Soil Fumigation Research Articles

Effects of soil factors on dimethyl disulfide desorption and the risk of phytotoxicity to newly-planted seedlings

Dimethyl disulfide (DMDS) is a relatively new soil fumigant used in agro-industrial crop production to control soil-borne pests that damage crops and reduce yield. The emissions of DMDS after fumigation reduce soil concentrations thus reducing the risk of phytotoxicity to newly planted crops. However, the factors affecting the desorption of DMDS from soil are unclear. In our study, the desorption characteristics of DMDS from soil were measured in response to continuous ventilation. The degradation of DMDS in soil was examined by thermal incubation. The phytotoxic response of newly-planted cucumber (Cucumis sativus) seedlings to DMDS residues was measured by a sand culture experiment. The results showed DMDS desorption and degradation rates fit a first-order model; that 92% of the DMDS desorption occurred in the first hour after fumigant application; and that residue concentrations in the soil at the end of the ventilation period were unlikely to be phytotoxic to newly-planted cucumber seedlings. By the third day of ventilation, the average desorption rate (ADR) of DMDS in Wenshan soil was 4.0 and 3.6 times, respectively, faster than that in Shunyi and Suihua soils and the ADR of DMDS in soil decreased by 40.0% when the soil moisture content increased from 3% to 12% (wt/wt). Moreover, within one hour of ventilation, the ADR of DMDS in soil decreased by 20.1% when the soil bulk density increased from 1.1 to 1.3 g cm-3. The degradation of DMDS in soil, however, was mostly influenced by soil type and moisture content. A slow degradation rate resulted in a high initial desorption concentration of DMDS in soil. Our results indicated that DMDS desorption from soil in response to continuous ventilation was affected by the soil type, moisture content and bulk density. Rapid degradation of DMDS in soil will lower the risk of phytotoxic residues remaining in the soil and reduce emissions during the waiting period. Acceleration of emissions early in the waiting period by managing soil moisture content or increasing soil porosity may shorten the duration of emissions. Alternatively, soil extraction technology could be developed to recover and reduce fumigant emissions.

Role of Reductive Soil Disinfestation and Chemical Soil Fumigation on the Fusarium Wilt of Dioscorea batatas Decne Suppression

Reductive soil disinfestation (RSD) and chemical soil fumigation (CSF) comprise the most popular pre-planting soil management strategies. Their efficiency in suppressing several plant diseases in agricultural production systems has been compared. However, the disease-control effect of these methods on Fusarium wilt disease in Dioscorea batatas Decne (D. batatas) remains unclear. Importantly, dissimilarities in the impact of their bio-predictors on plant health have not been well characterized. Herein, four treatments, including no treatment (CK), RSD with gran chaff (GC-RSD) and molasses (MO-RSD), and CSF with dazomet (DA-CSF), were performed in a pot experiment using D. batatas-diseased soil. Compared with the CK treatment, the Fusarium oxysporum population significantly decreased by 88.89–97.78% following the DA-CSF, GC-RSD, and MO-RSD treatments. The bacterial community and functional composition of the soil were considerably altered by these treatments. However, the incidence of Fusarium wilt disease in D. batatas was significantly decreased in the two RSD-treated soils, rather than in DA-CSF-treated soils. Bacterial α-diversity and population as well as some key nitrogen-related functional gene expressions as bio-predictors were significantly lower in DA-CSF-treated soil than in RSD-treated soil. In particular, the core (e.g., Azotobacter, Phenylobacterium, Clostridium, Bradyrhizobium, Microvirga, and Caulobacter) and unique (e.g., Pseudomonas, Brevundimonas, Flavobacterium, Ochrobactrum, and Sphingobacterium) functional microbiomes in RSD-treated soil exerted a positive impact on soil functional composition of the soil and plant growth. Taken together, our results indicate that RSD outperformed CSF in promoting plant health by regulating the bacterial community and functional composition.

Effect of 4-Ethylbenzaldehyde from the Volatilome of Annona muricata on Meloidogyne incognita.

The demand for new soil fumigants has increased as a result of more restrictive legislation regarding the use of pesticides. In the present study, the potent nematicidal activity of volatile organic compounds released by the Annona muricata leaf macerate was demonstrated. In addition, we searched in the A. muricata volatilome for a molecule with potential to be developed as a new fumigant nematicide. In the greenhouse, even the lowest concentration of soursop leaf macerate tested (1.0%) as a biofumigant caused a significant (P < 0.05) reduction in Meloidogyne incognita infectivity and reproduction when compared with the nontreated control (0%). Forty-one compounds were identified through gas chromatography-mass spectrometry analysis, of which three (sabinene, caryophyllene oxide, and 4-ethylbenzaldehyde) were selected for studies against the nematode. Among these compounds, in in vitro trails, only 4-ethylbenzaldehyde showed nematicidal activity at 250 µg ml-1. The effective doses of 4-ethylbenzaldehyde predicted to kill 50 and 95% of the M. incognita second-stage juvenile population after 48 h of exposure were 35 and 88 µg ml-1, respectively. In in vitro tests, 4-ethylbenzaldehyde at 150 µg ml-1 reduced M. incognita egg hatching to values similar (P > 0.05) to those of the commercial nematicide fluensulfone at a concentration of 200 µg ml-1. In plant experiments, as a soil fumigant, 4-ethylbenzaldehyde at a dose of 1 ml/liter of substrate had an effect similar (P > 0.05) to that of the commercial fumigant Dazomet (250 µg ml-1). Therefore, 4-ethylbenzaldehyde shows potential for development as a new nematicide.

How Does Watermelon Grafting Impact Fruit Yield and Quality? A Systematic Review

Globally, there has been an increase in stringent regulations governing the use of chemical soil fumigants for controlling diseases, pests, and weeds. Grafting has been identified as an effective alternative to soil fumigation for managing soilborne diseases and pests in intensive vegetable cropping systems. The majority of watermelon (Citrullus lanatus) grafting research confirms that selected rootstocks play a role in improving plant resistance or tolerance to common soilborne diseases. Currently, there is a lack of evidence-based literature on the effects of grafting on watermelon fruit quality attributes and yield components. Previous reviews report wide variation in the impact of grafting on watermelon production, depending on rootstock–scion combinations and environmental conditions. This review employed evidence-based synthesis methods to comprehensively and methodically summarize research results of the impact of grafting on watermelon, with a focus on fruit quality and yield. In this systematic review, 548 citations (studies published during 2011–21) were screened against strict inclusion criteria, and data were extracted from 47 studies. Meta-analysis of percent differences between the grafted watermelon treatment and the nongrafted or self-grafted watermelon control was performed using extracted data of yield components and a wide range of fruit quality attributes. Meta-analysis of research data with variance measures was also conducted based on a rather limited number of studies. Our findings showed higher levels of total yield, average fruit weight, fruit length and width, fruit lycopene and soluble solids content, rind thickness, flesh firmness, lightness, chroma, and flesh nitrogen (N) content in grafted watermelon treatments compared with the nongrafted or self-grafted control. In particular, total yield, average fruit weight, and flesh firmness exhibited significant increases of a more than 10% difference. In contrast, grafted plants demonstrated decreases in fruit pH, hue angle, and flesh calcium content, although the reduction was not greater than 10% relative to the control. Meta-analysis of research data with variance measures further confirmed significantly greater total yield and flesh N content in grafted watermelon treatments compared with the nongrafted or self-grafted control. In addition, the meta-analysis results confirmed greater benefits of watermelon grafting in the presence of known soilborne disease pressure in contrast to the production scenarios without soilborne disease problems.

The Impact of Organic, Inorganic Fertilizers, and Biochar on Phytochemicals Content of Three Brassicaceae Vegetables

The need for soil fumigants of natural origin such as glucosinolates (GSLs) has increased due to the general prevention of manmade soil fumigants. GSLs and other phytochemicals (vitamin C and phenols) present in Brassica vegetables such as turnips, arugula, and mustard have antioxidant properties, and hence have important health attributes. The study examined how different soil amendments (chicken manure CM, vermicompost Vermi, horse manure HM, sewage sludge SS, elemental inorganic fertilizer Inorg, organic fertilizer Org, and biochar) impact the concentrations of glucosinolates (GSLs), vitamin C, phenols, and reducing sugars in three varieties of turnips (Purple Top White Globe PTWG, Scarlet Queen Red SQR, and Tokyo Cross TC), arugula, and mustard greens grown under field conditions. The results showed that mustard greens contained higher concentrations of GSLs (974 µg g−1 fresh shoots) than arugula (651 µg g−1 fresh shoots), and the TC variety of turnip had the highest concentrations of GSLs, vitamin C, and sugars. Additionally, amending the soil with SS, CM, and HM significantly increased the vitamin C content in mustard shoots by 82%, 90%, and 31%, respectively, and the total phenols by 77%, 70%, and 36%, respectively, compared to the control treatment. The increased inorganic fertilizers cost, and availability of large amounts of animal manure made animal manure application to cropland an attractive disposal option.

Effect of Bed Preparation on Native Wildflower Establishment, Weed Control, and Arthropod Presence

Native flowering forbs plantings have been found to support diverse arthropod communities by providing year-round forage and refuge from prey and chemical pollutants. Typically, pollinator habitats are planted from seeds; however, poor establishment and weed pressure often result in limited success of the planting. In this study, we evaluated two bed preparation techniques, a glyphosate treatment with no tillage and tillage with soil fumigant (dazomet) to determine their impact on herbaceous perennial transplants establishment, weed control, and arthropod presence. Our results suggest that forbs grown in beds that are tilled and treated with dazomet exhibit greater growth, produce more blooms, and experience reduced weed pressure compared to plants grown in untilled beds treated with glyphosate. We also found that the bed preparation method had no effect on arthropod activity, despite higher bloom counts in plants grown in beds prepared with tillage and dazomet applications. This research indicates that of the fifteen native flowering forbs examined in this study, a majority attracted abundant and diverse insect populations, despite variations in plant growth and bloom counts due to bed preparation treatments.

Anaerobic soil disinfestation with ethanol or sucrose reduces the viability of Meloidogyne javanica and Stromatinia cepivora

Anaerobic soil disinfestation (ASD) is an ecological alternative to chemical soil fumigation. However, little is known about the potential of this technique for the management of Meloidogyne javanica and Stromatinia cepivora. To test the hypothesis that ASD reduces the viability of these two pathogens, we assessed ethanol (5%, v:v) and sucrose (5%, m:v) as carbon sources for ASD, for an incubation period of three weeks. Twenty kilograms of soil naturally infested with M. javanica (82 ± 43 J2 100 cm-3 soil) were placed into a plastic container. Polyester traps, each with 15 S. cepivora sclerotia, were buried at 10 and 20 cm depth per container. ASD with diluted ethanol or sucrose (5% v:v or m:v) was compared to the untreated control (UTC), chemical fumigant metam sodium (MS), and soil saturation with water. In comparison to the UTC, ASD using ethanol reduced the numbers of J2 in soil and the galls in tomato roots by more than 93%, a degree of suppression similar to that achieved when using MS. The viability of sclerotia of S. cepivora was reduced by ASD using ethanol or sucrose from 38.12 to 58.1% compared to the UTC. ASD for three weeks using ethanol or sucrose (5%) reduces the viability of M. javanica and S. cepivora in the microcosm.

Long-term effects of chloropicrin fumigation on soil microbe recovery and growth promotion of Panax notoginseng.

Panax notoginseng is a precious Chinese medicinal material. Soil fumigation can control soil-borne disease and overcome the continuous cropping obstacles of P. notoginseng. However, chloropicrin (CP) fumigation can kill non-target soil microorganisms and reduce microbial diversity, but the long-time impacts of CP fumigation on soil microbial are less reported. We studied the long-term effects of CP fumigation on soil microbes with high-throughput gene sequencing, and correlated the changes in the composition of microbial communities with environmental factors like soil physicochemical properties and soil enzyme activities. This study mainly focuses on the recovery characteristics of soil microbe after soil fumigation by evaluating the ecological restoration of P. notoginseng soil, its sustained control effect on plant diseases, and its promotion effect on crop growth by focusing on the CP fumigation treatment. The results showed that CP fumigation significantly increased soil available phosphorus (P) to 34.6 ~ 101.6 mg/kg and electrical conductivity (EC) by 18.7% ~ 34.1%, respectively. High-throughput gene sequencing showed that soil fumigation with CP altered the relative abundance of Trichoderma, Chaetomium, Proteobacteria, and Chloroflexi in the soil while inhibiting a lot of Fusarium and Phytophthora. The inhibition rate of Phytophthora spp. was still 75.0% in the third year after fumigation. Fumigation with CP enhanced P. notoginseng's survival rate and stimulated plant growth, ensuring P. notoginseng's healthy in the growth period. The impact of fumigation on microbial community assembly and changes in microbial ecological niches were characterized using normalized stochasticity ratio (NST) and Levins' niche breadth index. Stochasticity dominated bacterial community assembly, while the fungal community was initially dominated by stochasticity and later by determinism. Fumigation with CP reduced the ecological niches of both fungi and bacteria. In summary, the decrease in microbial diversity and niche caused by CP fumigation could be recovered over time, and the control of soil pathogens by CP fumigation remained sustainable. Moreover, CP fumigation could overcome continuous cropping obstacles of P. notoginseng and promote the healthy growth of P. notoginseng.

Mechanisms by which chloropicrin fumigation promotes soil potassium conversion and absorption.

Fumigation of soil using chloropicrin has been proven to significantly affect soil nutrient cycling, but the mechanism by which soil potassium conversion and plant uptake is promoted remains unclear. In this study, we conducted a fumigation experiment to investigate the effects of chloropicrin soil fumigation on the conversion of soil potassium post-fumigation (days 7-70), and its mechanisms, tomatos were planted in fumigated and non-fumigated soils to enable further comparisons. Results showed that the content of rapidly available potassium and available potassium decreased by 16-24% and 17-23% at day 28 respectively, when tomato was planted in chloropicrin-fumigated soils compared to the non-fumigated soils. The potassium content of tomato planted in fumigated soil was significantly higher than that planted in non-fumigated soil (30.3 vs. 21.9 mg g-1 dry weight). Chloropicrin fumigation resulted in a significant change in the soil bacterial and fungal community structures, and trigged a long-term (at least 70-day) decrease in microbial diversity. Network analysis showed that chloropicrin soil fumigation changed microbial co-occurrence patterns by decreasing bacterial total links, nodes, and average degree, and increasing fungal total links, nodes, and average degree. Chloropicrin fumigation caused significant changes in the relative abundance of Bacillus species, which are involved in potassium dissolution. Structural equation model (SEM) suggested that fumigation with chloropicrin enhanced the contribution of soil potassium to tomato growth and reduced the contribution of bacterial communities. Together, the results of our study help in understanding the crop yield enhancement mechanism of soil fumigation.

Response of soil phosphatase activity and soil phosphorus fractions to the application of chloropicrin and azoxystrobin in ginger cultivation.

Soil fumigation can change soil nutrient cycling processes by affecting soil beneficial microorganisms, which is a key issue for soil fertility. However, the effect of combined application of fumigant and fungicide on soil phosphorus (P) availability remains largely unclear. We investigated the effects of the fumigant chloropicrin (CP) and the fungicide azoxystrobin (AZO) on soil phosphatase activity and soil P fractions in ginger production using a 28-week pot experiment with six treatments: control (CK), a single application of AZO (AZO1), double applications of AZO (AZO2), CP-fumigated soil without AZO (CP), CP combined with AZO1 (CP + AZO1) and CP combined with AZO2 (CP + AZO2). AZO application alone significantly increased the soil labile P fractions (Resin-P + NaHCO3 -Pi + NaOH-Pi) at 9 weeks after planting (WAP) but decreased the soil phosphatase activity at 28 WAP. CP fumigation significantly reduced the soil phosphatase activity but increased the proportions of soil labile P fractions (Resin-P + NaHCO3 -Pi + NaHCO3 -Po) to total P (TP) by 9.0-15.5% throughout the experiment. The combined application of CP and AZO had a synergistic effect on soil phosphatase activity and soil P fractions compared with a single application. Although AZO application and CP fumigation can increase soil available P in the short term, they might negatively affect soil fertility in the long run by inhibiting soil phosphatase activity. Soil microbial activities, especially microorganisms related to P cycling, may be responsible for the variations in soil P availability, but further research is needed. © 2023 Society of Chemical Industry.

Comprehensive Control System for Ginger Bacterial Wilt Disease Based on Anaerobic Soil Disinfestation

Bacterial wilt is a soil-borne disease that causes severe damage in ginger-growing regions of Japan (eight prefectures in the Shikoku, Kyushu, and Honshu regions). Because the pathogen Ralstonia pseudosolanacearum usually lives in deeper soil and infects host plants via the roots, it is not easy to eliminate even with chemical pesticides (such as soil fumigants). In our previous study, we found that anaerobic soil disinfestation with diluted ethanol (Et-ASD) effectively eliminated this pathogen. We conducted field experiments to confirm the effectiveness of Et-ASD in a ginger monoculture system. Eight trials were conducted in seven different ginger fields from spring to autumn. Excluding one trial in early spring, seven trials in summer successfully eliminated the pathogen from the field soil (below the detection limit by the developed sensitive bio-PCR method), and no disease recurrence was observed after ASD treatment. In addition, other useful methods for controlling the disease were explored, including proper field management after the disease outbreak and the disinfection of seed rhizomes. Based on these results, a comprehensive control system for bacterial wilt disease in ginger was developed.

Managing Plant‐Parasitic Nematodes in Pacific Northwest Potatoes

AbstractSeveral plant‐parasitic nematode species are found in Pacific Northwest potato fields, and they can potentially cause agronomic damage alone or, in some cases, in conjunction with diseases. Because of interactions with other host crops and pathogens, not to mention fumigant costs, managing the soil‐borne pests requires a combination that may include soil sampling, crop rotation, nematicides, fumigation, and biofumigation. Earn 1 CEU in Integrated Pest Management by reading this article and taking the quiz at https://web.sciencesocieties.org/Learning‐Center/Courses.

Control of Globodera pallida Using Brassica juncea Seed Meal Extract and the Trap Crop Solanum sisymbriifolium.

Globodera pallida, the pale cyst nematode, is a regulated potato pest which is economically detrimental. Restrictions on use of the soil fumigant methyl bromide, and lack of resistant russet type varieties for US markets have led to investigations of alternative strategies to control this pest. The efficacy of Brassica juncea seed meal extract (SME) (0, 0.14, 0.28, 0.56, 1.12, and 2.24 t/ha) was studied, either alone or in combination with the trap crop Solanum sisymbriifolium under greenhouse and field conditions. The impact of the application of SME pre- or post-planting of S. sisymbriifolium was also determined. Solanum sisymbriifolium only induced hatch of G. pallida and significantly fewer (up to 57 and 55% in pre- and post-plant experiments, respectively) encysted eggs remained at termination of the experiment compared to the untreated control. However, when SME was applied pre-plant, the encysted eggs remained unchanged which may indicate that SME inhibited egg hatch in the presence of S. sisymbriifolium. When applied individually, S. sisymbriifolium in all experiments, or SME at all rates tested in greenhouse and 0.56 t/ha or higher rates of SME in the field significantly reduced the viability, hatch, and reproduction of G. pallida. Combined treatment with S. sisymbriifolium and SME at lower rates, 0.14 t/ha for pre-plant or 0.56 t/ha or less for the greenhouse post-plant experiment further reduced G. pallida egg hatch than each strategy alone. In the field, a combination of S. sisymbriifolium and SME at 1.12 t/ha or less reduced G. pallida more effectively than SME alone. SME alone applied at higher rates of 0.56 and 1.12 t/ha in pre-plant greenhouse trials, whether combined with S. sisymbriifolium, eliminated G. pallida reproduction. Under field conditions, SME applied at a rate of 1.12 t/ha highly reduced G. pallida reproduction compared to the untreated control by 97% and 61% in 2019 and 2020, respectively. Furthermore, reproduction of G. pallida was eliminated when SME was combined with S. sisymbriifolium. Our results indicated that a combination of SME and S. sisymbriifolium reduces the amount of SME needed to control G. pallida and further decreases the potential reserve of the viable population remaining after individual treatment with each strategy.

Farm Fields as Toxic Sinkhole

Farm Fields as Toxic Sinkhole

Recovery of the soil fungal microbiome after steam disinfection to manage the plant pathogen Fusarium solani.

Soil disinfection using high temperatures via steam is a promising approach to manage plant pathogens, pests, and weeds. Soil steaming is a viable option for growers who are moving away from dependence on chemical soil fumigants, especially in plant nursery or high tunnel environments. However, there are few studies that investigate how soil steaming causes substantial disturbance to the soil by killing both target pathogens and other soil biota. Steaming treatments also change the trajectory of the soil microbiome as it reassembles over time. Growers are interested in the health of soils after using steam-disinfection, especially if a virulent pathogen colonizes the soil and then flourishes in a situation where there are very few microbes to suppress its growth. Should recruitment of a virulent pathogen occur in the soil, this could have devasting effects on seed germination, seedling establishment and survival. Beneficial microbes are often used to prevent the colonization of plant pathogens, especially after a soil-steaming event. Here, we experimentally test how soil fungal communities assemble after steaming disinfection. We introduce to steam-treated soil Fusarium solani, an important fungal pathogen of soybean and Trichoderma harzianum, a known beneficial fungus used for soilborne pathogen suppression. Results show that F. solani significantly affects the relative abundance and diversity of the soil fungal microbiome, however, T. harzianum does not mitigate the amount of F. solani in the steam treated soil. Within the T. harzianum microbial addition, the soil fungal communities were similar to the control (steaming only). This result suggests inoculating the soil with T. harzianum does not drastically alter the assembly trajectory of the soil fungal microbiome. Other soil amendments such as a combination of Trichoderma spp. or other genera could suppress F. solani growth and shift soil microbiome composition and function post-steaming, however, more experimental research is needed.

Side-Effect of Soil Fumigation and Soil Drench by some Methyl Bromide Alternatives on three Soil Enzyme Activities

Side-Effect of Soil Fumigation and Soil Drench by some Methyl Bromide Alternatives on three Soil Enzyme Activities

Yield Response and Antioxidant Activity of Greenhouse Organic Pumpkin (Cucurbita moschata Duch.) as Affected by Soil Solarization and Biofumigation

In intensive cropping systems, soil fumigation, i.e., the use of gas chemical pesticides applied to the soil covered with impermeable plastic film, represents an effective method to control most of the soilborne pests. However, its general non-selectivity to the useful soil microflora and microfauna together with their significant environmental problems has limited their use. Numerous studies have concerned the application of less impactful but, at the same time, equally effective disinfection methods. These are techniques with a low environmental impact that are particularly suitable for horticultural systems. Among these, both soil solarization and biofumigation are popular techniques, even in organic vegetable cropping systems. This paper reports the results of a study to evaluate the effects of soil solarization on the yield response and the antioxidant levels of organic pumpkin (Cucurbita moscata Duch.). Solarization was carried out alone and with the addition of some organic matrices, such as compost, manure and green manure species. The evaluation of the antioxidant activity was carried out with DPPH (1,1-diphenyl-2-picrylhydrazyl radical) assay: DPPH has a specific absorption band, which disappears in presence of an antiradical compound, showing its antioxidant capacity. Our results revealed that the pumpkins grown in solarized soil had IC50, i.e., the concentration of sample which reduced the initial DPPH of 50%, values ranging between 0.6 to 18.0 mg mL−1, lower than the values of IC50 of pumpkins grown in non-solarized soil, which ranged from 36.0 to 43.6 mg mL−1. The obtained results highlighted the validity and utility of solarization for the organic vegetable crops. Furthermore, this technique has also shown its effectiveness in the long term since yield increases concerned several crops in succession. Finally, our results highlighted that heat treatment solarization can influence the level of several compounds in the pumpkin, and, therefore, also of the polysaccharides.

Diversity and function of soybean rhizosphere microbiome under nature farming.

Nature farming is a farming system that entails cultivating crops without using chemical fertilizers and pesticides. The present study investigated the bacterial and fungal communities in the rhizosphere of soybean grown in conventional and nature farming soils using wild-type and non-nodulating mutant soybean. The effect of soil fumigant was also analyzed to reveal its perturbation of microbial communities and subsequent effects on the growth of soybean. Overall, the wild-type soybean exhibited a better growth index compared to mutant soybean and especially in nature farming. Nodulation and arbuscular mycorrhiza (AM) fungi colonization were higher in plants under nature farming than in conventionally managed soil; however, fumigation drastically affected these symbioses with greater impacts on plants in nature farming soil. The rhizosphere microbiome diversity in nature farming was higher than that in conventional farming for both cultivars. However, the diversity was significantly decreased after fumigation treatment with a greater impact on nature farming. Principal coordinate analysis revealed that nature farming and conventional farming soil harbored distinct microbial communities and that soil fumigation significantly altered the communities in nature farming soils but not in conventional farming soils. Intriguingly, some beneficial microbial taxa related to plant growth and health, including Rhizobium, Streptomyces, and Burkholderia, were found as distinct microbes in the nature farming soil but were selectively bleached by fumigant treatment. Network analysis revealed a highly complex microbial network with high taxa connectivity observed under nature farming soil than in conventional soil; however, fumigation strongly broke it. Overall, the results highlighted that nature farming embraced higher microbial diversity and the abundance of beneficial soil microbes with a complex and interconnected network structure, and also demonstrated the underlying resilience of the microbial community to environmental perturbations, which is critical under nature farming where chemical fertilizers and pesticides are not applied.

Soil nitrification process played a key role in alleviating continuous cropping limitation induced by fumigation

Continuous cropping causes enormous crop produce reduction, and soil fumigation is an effective approach to alleviate the limitation. Understanding the impacts of agriculture management on microbial community and its association with nutrient availability would provide strong supports for alleviating continuous cropping limitation. However, the mechanisms of fumigants in enhancing plant growth and alleviating continuous cropping barriers was not clear. In this study, fumigation treatments including chloropicrin (CP), dazomet (DZ), and untreated control (CK) were carried out at field scale, and rhizosphere bacterial community and plant phytochrome were analyzed. The results showed that fumigation had strong effects on rhizosphere bacterial community and soil properties. Fumigation treatment caused significantly reduction in rhizosphere bacterial diversity. The nitrifiers (Nitrospira and Nitrospirillum) and functional gene (ammonia oxidizing bacterial AOB amoA) were significantly inhibited by fumigation treatment, which caused significant reduction in nitrification potential (PNF). The inhibition of nitrifiers, AOB amoA gene and PNF led to significant reduction of soil NO3−-N, but increase of NH4+-N. Subsequently, plant photosynthesis was enhanced as a result of increasing leaf chlorophyll a content caused by fumigation treatment. Therefore, fumigation treatment would promote crop growth through increasing the photosynthetic pigment. The study indicated the key mechanisms fumigation promoting plant growth and alleviating cropping limitation were closely related to soil nitrifiers and nitrogen nutrients.

Are root parasitic broomrapes still a good target for bioherbicide control?

Root parasitic weeds of the genera Orobanche and Phelipanche (commonly named broomrapes) are responsible for enormous yield losses of several crops all around the world. Traditional weed management methods, including among others the use of herbicides, soil fumigation and solarisation, and mechanical, agronomic, or physical methods, may have limits of use or can provide a modicum of control. Difficulties in controlling parasitic weeds are due both to the enormous number of seeds produced by each plant that can remain viable, even in the absence of a host, for many years and to the unique physiological and biological properties of the parasite. Although considered a suitable and promising approach for a long time, biological control, in particular with the use of microbial organisms or with compounds stimulating or inhibiting seed germination, has had no commercial success, and no products have reached the market. The present article aims at making a quick overview of the bioherbicide approaches attempted until now, briefly discussing the causes of the failures and the possibility to improve biocontrol agents' effectiveness. Indeed, despite the failures, the 'bioherbicide' approach deserves a renewed interest in light of the enormous scientific and technological progress made in the last years, which offers new chances of success. This article is protected by copyright. All rights reserved.