Effects of organic fertilizers produced from fish pond sediment on growth performances and yield of Malabar and Amaranthus vegetables

The increasing intensification of aquaculture production requires the development of strategies to reduce its environmental impacts such as the pollution caused by the discharge of nutrient-rich sediments into local water bodies. This research was undertaken to investigate and evaluate the effect of using organic fertilizers produced from the pond sludge of freshwater snakehead fish (Channa striata) composted with organic amendments of peanut shells and coir fiber on growth performance indices and yields of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables in the dry and wet seasons. An organic fertilizer quality experiment showed that the richest nutrient contents of the produced organic fertilizer were achieved when using 30% sludge mixed with 70% organic amendments (50% peanut shells + 50% coir fiber). This was selected and used for a vegetable cultivation experiment. For the reference treatment, only chemical fertilizer was applied, while in the other four treatments, 25, 50, 75, and 100% of the chemical fertilizer were substituted with the organic fertilizer. A 25–50% reduction in the chemical fertilizer application resulted in better growth performance indices and final yields than the other treatments, including the reference treatment, for both crops. The highest yields of Malabar spinach and Amaranthus cruentus vegetables were found in Treatment 3 (50% chemical fertilizer combined with 50% organic fertilizer), followed by Treatment 2 (25% organic fertilizer combined with 75% inorganic fertilizer) (P < 0.05). The results show that the reuse of sludge from snakehead fish ponds mixed with agricultural by-products as organic fertilizer for vegetables not only improves vegetable productivity but also reduces the costs of chemical fertilizer and decreases environmental pollution.

Introduction

Aquaculture is one of the fastest-growing industries in Vietnam, contributing to export revenues and increased income for many farmers. Vietnam is ranked the fourth biggest exporter of seafood in the world (FAO, 2020). The export revenue of aquaculture and agricultural products for Vietnam was US$ 40.02 billion (9.3 million tons) in 2019 and accounted for 7.2% of the total national export value, with 70 types of products sold to over 160 countries around the world (VASEP, 2019; MARD, 2020).

The Mekong Delta is a core region for aquaculture in Vietnam where intensive farming of striped catfish (Pangasianodon hypophthalmus), whiteleg shrimp (Litopenaeus vannamei), giant tiger prawn (Penaeus monodon), and giant freshwater prawn (Macrobrachium rosenbergii) are currently the most developed sectors. Furthermore, other inland freshwater species such as snakehead (Channa striata Bloch, 1973), red tilapia (Oreochromis sp.), climbing perch (Anabas testudineus), and Asian swamp eels (Monopterus albus) are produced at differing levels of intensification and extent in the region. In general, aquaculture in the Mekong Delta plays a crucial role to increase local livelihood income and provide economic benefits to society in the region. It has great potential to continue its current growth and development. However, there are a number of challenges and risks including environmental pollution, harsh weather, and climate change for sustainable growth of the aquaculture sectors (FAO, 2022).

The Binh Duong province, located in the Southeast region of Vietnam, has a well-developed grid of freshwater rivers and canals, which provide a good potential for inland aquaculture development. Due to a large demand for animal protein and fresh vegetables for local consumption, the availability of freshwater and land for aquaculture is decreasing. Snakehead fish is one of the most popular cultured fish species, which has a high economic value, and provides important animal protein and income to local people in the region (Bich et al., 2020; Gustiano et al., 2021). This freshwater fish is a carnivorous species, which is raised in high stocking densities, often fed commercial feeds and trash-fish with a high protein content.

The amount of sludge from fish feces and uneaten feed accumulating in the sediments of fish ponds is quite high with approximately 100–150 kg m⁻³ after a cultivation cycle. Most of the sludge from snakehead fish pond farming is usually discharged untreated directly into rivers and canals, causing water pollution in the province. Currently, there are few solutions to solve the problem of wastewater and sludge from aquaculture farming systems. As the sludge includes uneaten feed and fish feces and has high organic material (OM), nitrogen (N), phosphorus (P), and other macronutrient and micronutrient contents (Thanh et al., 2015; Haque et al., 2016; Da et al., 2020, 2021), one option could be to use it as a fertilizer for improving the productivity of vegetables and other crops. This would reduce the reliance on inorganic fertilizers and reduce the treatment cost of sludge/sediment while reducing the negative impacts and pollution from aquaculture production on the environment. There are a number of studies in Thailand, China, Vietnam, and Bangladesh that have focused on how to recycle wastewater and sludge/sediment from catfish pond farming and composting fish pond sludge/sediment mixed with agriculture waste residues (water hyacinth, rice straws, and weeds/green grass) as organic fertilizers for paddy rice, common vegetables (such as cucumber, water spinach, and Chinese mustard), and fodder grass (Graber and Junge, 2009; Phung et al., 2009; Karak et al., 2013; Da et al., 2015, 2020, 2021; Thanh et al., 2015; Haque et al., 2016).

Vietnam, located in the tropical monsoon region with high agricultural diversity and rich inland aquatic ecosystems, could be considered a potential country for developing large-scale freshwater aquaculture integrated with agriculture, with the aim to reduce production costs and environmental impacts. Malabar spinach and Amaranthus cruentus vegetables are popular vegetables cultured on many farms in Vietnam and other Asian countries. These vegetables have rich contents of vitamin A, vitamin C, vitamin K, Iron, and Calcium (Haskell et al., 2004; Makobo et al., 2010). The leaves of the vegetables contain vitamin K, organic acids, carotenoids, bioflavonoids, water-soluble polysaccharides, and betacyanin, and they constitute valuable sources of nutritional and medicinal importance for human health and wellbeing (Adebooye et al., 2008; Ajay et al., 2021). In recent years, the price of chemical fertilizer for agricultural crops and vegetables in Vietnam has dramatically increased, which has led to a large fertilizer deficit (Quynh and Kazuto, 2018). At the same time, the price of agricultural products (vegetables, fruits, and rice production) has remained comparatively low and unprofitable, and there is now a need for farmers to reduce their reliance on expensive chemical fertilizers. Previous studies have reported that the composting of sediment from Pangasius catfish pond farming mixed with locally sourced organic residues (rice straw and/or water hyacinth) could be used as organic fertilizers, which could provide an alternative to chemical fertilizers and help to mitigate water pollution, while still improving agricultural production and soil quality (Rahman et al., 2004; Rahman and Yakupitiyage, 2006; Thanh et al., 2015; Da et al., 2020, 2021).

This study aimed to investigate if composting a combination of different proportions of sludge from snakehead fish ponds with agricultural residues (peanut shells and coir fiber) could provide an organic fertilizer that could be used as a substitute for chemical fertilizers. The aim was also to assess how this organic fertilizer affected growth performance indices and yields of Malabar spinach and Amaranthus cruentus vegetables.

Materials and methods

Study area and organic amendment materials

The study was carried out in 2021 at a vegetable farm (total farm area is approximately 1,000 m²) in the Tan Uyen district in the Binh Duong province of the Mekong Delta in Vietnam (Figure 1). Most vegetable farmers in this area practice intensive vegetable farming with multiple cropping throughout the year. The experiment area is dominated by clay-alluvial soil. Sludge/sediment was collected from a snakehead fish pond (an earthen pond of approximately 2,000 m²) after the fish had been harvested. Peanut shells and coir fiber used as organic amendments were collected from local farms in the Tan Uyen district. High-yielding varieties of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) seeds were bought from Thu Dau city in the Binh Duong province. The experiments of the vegetable cultivation were carried out in the dry season (March–June 2021) and the wet season (September–October 2021), and the Malabar spinach and Amaranthus cruentus vegetables were grown in an area of 1,000 m² using an experimental design as presented in Figures 2, 3.

FIGURE 1

Figure 1. Study area in Binh Duong province, Vietnam.

FIGURE 2

Figure 2. Layout of the Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables cultivation fertilized by the different organic fertilizer and chemical fertilizer combinations.

FIGURE 3

Figure 3. Schematic outline of organic fertilizer production, experimental vegetable cultivation, experimental management, and harvesting. (a) Snakehead fish pond farming. (b) Sludge/sediment is collected from fish pond. (c) Sludge of fish pond is sun-dried. (d) Sludge/sediment mixed with peanut shells+coir fiber. (e) Experimental plots and soil preparation. (f) Malabar spinach and Amaranthus cruentus planting. (g) Malabar spinach at 20-day after planting. (h) Amaranth after 20 days of planting. (i) Harvested Malabar spinach vegetable. (j) Harvested Amaranthus cruentus vegetable.

Research layout

The scope of this study included (1) Collection and chemical analysis of sludge from fish pond farming, organic amendments (Peanut shell and coir fiber), and soil of the experiment (beginning and end); (2) Organic fertilizers composted and produced in different proportions (10, 30, 50, 70, and 90%) between sludge/sediment from snakehead fish pond and organic amendments for 95 days; (3) The organic fertilizers of each treatment were analyzed for chemical composition to estimate which organic fertilizer had the richest nutrient concentrations to be used in the vegetable cultivation experiment; (4) Soil preparation for experiment with the organic fertilizer with the highest nutrient content to partly replace inorganic fertilizers for vegetables cultivation of Malabar spinach and Amaranthus cruentus in the dry and wet seasons; (5) Conducting growth performance experiment of vegetables treated with different ratios of organic and inorganic fertilizers; (6) Harvest and evaluation of plant growth performance indices and final yield of the vegetable experiment.

Production of organic fertilizers

To determine the optimal ratio of sludge from fish ponds to be mixed with organic amendment materials (50% peanut shell + 50% coir fiber), an experiment was designed with five treatments and three replicates for each treatment as follows: Treatment 1 (reference treatment): 10% sludge + 90% organic amendment; Treatment 2: 30% sludge + 70% organic amendment; Treatment 3: 50% sludge + 50% organic amendment; Treatment 4: 70% sludge + 30% organic amendment; Treatment 5: 90% sludge + 10% organic amendment (Figure 4).

FIGURE 4

Figure 4. Layout of the compositing method applied and used in experimental organic fertilizer production (Hien, 2003).

All treatments were incubated in plastic bags for approximately 95 days. The experimental organic fertilizers were produced following the composting methods recommended by Hien (2003) and Thanh and Ty (2022). To each treatment of compost, the microbial fungal inoculum was added (TRICODHCT-LUA VON: 80% Trichoderma asperellum spp. with 20% Trichoderma atroviride Karsten) to increase the composting process.

Assessment of vegetable growth under different fertilizer treatments

Soil preparation and vegetable cultivation

The experimental soil was prepared by plowing. Soil samples were collected for chemical composition analysis at the beginning and the end of the experiment. Seeds of Malabar spinach and Amaranthus cruentus vegetables were soaked in warm water at 40–45°C for 60 min and incubated on wet paper for 24 h for their germination. The germinated seeds were raised in nursery trays and pots for approximately 2–3 days before they were transferred and planted in the soil plots of the experiments. The planting distance was 15 × 15 cm (approximately 2.5 kg of seeds 1,000 m⁻²). The plants were irrigated by well water daily at 7:00 a.m. and 4:00 p.m.

Malabar spinach and Amaranthus cruentus vegetables were cultivated in three replicated plots for each of the five fertilization treatments and during two consecutive cropping cycles (dry and wet seasons). Thus, a total of 15 plots for five treatments of each experiment of plant cultivation were used. Each plot area of the experiment was approximately 52 m² (3.5 m width × 15 m length × 0.3 m height) (Figure 2).

Growth of malabar spinach and Amaranthus cruentus vegetables under different fertilizer treatments

This experiment tested the use of different organic–chemical fertilizer ratios on Malabar spinach and Amaranthus cruentus vegetables. The organic fertilizer from Treatment 4, which was found to have the highest concentration of nutrients, was used in combination with different quantities of chemical fertilizer to fertilize the vegetables in the wet and dry seasons. Five different treatment levels, Treatment 1 (reference treatment)–Treatment 5, representing a gradient from 100% chemical fertilizers to 100% organic fertilizers, were used (Table 1 and Figure 2). The organic fertilizers were added to the soil plot of each plant before planting, while the inorganic fertilizers were added to the soil plot 15 days after sowing (DAS). The total amounts of N:P:K of the chemical and organic fertilizers applied in each treatment are presented in Table 1.

TABLE 1

Table 1. Proportion of inorganic and organic fertilizers used for Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables experiment.

Data collection and measurement

During the vegetable cultivation period of both the dry and wet seasons, growth performance indices including plant length, the length of leaves, the width of leaves, and the number of leaves in each treatment were measured at 10, 20, and 30 DAS in each crop cycle. The final yields of Malabar spinach and Amaranthus cruentus vegetables for each treatment were harvested by hand and weighed at the end of the cultivation season. The edible weight without plant roots of each treatment was measured and weighed.

Laboratory analysis of soil, organic amendment, and organic fertilizers

Soil samples used for analyses were taken on two diagonals at the experimental plot. Once dry, the samples were thoroughly mixed, and three samples (1 kg each) were collected and stored separately in labeled plastic bags for chemical analyses. The chemical analyses of soil, fish pond sludge, peanut shell, and coir fiber were carried out at the laboratory of Thu Dau Mot University, Binh Duong district. The pH was determined using a 1:5 soil:water suspension (McLean, 1982); TN and the effective N were analyzed using the Kjeldahl method. TP and effective P were measured using the spectrophotometry method (ISO 11261:1995, 1995), TK was measured by hydrofluoric acid digestion (Bartels, 1996), and SOC by Walkley–Black wet oxidation method (Walkley and Black, 1934). All soil analysis methods are, unless alternatively referenced, described by Houba et al. (1995).

Data analysis

All data of plant growth performance indices between each treatment at 10, 20, and 30 DAS of the Malabar spinach and Amaranthus cruentus vegetable experiments were entered in Microsoft Excel 2010 before the statistical analysis by IBM SPSS STATISTIC program, version 2020. All collected data were statistically analyzed by the general linear model (ANOVA), using Pairwise Comparison and Tukey's post-hoc tests for treatment comparisons (P ≤ 0.05 level of significance) (IBM SPSS Statistic, 2020).

Results

Chemical composition of soil, sludge, organic amendments, and organic fertilizers

The chemical composition of the organic fertilizers and experimental soil was found to be slightly different before and after the experiment (Table 2). The organic carbon (OC%) in peanut shells, waste sludge, and coir fiber were significantly different, with 21.2, 5.5, and 9.8%, respectively. Total N (%) in sludge and coir fiber showed a similar percentage (0.5%) but was almost 10 times lower than in the peanut shell material (5%). At the end of the experiment, the effective N and P in the soil had increased slightly while the effective K had decreased (Table 2). The results showed that the mineral nutrient composition in the soil was significantly changed by adding organic fertilizer.

TABLE 2

Table 2. Chemical composition of sludge from snakehead fish (Channa striata Bloch, 1973) pond, agricultural organic amendments, and organic fertilizer production.

Table 3 shows the chemical composition of the organic fertilizer produced from the five different mixtures of sludge from the snakehead fish pond and organic amendments. The results showed that Treatment 1 (reference treatment) had the lowest nutrient content (5.64% OC, 0.65% TN, 0.90% TP, and 0.22% TK), while Treatment 4 had the highest nutrient content (15.57% OC, 1.28% TN, 0.65% TP, and 0.38% TK) compared with the other treatments (P < 0.05). Therefore, Treatment 4 was used for the growth performance experiments of Malabar spinach and Amaranthus cruentus vegetable cultivation. The C/N ratios of the produced organic fertilizer ranged between 8.7 and 12.1 among treatments.

TABLE 3

Table 3. Chemical composition of organic fertilizer production.

Evaluation of growth performance indices of vegetables

The growth performance indices of Malabar spinach and Amaranthus cruentus vegetables are presented in Table 4. The results showed that there are significant differences between several treatments after 30 DAS planted in the dry and wet seasons, while there were fewer statistically significant differences after 10 and 20 DAS.

TABLE 4

Table 4. Growth performance indices of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables treated with experimental fertilizers in the wet and dry seasons at 10, 20, and 30-day after sowing (DAS).

The Malabar spinach growth indices differed slightly between the dry and wet seasons. Plant length at 10 DAS ranged between 5.9–6.3 cm and 6.1–6.4 cm in the dry season and wet season, respectively (P < 0.05). The plant length of Amaranthus cruentus at 10 DAS ranged between 6.1 cm and 6.4 cm and was similar between the seasons. Plant length, leaf length, and leaf width of Malabar spinach at 30 DAS in the dry and wet seasons ranged between 30.2–33.8 cm, 5.8–13.5, and 4.2–8.8 cm, respectively. The plant length, leaf length, and leaf width of Amaranthus cruentus at 30 DAS in the dry and wet seasons ranged between 29.1–32.7 cm, 5.2–6.6 cm, and 39–4.9 cm, respectively (P < 0.05). During the first 10 days of the experiment, the leaf number of each plant was approximately 5 leaves, and after 30 days it had reached 13–15 leaves in both seasons. The highest growth performance indices in both Malabar spinach and Amaranthus cruentus vegetables in the dry and wet seasons were found in Treatment 3 (50% inorganic fertilizer + 50% organic fertilizer), followed in descending order by Treatment 2 (75% inorganic fertilizer + 25% organic fertilizer), Treatment 1 (reference treatment) (100% chemical fertilizer), Treatment 4 (25% inorganic fertilizer + 75% organic fertilizer), and Treatment 5 (100% organic fertilizer) (P < 0.05) (Table 4).

Final yield and edible weight of malabar spinach vegetables

The results in Table 5 show that the final yield, individual plant weight, and edible part of Malabar spinach in the dry and wet seasons ranged between 17.5–18.0 t ha⁻¹, 43.8–44.6 g plant⁻¹, and 68.0–68.8%, respectively (P < 0.05). Malabar spinach had overall high adjusted-R² values (0.939–0.960) for the final yield (t ha⁻¹) (Figure 5a) and (0.945–0.964) and the edible weight (g plant⁻¹) (Figure 5b) from the different treatments.

TABLE 5

Table 5. Final yield and edible weight of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables of each treatment in the dry and wet seasons.

FIGURE 5

Figure 5. Final yield (ton ha⁻¹) (a) and edible weight (g plant⁻¹) (b) of Malabar spinach (Basella alba L.) vegetable fertilized with five different treatments for the two seasons.

The edible weight of Malabar spinach was higher in the wet season compared with the dry season in Treatment 3, Treatment 2, and Treatment 4, but there was no difference in Treatment 1 (reference treatment) and Treatment 5. The highest edible weight was found in Treatment 3 in the dry season (30.4 g) and wet season (30.7 g) (Figure 5b). Moreover, the lowest edible weight was identified in Treatment 5 in the dry season (29.8 g) and wet season (29.9 g). In terms of yield and edible weight, a mixture of inorganic and organic fertilizers resulted in a higher production than the treatments with only inorganic or organic fertilizers.

Final yield and edible weight of Amaranthus cruentus vegetable

The highest final yield, yield without roots, individual plant weight, and edible weight in the dry and wet seasons were found in Treatment 3 (50% inorganic fertilizer + 50% organic fertilizer) followed by Treatment 2 (75% inorganic fertilizer + 25% organic fertilizer) (P < 0.05) (Table 5). A mixture of inorganic and organic fertilizers resulted in a higher production than treatments with only inorganic fertilizer or organic fertilizer. There were a slightly higher final yield and edible weight in the wet season (adjusted-R² values ranged from 0.990 to 0.998) (Figure 6a) compared with the dry season (adjusted-R² values ranged from 0.987 to 0.995) (Figure 6b) for all treatments. The inorganic fertilizer and organic fertilizer proportion used for Amaranthus cruentus vegetable cultivation had a significant impact on the yield and edible weight. Therefore, applying appropriate proportions of inorganic and organic fertilizer to Amaranthus cruentus can improve the yield and the edible weight as well as minimize costs for fertilizers and the environmental impact.

FIGURE 6

Figure 6. Final yield (ton ha⁻¹) (a) and edible weight (g plant⁻) (b) of Amaranthus cruentus (Amaranthus L.) fertilized with five different treatments for the two seasons.

Economic efficiency of organic fertilizers for vegetable cultivation

In Treatment 1 (reference treatment), without organic fertilizer, the use of N, P, and K were 55, 75, and 60 kg ha⁻¹, respectively. This resulted in the highest cost of US$170 ha⁻¹ compared with the other treatments, but the yield of vegetables was not higher but often lower than in the other treatments (Table 6). While in Treatment 2, Treatment 3, and Treatment 4, a reduction in N, P, and K and an increase in organic fertilizer lead not only to reduced costs but also to increased vegetable yields. The present study found that Treatment 3 can be considered the optimal option when comparing the cost, vegetable yield, and edible weight with the other treatments. Treatment 3, which used 50% inorganic and 50% organic fertilizers required at 28 kg N:38 kg P:30 kg K ha⁻¹ with an estimated cost of US$87 ha⁻¹ and resulted in the highest yield and edible weight of Malabar spinach and Amaranthus cruentus vegetables in both the dry and wet seasons. Using 100% organic fertilizer, however, in Treatment 5 resulted in the lowest yield of vegetables in both the dry and wet seasons and reduced financial benefits. Thus, an optimized combination of inorganic and organic fertilizers can improve the financial and environmental performance of vegetable farming.

TABLE 6

Table 6. Economic efficiency of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables production by reducing inorganic fertilizers.

Discussion

Nutrient content of sludge/sediment of snakehead fish pond and organic amendments

Our results show that the carbon (OC%), nitrogen (TN), phosphorous (TP), and potassium (TK) contents of sludge/sediment from snakehead fish ponds were in the same range and in good agreement with the values measured in sludge/sediment from Pangasius catfish ponds in Vietnam (Phu and Tinh, 2012; Da et al., 2020, 2021), Bangladesh (Haque et al., 2016), and rainbow trout ponds in Poland (Drózdz et al., 2020). However, it was lower compared with the levels reported for manures from cattle, chicken, and horses (Rahman et al., 2004; Boyd et al., 2011; Karak et al., 2013). The sludge/sediment from the studied snakehead fish ponds had a good nutrient content, and our study shows that it can be used as a potential organic fertilizer, which not only could help to enhance the quality of soil for vegetable cultivation but also to reduce environmental pollution from aquaculture production through increased recycling of nutrients.

To make the sludge more suitable as organic fertilizer, it was complemented with peanut shell and coconut fiber, which contained higher contents of TN, TP, and TK than many other organic amendments that have been used in previous studies, such as rice straw, water hyacinth (Thanh et al., 2015; Da et al., 2020, 2021), wheat straw, potato plant residues, mustard stover, and freshly cut grass (Karak et al., 2013; Drózdz et al., 2020). Overall, the results show that organic composting is an effective way to reuse fish pond sediments and local agricultural waste in a mixture that can be converted into relatively valuable organic fertilizers for vegetable farming and other agricultural production (Karak et al., 2013; Thanh et al., 2015; Saldarriaga et al., 2019).

The nutrient quality of produced organic fertilizers

The physicochemical properties of the composting products varied between treatments (Table 3) because they were influenced by the initial material used, the duration of the decomposition step, and the conditions during the process (e.g., moisture content, temperature, pH, degree of aeration, the ratios of C/N, and the physical structure of the raw materials) (Zhu, 2007; Cofie et al., 2009; Saldarriaga et al., 2019). The nutrient content of the organic fertilizer produced in our study was in good agreement and within the range of the nutrient content found in green waste composts (Sun et al., 2012); organic fertilizers produced from combinations of fish pond sediments, water hyacinth, and rice straw (Thanh et al., 2015; Da et al., 2021); fish pond sediment composted with fresh grass and wheat straw (Drózdz et al., 2020); and agricultural wastes composted with FPS (Cofie et al., 2009; Karak et al., 2013).

The total nitrogen content and pH of the compost mixtures increased over time. According to Drózdz et al. (2020), the increase in pH in the initial stages of composting is associated with the release of ammonia. The pH of the produced organic fertilizer was approximately 6.5–7.5, which is a suitable pH for vegetables and plant growth (Agricultural Extension Center of Ho Chi Minh city, 2009; Zhang et al., 2016). The final C/N ratios (12.1–15.6) of the compost products were within the range of C/N ratios of compost products from fish pond sediment mixed with rice straw and water hyacinth (Zhu, 2007; Cofie et al., 2009; Thanh et al., 2015; Da et al., 2020), and it is in good agreement with the C/N ratios (12–26) of salmon trout fish pond sediment composted with fresh grass or wheat straw (Drózdz et al., 2020). A C/N ratio of 15–16:1 is recommended for composts used in agriculture (Emeterio and Victor, 1992; Hien, 2003; Cofie et al., 2009). Thanh et al. (2015) showed that the highest growth of vegetables was achieved at a C/N ratio of 30 for sediment–straw composts and a C/N ratio of 25 for sediment–hyacinth composts.

Benefits of organic fertilizers for vegetables and soil quality

Similar to several earlier studies, this study shows that the reuse and recycling of nutrients in integrated aquaculture and agricultural systems help to improve the efficiency of food production and help to reduce pollution by excessive nutrients, thereby contributing to improved living conditions for farmers through increased income and environmental health (Berg, 2002; Drózdz et al., 2020; Pueppke et al., 2020; Ahmed and Turchini, 2021; Farrant et al., 2021). We found that chemical fertilizer supplemented with 25 and 50% of organic fertilizers applied to the soil had a significant positive impact on the growth performance indices of Malabar spinach and Amaranthus cruentus and resulted in the highest final yield of these vegetables. The results of the present study are in good agreement with a study using Pangasius catfish pond sediments as organic fertilizer for vegetables (water spinach, cucumber fruit, and mustard greens) and fodder grass reported by Thanh et al. (2015), Haque et al. (2016), and Da et al. (2015).

The nutrient quality of the experimental soils in Table 2 shows that the OC and effective N–P–K contents in the soils at the end of the experiment in the last crop during the wet season are slightly higher than in the soils before the first experiment in the dry season. Similar soil quality improvements were found when fish pond sediment was used to fertilize soils for fodder grass, vegetables, and rice production in Bangladesh, China, and Palestine (Rahman et al., 2004; Karak et al., 2013; Haque et al., 2016).

Conclusion

This study found that the highest content of nutrients in the organic fertilizer was produced from a mixture of 30% sludge from snakehead fish ponds and 70% organic amendments (50% peanut shell and 50% coir fiber). The result shows that the organic fertilizers produced from snakehead fish sludge composted with organic amendment had a positive effect on growth performance and final yields of Malabar spinach and Amaranthus cruentus vegetables in both the dry and wet seasons. The study revealed that organic fertilizers can replace 25 to 50%, or even up to 75% of the chemical fertilizers used for vegetables. The use of organic fertilizers resulted in higher yields and was able to meet the nutritional demands of the tested vegetables. The present study confirmed that the recycling of fish pond sediments and local agricultural by-products can be used in integrated aquaculture–agriculture systems for enhanced and more efficient food production. This also has the potential to provide environmental benefits and improve the income of the farmers.

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

DT, NT, CD, and NH: conceptualization and design of research methodology. DT, NT, and CD: performed statistical data analyses. DT, NT, CD, and TN: completed writing—original draft preparation and compilation. HB, PV, and VM: contributed to editing and finalizing the manuscript. All authors read and contributed to the manuscript and approved the submitted final version.

Funding

This project has received funding from the innovation program of Thu Dau Mot University, Binh Duong, Vietnam (grant No. DT.22.1-014).

Acknowledgments

The authors wish to thank Thu Dau Mot University for funding this research. We also would like to thank the students and technician staff of the Institute of Applied Technology, Thu Dau Mot University for their support and field/lab assistance.

Conflict of interest

TN is employed by Mekolink Co. Ltd., Vietnam.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's note

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References

Adebooye, O. C., Vijayalakshmi, R., and Singh, V. (2008). Peroxidase activity, chlorophylls and antioxidant profile of two leaf vegetables (Solanum nigrum L. and Amaranthus cruentus L.) under six pretreatment methods before cooking. Inter. J. Food Sci. Tech. 43, 173–178. doi: 10.1111/j.1365-2621.2006.01420.x

CrossRef Full Text | Google Scholar

Agricultural Extension Center of Ho Chi Minh city (2009). Handbook of growing safe leafy vegetables. Department of Agriculture and Rural Development, Ho Chi Minh City, Vietnam 1–44.

Ahmed, N., and Turchini, G. M. (2021). The evolution of the blue-green revolution of rice-fish cultivation for sustainable food production. Sust. Sci. 16, 1375–1390. doi: 10.1007/s11625-021-00924-z

CrossRef Full Text | Google Scholar

Ajay, C., Rajesh, K. P., Pradeep, K. V., Avineet, K. R., and Narendra, K. (2021). An updated review on Malabar spinach (Basella alba and Basella rubra) and their importance. J. Pharm. Phyt. 10, 1201–1207. doi: 10.22271/phyto.2021.v10.i2p.13974

CrossRef Full Text | Google Scholar

Bartels, J. (1996). Part 3: Chemical Methods Methods of Soil Analysis. Madison, Wisconsin, USA: Soil Science Society of America, Inc. 1387.

Berg, H. (2002). Rice monoculture and integrated rice-fish farming in the Mekong Delta, Vietnam—economic and ecological considerations. Ecol. Econ. 41, 95–107. doi: 10.1016/S0921-8009(02)00027-7

CrossRef Full Text | Google Scholar

Bich, T. T. N., Tri, D. Q., Yi-Ching, C., and Khoa, H. D. (2020). Productivity and economic viability of snakehead (Channa striata) culture using an aquaponics approach. Aqua. Engi. 89, 102057. doi: 10.1016/j.aquaeng.2020.102057

CrossRef Full Text | Google Scholar

Bloch, M. E. (1973). Naturgeschichte der ausländischen Fische. Berlin. v. 7: i-xiv + 1-144, Pls. 325–360. (Also a French edition, Ichthyologie, ou Histoire naturelle, générale et particulière des poissons, v. 10, published 1797).

Google Scholar

Boyd, B. C. E., Rajts, F., and Firth, J. (2011). Sludge management at pangasius farm cuts discharges. Environmental and social responsibility. Glob Aqua Adv. Available online at: https://www.aquaculturealliance.org/advocate/sludge-managementpangasius-farm-cuts-discharges (accessed February 18, 2020).

Cofie, O., Kone, D., Rothenberger, S., Moser, D., and Zubruegg, C. (2009). Co-composting of faecal sludge and organic solid waste for agriculture: Process dynamics. Water Res. 43, 4665–4675. doi: 10.1016/j.watres.2009.07.021

PubMed Abstract | CrossRef Full Text | Google Scholar

Da, C. T., Phuoc, L. H., Duc, H. N., Troell, M., and Berg, H. (2015). Use of wastewater from striped catfish (Pangasianodon hypophthalmus) pond culture for integrated rice–fish–vegetable farming systems in the Mekong Delta, Vietnam. Agro. Sust. Food. Syst. 39, 580–597. doi: 10.1080/21683565.2015.1013241

CrossRef Full Text | Google Scholar

Da, C. T., Vu, T. H., Duy, D. T., Ty, N. M., Thanh, D. T., Nguyen-Le, M.-T., et al. (2021). Recycled pangasius pond sediments as organic fertilizer for vegetables cultivation: strategies for sustainable food production. Clean. Tech. Environ. Poli. 9, 1–10. doi: 10.1007/s10098-021-02109-9

CrossRef Full Text | Google Scholar

Da, T. C., Anh Tu, P., Livsey, J., Tang, V. T., Berg, H., and Manzoni, S. (2020). Improving productivity in integrated fish-vegetable farming systems with recycled fish pond sediments. Agronomy. 10, 1–19. doi: 10.3390/agronomy10071025

CrossRef Full Text

Drózdz, D., Malińska, K., Mazurkiewicz, J., Kacprzak, M., Mrowiec, M., Szczypiór, A., et al. (2020). Potential of fish pond sediments composts as organic fertilizers. Waste. Biom. Valor. 11, 5151–5163. doi: 10.1007/s12649-020-01074-6

CrossRef Full Text | Google Scholar

Emeterio, I. J., and Victor, P. G. (1992). Determination of maturity indices for city refuse composts. Agri. Ecosyst. Environ. 38, 331–343. doi: 10.1016/0167-8809(92)90154-4

CrossRef Full Text

FAO (2020). The State of World Fisheries and Aquaculture 2020. Sustainability in action. Rome: FAO.

FAO (2022). Fisheries and aquaculture. Text by Nguyen, T.P. and Truong, H.M.. Fisheries and Aquaculture Division [online]. Rome. Available online at: https://www.fao.org/fishery/en/countrysector/naso_vietnam (accessed July 6, 2022).

Farrant, D. N., Frank, K. L., and Larsen, A. E. (2021). Reuse and recycle: Integrating aquaculture and agricultural systems to increase production and reduce nutrient pollution. Sci. Total. Environ. 785, 146–859. doi: 10.1016/j.scitotenv.2021.146859

PubMed Abstract | CrossRef Full Text | Google Scholar

Graber, A., and Junge, R. (2009). Aquaponic Systems: Nutrient recycling from fish wastewater by vegetable production. Desalination. 246, 147–156. doi: 10.1016/j.desal.2008.03.048

CrossRef Full Text | Google Scholar

Gustiano, R., Kurniawan, K., and Kusmini, I. I. (2021). “Bioresources and diversity of snakehead, Channa striata (Bloch 1793): a proposed model for optimal and sustainable utilization of freshwater fish,” in IOP Conference Series: Earth and Environmental Science (IOP Publishing) 762, 012012. doi: 10.1088/1755-1315/762/1/012012

CrossRef Full Text | Google Scholar

Haque, M. M., Belton, B., Alam, M. M., Ahmed, A. G., and Alam, M. R. (2016). Reuse of fish pond sediments as fertilizer for fodder grass production in Bangladesh: Potential for sustainable intensification and improved nutrition. Agric. Ecosyst. Environ. 216, 226–236. doi: 10.1016/j.agee.2015.10.004

CrossRef Full Text | Google Scholar

Haskell, M. J., Jamil, K. M., Hassan, F., Peerson, J. M., Hossain, M. I., Fuchs, G. J., et al. (2004). Daily consumption of Indian spinach (Basella alba) or sweet potatoes has a positive effect on total-body vitamin A stores in Bangladeshi men. T. Ameri. J. Clinic Nutrit. 80, 705–714. doi: 10.1093/ajcn/80.3.705

PubMed Abstract | CrossRef Full Text | Google Scholar

Hien, N. T. (2003). Organic fertilizer: Biofertilizer and compost fertilizer. Institute for research and universalization for encylopaedic knowledge (IREUK). Vietnamese: Nghe An Punblisher.

Houba, V. J. G., Huijbregts, A. W. M., Wilting, P., Novozamsky, I., and Gort, G. (1995). Sugar yield, nitrogen uptake by sugar beet and optimal nitrogen fertilization in relation to nitrogen soil analyses and several additional factors. Biol. Fertil. Soils. 19, 55–59.

Google Scholar

IBM SPSS Statistic (2020). IBM SPSS Statistic Program, Version 22 Statistical Software Packages. New York, NY: IBM Corporation.

ISO 11261:1995 (1995). Soil quality - Determination of Total Nitrogen - Modified Kjeldahl Method. Geneva, Switzerland: International Organization for Standardization.

Google Scholar

Karak, T., Bhattacharyya, P., Paul, R. K., Das, T., and Saha, S. K. (2013). Evaluation of composts from agricultural wastes with fish pond sediment as bulking agent to improve compost quality. CLEAN – Soil. Air. Water. 41, 711–723. doi: 10.1002/clen.201200142

CrossRef Full Text | Google Scholar

Makobo, N. D., Shoko, M. D., and Mtaita, T. A. (2010). Nutrient content of amaranth (Amaranthus cruentus L.) under different processing and preservation methods. World. J. Agric. Sci. 6, 639–643.

Google Scholar

MARD (2020). Annual Reports of the Ministry of Agriculture and Rural Development, Vietnam. Unpublished documents (in Vietnamese).

McLean, E. O. (1982). “Soil pH and lime requirement,” in Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties, eds. A. L. Page, R. H. Miller, D. R. Keeney (WI: American Social Agronomy Madison) 199–224. doi: 10.2134/agronmonogr9.2.2ed.c12

CrossRef Full Text | Google Scholar

Phu, T. Q., and Tinh, T. K. (2012). Chemical compositions of sludge from intensive striped catfish (Pangasianodon hypophthalmus) culture pond (in Vietnamese). J. Sci. Can Tho Uni. 22a, 290–299.

Phung, V. C., Nguyen, B. P., Kim Hoang, T., and Bell, R. W. (2009). “Recycling of fishpond waste from rice cultivation in Cuu Long Delta, Vietnam,” in Technologies and Management for Sustain-able Biosystems, eds. J., Nair, C., Furedy, C., Hoysala, H., Doelle (New York, NY: Nova Science Publishers) 85–97.

Google Scholar

Pueppke, S. G., Nurtazin, S., and Ou, W. (2020). Water and land as shared resources for agriculture and aquaculture: insigh. Asia. Water. 12, 2787. doi: 10.3390/w12102787

CrossRef Full Text | Google Scholar

Quynh, H. T., and Kazuto, S. (2018). Organic fertilizers in Vietnam's markets: Nutrient composition and efficacy of their application. Sustainability. 10, 2–13. doi: 10.3390/su10072437

CrossRef Full Text

Rahman, M., and Yakupitiyage, A. (2006). Use of fishpond sediment for sustainable aquaculture - agriculture farming. Inter. J. Sust. Develop. Plan. 1, 192–202. doi: 10.2495/SDP-V1-N2-192-202

CrossRef Full Text | Google Scholar

Rahman, M. M., Yakupitiyage, A., and Ranamukhaarachchi, S. L. (2004). Agricultural use of fishpond sediment for environmental amelioration. Tham. Inter. J. Sci. Tech. 9, 1–10.

Google Scholar

Saldarriaga, J. F., Gallego, J. L., López, J. E., Aguado, R., and Olazar, M. (2019). Selecting monitoring variables in the manual composting of municipal solid waste based on principal component analysis. Waste. Biomas. Valor. 10, 1811–1819. doi: 10.1007/s12649-018-0208-y

CrossRef Full Text | Google Scholar

Sun, X., Wang, S., Wang, J., Lu, W., and Wang, H. (2012). Cocomposting of night soil and green wastes. Compost. Sci. Util. 20, 254–259. doi: 10.1080/1065657X.2012.10737056

CrossRef Full Text | Google Scholar

Thanh, D. T., and Ty, N. M. (2022). Processed making organic fertilizer from sludge of snakehead fish (Channa striata block, 1793) pond farming combined with organic materials (Vietnamese). Thu Dau Mot Univ J. Sci. (TDMUJS). 6, 17–22. doi: 10.37550/tdmu.VJS/2022.06.346

CrossRef Full Text

Thanh, X. B., Hien, V. T. M., Cong, T. T., Da, C. T., and Berg, H. (2015). Reuse of sediment from catfish pond through composting with water hyacinth and rice straw. Sust. Environ. Res. 25, 5.

Google Scholar

VASEP (2019). Vietnam's fisheries industry overview 2018 of Vietnam Assosiation of Seafood Exporters and Producers. Vietnam: Vietnam Association of Seafood Exporters and Producers of Ministry of Agriculture and Rural Development (MARD).

Walkley, A., and Black, I. A. (1934). An examination of the Degtjareff method for determining soil organic matter, and a proposed modification of the chromic acid titration method. Soil. Sci. 37, 29–38. doi: 10.1097/00010694-193401000-00003

CrossRef Full Text | Google Scholar

Zhang, J., Chen, G., Sun, H., Zhou, S., and Zou, G. (2016). Straw biochar hastens organic matter degradation and produces nutrient-rich compost. Biochem. Tech. 200, 876–883. doi: 10.1016/j.biortech.2015.11.016

PubMed Abstract | CrossRef Full Text | Google Scholar

Zhu, N. (2007). Effect of low initial C/N ratio on aerobic composting of swine manure with rice straw. Biochm. Tech. 98, 9–13. doi: 10.1016/j.biortech.2005.12.003

PubMed Abstract | CrossRef Full Text | Google Scholar