Expanding the use of Brassica cover crops in onion production

Expanding the use of Brassica cover crops in onion production

Summary

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.  The goal of this project is to expand use of Brassica cover crops to most of the muck onion farms in NY so that they too can reap their benefits and enjoy sustainable production. 

In 2014, we conducted 7 in-depth on-farm case studies to determine the effects of planting date and incorporation of mustard on onion stand, yield, bulb size, nutrient cycling, compaction, and suppression of bacterial diseases.  Small-plot trials were conducted at two locations to optimize onion plant population following Brassica cover crops.  A plug tray bioassay was conducted to determine if Brassica cover crops have an effect on onion seedling diseases caused by soil-borne pathogens. 

In 2015, research results will be analyzed and summarized and a cost-benefit analysis conducted, all of which will be reported to onion growers. 

Objectives/Performance Targets

Brassica cover crops were established by our grower cooperators in the Elba muck land in 2013 to study onion performance in 2014.  At Triple G Farms, we compared the optimal planting date (Aug-20) of yellow/brown mustard (Caliente 199) to planting 10 days after the optimal window (Aug-30) and to a bare ground control in direct seeded yellow onions.  At Mortellaro farm, we compared an optimal planting of mustard (cv. Caliente 199) on Aug 7 to a very late planting (Sep-26), both of which were incorporated, a late planting (Aug 27) that was left to winter-kill, and a late planting of forage radish (Aug 30) in transplanted yellow onions. 

 Prior to soil disturbance in the spring, composite soil samples were collected from reps 1, 3 & 5 and sent to CNAL for complete nutrient analysis and Potentially Mineralizable Nitrogen (PMN).  Available soil nitrate-N was later analyzed at the 8-10-leaf stages.  Also prior to soil disturbance, maximum soil compaction at depths 0-6” and 7-12” was measured using a penetrometer at 10 random locations in each of 6 replicates per treatment.  Onion stand was quantified at the loop-flag, 3- and 5-leaf onion stages in direct seeded onions, and in 8-10-leaf onions in both direct seeded and transplanted onions by counting the number of plants in four side-by-side 3-ft sections of row in two sub-samples per rep.  Onion growth was assessed in all but the loop-flag leaf stages by number of leaves per plant, plant height and neck diameter in two sub-samples of 10 randomly selected plants per rep.  At harvest, 100-bulb samples were collected from two sub-samples per replicate for yield assessment, which included number of bulbs and bulb weight of the total marketable and culls, and distribution among size classes.  Bacterial bulb decay was quantified at the harvest yield assessment, and the remaining sound bulbs were put into commercial onion storage and will be graded again for decay in February.  Also, when soil was sampled in the spring, a portion was sent to Steve Beer, Plant Pathologist at Cornell, for pathogenic bacterial suppressive analysis (funded independently of this project). 

 To evaluate the effect of the mustard cover crops on soil-borne pathogens, a plug tray bioassay was conducted.  The soil collected prior to soil disturbance was used to fill one 200-cell plug tray per field rep and one raw onion seed per cell was sown.  The seedlings were grown in the outdoors with daily watering as needed.  Emergence, seedling stage and mortality was quantified 2 and 5 weeks after planting.  Samples of unhealthy plants suspect of Damping-off pathogens, Phythium, Rhizoctonia and Fusarium were sent to Chris Smart, Cornell Plant Pathology for confirmation.    

Two small-plot plant population studies were conducted in order to 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 Aug-7 planting at Mortellaro.  Mustards primarily increase seedling survival in direct-seeded onions, and bulb growth in transplanted onions.  We wanted 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, treatments included the grower’s standard (267,981 plants/A = 7.7 seeds per ft), and 17% (~222,424 plants/A = 6.4 seeds per ft) and 38% (~166,148 plants/A = 4.8 seeds per ft) fewer seeds per acre, in a randomized complete block design with 5 replications.  The grower planted the trial using his commercial onion seeder stopping to adjust the seeding density according to the randomized plot plan.  Each plot was 2-beds wide (10-ft wide, 4 rows spaced 15”) by 15-ft long.  At harvest, stand, yield and bacterial bulb decay were collected from the inside 10-feet.

At Mortellaro, treatments included 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 off-set plant spacing.  For the higher plant populations, we spaced 5 rows 10-inch apart and used 4-, 3.5- and 3-inch plant spacing.  Plots were 1-bed wide (= 5 ft) by 10-ft long in a randomized complete block design with 5 replications.  Transplants were set by hand using custom fabricated dibbles.  Yield and grade was collected from the entire plot area.  Bacterial bulb decay was also quantified.

To date, all of the data for this project has been collected, except for bacterial decay out of storage from the field case studies and information from the growers to conduct cost-benefit analysis.  All data still needs to be entered, analyzed and summarized, and the cost-benefit analyses need to be conducted.

Accomplishments/Milestones

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

Collect samples of forage radish and over-wintering Caliente 199 for biomass determination.  Hoepting & technician collect samples and Bjorkman determine dry weight.  Late-November 2013. This was not accomplished: during the last week of November, temperatures unseasonably dipped into the mid-teens and the fields were covered in snow.  It was a long cold winter in Western NY.

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. Accomplished.  Note, we ended up with 7 study fields instead of 12: our third grower cooperator only planted onions on one of the fields leaving nothing for comparison, and Mortellaro did not plant three of his fields that were in mustard cover crops to onion in 2014, so we were unable to compare single vs. double seasons of mustard cover crops or late planted mustard/oat.

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.  Accomplished.  Note, the bioassay was conducted in the outdoors instead of in a greenhouse, because the study team felt that a greenhouse would be too hot in May through July.  The bioassay for the soil from the Mortellaro fields was re-planted using the same soil that was collected prior to soil disturbance (that had been sitting in plastic garbage bags in full shade in the outdoors), because the soil was too wet at the first planting and emergence was very poor.  Emergence improved in the second planting. 

Collect data on stand, onion growth and weed suppression.  Hoepting and technician.  May to July 2014. Accomplished.  Note, we did not collect data on weed suppression due to the inherent variability in weed pressure among fields.

Show-case trials at Elba Muck Onion Twilight Meeting.  Hoepting, technician, grower cooperators and Bjorkman.  Early-August 2014.  Not accomplished: At this time, there was nothing of visual impact to show the growers in the field.  However, the growers were told about the project and the impressive preliminary results from the Mortellaro mustard cover crop demonstration in 2012-2013 were shared with the 29 participants at this meeting.

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

Plant second-year cover crops in anticipation of future funding.  Grower cooperators.  August to September 2014. Not accomplished: harvest was generally late in 2014 with very little acreage suited for optimal timing of mustard cover crops.  Early harvested fields were destined for fall weed management programs that interfered with mustard cover crops.  It is anticipated that if results of this project are positive, more use of Brassica cover crops will occur in 2015.

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. Behind schedule, trumped by other deadlines, plans to complete in February-March 2015.

Present results-to-date in the onion session at the statewide Empire Produce Expo.  Hoepting and Bjorkman.  Late-January 2015. Delayed – results not available.

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

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. On-track.

Submit Final report to NESARE.  Hoepting.  June 15, 2015.  On-track.

Impacts and Contributions/Outcomes

Data entry, analysis and summary, and cost-benefit analysis still need to be completed.  No impacts or outcomes at this time.  The data team is looking forward to learning the results of this in-depth study and presenting the new information to onion growers in the New Year.

Collaborators: