Organic Vegetable Production Systems Research Articles

Accumulation and health risk of heavy metals in vegetables from harmless and organic vegetable production systems of China

Heavy metal accumulation in vegetables is a growing concern for public health. Limited studies have elucidated the heavy metal accumulation characteristics and health risk of different vegetables produced in different facilities such as greenhouses and open-air fields and under different management modes such as harmless and organic. Given the concern over the aforementioned factors related to heavy metal accumulation, this study selected four typical greenhouse vegetable production bases, short-term harmless greenhouse vegetable base (SHGVB), middle-term harmless greenhouse vegetable base (MHGVB), long-term harmless greenhouse vegetable base (LHGVB), and organic greenhouse vegetable base (OGVB), in Nanjing City, China to study heavy metal accumulation in different vegetables and their associated health risks. Results showed that soils and vegetables from SHGVB and OGVB apparently accumulated fewer certain heavy metals than those from other bases, probably due to fewer planting years and special management, respectively. Greenhouse conditions significantly increased certain soil heavy metal concentrations relative to open-air conditions. However, greenhouse conditions did not significantly increase concentrations of As, Cd, Cu, Hg, and Zn in leaf vegetables. In fact, under greenhouse conditions, Pb accumulation was effectively reduced. The main source of soil heavy metals was the application of large amounts of low-grade fertilizer. There was larger health risk for producers′ children to consume vegetables from the three harmless vegetable bases than those of residents′ children. The hazard index (HI) over a large area exceeded 1 for these two kinds of children in the MHGVB and LHGVB. There was also a slight risk in the SHGVB for producers′ children solely. However, the HI of the whole area of the OGVB for two kinds of children was below 1, suggesting low risk of heavy metal exposure through the food chain. Notably, the contribution rate of Cu and Zn to the HI were high in the four bases, yet current Chinese standards provide no limit for the concentrations of Cu and Zn; thus a potential health risk concerning these metals exists.

Accumulation and ecological effects of soil heavy metals in conventional and organic greenhouse vegetable production systems in Nanjing, China

The spatial variability of soil heavy metals in conventional and organic greenhouse vegetable production (CGVP and OGVP) systems can reveal the influence of different farming activities on their accumulation and plant uptake. This provides important basic data for soil utilization and pollution risk assessment. Based on horizontal and vertical spatial analysis, this paper presents the spatial variability and accumulation of soil heavy metals. The effects on plant uptake and factors influencing heavy metal accumulation are presented using the two typical greenhouse vegetable sites in Nanjing City, China as examples. Results showed that different greenhouse vegetable production systems had their own dominant heavy metal accumulation, specifically, Hg and Pb in CGVP system and Cd in OGVP system. The spatial analysis showed that horizontally, distribution of soil properties and heavy metal concentrations in the two sites showed decreases from specific regions to the periphery for organic matter (OM), Cd, Cu, Hg, Pb, and Zn in CGVP and OM, As, Cd, Cu, Hg, Pb, and Zn in OGVP. Vertically, soil properties and heavy metals mainly vary in the topsoil. The key factor for the accumulation was excess fertilizer input. Variation of soil properties and the accumulation of soil heavy metals significantly influenced heavy metal uptake by plants. However, accumulation risk varied according to different heavy metals and different plant species. Environmental management of these two kinds of production systems should pay more attention to fertilizer application, plant selection, and soil properties.

Effect of Volumetric Water Content and Clover (Trifolium incarnatum) on the Survival of Escherichia coli O157:H7 in a Soil Matrix

Studies aimed at understanding Escherichia coli O157:H7 soil survival dynamics are paramount due to their inevitable introduction into the organic vegetable production systems via animal manure-based fertilizer. Therefore, a greenhouse study was conducted to determine the survival of E. coli O157:H7 in highly controlled soil matrices subjected to two variable environmental stressors: (1) soil volumetric water content (25 or 45 % VWC), and (2) the growth of clover (planted or unplanted). During the 7-week study, molecular-based qPCR analyses revealed that E. coli O157:H7 survival was significantly lower in soils maintained at either near water-holding capacity (45 % VWC) or under clover growth. The significant reduction under clover growth was only observed when E. coli populations were determined relative to all bacteria, indicating the need to further study the competition between E. coli O157:H7 and the total bacterial community in organic soils. Given the significant effect of clover on E. coli O157:H7 survival under different moisture conditions in this greenhouse-based study, this work highlights the antimicrobial potential of clover exudates in arable soils, and future work should concentrate on their specific mechanisms of inhibition; ultimately leading to the development of crop rotations/production systems to improve pre-harvest food safety and security in minimally processed, ready-to-eat and organic production systems.

Soil enzyme activity under organic versus conventional vegetable production systems

There has been a growing trend in using soil enzymes as indicators for changes in soil quality under different management practices.Although literature on this subject has tremendously grown in the last 10 years,most of the studies have focused on cultivated fields.However,research on cultivated vegetable soils also has significant implications.Experiments were conducted at two close-by fields(one under organic farming and the other under conventional farming) in Shanghai to investigate the influence of different horticultural farm management practices on soil enzyme activities.Four combinations of field type and management system-organic management in greenhouse(GO),conventional management in greenhouse(GC),organic management in open-field(LO) and conventional management in open-field(LC) conditions-were evaluated.Soil sampled at the 0~20 cm depth were analyzed using the traditional soil analysis method.Furthermore,proteinase,urease,dehydrogenase,β-glucosidase and nitrate reductase activities were determined.The results presented here fostered an in-depth understanding of the impacts of management practices on soil enzyme activities.Soil electrical conductivity(EC) under organic managements was less than that under conventional management by averages of 12% and 16% in greenhouse and open-field conditions,respectively.The levels of microbial biomass C and N under organic managements were higher than those under conventional managements.Significant differences were noted in proteinase and prease activities among the different management practices.Proteinase,urease,dehydrogenase and β-glucosidase activities were comparatively high under organic management,while nitrate reductase activity was low.Management practices significantly affected proteinase and urease activities with P values of 0.006 8 and 0.012 4 respectively.Environmental conditions of cultivation significantly influenced proteinase,urease,β-glucosidase and nitrate reductase activities.Enzyme activities were higher in organic managements under greenhouse conditions than in other treatments.Analysis showed that proteinase,urease,dehydrogenase and β-glucosidase activities were closely correlated(at significant levels) with total dissolved nitrogen,microbial biomass C and microbial biomass N.In summary,organic systems significantly improved soil microbial characteristics and increased soil organic C,which in turn enhanced soil enzyme activities.Moreover,proteinase,urease,dehydrogenase and β-glucosidase activities were suitable indicators for soil fertility.Further studies that focus on determining the relationship between soil microbial diversity and specific enzyme activities under different management systems using the DGGE(denaturing gradient gel electrophoresis) technique were therefore recommended.

MULCHES INCREASE YIELD AND IMPROVE WEED CONTROL IN NO-TILL ORGANIC BROCCOLI (BRASSICA OLERACEA VAR. BOTRYTIS)

Weeds are a major limiting factor in organic vegetable production systems. The objective of this study was to determine the effects of tillage, cover crop and mulch on weed control and yield of organic broccoli. The experiment was a split plot with four replications, where tillage (conventional or no-till) was the main plot, cover crop [pearl millet (Pennisetum glaucum), cowpea (Vigna unguiculata), or soybean (Glycine max)] was the subplot, and mulch (black plastic film, wheat straw and unmulched) was the sub-sub plot. The cover crops were sown in the summer of 2005 and the broccoli plants were grown in the spring of 2006. Weed control over the season was 84.8 and 71.6% for the conventional tillage and no-till, respectively. Among cover crops, pearl millet tended to provide the highest weed control. Wheat straw and plastic film mulch both had higher levels of weed control compared to unmulched soil. Broccoli top biomass was higher in conventional tillage than in no-till, was not affected by cover crop and was highest in plastic mulch and lowest in unmulched soil. The marketable and total number of florets was unaffected by tillage, cover crop and mulch. Marketable and total floret yields and individual floret weight were highest on wheat straw and lowest on unmulched soil, and were unaffected by tillage and cover crop. Weed control was probably the main factor that explained the increased yields of plants grown on mulches. In conclusion, although cover crops residue alone partially inhibited weed growth, use of mulches (wheat straw or plastic film mulch) in combination with cover crop residue provided the best weed control.

Occurrence, fate, and ecotoxicity of antibiotics in agro-ecosystems. A review

Globally, besides human medicine, an increasing amount of antibiotics as veterinary drugs and feed additives are used annually in many countries with the rapid development of the breeding industry (livestock breeding and aquaculture). As a result, mostly ingested antibiotic doses (30–90%) and their metabolites to humans and animals, as emerging persistent contaminants, were excreted together with urine and feces, and subsequently disseminated into environmental compartments in forms of urban wastewater, biosolids, and manures. More importantly, significant amount of antibiotics and their bioactive metabolites or degradation products were introduced in agro-ecosystems through fertilization and irrigation with antibiotics-polluted manures, biosolids, sewage sludge, sediments, and water. Subsequently, accumulation and transport of antibiotics in soil–crop systems, particularly soil–vegetable systems, e.g., protected vegetable and organic vegetable production systems, poses great risks on crops, soil ecosystem, and quality of groundwater- and plant-based products. The aim of this review is to explore the sources, fates (degradation, adsorption, runoff, leaching, and crop uptake), and ecological risks of antibiotics in agro-ecosystems and possible food security and public health impacts. Three topics were discussed: (1) the occurrence, fates, and ecological impacts of antibiotics in agro-ecosystems, a global agro-ecological issue; (2) the potential ecological risks and public health threat of antibiotic pollution in soil–vegetable system, especially protected vegetable and organic vegetable production systems; and (3) the strategies of reducing the introduction, accumulation, and ecological risks of antibiotics in agro-ecosystems. To summarize, environmental contamination of antibiotics has become increasingly serious worldwide, which poses great risks in agro-ecosystems. Notably, protected vegetable and organic vegetable production systems, as public health closely related agro-ecosystems, are susceptible to antibiotic contamination. Occurrence, fate, and ecotoxicity of antibiotics in agro-ecosystems, therefore, have become most urgent issues among antibiotic environmental problems. Nowadays, source control, including reducing use and lowering environmental release through pretreatments of urban wastes and manures is a feasible way to alleviate negative impacts of antibiotics in agro-ecosystems.

Suitability of some farmscaping plants as nectar sources for the parasitoid wasp, Microplitis croceipes (Hymenoptera: Braconidae): Effects on longevity and body nutrients

In support of an ongoing study to evaluate potential farmscaping plants for utilization in organic vegetable production systems, we examined the effects of the nectar of three flowering plant species, sweet alyssum ( Lobularia maritima), buckwheat ( Fagopyrum sagittatum), and licorice mint ( Agastache foeniculum), on the lifespan and body nutrient levels of the wasp, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae), a key parasitoid of some caterpillar pests of vegetable crops in the USA. The greatest longevity (∼16 days) was recorded for honey-fed wasps (positive control). Buckwheat significantly increased the lifespan of female and male wasps by at least two-fold relative to wasps provided water only (longevity = 3–4 days). Licorice mint significantly increased female longevity and numerically increased male longevity. Sweet alyssum slightly increased longevity of both sexes but this was not significantly different from the water only control. Females had a significantly longer longevity than males on all the diet treatments. The greatest carbohydrate nutrient levels (sugar content and glycogen) were recorded in honey-fed wasps followed by wasps fed buckwheat, whereas very little nutrients were detected in wasps provided sweet alyssum, licorice mint or water only. However, female wasps were observed to attempt to feed on all three flowering plant species. Thus, the low nutrient levels detected in wasps provided sweet alyssum or licorice mint may be because the nectars were not accessible or were of poor quality. Further studies will evaluate the effects of the promising farmscaping plants on the beneficial and pest insect communities in the field.

Impact of organic amendments and compost extracts on tomato production and storability in agroecological systems

The sustainability of a farm system greatly relies on fertilizers and other inputs. Soil factors such as texture and local rainfall, along with management-related factors such as soil organic matter, aggregate stability and agronomic practices, have much greater influence on the sustainability of any given farm than do the type or amount of soil amendments. Growers use a wide variety of practices to maintain or improve soil health in organic vegetable production systems. These practices generally are part of long-term, site-specific management programs that aim at developing fertile and biologically active soils that readily capture and store water and nutrients, have good tilth, and suppress plant diseases. Field experiments were conducted in 2005 and 2006 in Mashhad, Iran, to study the effects of organic amendments, synthetic fertilizers and compost extracts on crop health, productivity and storability of tomato (Lycopersicon esculentum Mill.). Treatments included different fertilizers of cattle, sheep and poultry manures, green-waste and household composts and chemical fertilizers of urea and superphosphate; and five aqueous extracts from cattle manure, poultry manures, green-waste, and household composts plus water as control. Our results show that application of poultry manure showed lower disease incidence, as shown by 80% healthy tomato, compared with the other fertilizers. However, the organic fertilizers used did not give higher yields compared with chemical fertilizers. Sheep manure and chemical fertilizers led to the highest total tomato yield. Marketable yield was highest in poultry manures, of 16 t/ha, and lowest in chemical fertilizer, of 7 t/ha, 6 weeks after storage. The effect of aqueous extracts was not significant on either crop health or tomato yield and the results were inconsistent. The compost made of poultry manure therefore appears to be a promising ecological alternative to classical fertilizers.

Stale Seedbed Techniques for Organic Vegetable Production

Weed control in organic vegetable production systems is challenging and accounts for a large portion of production costs. Six methods to prepare a stale seedbed were compared on certified and transitional organic land in Salinas, CA, in 2004. Weed control operations occurred on raised beds 2 to 3 d before planting baby spinach or a simulated vegetable planting. A flamer and an herbicide application of 10% v/v of a clove oil mixture (45% v/v clove oil) at 280 L/ha (iteration 1) or 15% v/v of a clove oil mixture (45% clove oil) at 467 L/ha (iterations 2 and 3) were used to control weeds without disturbing the soil. Top knives on a sled, a rolling cultivator, and a rotary hoe were used to control weeds while tilling the bed top. A bed shaper–rototiller combination was also used, which tilled the entire bed. Broadleaf weed control was 36% with clove oil, 63% with the rotary hoe, and significantly higher (87 to 100% control) with the remaining treatments in iteration 1. Broadleaf weed control was consistently lower (72 to 86% control) with the flamer than all other treatments (95 to 100% control) in iterations 2 and 3. The difference between sites can probably be attributed to differences in weed size. The flamer and the clove oil herbicide had the lowest number of weeds emerging with the crop following stale seedbed formation. The most expensive technique was clove oil at $1,372/ha. The estimated cost of forming the stale seedbed with the remaining weed management tools ranged from $10 to $43/ha.

Effect of cover crop and management system on weed populations in lettuce

Changes in cropping systems can significantly impact pest population dynamics and management. Field experiments were conducted from 1998 to 2000 to study the effect of summer cover crop and in-season management system on weed infestations in lettuce ( Lactuca sativa L.). The experiment was a factorial with summer cover crop and management system as the two factors. Cover crops were cowpea [ Vigna unguiculata (L.) Walp.] incorporated into the soil in the fall (CWPI), cowpea used as mulch in the fall (CWPM), sudangrass ( Sorghum vulgare) incorporated into the soil in the fall (SDNG), and dry fallow (DFLW). Management systems were organic (ORG), integrated crop management (ICM), and conventional (CNV). In general, there was no interaction between cover crop and management system. Weed species richness was greatest early in the growing season and was affected by cover crop. Fewer species emerged in CWPM plots in general but perennial species became important with time. The DFLW showed greater weed populations than all cover crop treatments. Weed populations were similar in all management systems in 1999. However, in 2000, there was better weed suppression in the ORG and ICM systems than in the CNV system. CWPI significantly increased lettuce yield and DFLW yield declined the second year. Yield under the ORG system was low in 1999 and equivalent to that in the CNV and ICM systems in 2000. These results indicate that a prior summer cover crops can improve both conventional and organic vegetable production systems.

Sustainable Commercial Vegetable Production with Minimal Use of Synthetic Fertilizers and Pesticides

Sustainable production systems are characterized as systems that can be physically and biologically maintained in perpetuity, can avoid adverse environmental and health problems, and can be economically profitable. Organic vegetable production systems are one example of sustainable farming enterprises. In California, organic production and postharvest handling techniques are closely defined by legislation. Of the several grower groups representing organic farmers in the state, the California Certified Organic Farmers is the largest, representing 382 growers that farmed a total area of 10,375 ha in 1988. Of these, 200 growers are vegetable producers. Another organization active among organic growers in California, as well as Mexico, Central American countries, and the Caribbean, is the Organic Crop Improvement Association. Marketing organizations such as the Nutri-Clean Program, which tests produce for pesticide residues and certifies specific residue standards, and the Organic Market News and Information Service facilitate the sale of organic produce in California. Cultural practice information for organic vegetable production is difficult to find, particularly techniques that would allow a grower to switch from conventional to organic production. University researchers and extension workers have so far been of little help, although the Univ. of California Sustainability Program at Davis is beginning research and education activities. Funding for these activities is inadequate, and the program is understaffed. There is need for long-term, interdisciplinary, on-farm studies to study organic production techniques in a realistic setting. At present, the reward system in place in land-grant institutions offers little encouragement to researchers to engage in this kind of work. There are formidable obstacles to increasing the use of organic materials for crop fertilization. The nutrient content of the state's manure and organic waste supplies is probably insufficient to meet the fertility needs of California's crops. In addition, since the majority of land currently producing vegetable crops in California is leased, long-term soil fertility investments are a risky undertaking.

Sustainable Commercial Vegetable Production with Minimal Use of Synthetic Fertilizers and Pesticides: A Postlude

Sustainable production systems are characterized as systems that can be physically and biologically main- tained in perpetuity, can avoid adverse environmental and health problems, and can be economically profitable. Organic vegetable production systems are one example of sustainable farming enterprises. In California, organic production and postharvest handling techniques are closely defined by legislation. Of the several grower groups representing organic farmers in the state, the California Certified Organic Farmers is the largest, representing 382 growers that farmed a total area of 10,375 ha in 1988. Of these, 200 growers are vegetable producers. Another organization active among organic growers in California, as well as Mexico, Central American countries, and the Caribbean, is the Organic Crop Improvement Association. Marketing organizations such as the Nutri-Clean Program, which tests produce for pesticide residues and certifies specific residue standards, and the Organic Market News and Information Service facilitate the sale of organic produce in California. Cultural practice information for organic vegetable production is difficult to find, particularly techniques that would allow a grower to switch from conventional to organic production. University researchers and extension workers have so far been of little help, although the Univ. of California Sus- tainability Program at Davis is beginning research and education activities. Funding for these activities is inadequate, and the program is understaffed. There is need for long-term, interdisciplinary, on-farm studies to study organic production techniques in a realistic setting. At present, the reward system in place in land-grant institutions offers little encouragement to researchers to engage in this kind of work. There are formidable obstacles to increasing the use of organic materials for crop fertilization. The nutrient content of the state's manure and organic waste supplies is probably insufficient to meet the fertility needs of California's crops. In addition, since the majority of land currently producing vegetable crops in California is leased, long-term soil fertility investments are a risky undertaking.