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 fourth year of a study looking at Brassica green manures. 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 2005 season the project had a number of different facets encompassing several on-farm trials. Data on potatoes was collected from four on-farm trials where different green manure treatments had been imposed the year before. Results from the three on-farm trials where potatoes were grown in 2004, and the four trials in 2005, showed on average an 8 % increase in tuber yield following a mustard green manure versus barley grown for grain. The mustard green manure mustard consistently decreased or controlled Rhizoctonia; however, white mold incidence in the potato crop was greater following the mustard green manure than following barley. We did not see any effect of the mustard green manure on powdery scab in our trials. Preliminary economic analysis indicates that the mustard green manure would provide enough of a benefit for potatoes that it would be more profitable than growing barley. However, white mold is an issue that has to be contended with. Farmers interested in the mustard green manure should avoid potato varieties or fields where white mold is an issue. This is a work in progress, a full report will be issued in June of 2006.

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 and 2004 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 in three on-farm trials in the 2003 season, and on four on-farm trials, and seven on-farm observation blocks in the 2004 season. Growers are interested in continuing this work and we plan to follow through with the 2004 trials by monitoring performance of the following potato crop in 2005. Several farmers planted some area to mustard green manure (at their own expense) in the 2005 season.

4) In both the 2004 and 2005 seasons, the mustard green manure helped to control Rhizoctonia and increased total yield of ‘Russet Burbank’ and ‘Shepody’. Across seven on-farm trials there was an average yield increase of 8% following mustard versus barley. This yield benefit was statistically significant. We did not see control of powdery scab in our trials. White mold incidence was greater where mustard or canola were grown the previous season. Thus the mustard green manure provided a yield benefit, and it helped control Rhizoctonia. On the other hand, white mold incidence was worse following the mustard green manure. Therefore, where white mold is an issue, farmers may want to use a different green manure in their efforts to improve soil quality.

5) The Maine Potato Board, a grower controlled commodity group, contributed support for analysis of leaf and soil samples taken in the 2005 season. Farmers are interested in the outcome of the work.

Impacts and Contributions/Outcomes

This effort is a work in progress and we are still analyzing samples and evaluating data from the 2005 season.

Collaborators: