Mustard Green Manures for Potato Production

2004 Annual Report for SW03-018

Project Type: Research and Education
Funds awarded in 2003: $45,653.00
Projected End Date: 12/31/2007
Matching Non-Federal Funds: $18,324.00
Region: Western
State: Washington
Principal Investigator:
Andrew McGuire
Washington State University Extension

Mustard Green Manures for Potato Production


Washington potato growers, although producing record yields, are experiencing reduced profits due to decreasing market prices and increasing production costs. A major part of production costs for most growers is fumigation. They also have to spend more on inputs due to the decreasing soil quality.

Washington growers are increasingly interested in growing mustard as a green manure preceding potatoes to help control nematodes, weeds, and soil-borne diseases. This practice has the potential to replace some soil fumigation and to improve soil quality. We will conduct on-farm research aimed at reducing the risk to farmers of using mustards to replace fumigation.

Objectives/Performance Targets

Objective 1: Determine the measurable factors related to suppression or non-suppression of potato early dying in processing potatoes.

Objective 2: Determine the species and variety of mustard, or other Brassica, that will most benefit Washington potato growers.

Objective 3: Increase the adoption of mustard green manures by potato growers through an integrated program of on-farm research and education.

Increasing the Producer's Knowledge Base

This project will increase the knowledge base of potato growers by providing them with information on 1) the potential for mustard green manures to replace the fumigant, metham sodium, in diverse potato cropping systems, 2) management of mustard green manures for optimum results, 3) the best species/varieties to use in Washington. This outcome will be measured by the production of research summaries containing the results from +/- fumigant trials, wheat straw management trials, and green manure variety trials.

Dissemination of Information

The target audience is potato growers and their crop consultants. Targeted meetings will be the Washington Potato Conference, the Columbia Basin Crop Consultants Association, and the Pacific Northwest Vegetable Association. Targeted media outlets include Potato Country, Potato Progress, Agri-Focus Newsletter, Columbia Basin Farmer, and the Capital Press. The actions leading to this outcome are detailed under Objective 4. The outcome will be measured by keeping records of website users/hits, number of articles published, and attendance at presentations and the field day.

Number of Acres Impacted

We aim to increase acres planted to mustard green manures in Central Washington by 25% every year for the next five years (three covered by this proposal), from 9,260 acres in 2001, to 28,000 acres being planted the fall of 2006, or over 15% of Washington's potato acreage. We will continue to estimate the mustard acreage from the seed sales of the three seed companies providing mustard green manure seed in Washington.

Actual Positive Economic Impact

If 28,000 acres of mustard green manures are used to replace the metam sodium fumigant treatment, then potato farmers would save from $1.4 – 3.0 million dollars annually, depending on the production costs of the mustard crop and the amount of nitrogen cycled to the following potato crop. This replacement of fumigant will happen more slowly than the adoption of the mustard green manures, most likely after the project is over. Nonetheless, if we feel that a significant number of potato growers are replacing their fumigant with mustard green manures, we will conduct a survey to estimate this impact.


Objective 1

Soil sampling: soil samples were taken in May from 12 locations representing three conditions: fields receiving mustard green manures, neighbor fields not receiving green manures, neighboring native soils. These soils were tested for Zn, Mn, CEC, pH, organic matter, soil texture, and fluoride levels. These results were analyzed for trends and differences which led to a second round of soil sampling and testing in late summer. We took samples from five fields that were being planted to mustard green manures before 2005 potatoes, where the farmer cooperators had agreed to apply a fumigant treatment on only a portion of the field. The soil samples from these fields were tested for soil organic matter, pH, soil texture, nematode counts (for Pratylenchus sp.), active C, soil stability, soil respiration, and levels of Verticillium dahliae. After next year's potato harvest, we will try to correlate these measurements to either success or failure of the mustard green manures to produce potato yields equal to those produced with fumigant. This work will also be repeated next year in other fields.

Objective 2

We conducted a variety trial of 18 varieties of two mustard species and another trial comparing six non-mustard Brassica crops. We compared the varieties biomass production and also monitored when they began flowering. Biomass results for the mustard can be found at and results of the other Brassica species may be requested by sending an email to [email protected].

Samples of all the mustard varieties were taken and sent to a laboratory for analysis of glucosinolate concentrations. This work has not been completed.

Objective 3

The results of the variety trial, past research, and basic principles were disseminated to farmers and crop consultants at a Mustard Green Manure field day held Oct. 26th. Handouts from this event can be found at:
The field day was attended by approx. 45 people.

A website developed to disseminate information on mustard green manures received over 16,000 hits in 2004 through November. Mustard green manure publications were downloaded about 3,100 times in the same period. Through direct contact by presentations or posters, 1,324 people were made aware of the benefits and uses of mustard green manures. The results of this work were published in the Australian newsletter, Biofumigation Update, and in Potato Progress, the grower newsletter of the Washington State Potato Commission.

Impacts and Contributions/Outcomes


The use of mustard green manures has increased from 1,800 acres in 1999 to 20,630 acres in 2003. A majority of these acres will be planted to potatoes in 2005. Although I know of at least five large farming operations that are not using the fumigant metam sodium on their field receiving mustard green manures, it is difficult to estimate the acres on which this is occurring. If farmers replaced the fumigant metam sodium on all of these acres, farmers would save over $1.3 million (~$66 per acre) while improving the quality of their soil. The growers using green manures on these acres should begin to see improvements in their soil quality, their ability to manage soil-borne pests, and eventually increased profits.