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Article

Effects of the Integrated Use of Dairy Cow Manure on Soil Properties and Biological Fertility

by
Ziyu Han
1,
Wenjun He
2,
Huading Shi
1,
Chen Wang
1,
Chenfeng Liu
1,* and
Yao Feng
3,*
1
Technical Centre for Soil, Agriculture and Rural Ecology and Environment, Ministry of Ecology and Environment, Beijing 100012, China
2
National Institute for Curriculum and Textbook Research, Ministry of Education, Beijing 100012, China
3
Chinese Research Academy of Environmental Sciences, Beijing 100012, China
*
Authors to whom correspondence should be addressed.
Sustainability 2023, 15(15), 11693; https://doi.org/10.3390/su151511693
Submission received: 4 May 2023 / Revised: 21 July 2023 / Accepted: 26 July 2023 / Published: 28 July 2023
(This article belongs to the Special Issue Soil Fertility and Nutrient Management for Agricultural Sustainability)
Browse Figures
Versions Notes

Abstract

:
The appropriate use of manure is important for the sustainable development of dairy farms. To identify more advantageous ways of using manure and key factors in the recycling process, this study investigated differences in soil fertility between solid and liquid manure waste recycling at an integrated farm. Both types of manure waste recycling promote soil fertility. However, solid manure exerted a more pronounced effect on soil fertility, especially on available phosphorus (P), which increased by 93.83%, but only 26.67% with liquid manure. As the amount of solid manure was increased, a clear logarithmic relationship (correlation coefficient = 0.90) formed between manure use and available P, indicating that P was a key index for manure recycling. Solid manure had a more positive influence on soil fertility in terms of microbial community change, as revealed by redundancy analysis and Pearson’s correlation analysis. The results of this study can be applied to most large-scale breeding farms, that the combination of solid and liquid manure fertilizer can be used to meet sustainable development goals. And the findings highlight solid manure as a key component for improving soil fertility.

Graphical Abstract

1. Introduction

As the primary component of agricultural economic development, animal husbandry ensures the supply of livestock products and increases farmer income. In recent decades, manure discharge has increased synchronously with the development of intensive dairy cow farming in developing countries. The prevalence of nutrients such as nitrogen (N) and phosphorus (P) in manure makes it a precious resource for sustainable agricultural development [1,2]. Meanwhile, nutrient loss caused by manure recycling is a serious challenge for the sustainable development of the breeding industry [3]. Therefore, it is crucial to identify a key element for monitoring and evaluating the recycling systems of dairy cow farms in terms of soil fertility.
Research performed to date has generally suggested that N, P, and chemical oxygen demand are key factors in determining whether nutrients are discharged or lost during manure recycling processes [4]. However, limited studies have comprehensively considered soil fertility as a factor in manure recycling, especially in actual field experiments. Therefore, this study focused on the relationships between manure application and soil fertility improvement. Manure has been shown in previous studies to improve soil fertility by altering soil nutrients [5,6,7], soil physical structure [8], and the microbial ecosystem [9,10].
Another considerable process associated with manure recycling is that generally after fermentation, dairy cow manure must be separated into liquid and solid components before being recycled [11], but the scientific use of the two forms of manure is usually ignored by farm managers, who instead consider only economic feasibility. Therefore, this study also compared the effects of two types of manure application on soil properties. Liquid manure can be used more easily as it can be mixed with irrigation water and used in pipeline irrigation systems, whereas solid manure is generally used as a raw material for organic fertilizer production or directly used as soil amendments [12]. Few studies have discussed the different effects of liquid and solid manures on soil fertility. Separated liquid manure was shown to be more effective in increasing soil test P than separated solid manure [13]. Moreover, the P levels in the subsurface soil were higher in liquid-manure-modified soil than in solid manure-modified soil [14]. P accumulation in soil was observed following some liquid and solid manure treatments in both bromegrass (Bromus inermis Leyss) and oat (Avena sativa L.) plantations, with higher soil exchangeable K found after liquid manure application, which decreased over time. Thus, liquid cattle manure was found to be better than solid cattle manure for promoting bromegrass and oat production [15]. However, on an integrated farm, choosing the most appropriate method for manure recycling is essential for sustainable development.
Because the sustainable development of the livestock and poultry industries requires a comprehensive consideration of economic and environmental factors, this study investigated an integrated farm to (a) discuss differences in the changes in soil fertility upon solid and liquid manure recycling, (b) evaluate effects of manure on microflora, and (c) determine key factors in manure recycling with the goal of improving soil fertility.

2. Materials and Methods

2.1. Dairy Cow Farm Information

This study investigated an integrated farm that raises more than 6000 dairy cows and has a 13 km2 cornfield to recycle cow manure. A plan view of the farm and its location are shown in Figure 1. The farm is located in Zhangye City, Gansu Province, China, which has a continental desert steppe climate and is a desert-oasis ecosystem. The soil on the farm is loess soil.
In 2008, the farm began reclaiming uncultivated land while also feeding dairy cows. The manure was sorted into solid and liquid components before being disposed of in solid and liquid fermentation devices. After fermentation, liquid manure was mixed with irrigation water and used in pipeline irrigation systems in fields l–4 and 11–14, whereas solid manure was transported by a tractor via a delivery system (Figure 1).

2.2. Materials

The experimental soil was collected from the integrated farm. Most dairy cow waste was utilized as nutrition for corn growth. To examine the convenience of this approach, three different recycling methods were used at the farm: liquid, solid, and integrated (both liquid and solid manure). Fresh dairy manure was treated by a solid–liquid separator, which adopted the principle of physical separation, effectively separate the solid and liquid in cow manure through rotation, extrusion, filtration, and other technologies. Then, after about 30 days of fermentation, the liquid waste was mixed with irrigation water into the sprinkler irrigation system, while the solid manure continued to be stored in the fermentation tank until it was applied as a base fertilizer in the next year. A combined fermentation agent, which consists of Bacillus, Saccharomyces, Lactobacillus, and other bacteria, was used to promote the fermentation of both liquid and solid manure. The basic chemical fertilizer used at the farm consisted of 0.098 kg/m3 urea, 0.023 kg/m3 urea phosphate, and 0.053 kg/m3 potassium chloride, which means that equal amounts of the chemical fertilizer were used on all fields annually. The distribution of the three different manure recycling methods in the cornfield is shown in Figure 1, with the cumulative amount of manure applied per unit area of the manure in each field shown in Table 1.
Soil samples from three control (CK) groups were obtained on uncultivated land around the farm. Each field yielded 75 soil samples, which were combined into 3 samples. All samples were collected in August 2022. Three soil samples were collected randomly from near the center of each field. Each sample was fixed with five random soil samples within 5–10 m (depending on the field size) of the central point, and each sub-sample was mixed by five random soil samples from around 1–3 m. To determine the differences between plowed and deep layers, soil was collected from depths of 0–20 cm (plowed layer) and 20–40 cm (deep layer) for each sample. The soil samples were transported to the laboratory in sealed containers stored at −4 °C. Half of each sample was air-dried, stored in a cool dry place, and used for physical and chemical tests. The other half was stored in a freezer at −80 °C for DNA extraction. All tests were completed within 3 weeks. The basic properties of the original soil are presented in Table 2.

2.3. Detection Methods

2.3.1. Total N

Total N was measured using a modified version of the Kjeldahl method. Under the action of sodium thiosulfate, concentrated sulfuric acid, perchloric acid, and a catalyst, the total N in the soil was converted to ammonium nitrogen via a redox reaction. The ammonia extracted from the alkaline distillation of the dissolved solution was absorbed by boric acid and titrated against a standard hydrochloric acid solution. The total N content in the soil was calculated from the dosage of the standard hydrochloric acid solution required.

2.3.2. Available P

Available P was detected via citric acid extraction–vanadium platinum yellow colorimetry. At a certain acidity, P in the solution reacts with vanadate and platinate to form a yellow ternary heteropoly acid. Over a certain range, the yellow color is positively correlated with the concentration of P, which was measured using a spectrophotometer (V-560; Metash, Shanghai, China).

2.3.3. Available K

Available K was detected using a flame photometer. Soil available K includes exchangeable K and water-soluble K. The soil available K was extracted in a 1 mol·L−1 neutral acetic acid solution. The ions in the solution were exchanged with the K ions on the soil colloid surface and entered the solution with the water-soluble K ions. K in the extract was measured directly using a flame photometer (F-500; Metash, Shanghai, China).

2.3.4. Soil Organic Matter

Soil organic matter was detected using potassium dichromate. The organic carbon in the soil was quantitatively oxidized with a potassium dichromate sulfuric acid solution under heating in an electric sand bath. The remaining potassium dichromate was titrated with a ferrous sulfate standard solution, with silica used as the additive reagent for blank calibration. Based on the difference in the quantity of oxidizer before and after oxidation, the amount of organic carbon was calculated and then multiplied by a coefficient of 1.724 to calculate the content of organic matter in the soil.

2.3.5. Soil pH

Soil pH was determined using a pH meter. First, 10 g of soil was passed through a 1 mm mesh and prepared in a 25 mL beaker, to which 10 mL of a 0.01 mol·L−1 CaCl2 solution was added, mixed completely with the soil. After allowing it to stand for 30 min, a pH meter (PHSJ-4A, Shanghai Leici, Shanghai, China) was used to determine the pH.

2.3.6. Soil Particle Size

Soil particle size was analyzed with a laser particle analyzer (LS-POP9a; Omec Technology, Leeds, UK).

2.3.7. Soil Bulk Density

Soil bulk density was determined using thermogravimetry, and particle diameter was measured via laser particle analysis (LS-POP9a; Omec Technology, UK).

2.3.8. DNA Extraction and High-Throughput Sequencing

For the collected soil samples, DNA extraction was performed using a Power Soil DNA Isolation Kit (MOBIO Laboratories, Inc., New York, NY, USA) in accordance with the manufacturer’s instructions. The DNA quality, including integrity, purity, and concentration, was evaluated using a 1% agarose gel and a Nanodrop spectrophotometer (Nanodrop Technologies Inc., Wilmington, DE, USA). For the extracted genomic DNA, the 16S rDNA V3–V4 bacterial regions were amplified using the forward primer 5′-CCTAYGGGRBGCASCAG-3′ and reverse primer 5′-GGACTACNNGGGTATCTAAT-3′.
PCR reactions were performed in triplicate. Triplicate PCR products were mixed and purified using an ENZA Gel Extraction Kit (Omega Bio-Tek Inc., Norcross, GA, USA). Then, the amplification products were subjected to Illumina MiSeq high-throughput sequencing and analysis. The sequencing and bioinformatic services were provided by Shanghai Majorbio Bio-pharm Technology Co., Ltd. (Shanghai, China).

2.4. Bioinformatics and Statistical Analysis

The index and adapter tags on raw reads obtained from the Illumina MiSeq platform were trimmed, and reads with low-quality scores (<20) and those in nonamplified regions were removed using QIIME (http://qiime.org/index.html, accessed on 12 February 2023). The chimeras in the sequences were identified and removed using DADA2, and the eligible sequences were clustered into operational taxonomic units at a 97% read similarity. The bacterial sequences were comparatively analyzed using the Silva (http://www.arb-silva.de/, accessed on 23 February 2023) databases. The microbial community diversity was analyzed using the bacterial alpha diversity (including the Chao1 and Shannon indices) and beta diversity for the soil samples using QIIME2. Principal coordinate analysis (PCoA) was conducted using the vegan packages in R to visualize bacterial composition in all samples based on the Bray–Curtis distance. Redundancy analysis (RDA) was performed in Conoco 5.0 to compare the bacterial composition and physicochemical properties among the treatments. Other graphs were created using Origin 2019 (OriginLab, Northampton, MA, USA).

2.5. Mathematical Analysis

Soil nutrient content and fertilizer amounts were often log-transformed using either natural logarithms or base 10 logarithms to create a more linear relationship and reduce the influence of the highest concentrations. The positive correlation between them can be described in Equation (1):
Cf = C0 × eb(F0)
where C0 and Cf are the initial soil nutrient content and the soil nutrient content under the fertilizing conditions, respectively. F0 refers to the liquid or solid recycled dairy manure, and b is a coefficient.

3. Results and Discussion

3.1. Changes in Soil Nutrition

The fertility-related characteristics of the soil are shown in Figure 2. With the increasing amount of manure, the changes in total N, available P, available K, and organic matter differed in both plowed and deep soil layers.

3.1.1. Total N

As presented in Figure 2a, the overall tendency of total N increased with the increasing amount of manure application. For the liquid manure group, there was a clear increase in the plowed layer, from 462.26 to 837.25 mg/kg, whereas the values for the solid manure group and the integrated manure group fluctuated between 508.44 and 801.11 mg/kg. Compared with original soil (CK), the total N was increased by approximately 48.50% in the plowed layer and 31.18% in the deep layer. Recent evidence suggests that the main form of N in manure is organic N and that ammonium nitrogen mostly exists in liquid waste (biogas slurry) after solid–liquid separation [16]. This might explain the accumulation of N when using liquid manure. In contrast, no consistent growth trend in the deep layer of soil was observed in the liquid group, but the N content increased with the addition of solid manure (including the solid group and integrated group). For the process of nitrogen uptake by crops, organic N from manure must first be converted into inorganic N, indicating that the release of N or any other nutrient from manure depends on the rate of mineralization [7], which might be accelerated by the manure. Meanwhile, solid manure can significantly improve soil pore structure and soil aggregation [17], leading to the increases of total N, available P, available K, and organic matter in the deep layer of soil, as shown in Figure 2. Manure is not only applied to crop land but also eventually leaks into the soil and water environment; therefore, in terms of environmental and ecological protection, the total N might be one of the most important factors to be solved.

3.1.2. Available P

The change in available P is shown in Figure 2b. In almost all cases, the available P content increased as manure usage increased. This rise was most noticeable in the solid group, in which the P content in the plowed layer increased from 68.05 to 108.65 mg/kg. Available P increased by 46.59% and 210.87% in the plowed and deep layers, respectively, compared with the corresponding layers of the original soil. The deep layer has less available P than in the ploughed layer, although the difference for P is smaller than that for N. The N/P ratio is narrower at high values [18], but crops intake much more N than P from the manure [19]; thus, P accumulation is inevitable. Some studies have also reported that, compared with no manure, the application of manure increased soil P by 10-fold [20]; crops generally can utilize available P effectively, and may access unavailable’ P pools [21]. Moreover, if a large amount of organic matter enters the soil, the organic matter is decomposed to humic acid, which can activate P in the soil; concurrently, humic acid ions would compete for adsorption with phosphate ions, leading to increased free-state P in soil [22].

3.1.3. Available K

The fluctuation in available K is shown in Figure 2c. In the liquid group and the integrated group, the original soil’s composition was similar to that of the treated soil; however, the use of manure can enhance the availability of K [20]. In terms of the K utilization in high-K soil (the available K of the original soil was about 149.17 mg/kg), activation by manure may have a significant relationship with the amount of available K added by manure. For the solid manure group in this study, the growth of available K was closely related to solid manure usage, which might have been due to the changes in the soil structure caused by the application of solid manure. Such changes can lead to an enrichment in pore formation and an increase in soil weight by volume, allowing K salts to be adsorbed more stably by soil particles and slowing the rate of release of available K.

3.1.4. Organic Matter

Figure 2d depicts the effects of manure use on soil organic matter. The findings indicate that compared with the original soil, all three groups had significantly enhanced soil organic matter, but no special pattern was identified for each group as the amount of manure increased. For example, when increased manure was applied in the solid group, organic matter first increased and then decreased, fluctuating between 1.37 and 1.70 mg/kg. Soil organic matter is one of the most important indices of fertility, although the changes in exogenous organic matter are complicated [23]. First, the application of animal manure results in a higher amount of soil organic matter compared with inorganic fertilizer, which is the most basic cause of the increase in organic matter [20]. Second, in stimulated soil, microorganisms secrete a high amount of enzymes, which might enhance the decomposition of soil organic matter. Third, adding animal manure to the soil can slow the process of soil organic matter depletion [24]. From the standpoint of sustainable agricultural development, soil organic matter not only maintains soil fertility but also improves integrated environmental quality by reducing soil erosion, reducing atmospheric CO2 from soil, and reducing nonpoint source pollution [25].
In the integrated farm liquid manure and solid manure were used synchronously due to the fact that they were produced by dairy cows. Cows produced one ton of urine for every three tons of manure produced, but after solid liquid separation, the solid-to-liquid ratio was approximately about 1:10. To observe differences among the three different approaches to manure utilization during this process, box plot diagrams were constructed and are presented in the last column of Figure 2. The results showed that the plowed layer of soil in the solid group had the highest mean value of all nutrients among all plowed layers, indicating that although much less solid manure was used compared with liquid manure, it had a more significant impact on the three soil properties. For instance, available P after the application of solid manure increased by approximately 93.83% compared with that in the control group, whereas for liquid manure, the increase was approximately 26.67%. However, the differences in the average value of available K among the three groups and CK were insignificant owing to the high content of K in the original soil. Therefore, manure had a significant promoting effect on soil fertility. Particularly, solid manure had the greatest positive effects on total N, available P, and available K. Solid content such as cellulose and humus substances introduced into soil by solid manure fundamentally changed the soil structure.

3.1.5. Nutrient Accumulation

The above results reveal that the amount of fertilizer might positively correlate with the soil nutrient content. Regression approaches assume that there is a linear relationship between a dependent variable (soil nutrient content) and an independent variable (fertilizing amount). The linear relationships between fertilized manure accumulation and soil fertility properties are shown in Figure 3; and the related coefficients are presented in Table 3. The results reveal that liquid manure had almost no clear correlation with the four types of soil fertility-related properties because the coefficient of association R2 was below 0.5. For solid manure, the coefficient of association R2 for the linear relationship between available P and solid manure was 0.90, indicating that the amount of solid manure was strongly correlated with the amount of available P in the soil. The poor diffusibility of P may result in P accumulation through manure recycling, especially for solid manure waste, which reduces phosphorus diffusibility [13,26]. In addition, because only a small amount of P compounds can be absorbed by plants [15], the risk of P accumulation and immobilization during manure recycling should be considered. Moreover, excessive P in soil can promote crop respiration and the consumption of sugar and energy stored in crops, resulting in a reduction in agricultural production; therefore, the P might be a key nutrient factor during manure recycling.
According to the results of China’s second national survey on pollution sources, the breeding industry produced 42% and 56% of total N and P, respectively. A comprehensive consideration of this research revealed that P was correlated with the cumulative use of manure. Therefore, from the perspectives of the sustainable development of agriculture and the protection of aquatic environments, P can be considered a key element in evaluating whether a manure application method is optimal.
The comprehensive use of both liquid and solid manure can simultaneously resolve the issue of pollution from breeding manure and stabilize soil fertility. Regarding soil properties, the comprehensive recycling methods significantly increased organic matter and available nutrients, which can not only boost crop income but also improve the soil environment [27]. Moreover, the long-term application of organic matter fertilizer can help produce green, pollutant-free organic products [28], and it has been proved that crop yield can be sustained for many years after manure application ceases, due to the residual effect of manure [29].

3.2. Changes in Soil Physical and Chemical Properties

Physical and chemical properties are significant features of soil. This section describes an examination of the changes in plowed soil bulk density, pH, and soil particle diameter. Manure recycling decreased both soil bulk density and pH value as presented in Figure 4. In the liquid manure group, the pH and soil bulk density were decreased by 5.12% and 6.33%, respectively, compared with those in the CK group, whereas the percentages were 8.97% and 18.89% for solid manure, and 7.69% and 10.83% for liquid manure, respectively. Soil pH is controlled and driven by various processes and parameters, including soil composition, minerals, and soil microbial properties. The pH level greatly affects the cycling and availability of soil nutrients, enzymatic activity, and soil health [30]. In this study, the manure was composted before the solid–liquid separation, which produced organic acids and inorganic acids at levels higher than those of ammonia produced by ammonification, whereas the pH of the composted manure was decreased [31]. Because solid manure may continue the anaerobic fermentation process after the ploughing of the cultivated soil, it has a greater influence on soil pH. A meta-analysis reported that green manure decreased soil bulk density by 5.6% [32], which was less than that reported in this study, especially compared with solid manure. This difference might have occurred because cattle manure contains more lignin and cellulose.
The change in soil particle size provided further evidence that solid manure had a greater influence on soil physical properties (Figure 5). In the liquid manure group, it was difficult to determine whether manure recycling could increase particle size; however, in the solid manure group, the distribution of particles within the size range of 100–500 μm was greater than that in the control group. For the liquid and solid groups, the change was not obvious. The integrated use of liquid and solid manure wastes may result in a more complete intestinal microbiome, which might lead to a better ability to digest lignin and cellulose. Combined with previous changes in organic matter, the effects of manure and particle size on soil organic content interacted, suggesting that manure might influence soil organic matter by mediating soil aggregation [33]. An increase in soil organic matter content, in turn, improves aggregation because soil organic matter is an important binding agent for soil particles, hence the addition of manure might increase large aggregates by gluing smaller aggregates with organic binding agents [34]. Manure applications can improve soil pore structure, allowing the soil to store more water and nutrients, increasing crop productivity [35]. Thus, soil particle size and aggregation improvement through manure application is an important factor for improving soil fertility.

3.3. Changes to the Soil Microbial System

Microbial community diversity is an important indicator of soil ecological function [36]. To compare the effects of different manure recycling methods on soil ecological function, the richness and evenness of the microbial community were determined. In general, the patterns of changes in richness and evenness contrast with each other [37]. Alpha diversity can illustrate the microbial diversity of a single sample. The Chao1, Shannon, and Simpson indices represent richness, diversity, and evenness, respectively. These three indices are shown in Figure 6. Regarding species richness, the Chao1 index of soils with the three manure recycling methods was significantly higher than that of the CK group, indicating that manure recycling significantly increased the total microbial population. Another study found that the rise was a common phenomenon [38] owing to the large amount of nutrients supplied by the manure. Similarly, changes in the Shannon index indicated an increase in the diversity of microbial species, which might be attributed to the introduction of foreign species into the soil [39], or affected by soil pH [40].
However, the Simpson index results were different, indicating that the group that received solid manure had better species evenness, which might due to the high particle size level affecting the accessibility of organic compounds for microbes and extracellular enzymes by changing the proportion of small pores, due to the accumulation of soil organic matter in a relatively large pore structure [41]. Moreover, the group to which solid manure was applied had a wide range of fluctuation, especially among the solid groups, which could be attributed to enhanced soil heterogeneity due to solid manure recycling. It can be concluded that all three recycling methods can improve microbial community diversity, with solid and liquid integrated recycling having achieved the greatest improvement.
Research performed to date has proved that various bacterial species can positively impact plant growth and improve soil sustainability [42,43]. Another benefit of improving microorganism diversity is the facilitation of fixing atmospheric nitrogen in the soil by crops, which is then available for the crops themselves [44]. It can, thus, be concluded that the promoting effect of manure on microbial diversity is crucial for the development of sustainable agriculture.
In contrast to the intraspecific diversity shown by the alpha index, beta analysis compared the microbial community structure and composition of multiple groups. Figure 7 presents the PCoA results based on the Bray–Curtis distance [37]: PCoA1 and PCoA2 accounted for 25.33% and 14.18% of the variance, respectively. The PCoA showed that compared with soil in the CK group, the bacterial community structure of manure used soil was clearly different. Recycling manure can improve soil microbial diversity owing to the introduction of other microbes [39]; however, because the introduced microbes were homogeneous and derived from the same cow manure in this study, the change in the microbial diversity of soil differed depending on the recycling method. In particular, the application of liquid manure resulted in a greater difference in the soil microbial community structure than the other treatments.
A genus-level species composition analysis was performed (Figure 8) and the species composition of the top 20 dominant bacteria is presented below. The results indicated that compared with findings in the CK group, the use of manure appeared to improve the relative abundance of dominant bacterial genera, such as Sphingomonas, Pseudarthrobacter, Skermanella, and Gemmatimonadaceae. In contrast, the application of manure had a negative influence on Pontibacter, 0319-7L14, and Bacillus. Studies have shown that Sphingomonas could degrade organic matter [45], Pseudarthrobacter can efficiently improve the activity of urease and acid phosphatase [46], and Skermanella and Gemmatimonadaceae can participate in the fixation of N and phosphate [47]; therefore, manure recycling has a significant regulatory effect on the microorganisms and bioactivity of the soil in the present study.
Some of the dominant bacteria participating in nitrification, such as Nitrosospira and Bryobacter, are ammonia-oxidizing bacteria, whereas JG30-KF-CM45, Nitrospira, and Candidatus nitrosocosmicus are nitrobacteria; hence, the application of manure enhanced the richness of the dominant bacteria. Solid manure had a more significant influence on ammonia-oxidizing bacteria, whereas liquid manure greatly affected nitrobacteria; this might be the primary cause of the difference in the plot distribution in liquid manure in the PCoA. It had been proved that some microorganisms preferred to inhabit relatively large aggregates [48]. In addition, manure application promoted the richness of organic-matter-degrading bacterial species. Manure-introduced microorganisms included species capable of improving plant growth via plant hormone stimulation and root elongation (including the formation of root hairs and lateral roots) [49,50], implying that the impact of manure on soil microbial diversity may have a significant benefit for the sustainable development of agriculture.
RDA and Pearson’s correlation analysis were performed to determine the relationship between soil composition and fertility. Solid manure exerted the highest effect on soil fertility, whereas liquid manure exerted the lowest effect (Figure 9). Total N and available K were positively correlated with Pseudarthrobacter, Gemmatimonadaceae, and Bryobacter abundance; these findings were similar to those of other studies [41,42]. Pseudarthrobacter can promote the enzymatic activity of phosphatase, which can convert organic P to available inorganic P [51], whereas Gemmatimonadaceae can accumulate polyphosphate to prevent the loss of P [52]. The biofunction of microbes may be an essential reason for the increase in available P upon manure recycling. Soil organic matter had a significant positive correlation with Pseudarthrobacter and a significant negative correlation with Bacillus, which might have been due to the manure altering the richness of the soil microorganisms.

4. Conclusions

For the sustainability of global agricultural development, it is essential to improve the environmental performance of the livestock sector. In this study, differences in soil fertility caused by solid and liquid manure recycling were discussed. The results of this study suggested that manure significantly improves soil fertility.
The fertility indices, including total N, available P, available K, and organic matter, showed a positive relationship with the amounts of liquid and solid manure, but only available P had a strong correlation with the application of solid manure. Therefore, it was deduced that available P was a key element during manure recycling in terms of improving soil fertility.
The microflora in the liquid manure group differed from that in the solid manure and CK groups, which may have been due to the stronger effect of liquid manure on nitrobacteria. RDA and Pearson’s correlation analysis indicated that solid manure exerted the strongest positive effect on soil fertility, followed by integrated and liquid manure. In addition, nutrients were positively correlated with bacteria such as Pseudarthrobacter, Gemmatimonadaceae uncultured, and Bryobacter.
The results of this study indicated that solid manure recycling could significantly improve soil fertility; therefore, the fertilization method used on integrated farms should be adjusted to ensure the widespread use of solid manure. Moreover, the native bacteria, such as Pseudarthrobacter, were found to be positively correlated with nutrient indices. Such bacteria can be cultured and used experimentally for manure recycling to further improve manure application technology.

Author Contributions

Z.H., writing—original draft; W.H., data curation and formal analysis; H.S., resources; C.W., validation and visualization; Y.F., writing—review and editing; C.L., supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by [the National Natural Science Foundation for Young Scientists of China] grant number [41907108].

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data underlying this article will be shared on reasonable request to the corresponding author.

Acknowledgments

All the authors thank Huarui Agricultural Company for technical and financial support.

Conflicts of Interest

There are no conflicts of interest to declare.

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Figure 1. Plan view and location of the investigated farm.
Figure 1. Plan view and location of the investigated farm.
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Figure 2. Comparison of soil fertility-related characteristics upon different recycling methods: (a) total N; (b) available P; (c) available K; and (d) organic matter (P: ploughed layer; D: deep layer; CK: control group).
Figure 2. Comparison of soil fertility-related characteristics upon different recycling methods: (a) total N; (b) available P; (c) available K; and (d) organic matter (P: ploughed layer; D: deep layer; CK: control group).
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Figure 3. Linear relationship between fertilized manure accumulation and soil fertility properties: (a) liquid manure; (b) solid manure.
Figure 3. Linear relationship between fertilized manure accumulation and soil fertility properties: (a) liquid manure; (b) solid manure.
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Figure 4. Changes in pH and bulk density of soil (pH is written on top of the bars).
Figure 4. Changes in pH and bulk density of soil (pH is written on top of the bars).
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Figure 5. Influence of manure recycling on changes in soil particle size.
Figure 5. Influence of manure recycling on changes in soil particle size.
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Figure 6. Alpha indices: Chao1 (a), Shannon (b), and Simpson (c) indices of the soil treated with recycled manure.
Figure 6. Alpha indices: Chao1 (a), Shannon (b), and Simpson (c) indices of the soil treated with recycled manure.
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Figure 7. Principal coordinate analysis (PCoA) plot showing the bacterial community composition among different treatments based on the Bray–Curtis distance matrix.
Figure 7. Principal coordinate analysis (PCoA) plot showing the bacterial community composition among different treatments based on the Bray–Curtis distance matrix.
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Figure 8. Composition of bacterial species at the genus level with different species: (a) histogram showing the composition of bacterial species; (b) heat map showing the composition of the dominant bacterial species.
Figure 8. Composition of bacterial species at the genus level with different species: (a) histogram showing the composition of bacterial species; (b) heat map showing the composition of the dominant bacterial species.
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Figure 9. RDA (a) and Pearson’s correlation analysis (b) of soil nutrition characteristics and dominant bacterial species.
Figure 9. RDA (a) and Pearson’s correlation analysis (b) of soil nutrition characteristics and dominant bacterial species.
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Table
Table 1. Cumulative usage of manure in each field.
Table 1. Cumulative usage of manure in each field.
Soil Sample CodeManure Recycling MethodCumulative Usage of Liquid (t/Area)Cumulative Usage of Solid (t/Area)
1Liquid only (L)2150
23790
34080
44330
54650
6Solid only (S)06.7
7031.2
8044.4
9083.9
10077.5
11Liquid & solid (L&S)17.38
12352.79
13429.39.6
1469.212.8
15CK00
1600
1700
Table
Table 2. Basic properties of the original soil.
Table 2. Basic properties of the original soil.
Properties pHBulk Density (m3/kg)Total N
(mg/kg)		Available P
(mg/kg)		Available K
(mg/kg)		Organic Matter
(mg/kg)
Original soil7.88.9415.6140.62149.170.81
Table
Table 3. Coefficient b and correlation coefficient R2 of the linear relationship between fertilized manure accumulation and soil fertility properties.
Table 3. Coefficient b and correlation coefficient R2 of the linear relationship between fertilized manure accumulation and soil fertility properties.
Soil Fertility PropertiesLiquidSolid
−bR2−bR2
Total N0.0011 0.48 0.0081 0.16
Available P0.0016 <0.000010.0119 0.90
Available K0.0014 <0.000010.0142 0.26
Organic matter0.0013 <0.000010.0013 <0.00001
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Han, Z.; He, W.; Shi, H.; Wang, C.; Liu, C.; Feng, Y. Effects of the Integrated Use of Dairy Cow Manure on Soil Properties and Biological Fertility. Sustainability 2023, 15, 11693. https://doi.org/10.3390/su151511693

AMA Style

Han Z, He W, Shi H, Wang C, Liu C, Feng Y. Effects of the Integrated Use of Dairy Cow Manure on Soil Properties and Biological Fertility. Sustainability. 2023; 15(15):11693. https://doi.org/10.3390/su151511693

Chicago/Turabian Style

Han, Ziyu, Wenjun He, Huading Shi, Chen Wang, Chenfeng Liu, and Yao Feng. 2023. "Effects of the Integrated Use of Dairy Cow Manure on Soil Properties and Biological Fertility" Sustainability 15, no. 15: 11693. https://doi.org/10.3390/su151511693

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