Mustard cover crops as biofumigants for organic strawberry production

Final Report for FNE15-817

Project Type: Farmer
Funds awarded in 2015: $10,688.00
Projected End Date: 12/31/2017
Region: Northeast
State: Vermont
Project Leader:
Rico Balzano
Little Lake Orchard
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Project Information

Summary:

Strawberry production began on our farm, Little Lake Orchard, in 2012, and we implemented an organic system to capture a market niche. The land base limitations and pick-your-own marketing logistics on our farm demand that some strawberry ground will be on a relatively short rotation. The short time between strawberry plantings will require near constant intensive cover cropping to replenish organic matter, nutrient levels, and reduce or eliminate residual fungus and nematode populations. Varieties of two species of mustard (Sinapis alba and Brassica juncea) have been identified as producing chemical compounds known as glucosinolates that have been shown to reduce fungus and nematodes populations when mowed and incorporated into the soil. This process is known as biofumigation.

Six varieties of mustard have been trialed to test glucosinolate production for disease and nematode control, and biomass production. Test results showed differences in level of glucosinolate production and type of glucosinolate produced. ‘Caliente 199’ (S.alba and B. juncea blend) produced the highest level of the glucosinolate ‘sinigrin’, which has anti-fungal and anti-nematode properties. ‘Idagold’ (Sinapis alba) produced the highest level of the glucosinolate ‘sinalbin’, which has weed suppressing properties. Biomass measurements showed ‘Caliente 199’ to be the highest yielding of the six varieties tested.

There was no significant difference in yield of the strawberries. Eight varieties of strawberries were then planted perpendicularly across the plots. The eight varieties planted were: ‘Wendy’, ‘Galletta’, ‘Brunswick’, ‘Jewel’, ‘Darselect’, ‘Cabot’, ‘Valley Sunset’, and ‘Record’. ‘Cabot’ and ‘Jewel’ were the highest yielding across all mustard treatments. Also, there was significant deer damage in the trial block in the fall of 2015 that reduced yields across all treatments.

This project did not set out to specifically explore how mustard cover crops affect soil organic matter (SOM). However, the results show that the biofumigation process may have had a negative impact on SOM. The understanding of how SOM is formed, how it accumulates, and how it degrades is evolving. Recent research has shown that soil microbiology contributes to SOM far more than previously thought. The results of this project suggest that mustard biofumigation can work against SOM accumulation by suppressing soil microbiology.

Introduction:

Strawberries are a perennial fruit crop; over the life of the planting soil-borne diseases, nematodes, and weed populations tend to increase. Current recommendations indicate rotating away from strawberries, and alternate hosts such as solanaceous (e.g. tomatoes and potatoes) crops for a minimum of 5 years; 10 years being preferable. In addition to crop rotation, conventional (non-certified organic) strawberry farms have the option to fumigate the soil prior to planting with chemicals such as metam sodium, methyl bromide, and dichloropropene to control weeds, fungal disease and nematodes.  Diversified organic growers with limited acres may be challenged to meet the rotation requirements, and do not have fumigation as an option. Also, there is a growing interest among conventional growers to find alternatives to fumigation due to environmental risks, human health risks, and potential deregistration by the Environmental Protection Agency (EPA).

Alternative strategies to use of insecticides, herbicides, and fumigants, must be established to maintain consistent production in organic strawberry production. Farmers have used cover crops for many years to help suppress weeds, provide habitat for beneficial insects, and interrupt life cycles of pests and diseases. More recently, certain cover crops have been identified to be particularly useful for specific purposes. For example, tillage (daikon) radish has noted to break up compaction and suppress weeds; winter rye has been shown to suppress winter annual weeds and provide high amounts of biomass for harvest or incorporation in the spring; and buckwheat can provide quick summer cover and mine nutrients from deeper soil layers. Many farmers now choose cover crops to achieve specific goals on their farm.

Certain mustards have long been known to produce biochemicals that can be toxic to soil microbiology. Varieties of two species of mustard (Sinapis alba and Brassica juncea) have been identified as producing chemical compounds known as glucosinolates that have been shown to reduce fungus and nematodes populations when mowed and incorporated into the soil. This process is known as biofumigation. These cover crops not only have the potential for controlling pests and pathogens, but also fill the role of traditional cover crops by reducing erosion, scavenging nutrients, and increasing soil organic matter.

Project Objectives:

Six varieties of mustard will be trialed to test glucosinolate production for disease and nematode control, and biomass production for organic matter and nutrient cycling. The varieties will include: Kodiak (Brassica juncea), Pacific Gold (Brassica juncea), Ida Gold (Sinapis alba), Caliente 119 (S.alba and B. juncea blend), Caliente 199 (S.alba and B. juncea blend), and Nemat (Eruca sativa– also a Brassica, bred as a nematode trap crop). These varieties will be planted in the spring and allowed to grow for 60 days before incorporation. Strawberries will then be planted no sooner than 14 days later to allow the biofumigation process to run its course. Strawberries are typically planted May through July. Spring planting mustard cover crops and planting strawberries in July allow these biofumigant cover crops to fit into a strawberry rotation.

The project took place on former hay ground that has never been planted to strawberries and had a cover crop of oats and peas planted August 17, 2014. Soil testing was planned at the beginning (April 2015) and at the end (July 2016) of the project to measure any differences in organic matter and nutrient levels on all 14 plots.  Soil testing was done by the UVM soil testing lab.

Cooperators

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  • Jeff Carter

Research

Materials and methods:

Six varieties of mustard were planted with a grain drill in the spring of 2015 in 40’x 80’ plots to test glucosinolate production for disease and nematode control, and biomass production for organic matter. The plots were duplicated for a total of 2 plots for each of the treatments. The varieties included: Kodiak (Brassica juncea), Pacific Gold (Brassica juncea), Ida Gold (Sinapis alba), Caliente 119 (S.alba and B. juncea blend), Caliente 199 (S.alba and B. juncea blend), and Nemat (Eruca sativa– also a Brassica, bred as a nematode trap crop). The plots were established with an organic composted chicken manure fertilizer (5-4-3) applied at 400 lbs./ac. Eight varieties of strawberries were then planted perpendicularly across the plots. The eight varieties planted were: ‘Wendy’, ‘Galletta’, ‘Brunswick’, ‘Jewel’, ‘Darselect’, ‘Cabot’, ‘Valley Sunset’, and ‘Record’.

The biofumigant mustard seeding rates were as follows: Kodiak (20#/ac.), Pacific Gold (20#/ac.), Ida Gold (25#/ac.), Caliente 119 (15#/ac.), Caliente 199 (15#/ac.), Nemat (10#/ac.). Soil tests were taken before planting (one test for the one-acre block) and after incorporation (one test for each treatment plus the control – seven total). Immediately before incorporation, yield data was measured and samples were sent to the University of Idaho for glucosinolate testing. After all measurements were taken, all the mustard plots were mowed with a rotary mower. Because most glucosinolates are volatile, the plants must be macerated (mowed) and incorporated immediately to achieve acceptable biofumigation. Incorporation was accomplished with conventional tillage methods: chisel plow and disc harrow. Raised beds were then formed and black plastic was applied for the strawberry planting.

The project was initiated in the spring of 2015 with the planting of the mustard plots on May 8. Soil tests were taken prior to planting. Measurements of mustard cover crops for weights and glucosinolate levels occurred when each variety was in full bloom. Harvest for ‘Idagold’ was on June 17; ‘Pacific Gold’ was July 2; ‘Kodiak’, ‘Caliente 119’, ‘Caliente 199’, and Nemat was on July 15. Immediately after each harvest, a sample was frozen for later glucosinolate testing. Within 48 hours of harvest, each plot was rotary mowed and the residue was incorporated with a chisel plow and disk harrow. Because glucosinolates are very volatile, the University of Idaho recommended that the samples were freeze dried for transport. Frozen mustard samples were brought to Freeze Dry Inc., in White River Junction, Vermont for freeze drying in September 2015.

The strawberry planting was established on July 30, 2015. Seven soil samples were taken: one on each mustard plot and one control. The planting was successful, although suffered significant deer damage in the fall of 2015. In 2016, strawberry harvest lasted for three weeks, from June 6 to June 26. Marker flags were placed in the field to recreate the mustard plots. Harvested strawberries were brought to the edge of the field within the mustard plot and totaled.

Research results and discussion:

The strawberry yields did not show a difference across mustard plots (see Fig.1). Significant deer damage to the plots in the fall of 2015 had an effect across all mustard plots and strawberry varieties. Although we did not see a result in the strawberry yields, we did find interesting results in the mustard trial. It was found that ‘Caliente 199’ (S.alba and B. juncea blend) had the highest biomass yield and highest levels of the glucosinolate ‘sinigrin’, a volatile compound that has been shown to have anti-fungal and anti-nematode properties (see Fig.2). Interestingly, ‘Ida Gold’ (Sinapis alba) contained another gluscosinolate, ‘sinalbin’ (see Fig.3). This non-volatile compound has shown the ability to inhibit weed seed germination. Although measurements were not taken, it was observed there was less overall weed pressure in the ‘Ida Gold’ plots. This is similar to observations in trials of ‘tillage radish’, another Brassica species. It was not determined whether weed suppression was a result of biofumigation or a dense cover crop outcompeting weeds. Planting rate (density) in other cover crops such as winter rye and oats has been shown to effectively suppress weeds.

Further research and consultation with Dr. Matt Morra at the University of Idaho revealed some other interesting differences. Sinigrin is volatile, has anti-fungal and anti-nematode properties, and must be macerated and incorporated quickly to have the desired effect. Also, moist soil helps distribute the chemical for maximum effectiveness, therefore successful biofumigation is more likely in a wet year. However, sinalbin is non-volatile, suppresses weed seed germination, and does not need to be incorporated. Maceration helps distribute the chemical, but it is subject to leaching and a dry year will result in more successful biofumigation.

Soil test results indicated that soil organic matter (SOM) levels went down as a result of the mustard biofumigation. The baseline soil sample taken in May 2015 showed SOM at 4.9%. Soil samples taken in each plot after mustard cover crop termination showed that each treatment reduced the SOM, except the control of no cover crop. The control showed a slight SOM increase to 5.1%. This may be due to the fertilizer applied at mustard establishment (see Fig.4). Research conducted at UNH and published in the journal Nature Communications showed that SOM accumulated from dead microbial cells and microbial byproducts rather than from plants themselves, as previously thought. This suggests that the best way to increase SOM was to promote microbial communities. While not strictly scientific, these results indicate that biofumigant mustards may hinder the accumulation of soil organic matter as they are designed to suppress certain microbial communities.

Fig.1-Strawberry-Yields-after-Mustard-Cover-Crops Fig.2-Mustard-yields Fig.3-SARE-mustard-samples-2015 Fig.4-Organic-matter

Research conclusions:

This project set out some basic guidelines for type and level of glucosinolate production of the respective mustard cultivars. The results can be used to form general recommendations based on the goals of the farmer. For example, ‘Idagold’ would be recommended for weed control due to the production of ‘sinalbin’. For maximum biofumigation efficacy, ‘Caliente 199’ would be recommended due to the high levels of glucosinolate production and high biomass yields.

Unfortunately, no clear recommendations for strawberries could taken from this project. No significant yield differences were observed. This was due to a combination of deer damage to the strawberry plots and lack of disease and nematode pressure (see Fig.5).Fig.5-Deer-Damage-on-Strawberries

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary

Education/outreach description:

Results were reported in the Champlain Valley Crop, Soil, & Pasture Team winter 2016-2017 newsletter. The project and some of the results were discussed. A copy is attached.

11x17CV-Crops-Winter-2016-Newsletter

In April 2017, this article and a field photo were shared with regional horticultural specialists to post on their websites or to be included in their newsletters.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

Potential Contributions

This project did not set out to specifically explore how mustard cover crops affect soil organic matter (SOM). However, the results show that the biofumigation process may have had a negative impact on SOM. The understanding of how SOM is formed, how it accumulates, and how it degrades is evolving. Recent research has shown that soil microbiology contributes to SOM far more than previously thought. The results of this project suggest that mustard biofumigation can work against SOM accumulation by suppressing soil microbiology.

Future Recommendations

Further study is needed to determine how planting rates of mustards and other Brassica species effect glucosinolate production, disease suppression, and weed control. The results of this project show that different species and cultivars of mustard produce varying levels and types of glucosinolates. Future research in this area can work to develop recommendations for mustard cultivars based on the goals of the farmer. Also, further study is recommended to determine the timing and place in the rotation. of the mustard cover crop. For example, is biofumigation most effective in the spring or the fall, or before or after the main crop?

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.