Organic matter stabilization and phosphorus activation during vegetable waste composting: Multivariate and multiscale investigation

The conversion of organic matter and P in the waste composting process affects the efficiency of the composted product. However, the addition of microbial inoculants may improve the conversion characteristics of organic matter and P. In this study, straw-decomposing microbial inoculant (SDMI) was added to investigate its effects on the organic matter stabilization and phosphorus activation during the composting of vegetable waste (VWs). Aliphatic carboxyl-containing compounds were degraded during composting, but the stability of the organic matter and P was improved. The addition of SDMI promoted the degradation of dissolved organic carbon by 81.7 % and improved P stability and thermal stability of organic matter. Hedley sequential P fractionation showed a decrease in the H₂O-P proportion by >12 % and increased in the HCl-P proportion by >4 % by the end of composting. Stable forms of P, such as AlPO₄ and iron-containing phosphate, were the main forms of P in the final compost. The results provide a basis for producing high-quality vegetable compost products and improving the reutilization potential of VWs.

Assessing the environmental impacts of organic and conventional mixed vegetable production based on the life cycle assessment approach

This study aims to assess the environmental impacts and the energy efficiency of organic and conventional vegetable production in Palas Basin, Kayseri, Turkey. Three organic and three conventional farmers representing the vegetable production in the region participated in face-to-face questionnaires. Life cycle assessment (LCA) was implemented to assess the global warming potential (GWP), eutrophication potential (EP), acidification potential (AP), and energy use, which were selected as environmental impact potentials. Additionally, the environmental risk assessment was conducted to understand the impact of pesticide use in the region. Six farmers were investigated individually, and it was found that all of the farmers had a common cultivation calendar, but there were differences in the application. Particularly, mineral fertilizer use and irrigation were excessive in some agricultural practices. Although the use of N- and P-based mineral fertilizers was one of the main differences between organic and conventional farming, irrigation was a common practice. Irrigation, the most influential practice, elevated not only water consumption but also EP, AP, and GWP as a result of electricity consumption by electrical pumps. Electricity consumption from irrigation contributed to the GWP most, and this value was in the range of 45%-95%. Mineral fertilizer use covered up to 40% of the EP, 31% of the GWP, and 37% of the AP for conventional farmers. Three different scenarios were developed to reduce the environmental impacts of the use of excessive mineral fertilizer and irrigation. The developed scenarios recommended the reductions by 38%, 44%, 25%, and 60% in GWP, EP, AP, and total energy inputs, respectively. This study demonstrates that LCA is beneficial in determining the environmental impact of hotspots in vegetable production and allows the development of different solutions to mitigate environmental impacts for agricultural sustainability. Integr Environ Assess Manag 2022;18:1733-1746. © 2022 SETAC.

The immobilization, plant uptake and translocation of cadmium in a soil-pakchoi (Brassica chinensis L.) system amended with various sugarcane bagasse-based materials

Many organic materials have been used to decrease heavy-metal bioavailability in soil via in-situ remediation due to its high efficiency and easy operation; meanwhile, cheap materials have also been pursued to decrease the cost of remediation. Agricultural wastes exhibit their potential in remediation materials due to their low cost; however, raw agricultural wastes have a low ability to immobilize heavy metals in soil. Attempts have been made to modify agricultural wastes to improve the efficiency of heavy-metal passivation. In this study, novel agricultural waste-based materials, raw sugarcane bagasse (SB), citric acid modified (SSB) and citric-acid/Fe₃O₄ modified (MSB) sugarcane bagasse at 0.5% and 1% addition rates, were compared for their effectiveness in soil Cd passivation and Cd accumulations in pakchoi plants in a 30-day pot experiment. The addition of SB did not decrease soil bioavailable Cd effectively and slightly decreased Cd accumulation in plant roots and leaves. In comparison, SSB and MSB exhibited a great potential to decrease the transformation, translocation and accumulation of Cd with the decrease being greater at 1% than 0.5% rate in the soil-pakchoi system. For example, the addition of SSB and MSB at 0.5% decreased the concentration of Cd in leaves by 10%, and 16%, and at 1% decreased the concentration by 25% and 30%, respectively. High pH and abundant functional groups of three amendments played important roles in Cd immobilization. The enhanced microbial activities might also contribute to Cd passivation. However, plant growth was decreased in the amended treatments except SSB at 0.5% rate. The results suggest that citric-acid-modified sugarcane bagasse at addition rate of 0.5% has a potential to immobilize Cd in soil and decrease Cd accumulation in edible part of pakchoi effectively without decreasing vegetable growth.

A simplified non-greenhouse hydroponic system for small-scale soilless urban vegetable farming

Majority of under-developed countries continue to face a challenge of food insecurity around urban areas resulting from factors such as; limited access to arable land. This study aimed at developing a simplified low-tech hydroponic system for growing leafy vegetables alongside testing its economic viability. This was intended to support urban vegetable production and henceforth contributing to food security more so in under-developed states dealing with the challenge of increasing urban population vs. reducing arable land around urban/ peri-urban areas. A hydroponic unit for growing 60 leafy vegetables (using lettuce as a study crop) under non-controlled environmental conditions was designed and developed using low-cost and low-tech materials. Kratky hydroponic method which involves growing crops using water as a media without the need for water pumps and electricity was used. A study was also carried out to assess the profitability of the system. The results indicated a: net present values of 16.37$, internal rate of return of 12.57%, profitability index of 1.1 and non-discounted payback period of approximately 8 months (4 cropping seasons). These findings showed that the system has the potential to improve urban food production and availability in especially in developing countries in a profitable manner. Vegetable production using the hydroponic system can also contribute to:•tachievement of sustainable development goals, 2 (zero hunger) and 3 (good health and wellbeing);•improvement in urban agriculture production and income generation among urban farmers;•enhanced adoption of low-cost, low-tech, environmental-friendly and sustainable farming systems.

Distinguishing N2O and N2 ratio and their microbial source in soil fertilized for vegetable production using a stable isotope method

Vegetable production systems with excessive nitrogen fertilizer result in severe N₂O emission. It is pivotal to identify the source of N₂O for reducing N₂O emission, but estimating microbial pathways of N₂O production is very difficult due to the existence of N₂O reduction. A promising tool can address this problem by using δ¹⁸O and δ¹⁵N^SP of N₂O to construct a dual isotopocule plot. For ascertaining the microbial pathways of N₂O production and consumption in soil fertilized for vegetable production, four treatments were set up: urea (U), half urea and half organic fertilizer (UO), organic fertilizer (O) and no fertilizer (NF), and the experiment was carried out continuously for two years. The δ¹⁸O vs. δ¹⁵N^SP plot method indicated that the nitrification/fungal denitrification was a dominant in N₂O emission, and the U treatment was the highest, followed by OU, O and NF in the both years. Among the different treatments, furthermore, the N₂O flux had the same trend, whereas the extent of N₂O reduction showed an opposite trend. Overall, inorganic fertilizer enhances nitrification/fungal denitrification and hinders reduction of N₂O to N₂, resulting in a larger amount of N₂O emission. However, organic fertilizer increases the contribution of denitrification and greatly improves the extent of N₂O reduction, which helps to reduce N₂O emission. Therefore, organic fertilizer is crucial to reducing N₂O emission by enhancing N₂O reduction and should be properly applied in production practice.

The impact of improved road networks on marketing of vegetables and households' income in Dedo district, Oromia regional state, Ethiopia

Rural infrastructures are important factors which are involved in agricultural development in Ethiopia. Among them, rural road facilities play a very significant role in the improvement of agricultural production and household income. This is because a good rural road network hurries efficient delivery of agricultural farm input and creates an opportunity to supply product to market. Currently, poor road conditions are hindering supply of product to market, which in turn affects households' annual income in most rural areas of Ethiopia. Therefore, this study aimed to asses the impact of improved road networks on marketing of vegetables and households' income in Dedo district in Ethiopia. For the study, two kebele were selected and data were collected from randomly selected 176 households from two kebele in the district. In addition to this, key informant interviews and focus group discussions were also conducted. Data were analyzed by multiple response tests and multiple linear regression models on statistical packages of the social sciences (SPSS). Study found that, from the total annual income of households; 58.5% of income was earned from vegetable production and it takes a lion share of households’ annual income in the study area. Regression results revealed that independent variables in the study had an insignificant influence on rural household annual income (p < 0.05). The multiple correlation coefficient measure (R = 0.845) also indicates that the relationship between rural household annual income and independent (set of explanatory) variables was strongly correlated. Findings also expose that high transportation costs incurring, spoilage of the product, deprived extension, service and market information, and reduction of household income are among the major impacts of road infrastructure in the district. Therefore, study suggested that rural households must have gained road access and federal and local road authorities should give attention to rural area road infrastructural development.

Intensive vegetable production results in high nitrate accumulation in deep soil profiles in China

A comprehensive understanding of the patterns and controlling factors of nitrate accumulation in intensive vegetable production is essential to solve this problem. For the first time, the national patterns and controlling factors of nitrate accumulation in soil of vegetable systems in China were analysed by compiling 1262 observations from 117 published articles. The results revealed that the nitrate accumulation at 0-100 cm, 100-200 cm, 200-300 cm, and >300 cm were 504, 390, 349, and 244 kg N ha^-1, with accumulation rates of 62, 54, 19, and 16 kg N ha^-1 yr^-1 for plastic greenhouse vegetables (PG); for open field vegetables (OF), they were 264, 217, 228, and 242 kg N ha^-1 with accumulation rates of 26, 24, 18, and 10 kg N ha^-1 yr^-1, respectively. Nitrate accumulation at 0-100 cm, 0-200 cm, and 0-400 cm accounted for 5%, 11%, and 17% of accumulated nitrogen (N) inputs for PG, and represented 4%, 9%, and 13% of accumulated N inputs for OF. Nitrogen input rates and soil pH had positive effects and soil organic carbon, water input rate, and carbon to nitrogen ratio (C/N) had negative effects on nitrate accumulation in root zone (0-100 cm soil). Nitrate accumulation in deep vadose zone (>100 cm soil) was positively correlated with N and water input rates, and was negatively correlated with soil organic carbon, C/N, and the clay content. Thus, for a given vegetable soil with relatively stable soil pH and soil clay content, reducing N and water inputs, and increasing soil organic carbon and C/N are effective measures to control nitrate accumulation.

Gasification biochar from horticultural waste: An exemplar of the circular economy in Singapore

Organic waste, the predominant component of global solid waste, has never been higher, resulting in increased landfilling, incineration, and open dumping that releases greenhouse gases and toxins that contribute to global warming and environmental pollution. The need to create and adopt sustainable closed-loop systems for waste reduction and valorization is critical. Using organic waste as a feedstock, gasification and pyrolysis systems can produce biooil, syngas, and thermal energy, while reducing waste mass by as much as 85-95% through conversion into biochar, a valuable byproduct with myriad uses from soil conditioning to bioremediation and carbon sequestration. Here, we present a novel case study detailing the circular economy of gasification biochar in Singapore's Gardens by the Bay. Biochar produced from horticultural waste within the Gardens was tested as a partial peat moss substitute in growing lettuce, pak choi, and pansy, and found to be a viable substitute for peat moss. At low percentages of 20-30% gasification biochar, fresh weight yields for lettuce and pak choi were comparable to or exceeded those of plants grown in pure peat moss. The biochar was also analyzed as a potential additive to concrete, with a 2% biochar mortar compound found to be of suitable strength for non-structural functions, such as sidewalks, ditches, and other civil applications. These results demonstrate the global potential of circular economies based on local biochar creation and on-site use through the valorization of horticultural waste via gasification, generating clean, renewable heat or electricity, and producing a carbon-neutral to -negative byproduct in the form of biochar. They also indicate the potential of scaled-up pyrolysis or gasification systems for a circular economy in waste management.

Pyrolyzed biowastes deactivated potentially toxic metals and eliminated antibiotic resistant genes for healthy vegetable production

Potentially toxic metals (PTEs) and antibiotic resistance genes (ARGs) present in bio-wastes were the major environmental and health risks for soil use. If pyrolyzing bio-wastes into biochar could minimize such risks had not been elucidated. This study evaluated PTE pools, microbial and ARGs abundances of wheat straw (WS), swine manure (SM) and sewage sludge (SS) before and after pyrolysis, which were again tested for soil amendment at a 2% dosage in a pot experiment with a vegetable crop of pak choi (Brassica campestris L.). Pyrolysis led to PTEs concentration in biochars but reduced greatly their mobility, availability and migration potential, as revealed respectively by leaching, CaCl₂ extraction and risk assessment coding. In SM and SS after pyrolysis, gene abundance was removed by 4-5 orders for bacterial, by 2-3 orders for fungi and by 3-5 orders for total ARGs. With these material amended, PTEs available pool decreased by 25%-85% while all ARGs eliminated to background in the pot soil. Unlike a >50% yield decrease and a >30% quality decline with unpyrolyzed SM and SS, their biochars significantly increased biomass production and overall quality of pak choi grown in the amended soil. Comparatively, amendment of the biochars decreased plant PTEs content by 23-57% and greatly reduced health risk of pak choi, with total target hazard quotient values well below the guideline limit for subsistence diet by adult. Furthermore, biochar soil amendment enabled a synergic improvement on soil fertility, product quality, and biomass production as well as metal stabilization in the soil-plant system. Thus, biowastes pyrolysis and reuse in vegetable production could help build up a closed loop of production-waste-biochar-production, addressing not only circular economy but healthy food and climate nexus also and contributing to achieving the United Nations sustainable development goals.

Manure fertilization increase antibiotic resistance in soils from typical greenhouse vegetable production bases, China

A large quantity of manure is applied in greenhouse vegetable production (GVP) soils, while manure fertilization often leads to the proliferation of antibiotic resistance genes (ARGs) in soils. However, comprehensive study on the effects of different types of manure on ARGs in GVP soils remains unknown, and the baseline level of ARGs in GVP soil is poorly quantified. This study conducted a comprehensive survey of ARGs in GVP soils using high-throughput quantitative PCR. We found elevated ARG diversity and absolute abundance in fertilized soil, whereas no significant difference in soil ARGs amended with different types of manure. Redundancy analysis indicated that the change of bacterial community compositions and environmental factors contributed partially to the shift in ARG profiles. Bipartite network analysis indicated that one ARG was detected in non-manured soils, while 50 ARGs and 4 mobile gene elements were exclusively detected in fertilized soils, suggesting introduction of ARGs from manure into soils largely explained the increased ARG diversity in fertilized soil. By comparison of ARG absolute abundance between manured and non-manured soil, we estimated the typical level of ARG absolute abundance in non-manured soil, which provided the first rough baseline level of ARGs to assess ARG contamination in GVP soils.

Strategies to mitigate nitrate leaching in vegetable production in China: a meta-analysis

Nitrate leaching is a main nitrogen (N) loss pathway in vegetable production. Although there are numerous mitigation practices that control nitrate leaching, an integrated assessment of these measures is lacking. Thus, we conducted a meta-analysis to integrate the assessment of strategies for controlling nitrate leaching from vegetable systems in China. The main strategies included improved N fertilizer management (INFM), reduced water management (RWM), comprehensive regulation of N fertilizer and water management (CFWM), and catch crops (CCs). Each mitigation measure decreased nitrate leaching significantly and did not reduce vegetable yields. CFWM reduced nitrate leaching the most at 41% on average, followed by CCs, RWM, and INFM (35%, 24%, and 22%, respectively). The nitrate leaching scaled yields (NLSY, defined as yield divided by the quantity of nitrate leaching) were significantly increased by 87%, 44%, 32%, and 27% for CFWM, CCs, INFM, and RWM, respectively. The efficacies of the strategies were dependent on soil properties. CFWM, INFM, and RWM were more effective in soils with low pH and coarse texture than in other soils. In conclusion, the risk of nitrate leaching from vegetable production systems is high, and INFM and CFWM are suggested to decrease nitrate leaching from vegetable production.

Bioaccumulation and human exposure of perfluoroalkyl acids (PFAAs) in vegetables from the largest vegetable production base of China

This study investigated perfluoroalkyl acids (PFAAs) in edible parts of vegetables, soils, and irrigation water in greenhouse and open filed, for the first time, in Shouguang city, the largest vegetable production base in China, which is located nearby a fluorochemical industrial park (FIP). The bioaccumulation factors (BAFs) were calculated, and the human exposures of PFAAs via consumption of the vegetables for different age groups assuming the maximum levels detected in each vegetable and average consumption rates were also estimated. The ΣPFAA levels ranged from 1.67 to 33.5 ng/g dry weight (dw) in the edible parts of all the vegetables, with perfluorobutanoic acid (PFBA) being the dominant compound with an average contribution of 49% to the ΣPFAA level. The leafy vegetables showed higher ΣPFAA levels (average 8.76 ng/g dw) than the fruit and root vegetables. For all the vegetables, the log₁₀ BAF values of perfluorinated carboxylic acids showed a decreasing trend with increasing chain length, with PFBA having the highest log₁₀ BAF values (average 0.98). Cabbage had higher bioaccumulation of PFBA (log₁₀ BAF 1.24) than other vegetables. For the greenhouse soils and vegetables, the average contribution of perfluorooctanoic acid (PFOA) to ΣPFAA was lower than that in the open field samples, while the contributions of PFBA, PFHxA, PFPeA to ΣPFAA were higher. Irrigation water may be an important source of PFAAs in greenhouse, while for open field vegetables and soils, atmospheric deposition may be an additional contamination pathway. The estimated maximum exposure to PFOA through vegetable consumption for urban preschool children (aged 2-5 years) was 63% of the reference dose set by the European Food Safety Authority. Suggestions are also provided for mitigating the health risks of human exposure to PFAAs.

Estimating greenhouse gases emissions from horticultural peat soils using a DNDC modelling approach

Peat soils represent an important global carbon (C) sink, but can also provide a highly fertile medium for growing horticultural crops. Sustainable crop production on peat soils involves a trade-off between ensuring food security and mitigating typically high greenhouse gas (GHG) emissions and rates of soil C loss. An alternative approach to resource intensive field-based monitoring of GHG fluxes for all potential management scenarios is to use a process-based model driven by existing field data to estimate emissions. The aim of this study was to evaluate the suitability of the Denitrification-Decomposition (DNDC) model for estimating emissions of CO₂, N₂O and CH₄ from horticultural peat soils. The model was parameterised using climatic, soil, and crop management data from two intensively cultivated sites on soils of contrasting soil organic matter (SOM) contents (∼35% and ∼70% SOM content). Simulated emissions of CO₂, N₂O and CH₄, and simulated soil physical and crop output values, were compared to actual GHG, soil and crop measurements. Model performance was assessed using baseline parameterisation (i.e. model defaults), then calibrated using pre-simulation and sensitivity analysis processes. Under baseline parameterisation conditions, DNDC proved poor at predicting GHG emissions and soil/crop variables. Calibration and validation improved DNDC performance in estimating the annual magnitude of emissions, but model refinement is still required for reproducing seasonal GHG patterns in particular. Key constraints on model functioning appear to be its ability to reliably model soil moisture and some aspects of C and nitrogen dynamics, as well as the quality of input data relating to water table dynamics. In conclusion, our results suggest that the DNDC (v. 9.5) model cannot accurately reproduce or be used to replace actual field measurements for estimation of GHG emission factors under different management scenarios for horticultural peat soils, but may be able to do so with further modification.

Characteristics of nitrogen balance in open-air and greenhouse vegetable cropping systems of China

Nitrogen (N) loss from vegetable cropping systems has become a significant environmental issue in China. In this study, estimation of N balances in both open-air and greenhouse vegetable cropping systems in China was established. Results showed that the total N input in open-air and greenhouse vegetable cropping systems in 2010 was 5.44 and 2.60 Tg, respectively. Chemical fertilizer N input in the two cropping systems was 201 kg N ha(-1) per season (open-air) and 478 kg N ha(-1) per season (greenhouse). The N use efficiency (NUE) was 25.9 ± 13.3 and 19.7 ± 9.4% for open-air and greenhouse vegetable cropping systems, respectively, significantly lower than that of maize, wheat, and rice. Approximately 30.6% of total N input was accumulated in soils and 0.8% was lost by ammonia volatilization in greenhouse vegetable system, while N accumulation and ammonia volatilization accounted for 19.1 and 11.1%, respectively, of total N input in open-air vegetable systems.

Soil contamination by phthalate esters in Chinese intensive vegetable production systems with different modes of use of plastic film

The concentrations of six priority phthalic acid esters (PAEs) in intensively managed suburban vegetable soils in Nanjing, east China, were analyzed using gas chromatography-mass spectrometry (GC-MS). The total PAE concentrations in the soils ranged widely from 0.15 to 9.68 mg kg(-1) with a median value of 1.70 mg kg(-1), and di-n-butyl phthalate (DnBP), bis-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DnOP) were the most abundant phthalate esters. Soil PAE concentrations depended on the mode of use of plastic film in which PAEs were incorporated as plasticizing agents and both the plastic film and poultry manure appeared to be important sources of soil PAEs. Vegetables in rotation with flooded rice led to lower concentrations of PAEs in soil. The results indicate that agricultural plastic film can be an important source of soil PAE contamination and further research is required to fully elucidate the mechanisms of PAE contamination of intensive agricultural soils with different use modes of use of plastic film.