Improving Organic Crop Production with Enhanced Biofumigation and Composting Systems

Improving Organic Crop Production with Enhanced Biofumigation and Composting Systems

Summary

Mustard meal can act as an alternative to synthetic fumigants for the control of soilborne diseases in organic vegetable production. When activated in moist soil this biofumigant releases the bioactive compound, isothiocyanate. Biofumigation is the process of incorporating bioactive compounds into the soil and utilizing the release of volatiles for pathogen suppression. The viability of biofumigation to control soilborne diseases has been investigated for many years. Our current project, funded through the Southern SARE program, is focused on developing an integrated production system that combines an enhanced form of biofumigation with the many benefits of composts. Research has shown that certain Brassica cover crops, as well as mustard seed meal, contain high concentrations of isothiocyanates (ITCs). The seed meal is also a significant source of nitrogen and other nutrients. When incorporated into the soil ITCs act as an effective biofumigant, reducing populations of pathogenic fungal species (Sclerotium, Rhizoctonia, and Phytium), nematodes, weeds, and certain insect species. Compost incorporation improves plant health and productivity due to enhanced soil nutrient levels and improved physiochemical properties, including increased water-holding capacity.

The control of soilborne diseases through the use of chemical fumigation has several inherent problems. Commercially available synthetic fumigants have potential for toxicity and persistence in soil with a resulting threat of groundwater contamination. The gaseous by-products of fumigants such as methyl bromide have been targeted as class-1 ozone depletors. Concerns for the safety of farm workers that handle such compounds is an important issue, as are elevated costs of application. Fumigants act to sterilize the soil, however, either residual or re-introduced pathogens can quickly re-populate in the subsequent weeks and months. Biologically based management techniques both suppress pathogen numbers and re-establish a balanced soil microecology that is capable of providing extended and sustainable disease suppression.

An expansive field experiment was conducted during the 2003 growing season on the Knoxville Experiment Station. An integrated strategy of biologically based treatments was tested to assess their level of disease management and ability to enhance tomato yields. This experiment was also conducted at the Mountain Experiment Station in Fletcher, NC in cooperation with NC State University.

At the Knoxville location tomato yields for the plants grown in the mustard meal and compost treated plots were higher than yields of plants in the control . Fruit yields for the controls averaged 9.6 lbs per plant. Plots amended with an incorporated Brassica cover crop averaged 11.6 lbs of fruit per plant, a 21% increase above the control plants. When meal was also added to the incorporated cover crop, yields increased to 13.1 lb/plant, 37 % above controls. Mustard meal used as an amendment alone also resulted in yields increases. The largest increases in tomato yields came from the plants grown in soil that had been amended with spent mushroom compost (30 tons per acre) as well as mustard meal (2000 lb/acre). These plants produced 54% more fruit than the control plants. The data supports the concept that adding organic matter to production soils will enhance yields. Integrating two or more organic treatments, such as Brassica (mustard) plant tissue and compost is favorable. The superior yields can be attributed to an increase in available nutrients in combination with improved physical and chemical soil properties and/or to control of soilborne diseases.

The phytopathogenic fungus, Sclerotium rolfsii, causes southern Blight. This organism is favored by warm, humid conditions and is directly responsible for major losses in a variety of crops that utilize plasticulture production. Commonly controlled by pre-plant soil fumigation with chemicals such as methyl bromide, biologically based treatments have shown promise as an alternative, sustainable disease management tactic. A high incidence of disease was observed in the control plots of our experiment. Sixty percent of control plants developed symptoms of Southern Blight. This percentage was significantly reduced in all of the experimental treatments. Biofumigation, utilizing mustard meal or a Brassica cover crop, reduced disease to 24-29% of all plants. Interestingly, the rate of meal used did not impact disease suppression. The 1000, 2000, and 4000 lb/acre rates had similar results.

There were no significant differences among the treatments for yield or disease control at the Fletcher location in 2003. This field had not been in tomato production the previous year and this was the first year the biological amendments were applied. At the Knoxville location this was the fourth year that the treatments had been applied. The establishment of a healthy soil microenvironment likely requires repeated treatments. At the Fletcher location the biological treatments were compared to a commercial soil fumigant. There was no difference in this year between this treatment and the control. Thus, indicating that the disease pressure in this site was not significant. In the following years this will likely change as tomatoes are grown in the same field for several years.

A demonstration was established in the fall of 2003 on a commercial organic production farm. Two replications of one quarter acre each were planted in Brassica juncea as a fall cover crop. This crop will be incorporated into the soil in the spring of 2004 with the addition of mustard meal and compost. The biofumigation treatments will be compared to an organic production control. A replicated experiment comparing biofumigation amended organic production with conventional tomato production was established with a second grower.

Objectives/Performance Targets

Objective for the first year (2003) were:
1)Testing biofumigation by cover crops.
2)Testing Biofumigation with mustard meal to refine concentrations.
3)Testing combinations of cover crops and mustard meal.
4)Testing combined treatments with compost addition.
Brassica cover crops were evaluated and found to successfully impact yield and disease resistance in the fourth year of and experiment at the Knoxville location. Mustard meal and mustard meal compost combinations were found to increase tomato yield and reduce disease at the Knoxville location. The concentration of mustard meal affected yield but even low concentrations had an impact on disease. In the first year at the Fletcher location there were no differences among the treatments for yield or disease. There was likely not sufficient disease pressure in this field the first year. Both of these experiments were re-established on the stations and will be repeated in the same locations in the 2004 season. Two experiments were established with commercial growers in 2003. These experiments were not planned in the Project until the second (2004) year of the project.
A large replicated demonstration was seeded with a Brassica cover crop in the fall of 2003. This experiment will be continued into the 2004 season and will compare one quarter acre plots of a combined biofumigation, meal, compost treatment with a conventional organic production system. This experiment will investigate production of several other crops in addition to tomato. Another experiment was established with a commercial grower. Meal treatments and meal plus compost treatments were established in a replicated tomato trial.

Accomplishments/Milestones

1) Grower interest in biofumigation and combined organic production treatments was increased by presentation at several meetings and field days.
2) A large scale demonstration project was established in the first year of the project (earlier than projected in the project) to demonstrate in a replicated commercial production system the impact of the combined treatments on disease control and yield.
3) Experiments were established in two locations to determine the optimum concentration of meal in combination with compost treatments.
4) Grower contacts were initiated to establish demonstration experiments in 2004 at several locations.
5) Demonstration plots were established in 2003 to establish the impact of biofumigation and compost treatments on strawberry production utilizing plastic mulch.
6) The Extension Service disease diagnostics laboratory of the University of Tennessee began development of diagnostic techniques that will be used in 2004 and 2005 to determine levels of pathogens in soil from the experimental plots and from the commercial farm demonstration plots in the project.
7) Planning for a biofumigation web page was initiated and will be continued in 2004. This page will be used to communicate project findings to growers and agents.

Impacts and Contributions/Outcomes

1)Significant yield and disease resistance was achieved in a field that had been in production for four years. In this experiment the potential to increase tomato yield and improve disease resistance in organic production systems was demonstrated. A second experimental location was established to compare the treatments over successive seasons in the same location.
2)A large replicated demonstration project was initiated with an established commercial organic producer and a second experiment was planted with a commercial grower.
3)Several presentations were given in 2003 to professional societies, grower and extension groups to begin training on the biofumigation treatments:

A) Integrated systems that utilize biofumigation,solarization and composts for commercial vegetable production. In: A “Statewide Journey” of Sustainable Success. The University of Tennessee Agricultural Extension Service Manual: p13-14. This presentation was given at a SARE sponsored training session for growers and agents in 2003.

B) Membrane lipid analysis of soil microecology in S. rolfsii infested tomato fields.
Presented at the annual meeting of the American Society of Plant Biologist in 2003.

C) Mustard meal and compost as methyl bromide alternatives. Presented at the Fresth Market Tomaot Field Day (August 7, 2003), Mountain Horticultural Research Station, Fletcher, North Carolina. This presentation was attended by growers and agents. Several growers expressed interest in the biofumigation treatments. One of the growers in North Carolina will be cooperating in a trial in 2004.

D) Integrating Soil fumigation with Organic Amendments for Enhanced Vegetable Production. p. 385 Agronomy Abstracts. Madison, WI. 2003. This presentation was given at the annual meeting of the American Society of Agronomy.

4)Two other growers have been contacted and will cooperate on demonstrations in 2004.

Collaborators: