTU units in the L and P treatments were 489 and 464, respectively, indicating a relative increase of 5.39%.
Figure 2 shows that the number of common bacterial OTUs across the different treatments was 1572, with 0 unique bacterial OTUs in the P treatment and 17 unique bacterial OTUs in the L treatment. The number of fungal OTUs common to both treatments was 541, with 187 unique fungal OTUs in the P treatment and 206 unique fungal OTUs in the L treatment.

3.3. Effects of Continuous Tillage at Two Fertilizer Depths on the Diversity and Abundance of Soil Microorganism Communities

Table 6 shows that the L treatment increased the ACE and Chao indices of soil bacteria and fungi. Compared with the P treatment, the ACE and Chao indices of bacteria in the L treatment were increased by 1.46% and 1.83%, respectively, while the ACE and Chao indices of fungi were increased by 5.26% and 5.48%, respectively.

3.4. Effects of Continuous Ridge Tillage at Two Fertilizer Depths on the Microbial Community Structure

Figure 3 shows the changes in the relative abundances of soil bacteria and fungi at the phylum level. Figure 3a shows that L treatment increased the relative abundances of Proteobacteria, Acidobacteria, and Gemmatimonadetes. Compared with the P treatment, the relative abundances of Proteobacteria, Acidobacteria, and Gemmatimonadetes in the L treatment were increased by 10.85%, 2.95%, and 3.21%, respectively. Figure 3b shows that fungi in the soil included Ascomycota, Aphelidiomycota, Basidiomycota, Mortierellomycota, Chytridiomycota, Rozellomycota, and other fungi. Ridge tillage at two fertilizer depths increased the numbers of Ascomycota, Chytridiomycota, and Cercozoa by 38.00%, 27.41%, and 77.71%, respectively. However, the L treatment also decreased the numbers of Aphelidiomycota, Basidiomycota, and Mortierellomycota by 87.89%, 42.10%, and 33.09%, respectively.
Figure 4 presents the soil bacteria and fungi at the genus level. Figure 4a shows that, compared with the P treatment, the L treatment increased the relative abundances of Sphingomonas, uncultured_bacterium_f_Gemmatimonadaceae, Gemmatimonas, and others by 16.31%, 1.81%, 1.74%, and 0.73%, respectively. However, compared with P, the relative abundances of uncultured_bacterium_f_Anaerolineaceae, Anaerolineae, and unclassified in the L treatment were decreased by 30.54%, 40.06%, and 8.19%, respectively. Figure 4b shows that, compared with P, the L treatment increased the relative abundances of Schizothecium, Cistella, and Geomyces fungi by 2791.67%, 205.21%, and 24.19%, respectively. However, the relative abundances of Fusicolla, Cephalotrichum, Mortierella, Venturia, and unclassified were decreased by 97.97%, 33.12%, 32.71%, 94.72%, and 15.55%, respectively.
Figure 5 shows that when an LDA value of >4 was set, the soil bacteria were enriched in both the L and P treatments; the significant differential markers of soil bacteria under L and P treatments were 1 and 5, respectively. Significant differential markers of soil fungi were abundant in both L and P treatments, with L having five markers and P having one marker.

3.5. Effects of Continuous Tillage at Two Fertilizer Depths on the Interaction between Soil Bacteria and Fungi

Horizontal correlation network diagrams revealed significant interactions between the different genera. Figure 6 shows that the highest relative abundances of microorganisms in the P treatment were uncultured_bacterium_f_Gemmatimonadaceae, uncultured_bacterium_f_Anaerolineaceae, and Anaeromyxobacter. The highest relative abundances in the L treatment were Sphingomonas and uncultured_bacterium_f_Gemmatimonadaceae. In the P treatment, 37 cases were negatively correlated, and 29 cases were positively correlated. In the L treatment, 39 cases were negatively correlated, and 35 cases were positively correlated.
Figure 7 shows that, in the interaction network of major soil fungi genera, the highest relative abundances in L were of Cephalotrichum, Aspergillus, and Geomyces. Cephalotrichum, Chaetomium, and Podospora exhibited the highest relative abundances in P. In the L treatment, there were 28 negative correlations and 32 positive correlations. In the P treatment, 35 fungi genera showed negative correlations, and 42 fungi genera showed positive correlations.

3.6. Effects of Continuous Tillage at Two Fertilizer Depths on Yield and Yield Components

Table 7 shows that, from 2016 to 2018, the number of panicles per square meter in the L treatment all increased significantly, compared with the P treatment; the weight of 1000-grains in the L treatment all decreased, compared with the P treatment, but not significantly, except for the number of grains per panicle in 2016 and seed setting rate in 2017; the L treatment increased the number of grains per panicle and seed setting rate, compared with the P treatment; lastly, the yield of the L treatment increased by 7.8%, 18.8%, and 36.5%, compared with P, respectively. Yields of L significantly increased in 2017 and 2018, compared with P. There was no significant difference between L and P in 2016 because the number of grains per panicle in L decreased significantly, compared with P. From 2016 to 2018, the average yield of the L treatment was 9781.51 kg/ha, which was 19.23% higher than that in the P treatment.

3.7. Correlation between Rice Yield and Alpha Diversity of Soil Bacteria and Fungi

Table 8 shows that the weight of panicles, number of real grains, weight of real grains, and yield were significantly positively correlated with OTU, ACE, and Chao indices. The seed setting rate was significantly positively correlated with OTU, ACE, and Chao indices. Yield and its composition were not significantly correlated with the Simpson index or Shannon index.
Table 9 shows that yield and its components were positively correlated with OTU, ACE, and Chao indices, except for the number of panicles per hill and the number of shattered grains. However, there was no significant difference among all indices.

4. Discussion

4.1. Effects of Continuous Tillage at Two Fertilizer Depths on Soil Nutrient Content and Physical Properties

Studies have shown that conservation tillage can significantly increase the accumulation of N, P, and K nutrients in the soil. With increased years of conservation tillage, total soil nitrogen, available nitrogen, and organic carbon gradually increased [34,35]. In this experiment, the L treatment increased soil nutrient content (Table 3). This could be because continuous tillage at two fertilizer depths makes the soil loose and has a rich porous structure, allowing it to absorb free nutrient ions. In addition, conservation tillage can promote good soil structure to better store nutrients. Similarly, strong water retention and aeration improve soil’s physical properties and can provide a good environment for crop growth [36,37]. The results of this study also show that the L treatment improved soil’s physical properties (Table 4). This is consistent with previous studies.

4.2. Effects of Continuous Tillage at Two Fertilizer Depths on the Abundance and Diversity of Soil Microorganism Communities

OTU is the classification unit of microorganisms, which reflects the diversity and species richness of microorganisms in soils under different treatments. The relative abundance and composition of microorganisms in soil changed after 3 years of ridge tillage at two fertilizer depths. We observed that, compared with the P treatment, bacterial and fungal OTUs increased by 5.73% and 5.39%, respectively, under the L treatment (Table 5). Venn diagrams can visually indicate the degree of overlap between groups or samples. As can be seen in Figure 2, the number of unique bacterial and fungal OTUs in the L treatment was more than that in the P treatment. The number of unique OTUs of microorganisms in soil altered the composition of microorganism groups, indicating that the L treatment increased the abundance and diversity of soil microorganisms. The L treatment might also have affected soil biological characteristics and chemical and physical properties, thus creating a conducive ecological environment for microorganisms. The results of this study are basically consistent with those of a previous study [38].
The variation in soil microbial abundance under ridge tillage at two fertilizer depths has become a problem worth taking into account. Ace and Chao indices are indicators of community species richness [39,40]. Here, we showed that the L treatment increased the ACE and Chao indices of soil bacteria and fungi (Table 6). This might be due to the loosening of the soil in the L treatment, which provided a good environment for microorganisms, protected them from adverse environmental effects, and reduced the competition for survival among microorganisms. Continuous ridge tillage at two fertilizer depths significantly increased soil microbial abundance and loosened the soil structure, which allows the release of more nutrients by soil microbes. Continuous ridge tillage at two fertilizer depths can improve soil pH, adhesion, and other soil properties, thus directly changing the soil bacterial and fungal community composition.

4.3. Effects of Continuous Ridge Tillage at Two Fertilizer Depths on the Microbial Community Structure

Many studies have demonstrated that ridge tillage at two fertilizer depths has an impact on rice yield and quality in the short term and long term [41,42,43,44,45]. However, the mechanism by which this method affects the composition of microorganisms remains unclear.
Proteobacteria made up the largest proportion of soil relative abundance and community composition. This is consistent with previous research [46,47]. This is most likely because Proteobacteria are nutrient-rich bacteria, and the L treatment improved soil nutrient properties, which led to an increase in Proteobacteria [48]. The relative abundance of acidified bacteria is the highest in a low-pH soil environment [49]. By adjusting the soil pH, the number of acidified bacteria increased under the L treatment. However, the numbers of Chloroflexi, Bacteroidetes, and Ignavibacteriae were reduced in the L treatment. Chloroflexi species usually decompose plant compounds by degrading cellulose, starch, and long-chain sugars, and they compete with other organisms for unstable carbon. Therefore, their low relative abundance may limit the rate of decomposition of organic matter [50]. Mortierella can effectively inhibit the occurrence of clubroot disease, including saprophytic fungi, due to the high content of cellulose in soil.
This study indicated that ridge tillage of two fertilizer depths affected the relative abundance of bacteria and fungi. At an LDA value of >4, there were fewer significant differential markers for soil bacteria and more significant differential markers for soil fungi in the L treatment than in the P treatment (Figure 5). Compared with the conventional treatment, ridge tillage at two fertilizer depths was more beneficial to the formation of differences between fungal groups.

4.4. Effects of Continuous Tillage at Two Fertilizer Depths on the Interaction between Soil Bacteria and Fungi

For some microbes, there is a significant role of temperature and relative humidity in controlling competitive saprophytic capacity. Therefore, the interaction between soil bacteria and fungi was affected by different tillage methods. However, research on this is scarce.
The results of our experiment showed that the correlation between the main soil bacterial genera was stronger in L than in P, and there were more positive correlations in L than in P (Figure 6). We discovered that the correlations between soil fungal genera were stronger in P than in L, and there were significantly more positive correlations in P than in L (Figure 7). Ridge tillage at two fertilizer depths increased the interactions between soil bacterial genera and decreased the interactions between soil fungal genera. However, the mechanism of this phenomenon remains to be studied further.

4.5. Effects of Continuous Tillage at Two Fertilizer Depths on Yield and Yield Components

Conservation tillage is beneficial to soil water conservation, and soil bacteria are better able to survive in humus, especially on the soil surface. Compared with conventional fertilization, slow/controlled-release fertilizer can significantly increase nitrogen uptake and the efficiency of fertilizer use in rice [18,51]. The deep application of controlled-release compound fertilizer on the side of the rice transplanter ensures a nitrogen supply in the key periods (middle and late periods), which significantly improves rice yield and nitrogen use efficiency. Yield significantly increases in long-term no-tillage rice [52,53,54].
Ridge tillage at two fertilizer depths does not completely destroy the soil layer, and the fertilizer is applied at two depths, close to the seedlings, to improve fertilizer efficiency and protect the soil [43]. This study showed that ridge tillage at two fertilizer depths increased the species diversity of soil microbes, and compared with P, the yield increased by 7.8%, 18.8%, and 36.5% in 2016, 2017, and 2018, respectively. From 2016 to 2018, the percentage of rice yield increase increased every year, which may be related to the increase in soil microbial abundance under continuous ridge tillage at two fertilizer depths. The average yield of the L treatment was 9781.51 kg/ha, which was 19.23% higher than that of the P treatment. The results of this study are consistent with previous studies [55,56].

4.6. Correlation between Rice Yield and Alpha Diversity of Soil Bacteria and Fungi

The diversity of soil bacteria, revealed by the OTU, ACE, and Chao indices, is a great stimulant for the increase in rice yield. However, very little research has correlated rice yield with the alpha diversity of soil bacteria and fungi. In our experiment, the weight of panicles, number of real grains, weight of real grain, seed setting rate, and yield were significantly positively correlated with OTU, ACE, and Chao indices. Yield and its composition were not significantly correlated with the Simpson index or Shannon index (Table 8). Table 9 shows that yield and its components were not significantly correlated with the alpha diversity of soil fungi under the conditions of the L treatment, which needs further study.

5. Conclusions

In summary, the L treatment increased soil nutrient content, improved soil physical properties, and increased the ACE and Chao indices of soil bacteria and fungi. Furthermore, the L treatment increased the abundance of bacteria in the aerobic zone, reduced the abundance of bacteria in the anaerobic zone, and increased the abundance and species diversity of bacteria and fungi. The average yield of rice after ridge tillage at two fertilizer depths over 3 years was 9781.51 kg/ha, which was 19.23% higher than that of conventional cultivation. The relationships between soil bacteria and fungi in the L treatment were stronger than that in the P treatment. These results provide points of reference and a basic understanding of the application of ridge tillage at two fertilizer depths. Some unclear indicators in this experiment, such as the correlation between rice yield and soil microbial diversity and the interaction between soil bacteria and fungi, need to be studied in future research to utilize ridge tillage at two fertilizer depths in rice production in northern China.

Author Contributions

Experiment design, writing—review and editing, L.L.; writing—original draft preparation, writing—review and editing, S.C.; experimental studies, data collection, formal analysis, M.Q. and L.C.; writing—review and editing, D.Y. and X.G.; conceptualization, writing—original draft preparation, writing—reviewing and editing, H.L. and G.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Natural Science Foundation of Heilongjiang Province (C2018048), Heilongjiang Bayi Agricultural University Support Program for San Heng San Zong (TDJH201802) and received support from The Central Government’s Talent Training Program of Reform and Development Fund for Local Colleges and Universities (2022010006).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data generated and analyzed during the current study are available. Raw data of rice yields can be found in the uploaded Excel sheet, and the 16S rRNA sequences of the samples were submitted to the NCBI database; the accession numbers of the sequences were PRJNA795656-PRJNA795609.

Acknowledgments

We are grateful for the support provided by the Heilongjiang Provincial Key Laboratory of Modern Agricultural Cultivation and Crop Germplasm Improvement.

Conflicts of Interest

The authors have no relevant financial or non-financial interest to disclose.

References

  1. Peng, Y.Q.; Zheng, H.B.; Hu, T.; Chen, Y.; Huang, H. Effect of rice ridge tillage and terrace cultivation technology on rice root growth. Crop Res. 2012, 26, 14–17. (In Chinese) [Google Scholar] [CrossRef]
  2. Ding, J.; Zhu, D.; Chen, Q.L.; Zheng, F.; Wang, H.T. Effects of long-term fertilization on the associated microbiota of soil collembolan. Soil Biol. Biochem. 2019, 130, 141–149. [Google Scholar] [CrossRef]
  3. Heijden, M.; Wagg, C. Soil microbial diversity and agro-ecosystem functioning. Plant Soil 2013, 363, 1–5. [Google Scholar] [CrossRef] [Green Version]
  4. Ojuederie, O.B.; Olanrewaju, O.S.; Babalola, O.O. Plant Growth Promoting Rhizobacterial Mitigation of Drought Stress in Crop Plants: Implications for Sustainable Agriculture. Agronomy 2019, 9, 712. [Google Scholar] [CrossRef] [Green Version]
  5. Sarfraz, R.; Hussain, A.; Sabir, A.; Fekih, I.B.; Ditta, A.; Xing, S. Role of biochar and plant growth promoting rhizobacteria to enhance soil carbon sequestration—A review. Environ. Monit. Assess. 2019, 191, 251. [Google Scholar] [CrossRef]
  6. Brockett, B.F.; Prescott, C.E.; Grayston, S.J. Soil moisture is the major factor influencing microbial community structure and enzyme activities across seven biogeoclimatic zones in western Canada. Soil Biol. Biochem. 2012, 44, 9–20. [Google Scholar] [CrossRef]
  7. Kulmatiski, A.; Beard, K.H.; Stevens, J.R.; Cobbold, S.M. Plant-soil feedbacks: A meta-analytical review. Ecol. Lett. 2008, 11, 980–992. [Google Scholar] [CrossRef]
  8. Degens, B.P.; Schipper, L.A.; Sparling, G.P.; Vojvodic-Vukovic, M. Decreases in organic C reserves in soils can reduce the catabolic diversity of soil microbial communities. Soil Biol. Biochem. 2000, 32, 189–196. [Google Scholar] [CrossRef]
  9. Hewedy, O.A.; Lateif, K.S.; Seleiman, M.F.; Sham, A.; Albarakaty, F.M.; El-Meihy, R.M. Phylogenetic Diversity of Trichoderma Strains and Their Antagonistic Potential against Soil-Borne Pathogens under Stress Conditions. Biology 2020, 9, 189. [Google Scholar] [CrossRef]
  10. Chu, G.; Wang, Z.Q.; Zhang, H.; Liu, L.J.; Yang, J.C.; Zhang, J.H. Alternate wetting and moderate drying increases rice yield and reduces methane emission in paddy field with wheat straw residue incorporation. Food Energy Secur. 2015, 4, 238–254. [Google Scholar] [CrossRef]
  11. Ghimire, R.; Norton, J.B.; Stahl, P.D.; Norton, U. Soil Microbial Substrate Properties and Microbial Community Responses under Irrigated Organic and Reduced-Tillage Crop and Forage Production Systems. PLoS ONE 2014, 9, e103901. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  12. Lienhard, P.; Terrat, S.; Prévost-Bouré, N.C.; Nowak, V.; Régnier, T.; Sayphoummie, S.; Panyasiri, K.; Tivet, F.; Mathieu, O.; Levêque, J.; et al. Pyrosequencing evidences the impact of cropping on soil bacterial and fungal diversity in Laos tropical grassland. Agron. Sustain. Dev. 2014, 34, 525–533. [Google Scholar] [CrossRef]
  13. Madejón, E.; Murillo, J.M.; Moreno, F.; López, M.V.; Arrue, J.L.; Alvaro-Fuentes, J.; Cantero, C. Effect of long-term conservation tillage on soil biochemical properties in Mediterranean Spanish areas. Soil Tillage Res. 2009, 105, 55–62. [Google Scholar] [CrossRef] [Green Version]
  14. Mbuthia, L.W.; Acosta-Martínez, V.; Debryun, J.; Schaeffer, S.; Tyler, D.; Odoi, E.; Mpheshea, M.; Walker, F. Long term tillage, cover crop, and fertilization effects on microbial community structure, activity: Implications for soil quality. Soil Biol. Biochem. 2015, 89, 24–34. [Google Scholar] [CrossRef]
  15. Souza, R.C.; Hungria, M.; Cantão, M.E.; Vasconcelos AT, R.; Nogueira, M.A.; Vicente, V.A. Metagenomic analysis reveals microbial functional redundancies and specificities in a soil under different tillage and crop-management regimes. Appl. Soil Ecol. 2015, 86, 106–112. [Google Scholar] [CrossRef]
  16. Wang, Z.; Liu, L.; Chen, Q.; Wen, X.; Liao, Y. Conservation tillage increases soil bacterial diversity in the dryland of northern China. Agron. Sustain. Dev. 2016, 36, 28. [Google Scholar] [CrossRef] [Green Version]
  17. Chapin, F.S.; McFarland, J.; McGuire, A.D.; Euskirchen, E.S.; Ruess, R.W.; Kielland, K. The changing global carbon cycle: Linking plant-soil carbon dynamics to global consequences. J. Ecol. 2009, 97, 840–850. [Google Scholar] [CrossRef]
  18. Groenigen, K.; Bloem, J.; Bååth, E.; Boeckx, P.; Rousk, J.; Bode, S.; Forristal, D.; Jones, M.B. Abundance, production and stabilization of microbial biomass under conventional and reduced tillage. Soil Biol. Biochem. 2010, 42, 48–55. [Google Scholar] [CrossRef]
  19. Luo, Z.Z.; Cai, L.Q.; Li, L.L.; Niu, Y.N.; Zhang, R.Z.; Xie, J.H. Long-term effects of tillage system on soil nutrients and grain yields in rainfed area of Loess Plateau. Agric. Res. Arid. Areas 2015, 33, 171–176. (In Chinese) [Google Scholar] [CrossRef]
  20. Li, T.; Wang, Z.T.; Liu, L.; Liao, Y.C.; Liu, Y.; Han, J. Effect of Conservation Tillage Practices on Soil Microbial Spatial Distribution and Soil Physico-Chemical Properties of the Northwest Dryland. Sci. Agric. Sin. 2017, 50, 859–870. (In Chinese) [Google Scholar] [CrossRef]
  21. Gao, J.S.; Cao, W.D.; Li, D.C.; Xu, M.G.; Zeng, X.B.; Nie, J.; Zhang, W.J. Effects of long-term double-rice and green manure rotation on rice yield and soil organic matter in paddy field. Acta Ecol. Sin. 2011, 31, 4542–4548. (In Chinese) [Google Scholar]
  22. Huang, G.Q.; Yang, B.J.; Wang, S.B.; Huang, X.Y.; Zhang, Z.F.; Yao, Z.; Huang, L.X.; Zhao, Q.G. Effects of 8 years of conservational tillage on rice yield and soil physical, chemical and biological properties. Acta Ecol. Sin. 2015, 35, 1225–1234. (In Chinese) [Google Scholar] [CrossRef] [Green Version]
  23. Li, J.M.; Huang, Q.H.; Yuan, T.Y.; Cao, J.H.; Yu, X.C. Effect of long term green manure application on rice yield and soil nutrients in paddy soil. J. Plant Nutr. Fertil. 2011, 17, 563–570. (In Chinese) [Google Scholar] [CrossRef]
  24. Zhang, Z.C.; Li, H.W.; Chen, T.T.; Wang, X.M.; Wang, Z.Q.; Yang, J.C. Effect of Furrow Irrigation and Alternate Wetting and Drying Irrigation on Grain Yield and Quality of Rice. Sci. Agric. Sin. 2011, 44, 4988–4998. (In Chinese) [Google Scholar] [CrossRef]
  25. Hu, T. Effect of Ridge-Bed Cultivation on Rice Morphological Structure, Physiological Characteristics and Grain Yield. Mester’s Thesis, Hunan Agricultural University, Changsha, China, 2013. (In Chinese). [Google Scholar]
  26. Tang, Z.W.; Zhou, W.T.; Wang, B.R.; Zhong, K.Y.; Xiong, R.; Long, P.; Xu, Y.; Fu, Z.Q. Effects of ridge-bed cultivation on rice root characteristics and soil physical properties. Chin. J. Ecol. 2021, 40, 3961–3969. (In Chinese) [Google Scholar] [CrossRef]
  27. Zheng, H.B.; Yao, L.; Liu, J.X.; He, H.; Chen, Y.; Huang, H. Effect of Ridge & Terraced Cultivation on Rice Yield and Root Trait. Acta Agron. Sin. 2014, 40, 667–677. (In Chinese) [Google Scholar] [CrossRef]
  28. Qian, Y.D.; Li, J.F.; Zheng, G.P.; Lv, Y.D.; Guo, X.H.; Sun, C.Y. Effect of Ridge Cultivation on Root Growth of Rice in Cold Region. Chin. J. Rice Sci. 2005, 19, 238–242. (In Chinese) [Google Scholar] [CrossRef]
  29. Qian, Y.D.; Liu, L.H.; Li, H.Y.; Zheng, G.P.; Liu, C.W. Effects of Cold Terra Protective Tillage and Cultivation Technology on Rice Yield and Yield Components. Crops 2010, 2, 41–44. (In Chinese) [Google Scholar] [CrossRef]
  30. Zheng, G.P.; Han, D.L.; Lv, Y.D.; Ding, Z.L.; Li, H.Y.; Sui, Y.G.; Song, J.; Chen, H.L.; Jiang, Y.W.; Zhao, T.T. New Efficient Cultivation Pattern and Technical Code of “Dry Land Regulation and Bilateral Deep Fertilization on Ridge” for Rice. J. Heilongjiang Bayi Agric. Univ. 2016, 28, 1–3, 24. (In Chinese) [Google Scholar] [CrossRef]
  31. Al-Shammary, A.A.G.; Kouzani, A.Z.; Kaynak, A.; Khoo, S.Y.; Norton, M.; Gates, W. Soil bulk density estimation methods: A Review. Pedosphere 2018, 4, 581–596. [Google Scholar] [CrossRef]
  32. Chinese Academy of Sciences. Soil Physical and Chemical Analysis; Shanghai Science and Technology Press: Shanghai, China, 1978. (In Chinese) [Google Scholar]
  33. Bao, S.D. Soil and Agricultural Chemistry Analysis, 3rd ed.; Chinese Agriculture Press: Beijing, China, 2000. (In Chinese) [Google Scholar]
  34. Zhang, X.; Zhu, A.; Yang, W.; Zhang, J. Accumulation of organic components and its association with macroaggregation in a sandy loam soil following conservation tillage. Plant Soil 2017, 416, 1–15. [Google Scholar] [CrossRef]
  35. Jaziri, S.; M’hamed, H.C.; Rezgui, M.; Labidi, S.; Souissi, A.; Rezgui, M.; Barbouchi, M.; Annabi, M.; Bahri, H. Long Term Effects of Tillage–Crop Rotation Interaction on Soil Organic Carbon Pools and Microbial Activity on Wheat-Based System in Mediterranean Semi-Arid Region. Agronomy 2022, 12, 953. [Google Scholar] [CrossRef]
  36. Harasim, E.; Antonkiewicz, J.; Kwiatkowski, C.A. The Effects of Catch Crops and Tillage Systems on Selected Physical Properties and Enzymatic Activity of Loess Soil in a Spring Wheat Monoculture. Agronomy 2020, 10, 334. [Google Scholar] [CrossRef] [Green Version]
  37. Chichongue, O.; van Tol, J.; Ceronio, G.; Du Preez, C. Effects of Tillage Systems and Cropping Patterns on Soil Physical Properties in Mozambique. Agriculture 2020, 10, 448. [Google Scholar] [CrossRef]
  38. Chen, H.; Boutros, P.C. VennDiagram: A package for the generation of highly-customizable Venn and Euler diagrams in R. BMC Bioinform. 2011, 12, 35. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  39. Lucheta, A.R.; Cannavan, F.D.S.; Roesch, L.F.W.; Tsai, S.M.; Kuramae, E.E. Fungal community assembly in the amazonian dark. Earth Microb. Ecol. 2016, 71, 962–973. [Google Scholar] [CrossRef] [Green Version]
  40. Li, S.; Wang, S.; Fan, M.; Wu, Y.; Shangguan, Z. Interactions between biochar and nitrogen impact soil carbon mineralization and the microbial community. Soil Tillage Res. 2020, 196, 104437. [Google Scholar] [CrossRef]
  41. Chen, L.Q.; Zhao, H.C.; He, C.; Zhou, J.; Lv, Y.D.; Li, H.Y.; Yin, D.W.; Zheng, G.P. Effects of Dry Land Regulation and Bilateral Deep Fertilization on Ridge on Yield and Quality of Rice under Nitrogen Fertilizer Operation Model. J. Henan Agric. Sci. 2018, 47, 20–26. (In Chinese) [Google Scholar] [CrossRef]
  42. Kang, K.; Liu, L.H.; Qing, M.; Zheng, G.P.; Zhang, X.S.; Bai, C.Y.; Zhao, S.; Gao, X.H. Effects of Ridge Tillage of Double Depth and Planting Space on Photosynthesis, Yield and Panicle Traits of Rice. Crops 2020, 5, 164–169. (In Chinese) [Google Scholar] [CrossRef]
  43. Li, H.Y.; Zhang, G.L.; Zheng, G.P.; Chen, L.Q.; Lv, Y.D. Evaluation on Technical Effect of Double Depth Ridge Cultivation Mode of Rice in Cold Region. Res. Soil Water Conserv. 2020, 27, 164–170. (In Chinese) [Google Scholar] [CrossRef]
  44. Wang, W.Y.; Wan, S.Y.; Zhang, X.S.; Wei, Y.Y.; Zhang, J.Z.; Li, H.Y.; Zheng, G.P. The Effects of Transplanting Rice Seedling Period and Seedling Type on Yield and Quality under Different Cultivation Modes. Acta Agric. Boreali-Sin. 2021, 36, 116–126. (In Chinese) [Google Scholar] [CrossRef]
  45. Zheng, H.B. The Law of Water Utilization and Its Mechanism of Increasing Yield of Rice Ridge Tillage and Terrace Cultivation Technology. Ph.D. Thesis, Hunan Agricultural University, Chang, China, 2014. (In Chinese). [Google Scholar]
  46. Ji, F.Y.; Ming, H.X.; Li, H.B.; Zan, S.J.; Wang, J.N.; Su, J.; Guo, L.M.; Chang, Y.K.; Shi, Y.; Guan, C.J.; et al. Diversity of CO2 fixation gene in the surface waters of northern South China Sea in the Calvin cycle. Acta Sci. Circumstantiae 2016, 36, 4037–4043. (In Chinese) [Google Scholar] [CrossRef]
  47. Liu, Q.; Wei, X.M.; Wu, X.H.; Yuan, H.C.; Wang, J.R.; Li, Y.Y.; Ge, T.D.; Wu, J.S. Characteristic of Abundances and Diversity of Carbon Dioxide Fixation Microbes in Paddy Soils. Environ. Sci. 2017, 38, 760–768. (In Chinese) [Google Scholar] [CrossRef]
  48. Fierer, N.; Bradford, M.A.; Jackson, R.B. Toward an ecological classification of soil bacteria. Ecology 2007, 88, 1354–1364. [Google Scholar] [CrossRef] [PubMed]
  49. Jones, R.T.; Robeson, M.S.; Lauber, C.L.; Hamady, M.; Knight, R.; Fierer, N. A comprehensive survey of soil acidobacterial diversity using pyrosequencing and clone library analyses. ISME J. 2009, 3, 442–453. [Google Scholar] [CrossRef] [PubMed]
  50. Hug, L.A.; Castelle, C.J.; Wrighton, K.C.; Thomas, B.C.; Sharon, I.; Frischkorn, K.R.; Williams, K.H.; Tringe, S.G.; Banfield, J.F. Community genomic analyses constrain the distribution of metabolic traits across the Chloroflexi phylum and indicate roles in sediment carbon cycling. Microbiome 2013, 1, 22. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  51. Wu, L.; Wang, Y.; Zhang, S.; Wei, W.; Kuzyakov, Y.; Ding, X. Fertilization effects on microbial community composition and aggregate formation in saline-alkaline soil. Plant Soil 2021, 463, 523–535. [Google Scholar] [CrossRef]
  52. Cui, H.H.; Chen, Z.G.; Zhang, Q.; Zhu, Q.; Li, J.; Lu, S.; Zhang, D.P.; Gu, Y.B. Improvement and Rice Fewer-tillage Cultivation Techniques in Cold Waterlogged Field. Farming Cultiv. 2014, 2, 44–46, 60. (In Chinese) [Google Scholar] [CrossRef]
  53. Liu, L.J.; Liu, C.Y.; Wan, Z.H. Effects of Different Cultivation Methods and Nitrogen Fertilizer Application on Rice Yield. Hubei Agric. Sci. 2015, 54, 2061–2064. (In Chinese) [Google Scholar] [CrossRef]
  54. Sun, Y.J.; Ma, J.; Sun, Y.Y.; Xu, H.; Yang, Z.Y.; Liu, S.J.; Jia, X.W.; Zheng, H.Z. The effects of different water and nitrogen managements on yield and nitrogen use efficiency in hybrid rice of China. Field Crops Res. 2012, 127, 85–98. [Google Scholar] [CrossRef]
  55. Chen, J.; Ma, Z.M.; Liu, L.L.; Lv, X.D. Effect of tillage system on soil organic carbon, microbial biomass and enzyme activities. J. Plant Nutr. Fertil. 2016, 22, 667–675. (In Chinese) [Google Scholar] [CrossRef]
  56. Lu, D.; Lei, J.; Wei, Y.Y.; Shen, W.K.; Huang, Y.F.; Gu, M.H. Effect of Microbial Community and Diversity Index of Paddy Soil under Short No-tillage and Ridge Tillage. Southwest China J. Agric. Sci. 2015, 28, 1670–1674. (In Chinese) [Google Scholar] [CrossRef]
Agriculture 12 00923 g001 550
Figure 1. The rice ridge tillage at two fertilizer depths: (a) cultivation model field demonstration; (b) schematic diagram.
Figure 1. The rice ridge tillage at two fertilizer depths: (a) cultivation model field demonstration; (b) schematic diagram.
Agriculture 12 00923 g001
Agriculture 12 00923 g002 550
Figure 2. Venn diagrams of (a) bacterial and (b) fungal communities in soil. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Figure 2. Venn diagrams of (a) bacterial and (b) fungal communities in soil. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Agriculture 12 00923 g002
Agriculture 12 00923 g003 550
Figure 3. Changes in the relative abundances of (a) soil bacteria and (b) fungi at the phylum level. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Figure 3. Changes in the relative abundances of (a) soil bacteria and (b) fungi at the phylum level. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Agriculture 12 00923 g003
Agriculture 12 00923 g004 550
Figure 4. Changes in relative abundances of (a) soil bacteria and (b) fungi at the genus level. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Figure 4. Changes in relative abundances of (a) soil bacteria and (b) fungi at the genus level. L: ridge tillage at two fertilizer depths; P: conventional cultivation.
Agriculture 12 00923 g004
Agriculture 12 00923 g005 550
Figure 5. Significance analysis of differences among different treatment groups: L: ridge tillage at two fertilizer depths; P: conventional cultivation; (a) bacteria; (b) fungi. The circles radiating from inside to outside represent the classification level from phylum to species; each small circle represents a classification at a particular level. The diameter of the small circle is proportional to the relative abundance. Red and green represent ridge tillage at two fertilizer depths (L) and conventional cultivation (P), respectively, and nodes of different colors represent the microbiome that plays an important role in the groups represented by the color.
Figure 5. Significance analysis of differences among different treatment groups: L: ridge tillage at two fertilizer depths; P: conventional cultivation; (a) bacteria; (b) fungi. The circles radiating from inside to outside represent the classification level from phylum to species; each small circle represents a classification at a particular level. The diameter of the small circle is proportional to the relative abundance. Red and green represent ridge tillage at two fertilizer depths (L) and conventional cultivation (P), respectively, and nodes of different colors represent the microbiome that plays an important role in the groups represented by the color.
Agriculture 12 00923 g005
Agriculture 12 00923 g006 550
Figure 6. Interaction networks of the main bacterial genera in the soil: (a) ridge tillage at two fertilizer depths (L); (b) conventional cultivation (P). Orange and green lines represent positive and negative correlations, respectively; line thickness represents correlation coefficient, and line number represents the degree of closeness between nodes.
Figure 6. Interaction networks of the main bacterial genera in the soil: (a) ridge tillage at two fertilizer depths (L); (b) conventional cultivation (P). Orange and green lines represent positive and negative correlations, respectively; line thickness represents correlation coefficient, and line number represents the degree of closeness between nodes.
Agriculture 12 00923 g006
Agriculture 12 00923 g007 550
Figure 7. Interaction networks of the main fungal genera in the soil: (a) ridge tillage at two fertilizer depths (L); (b) conventional cultivation (P). Orange and green lines represent positive and negative correlations, respectively; line thickness represents correlation coefficient, and line number represents the degree of closeness between nodes.
Figure 7. Interaction networks of the main fungal genera in the soil: (a) ridge tillage at two fertilizer depths (L); (b) conventional cultivation (P). Orange and green lines represent positive and negative correlations, respectively; line thickness represents correlation coefficient, and line number represents the degree of closeness between nodes.
Agriculture 12 00923 g007
Table
Table 1. Types and application rates of fertilization at Daqing Campus from 2016 to 2018 (kg/ha).
Table 1. Types and application rates of fertilization at Daqing Campus from 2016 to 2018 (kg/ha).
YearTreatment Base
Fertilizer		Regulating FertilizerPanicle
Fertilizer
NPKNNK
2016–2018LUpper layer40.855.169.9210.35—12.96
Lower layer47.507.4015.02———
PFull layer88.3512.5624.9410.35—12.96
Table
Table 2. Basic physical and chemical properties of the soil.
Table 2. Basic physical and chemical properties of the soil.
YearTreatmentAlkali-Hydrolyzed Nitrogen (AN) (mg/kg)Available
Phosphorus (AP) (mg/kg)		Available
Potassium (AK) (mg/kg)		Organic
Matter
(OC) (g/kg)		pH
2016L155.9030.75189.4735.507.25
P155.9030.75189.4735.507.25
2017L171.5832.97134.7533.007.23
P173.3836.89136.0535.007.12
2018L144.8928.17179.3527.307.55
P158.0631.94184.9635.307.34
Table
Table 3. Effects of continuous tillage at two fertilizer depths on soil nutrient content.
Table 3. Effects of continuous tillage at two fertilizer depths on soil nutrient content.
TreatmentpHOrganic
Matter
(OC) (g/kg)		Alkali-Hydrolyzed Nitrogen (AN) (mg/kg)Available
Phosphorus (AP) (mg/kg)		Available
Potassium (AK) (mg/kg)		Total
Nitrogen (TN) (g/kg)		Total
Phosphorus (TP) (g/kg)		Total
Potassium (TK) (g/kg)
L7.81 a32.27 a146.67 a47.22 a122.06 a1.76 a0.94 a18.36 a
P8.08 a29.77 b138.33 b39.13 b109.27 b1.59 b0.86 a18.07 a
Notes: L: rice cultivation under ridge tillage at two fertilizer depths; P: conventional rice cultivation. a,b: columns with different letters denote significant differences at p < 0.05 (n = 2, LSD test).
Table
Table 4. Effects of continuous tillage at two fertilizer depths on soil physical properties.
Table 4. Effects of continuous tillage at two fertilizer depths on soil physical properties.
Treatment0–5 cm5–10 cm10–15 cm15–20 cm
Bulk density (g·cm−3)L1.19 b1.29 b1.36 a1.35 a
P1.35 a1.44 a1.50 a1.35 a
Total porosity (%)L59.56 a51.26 a42.50 a40.25 a
P45.23 b40.15 b39.21 a38.25 a
Total aggregates (%)L22.30 a28.90 a
P19.60 b24.50 b
Notes: a,b: columns with different letters denote significant differences at p < 0.05 (n = 2, LSD test).
Table
Table 5. Operational taxonomic units for soil bacteria and fungi.
Table 5. Operational taxonomic units for soil bacteria and fungi.
TreatmentBacterial (V3 + V4)
OTU Numbers		CoverageFungal (ITS1)
OTU Numbers		Coverage
L1549 a0.9974 a489 a0.9998 a
P1465 b0.9905 b464 a0.9998 a
Notes: L: rice cultivation under ridge tillage at two fertilizer depths; P: conventional rice cultivation. OTU: operational taxonomic unit; a,b: columns with different letters denote significant differences at p < 0.05 (n = 2, LSD test); ITS1: internal transcribed spacer-1 region.
Table
Table 6. The abundance and diversity of operational taxonomic units from soil samples.
Table 6. The abundance and diversity of operational taxonomic units from soil samples.
TreatmentACE
Index		Chao
Index		Simpson
Index		Shannon
Index		ACE
Index		Chao
Index		Simpson
Index		Shannon
Index
Bacterial (V3 + V4)Fungal (ITS1)
L1572.069 a1576.272 a0.005 a6.360 a493.631 a498.000 a0.115 a4.096 a
P1549.379 a1547.933 a0.005 a6.332 a468.986 a472.095 a0.078 a3.835 a
Notes: a: columns with different letters denote significant differences at p < 0.05 (n = 2, LSD test); ITS1: internal transcribed spacer-1 region.
Table
Table 7. Comparison of rice yield and yield components.
Table 7. Comparison of rice yield and yield components.
YearTreatmentNumber of
Panicles (m2)		Number of Grains Per PanicleSeed Setting
Rate (%)		Weight of
1000-Grain (g)		Rice Yield (kg/ha)
2016L629.33 a70.03 b93.77 a24.29 a10,027.13 a
P508.00 b79.36 a91.38 a25.23 a9294.45 a
2017L563.17 a78.93 a92.95 b25.81 a10,664.51 a
P508.33 b69.11 b95.25 a26.83 a8977.00 b
2018L532.17 a68.73 a86.95 a27.22 a8653.08 a
P447.67 b61.55 a83.41 a27.53 a6340.92 b
Notes: a,b: columns with different letters denote significant differences at p < 0.05.
Table
Table 8. Correlation between rice yield and alpha diversity of soil bacteria.
Table 8. Correlation between rice yield and alpha diversity of soil bacteria.
CorrelationOTUACE indexChao IndexSimpson IndexShannon Index
Weight of panicles0.989 **0.942 **0.947 **0.0930.545
Number of panicles per hill0.5550.4860.419−0.2910.595
Number of real grains0.981 **0.927 **0.931 **0.1330.51
Number of shattered grains−0.686−0.657−0.626−0.60.061
Number of empty particles0.884 *0.816 *0.7750.3260.312
Weight of real grain 0.979 **0.932 **0.932 **0.1640.482
Number of panicles per m20.7090.6550.593−0.1630.575
Number of grains per panicle0.7520.7350.7980.2310.283
Seed setting rate0.845 *0.818 *0.835 *0.4270.166
Weight of 1000-grain−0.619−0.559−0.5880.508−0.796
Yield0.971 **0.931 **0.922 **0.1720.464
* p < 0.05; ** p < 0.01.
Table
Table 9. Correlation between rice yield and alpha diversity of soil fungi.
Table 9. Correlation between rice yield and alpha diversity of soil fungi.
CorrelationOTUACE IndexChao IndexSimpson IndexShannon Index
Weight of panicles0.4550.4650.438−0.0520.394
Number of panicles per hill−0.212−0.183−0.1750.288−0.158
Number of real grains0.4520.4630.441−0.0450.389
Number of shattered grains−0.717−0.736−0.7520.272−0.589
Number of empty particles0.5050.5240.5190.0020.369
Weight of real grain 0.50.5110.489−0.0760.426
Number of panicles per m20.0210.0490.0550.1380.055
Number of grains per panicle0.5750.5630.523−0.1880.48
Seed setting rate0.6720.6830.681−0.2910.607
Weight of 1000-grain0.3180.3080.327−0.2440.169
Yield0.5160.530.513−0.1080.452
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Liu, L.; Cui, S.; Qin, M.; Chen, L.; Yin, D.; Guo, X.; Li, H.; Zheng, G. Effects of Continuous Ridge Tillage at Two Fertilizer Depths on Microbial Community Structure and Rice Yield. Agriculture 2022, 12, 923. https://doi.org/10.3390/agriculture12070923

AMA Style

Liu L, Cui S, Qin M, Chen L, Yin D, Guo X, Li H, Zheng G. Effects of Continuous Ridge Tillage at Two Fertilizer Depths on Microbial Community Structure and Rice Yield. Agriculture. 2022; 12(7):923. https://doi.org/10.3390/agriculture12070923

Chicago/Turabian Style

Liu, Lihua, Shize Cui, Meng Qin, Liqiang Chen, Dawei Yin, Xiaohong Guo, Hongyu Li, and Guiping Zheng. 2022. "Effects of Continuous Ridge Tillage at Two Fertilizer Depths on Microbial Community Structure and Rice Yield" Agriculture 12, no. 7: 923. https://doi.org/10.3390/agriculture12070923

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop