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Role of Biochar in Improving Plant Biomass and Reducing Sclerotinia Sclerotiorum in Canola

Updated on March 12, 2018

Abstract

The application of organic amendment has frequently been proposed for the control of pathogens and improving plant biomass. In this article, research concerning the role of bio char in controlling pathogens and improving plant performance were reviewed to support the arguments. Bio char can be useful in the control of both airborne and soil borne diseases. Also, it helps in controlling different bacterial and fungal diseases in the soil. Amendment of soil using bio char results in both positive and negative effect on soil productivity, but positive effects prevail. The proposed adverse effects of bio char amendments include the availability of non-degradable materials which limits microbial activities. The study shed light on the economic and environmental benefits incurred by the producer in adopting bio char technology. The focus is in West Australia, where the study explains the application of bio char in sandy soils while identifying the agrochemical applications in the same region. The research concludes with a sustainable agricultural production in a socially responsible environment due to the application of bio char amendments in soils. However, the study recommends for extensive research to find out more mechanisms in controlling pathogens and improving plant biomass.
Key words: Pathogen, bio char, soil, plant biomass.

Introduction

Canola is a popular crop in Western Australia, which is grown primarily for the production of edible oil. However, its purpose varies on the level+s of production. Its by-product is crushed and fed to livestock. There is growing demand for Canola oil worldwide due to its low concentration in acidic fats. For economic reasons, farmers apply various strategies to control weeds, diseases and improve the productivity of canola (Agric.wa.gov.au, 2017). Researchers are always developing a new hybrid variety with improved quality and quantity of production.
Several diseases attack Canola at different stages of growth. The severity of attack depends on the crop variety and its exposure to pathogens and the climatic conditions (Mihajlović et al., 2017). For example, regions experiencing high unseasoned rainfall or extreme temperatures have high incidences of fungal infections in plants. If colon producers are aware of the associated risks, they would formulate strategic management methods and probably consider adopting a more economically integrated approach such as the application of bio char in pathogen control and improvement of plant biomass.

Problem of the Study

Two key problems affecting farm productivity today is soil fertility and pests. Growing crops on a single piece of land often lead to a decline in production due to depletion of nutrients in the soil (Li et al., 2012). To overcome this challenge, mankind came up with the idea of synthetic fertilizers to replenish fertility of the soil and ensure continued production of the land. However, continuous use of synthetic fertilizers has its own consequences to the soil and the biodiversity. For instance, synthetic fertilizers lower the pH leading to increase in acidity of the soil (Sebilo et al, 2013). In the end, it results in the death of micro-organisms which cannot survive at a lower pH, and in turn reduced crop productivity.
Sclerotinia sclerotiorum is known to cause white mold disease to the plant and has proved difficult to eliminate (Miklas et al., 2015). Eliminating this pathogen causes incurring substantial costs in terms of controlling it, which eats into the profitability in the case of commercial farms. In some cases, farmers may incur losses due to this pathogen; therefore, it is a relief to find that bio char can be used to control it. It is imperative to note that continued presence of this pathogen is a threat to food security not only in Western Australia but also the whole territory. Furthermore, it is a threat at the doorstep that requires being handled with a sense of urgency in order to save the food basket of Western Australia. White mold, a disease caused by Sclerotinia sclerotiorum is a serious disease as it can affect the crop at any stage of growth (Kabbage, Williams & Dickman, 2013). With this behavior, it can be deduced that the disease requires constant monitoring until the crops have been harvested. This phenomenon implies that the farmers’ woes could be high if the occurrence of the pathogen recurred during the growing cycle of the crops. A heavy infestation of the pathogen on the farm could mean that the farmer would not only go hungry by also without a source of income.
The study aimed at providing more insight on ways bio char can be used in reducing the impact of Sclerotinia sclerotiorum menace and promoting plant biomass. Having a clear overview of the roles of bio char could not only help in promoting food security but also farmers’ standards of living in Western Australia. According to Garnett et al., (2013), having stable food security is essential for economic development and food self-reliance. The fact that Western Australia is the breadbasket of the nation asserts the urgency of this study since any effect on food production in this region would have a direct impact on the country, Australia. It is worth noting that the impact of Sclerotinia sclerotiorum goes just beyond the crops; thus, affecting other agricultural sectors too. For instance, infestation by the pathogen on agricultural crops suchlike animal feeds could affect livestock production in the region where the effect is like a chain of reactions. The fact that bio char has the potential to increase agricultural production was an indication of an information gap. This study aimed to fill the information gap by seeking out to provide more insight on how bio char can be used in improving soil fertility and control of Sclerotinia sclerotiorum pathogen.

Control steps of the Pathogen

Sclerotinia sclerotiorum pathogen can only be controlled but not eliminated using biological, cultural and chemical measures (Kabbage, Williams & Dickman, 2013). Some of these control methods require a considerable amount of time in controlling the pathogen while others are done in an instant. In controlling the pathogen, it is important to first analyze the extent of the infestation to allow for selection of appropriate control measures. Doing this will increase the likelihood of success in the control measure employed and reducing the risk of the pathogen spreading. It is imperative to note that the most effective way of control this pathogen is through the integration of the three control methods. Farmers need to keep farming records about Sclerotinia disease so that if affected they can select the most appropriate control method.

Biological Control Methods

The affected plant parts can be isolated and taken to a controlled area where they can be air-dried to eliminate Sclerotinia sclerotiorum pathogen. It involves the collection of sclerotinia from the affected plants and the soil (Alvarez et al., 2012). Furthermore, it involves the use of special types of fungi such as Gliocladium roseum, Trichoderma viride, Coniothyrium minitans, Sporodesmium sclerotivorum, and Gliocladium virens. Here, the mycoparasitic fungi help in controlling the pathogen through the destruction of the Sclerotia thus, killing Sclerotinia sclerotiorum. Besides, it inhibits the pathogen from forming new sclerotia.
Sclerotinia sclerotiorum pathogen can also be controlled using parasites Coniothyrium minitans and Trichoderma spp. They control the pathogen through secreting á-1,3 glucanase; this works through degradation and shredding of sclerotial tissues in Sclerotinia (Guyon et al., 2012). However, for this to yield optimal results, there must be warmers temperatures and an optimal level of humidity. Bio char also helps in control of Sclerotinia sclerotiorum pathogen as it triggers the crops’ systemic responses to fungal diseases such as sclerotinia.

Cultural Control Methods

Cultural methods incorporate two control strategies which include putting the pathogen under a condition that it cannot survive or physically killing it (Peltier et al., 2012). For instance, some of the farmers prefer burning their field as a way of controlling the pathogen. Such a method is attributed to the fact that the pathogen cannot survive under conditions of high temperature. It is worthy to note that the effectiveness of this method is dependent on the cooperation among farmers in the region affected, in this case, the Western Australia.
Other cultural methods that can be effective in control of the pathogen include ensuring proper field sanitation through weeding and proper spacing of the crops. Ventilation is important to allow for free movement of air in the farm, in turn, eliminating humid conditions which are a perfect spreading ground for the pathogen. One should also ensure that the crops with hanging foliar should be supported with wire trellis to raise them from the ground.
Since Sclerotinia sclerotiorum pathogen can stay in the soil for up to 5 years, farmers can grow more tolerant crops and/or apply biofumigant green manure to prevent the accumulation of the paste in the soil (Xie and Ghabrial, 2012). Such a process could involve crop rotation where the farmer shifts planting susceptible crops to the unaffected field. However, this method is limited if the infestation of the pathogen is spread across a whole region.

Chemical control methods

The most desirable chemical method of controlling Sclerotinia sclerotiorum pathogen is through fumigation. Fumigation is aimed at lowering the levels of inoculum present in the soil. Chemical control is also carried out on established crops where chemicals such as Fluazinam and procymidone have proved to be very effective in the control of sclerotinia (Sumida et al., 2015). It is imperative to note that the effectiveness of control of the pathogen using chemical methods varies from one plant to another. Therefore, to increase the likelihood of success, the farmers have to seek chemical control methods suitable for their crops. It should be noted that chemical method is facing some challenges such as pollution of the soil, high cost, and resistance to some chemical controls by Sclerotinia sclerotiorum pathogen.
The effectiveness of chemical control approach is dependent on the method of application, volume of water used and timing of the chemical sprays. The ideology behind the volume of water is the depth at which the water shall percolate into the soil (Tjamos, Papavizas & Cook, 2013). Using a small volume of water means that only the top part of the soil shall be fumigated while the lower part remains undisturbed. Conversely, using the optimal amount of water ensures that all areas of the soils are fumigated hence, high effectiveness. During application, care should be taken to ensure that the required volume of water is used to avoid pollution of groundwater and run-off.
The use of bio char is another chemical method used in controlling Sclerotinia sclerotiorum pathogen. In this case, the method involves the addition of carbon to the soil which in turn raises the pH of the soil. Pathogens such as Sclerotinia sclerotiorum thrive in acidic soils hence, raising the pH is a measure of providing an unsuitable environment for its spread. Raising the pH is needed for increasing activity of soil microorganisms, some of which are helpful in the control of the pest.

Literature Review

Improvement of Agriculture in West Australia using organic approach

For decades people have embedded in the application of phosphorus fertilizer on the sandy soil in South Australia. However, the level of PH in the soil seems decreasing season after another. Also, the use of fungicides has prevailed, and the Department of Agriculture and Food reports that most primary producers incorporate adverse chemical applications in agricultural enterprises (Agric.wa.gov.au, 2017). The Department, therefore, raises a concern for implementation of policies to control the use of veterinary and agricultural chemicals which will indirectly minimize the risk of the trade, animal health, and animal welfare. Therefore, the government is institutionalizing licensing, validity of chemical products and noncompliance enforcement strategies (Agric.wa.gov.au, 2017). Persistent global warming effect and the irrational chemical application by the producers have raised concern for government intervention. The discussion below reviews literature to provide insights for the efficiency of adopting organic approaches in controlling pathogens and plant crop biomass.
Production of Bio char
Bio char is produced in a similar approach as charcoal, but the difference prevails where the end application is soil amendment. Mitchell, Dalley, and Helleur, (2013), postulate that the product can be prepared following various approaches such as gasification and slow pyrolysis. These procedures in making bio char give it a high Carbon content. In most instances, lignocellulosic materials such as manure, crop residues, and wood can be used to develop the product through a combustion process (Mitchell, Dalley, & Helleur, 2013). With optimal observation of standards, the bio char can impound carbon in soils, which substantially improve soil productivity.
Recent studies indicate that applying bio char has a range of effect on the soil properties and thus, productivity (Agric.wa.gov.au, 2017; Sumida et al., 2015). For future advancement, the scientists are assessing the best approaches in preparing the bio char. The primary effect of bio char in the soil is increasing water holding capacity and boosting the soil potential in retaining nutrients (Ahmed & Schoenau, 2015). It also has oxidation effect when applied to the soil. Additionally, bio char has a hydrophobic nature when freshly prepared and therefore, has a low surface charge.
Effect of Bio char on Plant biomass
An increasing body of literature suggests that bio char changes the chemical composition of the soil which results in a relative alteration in plant responses in the diverse soil ecosystem. (Kelly et al., 2015; Sumida et al., 2015; Knox et al., 2015). Some scholars differ from others and criticize the technology as a factor for soil degradation. They support an argument that the substance constitutes non-degradable elements which cannot be decomposed by the microbial effect (Ahmad et al., 2015; Alvarez et al., 2012). As a result, they inhibit vital microbial activities such as nitrification and enzyme activities.
From different agronomic contributions, it is evident that the effect of bio char might be positive or negative to soil productivity with respect to nutrient retention and water holding capacity. Therefore, it is vital for producers to carry out soil sampling before implementing the technology in various soil types by considering: Soil porosity, bulkiness and grain distribution. Understanding these properties helps the producer enact practical application procedures which contribute to increase in the plant biomass.
Mainly, the aspect of microporosity of bio char contributes to greater water retention and soil porosity, soil hydraulic conductivity and available water content (AWC) for plant utilization (Barnes, Gallagher, Masiello, Liu, & Dugan, 2014). As a result, the processes support efficient nutrient absorption and utilization hence, improving the plant biomass. Bio char alone has a lower effect on soils in West Australia, but the inclusion of fertilizer indicates improved yield. The soil type in West Australia is sandy and dominated by clay stones. Therefore, the addition of fertilizer would provide essential nutrients such as Nitrogen and Phosphorous. Notably, the effects of bio char on plant germination, productivity and consequently on biomass production varies on the materials used.
If producers intend to improve plant biomass using bio char, then they might be obliged to apply fertilizer as a compliment. Particularly, the changes imposed by the bio char have effects on PH and efficiency of nutrient utilization (Knox et al., 2015). It might be of great support to plants life in tropical soils, but prairie soils might require more amendments.
Reducing Pathogen
In recent years research has been carried out to establish effective methods of controlling pathogens with limited effect on the environment. In this proceeding, the organic control measures such as green manure, compost manure and organic wastes from agro-industries are considered appropriate by both farmers and scientists. Organic amendment in the soil has a suppressive characteristic to both soil borne and airborne pathogens. Among the mostly applied materials, compost manure is broadly studied and identified to have effective control result in regards to pathogens like Sclerotium spp, Fusarium spp, and Rhizoctonia solani (Ahmad et al., 2014). The organic control of pathogen has a limited practicality where compost manure is identified to cause severity and several side effects by releasing phytotoxic compounds that destroy roots.
Bio char effects on the soil have been reported to inhibit survival of pathogens. An experiment by scientists provided that, dry bio char can emit C2H4; wet bio char produce more capacity while the bio char mixed at the ground emit average amount. The research is limited in explaining the mechanism involved in the emission of ethylene from bio char in the soil. This process of emission has a toxification effect to the fungal disease such as Sclerotinia sclerotiorum. However, the research is underperformed to define the extent of emission. Also, studies have reported direct fungitoxic effect where a range of organic compounds, aromatic and aliphatic C compounds are produced (Graber et al., 2014). On the contrary, the use of transgenic plants might be an efficient mechanism in particular pathogen control approaches.


Conclusion

For decades, relevant studies have been established to determine the role of bio char in improving plant biomass and controlling soil borne diseases. However, the research on bio char in controlling pathogens is still limited and further studies are necessary to establish wide-scaled pathogen control mechanisms. However, the current research avers that bio char is a promising technique which conserves the environment while providing an exceptional experience to the producers. The low-cost demand in implementing this technology has a positive effect on the farmers. Also, its implementation establishes an additional supply of plant nutrients, positive soil harmonization and therefore, a reduced cost in purchasing farm inputs. Most importantly, the agricultural production becomes economically sustainable in a socially responsible environment.

References

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