Assessing microbial communities of aqueous compost extracts and their effects on mulch and crop residue degradation

View the project final report

Commodities

Practices

• Crop Production: biological inoculants, municipal wastes, organic fertilizers
• Pest Management: compost extracts, mulches - general
• Production Systems: organic agriculture
• Soil Management: composting, soil microbiology

With the rise of interest in eco-friendly foods, soil microbiology has captured the fascination of farmers at all scales. A suite of organisms is invariably present in highly productive and resilient soils, but often deficient in poor soils. This soil food web including diverse bacteria, fungi, protozoa, nematodes and microarthropods can also be found in some (but not all) composts and extracted into an aqueous suspension called "compost extract." These biotic properties of compost extracts may function in particular scenarios to prevent plant disease, accelerate soil carbon sequestration, build soil structure, and/or accelerate nutrient cycling and residue degradation. Several studies reporting efficacy in preventing plant disease and accelerating plant growth, along with compelling anecdotal evidence, have led some farmers and horticulturists to integrate compost extracts into their field and greenhouse operations.  In light of mixed experimental results, more study is needed to understand indications for use and best practices for optimizing the use and efficacy of compost extracts.

Meanwhile, an extensive, but financially and environmentally costly, dependence on polyethylene mulch is the current norm in organic vegetable production.  This dependence is philosophically out of line with the organic movement.  Prototype bio-based biopolymer alternatives may address these concerns. These biopolymers will only be allowed for organic production if their fate in diverse field conditions is full and timely biodegradation to carbon dioxide.  Like mulch films, cover crops managed with minimal tillage serve to control weeds and moisture while also adding carbon and immobilizing nutrients.  Mulch films and cover crops may provide the most benefit when they degrade relatively rapidly into humus and carbon dioxide.

The proposed study focuses on residue degradation.  Our hypothesis is that compost extracts containing more fungi and microbial predators will accelerate degradation of polylactic acid (PLA) biomulch and rye cover crop residue, especially in poor soil.

Results supporting this hypothesis will inform use of compost extract as a cost-effective residue management strategy in intensively and extensively cropped soils.  Results may also justify use of PLA mulch in certified organic systems on soils that may degrade PLA too slowly without microbial treatment. If biological properties of a compost can predict its influence on residue degradation, this will inform agronomic systems where the extent and timing of crop residue degradation is important for erosion control, nutrient cycling and soil structural improvement.  Compost extract may influence the decomposer community associated with fresh residues to influence soil function and crop health

Research on decomposer community and degradation rate response under different inoculant regimes will positively impact farmers at all scales in formulating best practices for mulch and residue management and increase stakeholder knowledge (e.g. extension, compost producers, and laboratories) about the regenerative potential of soil microbes.  Learning and action outcomes will influence at least 100 farmers and compost producers across the North Central Region (NCR) and beyond. Stakeholders will gain knowledge about attributes of compost and soil that may have management relevance but are commonly overlooked including nematode diversity, fungal biomass, and protozoan diversity. We aim to reach farmers, including limited resource growers, through Extension bulletins, a website, YouTube videos, coverage on WIBW 13 (a Kansas television station), classes through Community Crops' "Growing Farmers" training program, and a SARE webinar. Farmers will adjust their soil management based on the knowledge we disperse regarding soil microbiology; even if producers have been exposed to ideas of management for soil biology, our evidence-based platform will validate the perspective for hesitant farmers. Increased knowledge of ecological processes (soil microbial community and carbon dynamics) in low functioning soils amended with fresh residues will inform limited resource farmers especially as access to poor quality soil is more affordable. Poor soils and farm profitability will improve with dissemination of science-based information on the feasibility of accelerated soil quality improvement in the near term through better methods for selecting compost-based biological inoculum.