Integration of a Brassica Green Manure into the Potato-Barley Rotation

Integration of a Brassica Green Manure into the Potato-Barley Rotation

Summary

This summary covers the second year of a three-year study. The objective of this project is to assist New England potato farmers in determining the most efficient way to integrate a Brassica green manure in their current potato – small grain rotation. Some members of the Brassicaceae have been reported to suppress soil pathogens when incorporated as green manures. The predominant rotation among potato growers is to plant potatoes followed by oats or barley, and then go back to potatoes. Our initial goal was to grow a Brassica green manure in the same season as a cash crop of barley. However, from results of the first season of the study, this appears to be unworkable in northern Maine. Where the winter rapeseed green manure became well established, it interfered with barley harvest when the grain lodged into the underseeded green manure. Where the green manure was established after barley harvest, the remaining growing season was too short to obtain significant growth from the green manure. Accordingly, the grower cooperators choose to redirect the study and work on evaluation of a Brassica green manure as a sole crop completely replacing the barley crop in northern Maine. Also, it was decided to work on establishing a Brassica green manure after barley further south, in central Maine, where the growing season is longer, and barley is often harvested early as silage. The grower-cooperators also chose to conduct the experiment with large plots (60 feet wide) that better fit their farming equipment. This limited the number of treatments that could be evaluated. It was decided to work with ‘Caliente’ green manure mustard, as this variety has been shown to benefit potatoes in Washington. The growers felt with limited treatments they preferred to work with a variety that had been proven elsewhere.

In the 2003 season, three on-farm trials were conducted, with two locations in northern Maine and one in central Maine. In the northern Maine trials ‘Caliente’ green manure mustard (mixture of Brassica juncea and Sinapis alba) was planted in mid-May and replaced the barley crop. Each trial had barley as a check, and one site also had canola. The trials were replicated at least three times at each site. In central Maine, ‘Caliente’ mustard, and ‘Dwarf Essex’ winter rapeseed were planted in early August following a barley crop harvested for silage. In northern Maine the mustard was mowed and disked in during early seed-filling. Average dry matter production of the mustard green manure in northern Maine was 4330 lb per acre at one site, and 4230 lb per acre at the other site. In central Maine where the green manure crop was planted after barley harvest, the mustard was mowed and disked in during early flowering and dry weight averaged 2750 lbs per acre. Published work with this variety shows incorporation of 4770 lbs per acre was associated with suppression of verticillium wilt (A.M. McGuire. 2003. Mustard green manures replace fumigant and improve infiltration in potato cropping system. Plant Management Network, August 2003). The green manure treatments will be repeated again in the coming year, and the potato crop following the 2003 green manure will be monitored for disease incidence.

The project team has been expanded to include Mr. John Dorman, a grower from central Maine, Mr. Andrew Plant, IPM Professional (and a graduate student in Plant Pathology), and Dr. Dave Lambert, a plant pathologist at Orono. The additional cooperators allow us to increase the scope of the trial geographically and also to increase the precision of disease monitoring.

Objectives/Performance Targets

1) The feasibility of intercropping and the optimum time of planting will be well-defined by the third year of the project.

2) The farmers working with the project will be planting a rapeseed (or other Brassica) green manure on a production scale (either intercropped or sole cropped – depending on results) on fields outside the study area by the third year of the project.

3) We will have large demonstration/observation strip plots (1 acre in size) incorporating a rapeseed green manure into the potato cropping system on other farms by the third year of the project.

Accomplishments/Milestones

1) Trials to evaluate intercropping a Brassica green manure with barley were implemented and evaluated with growers in the 2002 season.

2) Based on the outcome of these trials, growers decided that it would be good to focus the trial work in 2003 on evaluating the benefit of sole-cropped Brassica green manures in northern Maine. They are particularly interested in evaluating the ‘Caliente’ oriental mustard used by potato growers in the Columbia Basin of Washington.

3) Replicated field trials to evaluate a Brassica green manure as compared to the standard barley rotation were implemented on three farms in the 2003 season. Growers are interested in continuing this work and the trials will be repeated in the 2004 season.

4) Several additional growers have been recruited to run two-acre observation plots on their farms in 2004. This will provide a broader evaluation of the mustard green manure and, if it proves beneficial, will help to disseminate the technology.

Impacts and Contributions/Outcomes

This effort is a work in progress.

Collaborators: