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Article

Toward Green Farming Technologies: A Case Study of Oyster Shell Application in Fruit and Vegetable Production in Xiamen

by
Yan Wang
1,
Mengya Ji
1,
Min Wu
1,
Ling Weng
1,
Yongming Wang
2,
Lingyi Hu
1 and
Min-Jie Cao
1,*
1
College of Ocean Food and Biological Engineering, Jimei University, Xiamen 361021, China
2
Xiamen Mata Ecology Co., Ltd., Xiamen 361006, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(1), 663; https://doi.org/10.3390/su15010663
Submission received: 10 November 2022 / Revised: 25 December 2022 / Accepted: 26 December 2022 / Published: 30 December 2022
Browse Figures
Versions Notes

Abstract

:
In recent decades, due to the intensification of human production and living activities, the process of soil acidification in China has been greatly accelerated, which has become an important factor limiting the sustainable development of agriculture. In this paper, an oyster shell soil conditioner prepared from discarded oyster shells was applied to the field and Shixia longan and chives were used as experimental objects for field experiments. Each crop was comprised of two groups. The application amount of longan in the control group was 0 kg/tree, and that in the experimental group was 8 kg/tree. The distribution of chives applied in the control group was 0 kg/m2, while that in the experimental group was 0.65 kg/m2. The results showed that, after the application of oyster shell soil conditioner, the soil pH value in Shixia longan experimental field increased by 1.30 units, and the content of soil organic matter, alkali hydrolyzed nitrogen and exchangeable calcium increased by 57.63%, 71.98%, and 49.13%. At the same time, the single fruit weight of Shixia longan increased by 6.37%, the soluble sugar content increased by 16.18%, and the titratable acid of the fruit decreased by 10.95%. Compared with the control group, the soil pH value of chives increased by 1.03 units, its yield increased by 57.8%, and various morphological indicators were improved. The results showed that the application of oyster shell soil conditioner could significantly improve the soil acidification of Shixia longan and chives, improve soil fertility, and effectively improve the yield and quality of fruits and vegetables.

1. Introduction

About 38% of the soil in the world has been degraded to varying degrees, and this trend is still spreading [1,2,3]. Soil degradation manifests in the loss of soil organic matter, unbalanced elements, decreased fertility, acidification, and many other issues [4,5]. Fujian Province is located in the southeast coastal area of China. The widely distributed red soil and abundant precipitation lead to strong soil leaching, which causes a large amount of loss of alkaline base ions in the soil. H+ is absorbed by soil colloids, causing soil acidification. Soil acidity and alkalinity result from the interaction of soil parent material, climate, biology, and human activities. Actually, the process of soil acidification caused by natural factors is very slow. However, in recent decades, soil acidification has been greatly accelerated due to the impact of human production and living activities [6,7]. Among them, acid deposition and improper agricultural measures are the main reasons for increasing soil acidification [8,9,10,11]. When the soil pH < 6, the availability of Fe, Mn, Cu, Zn, and other elements in the soil will be activated, leading to the accumulation of heavy metals in crops, thereby endangering human health. In strongly acidic soil with pH < 5.5, the content of exchangeable Al3+ can account for more than 90% of the cation exchange capacity, and it is easy to free Al3+, causing aluminum toxicity and adverse effects on the growth and development of crops [12,13]. The most direct manifestation of soil environment deterioration is that it affects the growth and development of crops, reduces crop yield and quality [14], and leads to farmers’ income reduction. Therefore, mitigating soil acidification and improving soil environmental quality are of great significance for increasing crop yield, quality, and efficiency.
Because of their wide geographical distribution, short growth cycle, and high yield, oysters occupy an important position in the world and China’s mariculture industry [15,16]. According to statistics, the total yield of oyster mariculture in China reached 5.82 million tons in 2021, of which the total yield in Fujian Province was 2.11 million tons [17]. In 2021, the yield of oyster shells in Fujian Province was estimated to exceed 1.4 million tons (taking oyster shells as 70% of the total mass of oysters). When the oyster shells are directly discarded as garbage [18,19], the oyster meat and liquid remaining in the shells are prone to corruption and deterioration, breed bacteria, and cause the growth of insects, which will lead to a series of environmental and health problems [20,21]. Thus, proper treatment of oyster shells is also an important problem puzzling the government and relevant enterprises.
On the other hand, China is the largest planting area and the highest total yield of longan in the world [22]. Longan is one of the subtropical fruits that Fujian Province focuses on. Tong’an District of Xiamen City is a famous major longan-producing area in China, but the increasingly serious soil acidification problem has led to continuous fruit cracking problems (especially Shixia longan), and the fruit quality has been gradually decreasing. In addition, chive, as a common seasoning vegetable, is often used in various restaurants and home kitchens, so the demand is great. Chive is suitable to grow in neutral soil, but its yield is seriously affected due to soil acidification.
Through previous studies, we found that oyster shells can form a honeycomb-like pore structure after high-temperature calcination, which is the basis for the oyster shell to form a good adsorption capacity. The main component in oyster shells is CaCO3 together with trace metal elements. CaCO3 will be partially converted into CaO during calcination. In our previous studies, calcined oyster shells were used as a soil conditioner for ‘Guanxi’ pomelo [23], ‘Chuntao’ tomato [24], and ‘Nandao seedless’ litchi [25]. After a one-year experiment, compared with the control group, the soil pH value of ‘Guanxi’ pomelo increased by 1.1 units, and the organic matter increased by 27.7%. Soil samples in the ‘Chuntao’ tomato exhibited that the content of exchangeable calcium in the experimental group was increased by 10.45%. After applying oyster shell soil conditioner to ‘Nandao seedless’ litchi, the soil pH value of the experimental group was 1.36 units higher than that of the control group. The contents of organic matter, alkali hydrolyzed nitrogen and exchangeable calcium in the experimental group increased by 48.26%, 69.19%, and 31.78%. The application of oyster shells can also fix the carbon element in the soil, which is conducive to carbon neutralization. At the same time, it solves the problem of waste disposal in oyster processing enterprises and achieves the goal of cleaner production as well as marine resource reutilization.
In this study, oyster shells calcined at a high temperature (800 °C) for 30 min were used as raw materials to prepare soil conditioner, which was then applied to the soils of Shixia longan and chive. The application of oyster shell soil conditioner was expected to neutralize soil acidification, improve the yield and quality of fruit and vegetable, and the results will provide an experimental basis for the high-value utilization of oyster shells.

2. Materials and Methods

2.1. Materials

Calcined oyster shell soil conditioner (pH 9.0–9.5) was provided by Xiamen Mata Ecology Co., Ltd. (Xiamen, China) Its basic chemical composition is shown in Table 1.
The tested fruit was Shixia longan. The soil type of the experimental field was red soil, and the tested soil was rhizosphere soil. The control group of ‘Shixia’ longan was cultured without the addition of oyster shell soil conditioner.
The tested crop was chive, which was kept by a farmer. The soil type of the experimental field was red soil.

2.2. Test Design

2.2.1. Shixia Longan Experimental Field

Shixia longan experimental field was located in Zaoshui Village, Tingxi Town, Tong’an District, Xiamen, Fujian Province (24°83′46″ N, 118°17′42″ E). The experimental field was characterized as a subtropical marine monsoon climate with an average altitude of 215 m, annual mean temperature of 24 °C, and annual mean precipitation of 1800 mm; the total duration of sunshine throughout the year was 2124 h, so the light and heat were sufficient.
The experimental field covers an area of approximately 2 ha, with a total of 530 Shixia longan trees, an average tree age of 31 a, an average tree height of 3.5 m, an average crown diameter of 3 m, and row spacing of 5 m × 5 m. According to the measurement, the initial soil pH value of the experimental field was 4.57, the organic matter content was 24.10 g/kg, the alkali hydrolyzed nitrogen content was 49.93 mg/kg, and the soil exchangeable calcium content was 8.06 cmol/kg.
Field experiments began in December 2021, and the oyster shell soil conditioner was applied to Shixia longan in March 2022. The experiment ended in August 2022. The application amount of oyster shell soil conditioner was determined by the application amount used in previous field experiments, the fertilization experience of fruit tree farmers, the age and crown size of fruit trees, and other factors. The experiment was set up with 2 application amounts of oyster shell soil conditioner: control group (0 kg/tree) and application of oyster shell soil conditioner (the experimental group, 8 kg/tree). The application method of oyster shell soil conditioner was spreading. The application area was a round area with a radius from the trunk to the drip line. Each treatment applied the same amount of organic fertilizer and a small amount of nitrogen, phosphorus, and potassium chemical fertilizer in the same way. The field management was carried out according to the conventional method (Figure 1).

2.2.2. Chive Experimental Field

The chive experimental field was located in Ernong Community, Houxi Town, Jimei District, Xiamen, Fujian Province (24°39′7″ N, 118°1′17″ E). The experimental field was characterized as having a subtropical marine monsoon climate with an average altitude of 45 m, annual mean temperature of 22.3 °C, and annual mean precipitation of 1167 mm; the light and heat were sufficient.
The area of the experimental field was 3.15 m2/group, and the row spacing was 25 × 25 cm. According to the measurement, the initial soil pH value of the experimental field was 6.39, the organic matter content was 31.78 g/kg, the alkali hydrolyzed nitrogen content was 133.89 mg/kg, and the soil exchangeable calcium content was 12.37 cmol/kg.
The experiment began in December 2021, and the oyster shell soil conditioner was applied to the chives at the seedling stage on 5 January 2022. The experiment ended on 27 February 2022. The application amount of oyster shell soil conditioner was determined according to the application amount of previous field experiments. The experiment was set up with two application amounts of oyster shell soil conditioner: the control group, (0 kg/m2) and the experimental group (0.65 kg/m2). The application method of oyster shell soil conditioner was spreading, and the other field management method was conventional (Figure 2).

2.3. Test Method

2.3.1. Collection of Soil Samples

Collection of Soil Samples of Shixia Longan

The soil samples of the experimental field were collected in December 2021 (before the application of the soil conditioner), May 2022 (after application, the flowering period of Shixia longan), and August 2022 (after application, maturing period). Each group collected soil samples from six longan trees. The five-point sampling method was adopted for soil collection. After removing the topsoil on the surface, soil layer samples of 0–20 cm near the tree crown drip line were collected. Four points were taken from each tree, bagged, and mixed evenly. After being transported to the laboratory, soil samples were placed in a cool place for natural air drying to avoid direct sunlight. After the air-dried soil was sieved, its basic physical and chemical indexes were analyzed.

Collection of Soil Samples of Chives

The soil samples of the experimental field were collected in January 2022 (before the application of the soil conditioner) and February 2022 (after application and after maturing of chives). The S-type sampling method was adopted. After removing the topsoil on the surface, 6~20 cm deep topsoil samples were collected with a soil sampler and put in plastic bags. After the samples were transported to the laboratory, they were placed in a cool place for natural air drying to avoid direct sunlight. After the air-dried soil was sieved, its basic physical and chemical indexes were analyzed.

2.3.2. Determination of Soil Physical and Chemical Indexes

Soil pH value was measured by potentiometry. Soil organic matter was determined by the potassium dichromate volumetric method (dilution heat method) [24]. Soil alkali hydrolyzed nitrogen was determined by the alkali hydrolyzed nitrogen diffusion method. Soil exchangeable calcium was determined by atomic absorption spectrophotometer (Beijing Puxi Scientific Instrument Co., Ltd. Model:TAS-986) [25].

2.3.3. Collection of Fruit and Vegetable Samples

Collection of Shixia Longan Samples

In August 2022, when the Shixia longan was mature, it was timely harvested and transported to the laboratory, and it was placed at room temperature to dissipate the field heat. The Shixia longan, which had the same maturity, color, size, shape, and plumpness, was selected for the experiment (the control group was treated similarly). Each group has about 1200 longans.

Collection of Chive Samples

In February 2022, five samples of chives were randomly collected from each treatment group and taken back to the laboratory immediately. After the root soil was washed with tap water, excess water was wiped dry, and the quality indicators were analyzed immediately.

Determination of Quality Indexes of Fruits and Vegetables

The weight of single fruit was measured by the weighing method. Total soluble solids and titratable acid were determined by a sugar acid integrated machine (Guangzhou Aidang Scientific Instrument Co., Ltd. (Guangzhou, China) Model: PAL-BX/ACID) according to the protocol. Soluble sugar was determined by the anthrone reagent method. The ascorbic acid was determined by spectrophotometry (Shanghai Lengguang Technology Co., Ltd. (Shanghai, China) Model:759S) according to the protocol. The measurement of morphological indexes adopted tape or Vernier caliper.

2.4. Statistical Analyses

All data in this experiment were collated by Excel 2019, SPSS 26.0 was used for the sample T test, and GraphPad Prism 8 was used for graph drawing.

3. Results and Discussion

3.1. Effect of Oyster Shell Soil Conditioner on Soil pH Value of Shixia Longan

The soil pH value suitable for longan growth is 5.50–6.50. As shown in Figure 3, in December 2021 (before applying oyster shell soil conditioner), the soil samples of Shixia longan were collected for the first time. The initial soil pH value of the experimental field was 4.57 ± 0.10, which should be regarded as strong acidic soil. Compared with the control group (pH = 4.50 ± 0.16), there was no significant difference between the two groups (p > 0.05). After the application of oyster shell soil conditioner in March 2022, the soil pH value measured in May was 6.03 ± 0.11, which was 1.49 units higher than the control group (pH = 4.54 ± 0.11) (p < 0.01). In August 2022, after the Shixia longan was harvested, the soil pH value of the experimental field was 5.87 ± 0.08. Compared with the control group (pH = 4.58 ± 0.08), the pH value increased by 1.29 units (p < 0.01). Compared with the data in December 2021, the pH value of the experimental field increased by 1.30 units. The results showed that the application of oyster shell soil conditioner could improve the soil pH value and make it more suitable for the growth of Shixia longan.
Our present work was similar to the results of Huang et al. [26]. They reported that the application of 2250 kg/hm2 oyster shell powder could reduce the acidity of rice soil and increase the soil pH value by 4.10~24.50%. The oyster shell soil conditioner is slightly alkaline. When applied in acidic soil, CaO in calcined oyster shell powder can react with water to generate Ca(OH)2, of which free OH− can effectively neutralize H+ in the soil and increase the soil pH value. Additionally, a large amount of Ca2+ can be replaced by Al3+ and H+, the content of alkaline base ions in soil colloids, and the soil pH value increased, improving the soil environment.

3.2. Effect of Oyster Shell Soil Conditioner on Soil Organic Matter of Shixia Longan

Soil organic matter is one of the most important bases of soil fertility and the core of maintaining cultivated land quality. Organic matter participates in the composition and stability of soil structure and also provides nutrients for plant growth and development [27,28]. As shown in Figure 4, in December 2021, the initial content of soil organic matter in the experimental group was 24.10 ± 4.40 g/kg, which had no significant difference from the control group (20.38 ± 0.40 g/kg) (p > 0.05). After the application of oyster shell soil conditioner in 2022, the soil organic matter content increased to 52.67 ± 1.46 g/kg, which was 121.49% higher than that of the control group (23.78 ± 1.41 g/kg) (p < 0.01). In August 2022, soil samples were collected after the Shixia longan was harvested. The soil organic matter content in the experimental field was 37.99 ± 1.96 g/kg. Compared with the control group (17.82 ± 0.83 g/kg), soil organic matter increased by 113.19% (p < 0.01). During the whole period, the organic matter content in the experimental field increased by 57.63%. It can be seen that the application of oyster shell soil conditioner effectively improved the content of soil organic matter. The optimalization of soil pH value had a certain impact on the species and quantity of soil microorganisms, where soil organic matter mainly comes from animal and plant residues. The decomposition of animal and plant residues depends on microorganisms. After the optimalization of soil pH value, the activity of soil microorganisms and enzymes should improve, promoting the formation of humic acid and mineralization of mineral elements, as well as increasing the soil organic matter content. It is speculated that the reasons for the significant increase of soil organic matter in May are as follows: first of all, the application of oyster shell soil conditioner neutralized soil acidification, improved the activity and amount of soil microorganism and enzyme activity, and was conducive to the decomposition and transformation of organic matters. Secondly, since May is the growing season of longan, the farmer applied organic fertilizer to provide nutrition for fruit growth. Finally, there were many fallen leaves under longan trees in the experimental field, which could be decomposed and produce humus, further increasing the content of soil organic matter.

3.3. Effect of Oyster Shell Soil Conditioner on Soil Alkali Hydrolyzed Nitrogen Content of Shixia Longan

Soil alkali hydrolyzed nitrogen is a major source of nitrogen income for soil. Plants can absorb and utilize this form of nitrogen as it is mostly soluble when captured by roots. Determinant for this vital nitrogen income includes soil organic matter content and nitrogen fertilizer application amount [29]. In Figure 5, the initial content of soil alkali hydrolyzed nitrogen (December 2021) was 49.93 ± 2.46 mg/kg. The content of alkali hydrolyzed nitrogen in May 2022 was 113.17 ± 10.90 mg/kg, 29.34% higher than the control group (87.50 ± 10.50 mg/kg) (p < 0.01). In August 2022, when Shixia longan was harvested, the soil alkali hydrolyzed nitrogen content was 85.87 ± 6.50 mg/kg. There was a significant difference with the control group (58.80 ± 10.57 mg/kg) (p < 0.01). This showed that the application of oyster shell soil conditioner could increase the content of soil alkali hydrolyzed nitrogen. The content of soil alkali hydrolyzed nitrogen is positively correlated to the content of organic matter.

3.4. Effect of Oyster Shell Soil Conditioner on Soil Exchangeable Calcium Content of Shixia Longan

Soil exchangeable calcium is soluble calcium that can be absorbed and utilized by plants, accounting for 20–30% of the total calcium content in the soil. The amount of exchangeable calcium can be used to evaluate the calcium supply ability of the soil. As shown in Figure 6, the initial content of soil-exchangeable calcium in the experimental field was 8.06 ± 0.36 cmol/kg, which had no significant difference from the control group (8.23 ± 0.10 cmol/kg) (p > 0.05). During the flowering period of Shixia longan in May 2022, the content of exchangeable calcium significantly increased. Compared with the control group (8.40 ± 0.13 cmol/kg), the soil exchangeable calcium content of the experimental group increased to 13.36 ± 0.57 cmol/kg, a significant increase of 59.05% (p < 0.01). In August 2022, compared with the control group (7.06 ± 0.63 cmol/kg), the soil exchangeable calcium content of the experimental group was 12.02 ± 0.35 cmol/kg, increased by 70.25% (p < 0.05). Compared with the initial content of exchangeable calcium, the experimental group increased by 49.13%. Throughout the whole growth period of Shixia longan, applying oyster shell soil conditioner can significantly increase the content of soil exchangeable calcium.

3.5. Effect of Oyster Shell Soil Conditioner on Single Fruit Weight and Appearance Quality of Shixia Longan

As can be seen from Table 2, the application of oyster shell soil conditioner can significantly increase the single fruit weight of Shixia longan. Compared with the control group, the single fruit weight of the experimental group increased by 6.37% (p < 0.05). Similar conclusions can be drawn from the appearance quality of longan as compared with the control group, the transverse and longitudinal diameters of the experimental group were increased by 3.60% (p < 0.05) and 0.48% (p > 0.05), respectively. The pericarp thickness of the experimental group increased by 6.67% (p < 0.05), while the pulp thickness increased by 3.03% (p < 0.05). After applying oyster shell soil conditioner, fruit cracking, a key indicator affecting the appearance and market value of longan, nearly diminished. This came with a yield increase of 66.5%. Ma et al. [30] studied the effect of exogenous calcium supplementation on the fruit growth and pulp quality of Cabernet Sauvignon grapes. After spreading the calcium agent, the photosynthetic characteristics of grape leaves were significantly improved, which could enlarge the transverse and longitudinal diameter, optimize the fruit type index, increase yield, and ‘harmonize’ the sugar acid ratio of the grapes. The application of oyster shell soil conditioner increases the content of Ca, P, K, Mg, and other nutrient-attributing elements in the soil. A balance of soil nutrient-attributing elements promotes the growth and development of plants, which is conducive to the synthesis and accumulation of substances, thus improving fruit quality [31,32].

3.6. Effect of Oyster Shell Soil Conditioner on Solid Acid Ratio and Sugar Acid Ratio of Shixia Longan

The application of oyster shell soil conditioner can also increase the content of total soluble solids and soluble sugar in Shixia longan. As shown in Table 3, compared with the control group, the content of total soluble solids in the experimental group increased by 15.93% (p < 0.05), and the content of soluble sugar increased by 16.18% (p < 0.05). After the application of the oyster shell soil conditioner, the content of titratable acid decreased by 10.95%, forming a significant difference with the control group (p < 0.05). In the experimental group, the solid acid ratio and sugar acid ratio increased by 30.19% and 30.42%, respectively. The input of calcium promoted the absorption and utilization of other elements in the fruit, thus increasing the content of soluble solids. Previous studies by Chen et al. [33] indicated that an application of calcium fertilizer to the leaves of citrus trees and soil could reduce the frequency of cracking fruit, as well as optimize fruit taste by balancing sweet and acid content thereof, as well as increased fruit size.

3.7. Effect of Oyster Shell Soil Conditioner on Ascorbic Acid of Shixia Longan

The application of oyster shell soil conditioner can effectively increase the content of ascorbic acid in Shixia longan. Compared with the control group, the content of ascorbic acid in the experimental group increased by 6.85% (p < 0.05). Galactonolactone is an effective precursor of ascorbic acid synthesis, which is produced by the catalysis of L-Galactono-1,4-Lactone Dehydrogenase (Gal LDH) [34]. Dehydroascorbic acid is the oxidative metabolite of ascorbic acid, which is produced by the catalysis of ascorbic acid oxidase, thus reducing the content of ascorbic acid [35]. The oyster shell soil conditioner contains a large amount of Ca2+, which can promote the activity of Gal LDH and the synthesis of ascorbic acid. At the same time, the activity of ascorbic acid oxidase will be inhibited under a certain concentration of Ca2+. On the one hand, Ca2+ promotes the synthesis pathway of ascorbic acid, on the other hand, it inhibits its oxidative metabolism pathway, which significantly increases the content of ascorbic acid in the longan (Figure 7).

3.8. Effect of Oyster Shell Soil Conditioner on Soil pH Value of Chive

As shown in Figure 8 the initial soil pH value of the chive experimental field was 6.39 ± 0.10. In January 2022, an oyster shell soil conditioner was applied to the experimental field. In February of the same year, soil samples were collected after the chive was harvested. Compared with the control group (5.69 ± 0.01), the soil pH value of the experimental group was 6.72 ± 0.01, increased by 1.03 units, with a significant difference between the two groups (p < 0.05). It is proved again that the application of oyster shell soil conditioner can neutralize soil acidification.

3.9. Effect of Oyster Shell Soil Conditioner on Soil Organic Matter and Alkali Hydrolyzed Nitrogen of Chives

As shown in Figure 9, the initial content of soil organic matter and alkali hydrolyzed nitrogen of the chive experimental field were 31.78 ± 0.74 g/kg and 133.89 ± 2.91 mg/kg, respectively. Soil samples were collected in February 2022. The content of soil organic matter in the experimental group was 21.75 ± 0.00 g/kg. Compared with the control (22.90 ± 0.11 g/kg), the organic matter content in the experimental group decreased by 5.29%. The content of soil alkali hydrolyzed nitrogen in the experimental group was 80.73 ± 4.04 mg/kg. There was no significant difference with the control group (79.33 ± 1.62 mg/kg) (p > 0.05). We proposed that the reason for the conflicting results was that no organic fertilizer was applied, and a deficit of withered leaves nor plants led to low microbial activity in the field, which is linked to the decomposition of animal and plant residues. The nutrient reserve in the field, nitrogen, and organic matter decreased after the plantation and harvest of chive, compounded with the application of shell oil conditioner. This is then demonstrated by the decline of soil organic matter and alkaline nitrogen content.

3.10. Effect of Oyster Shell Soil Conditioner on Soil Exchangeable Calcium in Chives

As shown in Figure 10, the initial content of soil exchangeable calcium in the experimental field was 12.37 ± 1.32 cmol/kg, which had no significant difference from the control group (p > 0.05). The oyster shell soil conditioner was applied in January 2022, and soil samples were collected after the chive was harvested in February. The content of soil exchangeable calcium in the experimental group was 6.76 ± 0.17 cmol/kg, which was 131.51% higher than that of the control group (2.92 ± 0.96 cmol/kg) (p < 0.05). As a vegetable with high calcium content, chives need to absorb calcium throughout their growth period. The application of oyster shell soil conditioner increased the content of exchangeable calcium in the soil. The harvested plant absorbed more calcium than the soil conditioner could provide throughout the timeframe, and a decrease in soil exchangeable calcium is then recorded. However, compared with the control group in the same period (February 2022), the soil retained more calcium at the time of the second sampling compared to the control.

3.11. Effect of Oyster Shell Soil Conditioner on the Yield and Single Plant Weight of Chive

It can be seen from Table 4 that in February 2022, the single plant weight of chive in the experimental group was 54.91% higher than that of the control group (p < 0.05). The yield of chive in the experimental group was 57.8% higher than that in the control group (p < 0.05). The results showed that the application of oyster shell soil conditioner could effectively improve the plant weight and yield of chive.

3.12. Effect of Oyster Shell Soil Conditioner on the Morphological Indexes of Chive

As shown in Table 5, the application of oyster shell soil conditioner has a positive impact on the plant height, root length, and pseudostem diameter of the chive. Compared with the control group, the plant height, root length, and pseudostem diameter of chives in the experimental group increased by 8.27%, 26.89%, and 23.33%, forming a significant difference (p < 0.05). In conclusion, the application of oyster shell soil conditioner can effectively improve the quality of chive.

4. Conclusions

In this study, we adopted oyster shell soil conditioner as the study material for soil condition optimization. These optimizations occurred in the soil pH value, soil organic matter, alkali hydrolyzed nitrogen, and exchangeable calcium content, as well as in the plants’ overall fertility. The application of soil conditioner eventually led to an increase in Shixia longan yield and several improved indexes on individual fruit for market value and consumer preference. Chive also observed an increase in yield and improvement in morphological indexes. We hereby demonstrate the yielded positive effect on the soil condition of the study material revealed by our experiments, and the potential for broader utilization in the agriculture industry, especially in fruits and vegetables.
At present, there is a lack of research on the mechanism of oyster shell soil conditioner to improve the quality of fruits and vegetables, and more experiments involving the mechanism will be carried out in our further study.

Author Contributions

Conceptualization, L.W. and M.-J.C.; Methodology, L.W. and M.-J.C.; Investigation, M.-J.C., L.W., Y.W. (Yan Wang), M.J., M.W., L.H.; Validation, L.W., M.-J.C., Y.W. (Yan Wang), M.J., M.W., Y.W.(Yongming Wang), L.H.; Visualization, M.-J.C., Y.W. (Yan Wang) and M.J.; Writing—original draft, Y.W. (Yan Wang) and M.J.; Writing—review & editing, M.-J.C. and Y.W. (Yan Wang); Project administration, M.-J.C., L.W. and Y.W. (Yongming Wang) All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the earmarked fund for CARS-49.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Shixia longan experimental field.
Figure 1. Shixia longan experimental field.
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Figure 2. Chive experimental field.
Figure 2. Chive experimental field.
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Figure 3. Effect of oyster shell soil conditioner on soil pH value of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
Figure 3. Effect of oyster shell soil conditioner on soil pH value of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
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Figure 4. Effect of oyster shell soil conditioner on soil organic matter of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
Figure 4. Effect of oyster shell soil conditioner on soil organic matter of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
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Figure 5. Effect of oyster shell soil conditioner on soil alkali hydrolyzed nitrogen content of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
Figure 5. Effect of oyster shell soil conditioner on soil alkali hydrolyzed nitrogen content of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
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Figure 6. Effect of oyster shell soil conditioner on soil exchangeable calcium content of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
Figure 6. Effect of oyster shell soil conditioner on soil exchangeable calcium content of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05), and different upper-case letters represent extremely significant differences among groups (p < 0.01), the same below.
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Figure 7. Effect of oyster shell soil conditioner on ascorbic acid of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Figure 7. Effect of oyster shell soil conditioner on ascorbic acid of Shixia longan. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
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Figure 8. Effect of oyster shell soil conditioner on soil pH value of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Figure 8. Effect of oyster shell soil conditioner on soil pH value of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
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Figure 9. Effect of oyster shell soil conditioner on soil organic matter (A) and alkali hydrolyzed nitrogen (B) of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Figure 9. Effect of oyster shell soil conditioner on soil organic matter (A) and alkali hydrolyzed nitrogen (B) of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
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Figure 10. Effect of oyster shell soil conditioner on soil exchangeable calcium content of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Figure 10. Effect of oyster shell soil conditioner on soil exchangeable calcium content of chives. Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
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Table
Table 1. Basic chemical composition of oyster shell soil conditioner.
Table 1. Basic chemical composition of oyster shell soil conditioner.
IndicatorContent
Ca48%
Mg0.81%
Cu0.00049%
Fe0.14%
Zn0.0022%
Mo<0.0001%
Se0.51 mg/kg
Table
Table 2. Effect of oyster shell soil conditioner on single fruit weight and appearance quality of Shixia longan.
Table 2. Effect of oyster shell soil conditioner on single fruit weight and appearance quality of Shixia longan.
GroupControlExperiment
Single fruit weight (g)7.85 ± 0.19 b8.35 ± 0.27 a
Transverse diameter (mm)23.63 ± 0.23 b24.48 ± 0.30 a
Longitudinal diameter (mm)22.94 ± 0.39 a23.05 ± 0.33 a
Pericarp thickness (mm)0.75 ± 0.02 b0.80 ± 0.01 a
Pulp thickness (mm)5.28 ± 0.11 b5.44 ± 0.17 a
Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Table
Table 3. Effect of oyster shell soil conditioner on solid acid ratio and sugar acid ratio of Shixia longan.
Table 3. Effect of oyster shell soil conditioner on solid acid ratio and sugar acid ratio of Shixia longan.
GroupControlExperiment
Total soluble solids (%)20.47 ± 0.06 b23.73 ± 0.06 a
Soluble sugar (%)18.05 ± 0.08 b20.97 ± 0.06 a
Titratable acid (%)1.37 ± 0.03 b1.22 ± 0.01 a
solid acid ratio14.9419.45
sugar acid ratio13.1817.19
Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Table
Table 4. Effects of oyster shell soil conditioner on the yield and single plant weight of chive.
Table 4. Effects of oyster shell soil conditioner on the yield and single plant weight of chive.
GroupControlExperiment
Single plant weight (g)127.8 ± 35.65 b197.98 ± 73.62 a
yield (kg/ha)18,13528,620
Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
Table
Table 5. Effect of oyster shell soil conditioner on the morphological indexes of chive.
Table 5. Effect of oyster shell soil conditioner on the morphological indexes of chive.
GroupControlExperiment
Tiller number14 ± 114 ± 4
Number of blades (piece)54 ± 761 ± 16
Plant height (cm)62.84 ± 3.17 b68.04 ± 4.13 a
Leaf length (cm)48.68 ± 3.2251.47 ± 3.68
Pseudo stem length (cm)6.06 ± 0.39 a6.19 ± 0.38 a
Root length (cm)8.18 ± 0.77 b10.38 ± 2.26 a
Pseudostem diameter (mm)7.80 ± 1.79 b9.62 ± 0.84 a
Note: Different lower-case letters in the chart represent significant differences among groups (p < 0.05).
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MDPI and ACS Style

Wang, Y.; Ji, M.; Wu, M.; Weng, L.; Wang, Y.; Hu, L.; Cao, M.-J. Toward Green Farming Technologies: A Case Study of Oyster Shell Application in Fruit and Vegetable Production in Xiamen. Sustainability 2023, 15, 663. https://doi.org/10.3390/su15010663

AMA Style

Wang Y, Ji M, Wu M, Weng L, Wang Y, Hu L, Cao M-J. Toward Green Farming Technologies: A Case Study of Oyster Shell Application in Fruit and Vegetable Production in Xiamen. Sustainability. 2023; 15(1):663. https://doi.org/10.3390/su15010663

Chicago/Turabian Style

Wang, Yan, Mengya Ji, Min Wu, Ling Weng, Yongming Wang, Lingyi Hu, and Min-Jie Cao. 2023. "Toward Green Farming Technologies: A Case Study of Oyster Shell Application in Fruit and Vegetable Production in Xiamen" Sustainability 15, no. 1: 663. https://doi.org/10.3390/su15010663

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