Expanding the use of Brassica cover crops in onion production

Project Overview

Project Type: Partnership
Funds awarded in 2014: $14,932.00
Projected End Date: 12/31/2016
Region: Northeast
State: New York
Project Leader:
Christine Hoepting
Cornell Cooperative Extension - Cornell Vegetable Program

Annual Reports


  • Vegetables: onions


  • Crop Production: cover crops, nutrient cycling
  • Education and Training: demonstration, extension, on-farm/ranch research
  • Farm Business Management: budgets/cost and returns
  • Natural Resources/Environment: soil stabilization
  • Pest Management: mulches - killed
  • Production Systems: general crop production
  • Soil Management: soil analysis, soil microbiology, soil quality/health

    Proposal abstract:

    Use of Brassica cover crops following harvest of early bulb onions has become common practice in Michigan as research from Michigan State University has demonstrated that their use results in improved stand, allowing growers to reduce their seeding rate by 10% or more. Other cited benefits from using Brassica cover crops include increased yield, improved drainage, nutrient cycling and, suppression of weeds and soil-borne diseases. The problem is that in New York, which accounts for 97% of onion production in the Northeast U.S., where over 10,000 acres of onions are grown on muck soils, Brassica cover crops are currently only being used on 6 of these 75 farms. The main reason for low adoption is that growers are not aware of their potential benefits. Our goal is to expand use of Brassica cover crops to most of the muck onion farms in NY so that they too can reap from their benefits and enjoy sustainable production. Our combined approach of in-depth case-studies, replicated research trials and a diverse educational and outreach program, will expand growers’ knowledge and ability to successfully implement use of Brassica cover crops in muck onion production. If we meet our conservative goal of 1000 acres planted to Brassica cover crops in fall 2016, then that will result in an increased return to growers of about $1.7 million dollars in increased yield and quality in the 2017 growing season, and may also reduce their costs for seed, nitrogen fertilizer and weed management.

    Project objectives from proposal:

    Brassica cover crops were established by our grower cooperators in the Elba muck land in 2013 to study onion performance in 2014. The plantings follow grower requirements rather than optimal experimental design, but the scale of the trials and grower involvement should make them effective for persuading growers to adopt useful practices. We will estimate the benefit of mustard planted according to current recommendations, and the effect of planting 10 days after the optimal window in comparison to a bare ground control (Triple G Farms, direct seeded yellow onions). We will test whether late-sown radish is effective, and also estimate biomass production and winter-kill date (CY Farms, direct seeded yellow onions). Radish with an oat nurse crop was sown 3.5 weeks later than the typical radish planting date adjacent to a control oat planting. We will test a very late mustard planting (Sep-26), compare incorporating vs. leaving mustard to winter-kill, and single-year vs. repeat treatment of mustard (Mortellaro, transplanted yellow onions). At this site we will also estimate the winter-kill date of both mustard and radish.  


    In total, we will have 12 individual case study sites including the controls – see attachment. We will obtain replication by using matched blocks within these fields. The fields are long and narrow, so there is typically less variation between two fields at a given point then there is along the length of the field. We will have six replications in this nonrandomized complete block design.


    Data collection for case studies:

    Biomass of cover crop for the over-wintering Caliente-199 and Forage radish (3 case- studies) will be taken in late-November, for which dry weight of the shoot and radish-root will be determined.

     Nutrient availability will be assessed in the spring prior to soil disturbance including total nutrient analysis and available nitrate-nitrogen. We will use this information to propose nitrogen credits based on cover crop biomass and time of decomposition.

     Drainage and soil compaction will be assessed in the spring prior to soil disturbance using a penetrometer to measure maximum compaction at depths 0-6” and 7-12”. Differences in ponding or grower’s ability to work ground will be noted.

     Onion stand will be quantified at the flag and 2-leaf onion stages. The final stand is the number of bulbs per harvested area.

     Onion growth will be assessed at the 2-, 5- and 8-leaf stages by number of leaves per plant, plant height and neck diameter. Maturity will be assessed by estimating the % lodging in mid-August.


    Yield will include number of bulbs and bulb weight of the total marketable and culls, and distribution among size classes.


    Bacterial bulb decay will be quantified at harvest, and the remaining sound bulbs will be put into commercial onion storage and graded again for decay in February. Also, when soil is sampled in the spring, a portion will be sent to Steve Beer, Plant Pathologist at Cornell, to analyze and quantify pathogenic onion bacteria that occur in muck soil (funded independently of this project).

     Weed suppression will be determined at the 2-, 5- and 8-leaf onion stages by number of weeds and fresh biomass per species present.

     Effect on soil-borne pathogens (greenhouse bioassay): Spring-collected soil from each case study will be bioassayed for pathogens by filling one 100-cell plug tray with each sample, then sowing one raw onion seed per cell, and raising them in a greenhouse. Seedling mortality will be counted every week from the loop-stage until the 2-leaf stage. Seedlings infected with smut will be counted. Damping-off pathogens, Phythium, Rhizoctonia and Fusarium will be identified microscopically on five wilted plants per replicate. Suspicious samples will be confirmed by Cornell Plant Pathologist, George Abawi.

     Cost-benefit analysis will be conducted for each case study. The input costs will include cover crops, onion seed/transplants, fertilizer, herbicides, labor and any other costs that might vary because of the treatments. Costs not affected by the treatments will not be included in the analysis. We will calculate the value of differences in yield, bulb size and losses due to bacterial bulb decay. Our grower cooperators will provide all required input costs and onion prices. With these data, we will determine the costs and returns from the several schemes tested.

     Statistics - Differences among treatments will be determined using a general analysis of variance (ANOVA). Mean separation will be determined using Fisher’s Protected test with probability of 5%.

     Plant Population Studies:

    We will determine whether the mustards will allow a reduced seeding rate of direct seeded onions in the Aug- 20 planting at Triple G, and whether they would allow a higher plant population in transplanted onions in the Sep-26 planting at Mortellaro. Mustards primarily increase seedling survival in direct-seeded onions, and bulb growth in transplanted onions. We want to determine how much the seeding rate can be reduced in direct-seeded onions, and how much the plant population of transplants can be increased without reducing bulb size, thus, increasing yield.

     At Triple G, three treatments will be the grower’s standard (267,981 plants/A), and 17% and 38% fewer seeds per acre, in a randomized complete block design with 5 replications. The grower will plant the trial using his commercial onion seeder and will stop and adjust the seeding density according to the randomized plot plan. Plots will be 2-beds wide (10-ft wide, 4 rows spaced 15”) by 15-ft long. Stand, yield and bacterial bulb decay will be collected from the inside 10-feet.

     At Mortellaro, four treatments will include the grower standard (128,938 transplants/A) and 21%, 38% and 62% higher plant population. The grower’s standard planting configuration is 15-inch between rows on a 5-ft bed with 3.25-inch plant spacing. For the higher plant populations, we will space rows 10-inch apart and use 4-, 3.5- and 3-inch plant spacing. Plots will be 1-bed wide by 10-ft long in a randomized complete block design with 5 replications. Transplants will be set by hand using custom fabricated dibbles. Yield and bacterial bulb decay will be measured as described above, and a cost-benefit analysis conducted.


    Brassica cover crops established. Grower cooperators. August to September 2013.

     Collect samples of forage radish and over-wintering Caliente 199 for biomass determination. Hoepting & technician will collect samples and Bjorkman will determine dry weight. Late-November 2013.

     Set up replications in 12 in-depth study fields; collect soil samples for nutrient analysis, greenhouse bioassay for soilborne diseases and bacterial pathogen analysis; evaluate soil compaction and make observations regarding drainage and cover crop decomposition and residue. Hoepting and technician. Early-April 2014.

     Conduct greenhouse bioassay for disease suppression; in-depth study fields are planted; small-plot plant population studies set up. Hoepting, technician and grower cooperators. Mid-April to late-May 2014.

     Collect data on stand, onion growth and weed suppression. Hoepting and technician. May to July 2014.

     Show-case trials at Elba Muck Onion Twilight Meeting. Hoepting, technician, grower cooperators and Bjorkman. Early-August 2014.

     Harvest, grade and first bulb rot assessment of in-depth studies and small-plot plant population studies. Hoepting and technician. Mid-August to mid-October 2014.

     Plant second-year cover crops in anticipation of future funding. Grower cooperators. August to September 2014.

     Data entry, analysis and summary; collect economic data from grower cooperators; identify research questions for second year of study, identify funding source and possibly (depending on funding source) write grant proposal to continue project; submit Annual report to NESARE. Hoepting, technician, Bjorkman and grower cooperators. Mid-October to December 2014.

     Present results-to-date in the onion session at the statewide Empire Produce Expo. Hoepting and Bjorkman. Late-January 2015.

     Evaluation of bacterial bulb decay out of storage. Hoepting and technician. February 2015.

     Complete data analysis; cost-benefit analysis; write and disseminate newsletter article highlighting what was learned in first year of study; add provisional recommendation to the Cornell cover crop website; project completed. Hoepting and Bjorkman. March 2015.

     Submit Final report to NESARE. Hoepting. June 31, 2015.


    The educational program will support adoption of using Brassica cover crops in muck onion production to increase yield, suppress pests and reduce input costs. Cornell Cooperative Extension has excellent educational outreach for onion growers throughout New York. The culture of innovation varies markedly among the different muck onion growing areas in New York. Increasing adoption beyond the most progressive growers will require an outreach message tailored to each group’s sensibilities.

     Selected Brassica cover crop case-studies and small-plot plant population studies will be show-cased at the Annual Elba Muck Onion Twilight Meeting to allow growers to see first-hand their effects on stand, plant vigor, yield and weeds under real-world growing conditions. Although this meeting is in Elba, it has historically been attended by muck onion growers from the other major muck onion growing regions in NY. To reach all muck onion growers in NY, results will also be disseminated statewide in Extension newsletter articles and at the Empire State Produce Expo, and online. Small-scale onion growers throughout the Northeast U.S. may also benefit from the results of this project, because they tend to harvest their onions in a timely manner for establishment of Brassica cover crops. Growers hosting on-farm trials will serve as resources to other interested growers.

     Our combined approach of in-depth case-studies, replicated research trials and outreach via field demonstration, formal presentation and newsletter article, will expand growers’ knowledge and ability to successfully implement use of Brassica cover crops in onion production. New York onion growers have a long standing history of adopting Cornell research-based recommendations.

    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.