Soil pathogens and pests, such as insects and weeds, are often a threat to most organic farming systems. Organic farmers control soil pathogens and pests by applying organic improvers such as compost, growing specific cover crops, using crop rotation, and planting resistant varieties.
Studies show that organically controlled fields tend to control soil pathogens more than traditional fields. However, organic crops can be mildly and catastrophically damaged by soil pathogens and pests, resulting in reduced yields. Organic farmers are always looking for a system-based approach to address soil problems, especially for high-value crops such as vegetables and fruits.
The first article in the two-part series discusses anaerobic soil disinfection (ASD). This is an organically acceptable method within an integrated management system to reduce losses from pathogens and other pests.
What is ASD? How was it developed?
ASD is a biological method of controlling pests and pathogens in various soils. It was originally developed in the Netherlands and Japan around 2000 as an alternative to fumigants. In both countries, floods are common on agricultural land and are known to control soil pathogens (such as Verticillium dahliae) in vegetables grown after drainage. Also, the use of solarization, which typically requires a maximum daily soil temperature of 110 degrees Fahrenheit or higher at a depth of 6 inches, is restricted due to inadequate solar radiation.
ASD was developed by combining the principles of flooding (that is, anaerobic decomposition) and solarization (that is, the use of plastic mulch) with the application of carbon-rich organic corrections. An important aspect of ASD treatment is the selection of unstable (easy to decompose) carbon (C). This can depend on the availability of agricultural by-products in different regions (Figure 1). Covered crops and crop residues can also be used as a C source for ASD (Figures 2 and 3). With this approach, ASD can be applied to areas with low soil temperatures where solarization is not effective, or areas where flood use is not permitted due to limited water, terrain, or soil characteristics.
How does ASD work?
SD controls soil-derived pests and pathogens by creating temporary anaerobic conditions that allow microbially-added C to carry out a series of fermentation processes. , And changes in the soil microbial community, altering the microbial ecology of the soil and providing direct and indirect activity against soil pathogens.
At the same time, a series of microbial communities begin to eat the fed unstable C, and then the metabolites derived from the fermentation process. The soil is not sterilized or emptied, but activity shifts from one group to the next, creating soil that controls pests and pathogens. Finally, when the unstable C source is depleted, the soil returns to aerobic conditions and crops are established.
In addition to controlling soil-borne pests and pathogens, common C-source ASDs alter the soil environment and benefit the following crops (Figure 4). ASD offers some of the same benefits that organic matter improvements generally offer, such as increased organic matter and cation exchange capacities in soils and improved physicochemical properties of soils. Increases in beneficial microorganisms such as non-pathogenic nematodes, fungi, and bacteria associated with disease control and growth promotion have been recorded in ASD. Many believe that this approach is suitable for soil regeneration, reduction of allerochemicals, and increased microbial activity.
What are the steps to implement ASD?
ASD is performed in three steps (Figure 5). First, an unstable C source is incorporated into the soil to feed indigenous soil microorganisms. Unstable forms of C are required for bacteria to initiate the fermentation process quickly. Non-unstable Cs such as bark, wood chips and compost have no effect. Unstable C sources available locally are available (see Part 2 of this article in the next issue for common C sources in different parts of the United States).
Then cover the soil with plastic mulch as soon as possible to limit oxygen supply and gas exchange. Third, drip irrigate 1.5 to 2 acres of water to initiate and maintain a 3-week fermentation process. The first irrigation should saturate the soil with the floor as evenly as possible without disrupting the floor structure. Then maintain above field capacity during treatment. For sandy soils, adding water in small increments can maintain soil moisture suitable for anaerobic conditions.
The stronger the anaerobic conditions and the higher the soil temperature, the more likely the ASD treatment will be suppressed. By measuring the redox potential (Eh) of the soil using a redox potential (ORP) sensor, researchers and growers can monitor the level of soil anaerobic state in the ASD (Figure 5f). The pungent odor of the soil core also indicates anaerobic fermentation.
After the treatment period, the plastic mulch is punctured for planting, facilitating aeration of the treated soil. It is usually safe to transplant within a week of drilling.
How widely is ASD used?
Studies in multiple regions of the United States in both field and high tunnel production systems, including California, Florida, Tennessee, North Carolina, Washington, Oregon, Pennsylvania, Virginia, Michigan, and Ohio. I was. The crop types tested include berries, vegetables, tree fruits, and cut flowers (Figure 6) (Part of this article for crops and target pests to which ASD applies in different parts of the United States. See 2)
ASD has been used on a commercial scale in California’s berry fields since 2011, but is still in its infancy in other regions and crops. There are studies on ASD conducted around the world, including ongoing studies in the Netherlands, Japan, China, Nepal, Spain and Italy. Many growers in these areas use ASD commercially, especially on small farms and protected cultivation systems with limited opportunities for proper rotation.
Various names for this practice
ASD was originally described as biological soil disinfection (BSD) or reducing soil disinfection (RSD). Studies in the United States on this topic have been more consistently referred to as ASD because the need for anaerobic conditions is the main difference between this approach and other methods. Each name highlights the components that each research group considered to be an important feature of the approach.
At this stage, everyone agrees that this is a biological method and that achieving certain levels of anaerobic conditions is important in controlling soil-borne pests and pathogens. Will do. Regardless of the name used by each group, research continues to characterize the physical, chemical, and biological changes that occur during treatment. The widespread effectiveness of ASD, which results in the simultaneous management of several soil-borne pests and pathogens, is likely due to multiple mechanisms that provide multiple easy-to-apply tactical approaches.
An alternative approach to ASD is biosolarization, which was developed by combining soil solarization with the application of organic fertilizers. This approach relies primarily on the development of high soil temperatures due to the solarization effect obtained using transparent mulching films. Therefore, its application is limited in areas where solarization is effectively used.
Does ASD Control Weeds?
When properly applied, especially in warmer regions, ASD significantly reduces weed pressure. In some studies, broad-leaved weed germination was reduced by 40% to 60%, and perennial weeds such as Cyperus microiria were reduced by more than 75% compared to fully opaque films without ASD treatment. ASD treatment keeps turf weeds under control and prevents weeds from growing in planting holes throughout the season. Changes in anaerobic conditions and soil chemistry can be responsible for inhibiting the growth of germinated weeds. This can be affected by the type of C source used and its rate of application.
Does ASD Affect Nutrient Availability?
The modifications used to apply ASD have a strong impact on nutrient dynamics. The increased availability of potassium, calcium, magnesium and micronutrients is common to many different organic modifications used in ASD. It depends heavily on the composition and rate of application of the correction used. When defining the applicability of all sources of C, it is important to consider the composition of organic improvements to avoid excess nutrients.
Inputs definitely affect the dynamics of nitrogen under ASD, and the C: N ratio of the C source can affect the subsequent release and availability of nitrogen and other nutrients in the crop. For example, when composted broiler litter is used in ASD, the combination of litter and molasses reduces soil ammonia and nitrates. In general, plant nutrient intake is improved by ASD. In some cases, this is also reflected in the high concentrations of nitrogen, phosphorus, potassium, calcium, magnesium, iron, boron and zinc in the fruit. See next month’s issue for more information on ASD’s commitment to organic farming systems.
http://organicfarmermag.com/2021/06/anaerobic-soil-disinfestation-as-an-organic-systems-based-approach/ Anaerobic soil disinfection as an organic system-based approach