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Scientists and farmers agree that it is economically feasible to grow potatoes successfully in a healthy way that improves the land's bug-tarn productivity. The U.S. Department of Agriculture's Sustainable Agriculture Research and Education Program conducted an analysis of four pairs of organic and conventional potato farms in Washington. The results showed that variable costs on the organic farms averaged 12 percent less than on the conventional ones, with essentially the same fields. Since organic growers have relatively low input Costs, they can survive a bad growing season with lower investment risks than conventional farmers There are many options available for farmers who grow potatoes sustainably.
The most important step in growing potatoes organically is to carefully plan a crop rotation scheme that allows a few years between potato crops on the same land. A good rotation includes crops that are nor hosts to common potato pests, as well as green manures that add nutrients and organic matter to the soil. Green manures are crops that are grown ova the winter or for an entire year, and are then incorporated into the soil. Some crops can be harvested for seed or hay and the plant residues that remain are used as a green manure. When an `effective cropping sequence is in place, pesticides and chemical fertilizers are not necessary.
Wheat, corn, and barley, which are commonly grown in rotations with potatoes, are hosts for the Columbia root-knot nematode Meloidogyne chitwoodi, a serious potato pest that blemishes tubers and renders them unmarketable. Nematodes are primarily controlled by fumigating soil with 1,3-dicloropropene (1,3-D) or metam sodium. Because these fumigants impact nontarget organisms, they disrupt many beneficial soil ecological processes, such as nutrient cycling and biological control. Root-knot nematodes can be suppressed by growing crops in rotation with potatoes which are not hosts for nematodes Plant pathologists at Oregon and Washington State Universities list asparagus, cowpea, fodder radish, lima bean, Scotch spearmint, sudangrass, popcorn, super sweet corn as nonhost crops 3,4 In any crop rotation, proper weed control is important since many weeds are suitable pest hosts.
There are some green manures that result in remarkably good nematode control when they are incorporated into the soil. Rapeseed, sudangrass, white mustard, and rye not only control nematodes, but they have also been shown to suppress weeds and diseases such as the soilborne fungus Verticillium dahliae, which causes potato early dying. 5,6,7 These plants are allelopathic That is, they release a compounds into the soil which are toxic to certain other plants and animals. Most researchers have found that rapeseed is the most consistent at controlling nematodes and weeds and increasing potato yields.3» Rapeseed contains glucosinolates, which break down to isothiocyanates, compounds that are toxic to these soil organisms.
All green manures have benefits to the soil that extend beyond the chemicals they may release. Cover crops can reduce erosion from rain or wind, especially in the winter or early spring. When green manures are incorporated into the soil, they build up the organic matter content, which improves water retention, reduces compaction, and makes the soil a healthy habitat for beneficial organisms. Pests have to compete with the beneficial organisms in the soil, so their populations are unlikely to rise to damaging levels.
Legumes are important green manures for any organic farms. They have a symbiotic relationship with bacteria that can fix nitrogen into a form that plants can use. When legumes are incorporated into the soil prior to a potato crop, the nitrogen is made available to the potatoes. It is released more gradually than chemical fertilizers, so potatoes benefit throughout the growing season and the nitrogen does not leach into the groundwater. Austrian peas and Nitro alfalfa are used most commonly by organic potato farmers. Researchers found that Nitro alfalfa or Austrian peas provided 40 to 1OO percent of the nitrogen needed by a subsequent potato crop, depending on how wet the intervening winter and spring were.' The nutrients provided by legume green manures can be supplemented by animal manures or kelp. To accomplish this, some farmers raise cattle or chickens and use the manure they produce.
When crop rotation~s and green manures are used and pesticides are eliminated, the resulting farm encourages beneficial organisms and becomes more diverse, much like a natural ecosystem. Consequently, organic farmers do not usually have large enough problems with pests or diseases to cause crop damage. One example of a rotation scheme comes from Steve Walser, who runs a 320-acre farm in Eastern Washington. He uses a 3-year rotation, following potatoes with squash or sweet corn. The year before potatoes is devoted to green manures, beginning with sudangrass, followed by Austrian peas over the winter. He also uses compost and animal manure.9 This is a shorter rotation than many farmers use, but it works for Steve. The right rotation scheme will be different for every farmer, depending on local conditions and markets. Organic farmers do have to keep up with the weeds that grow in their healthy soils, and they do so using mechanical methods rather than herbicides. Mechanical weeding is most important when the young potato plants are emerging, since as they get bigger they become strong enough to compete with weeds. Some hand weeding among the large plants may be necessary. When the potatoes are mature, conventional farmers use dessicants to kill the potato plants and cause the tuber skies to toughen. Organic farmers simply let the plants die on their own with the help of the first frost, or they use a flailing machine to rip up the plants. By using mechanical methods and a little hard work, dessicants can be replaced.
Teresa Huntsinger
1. Sustainable Agriculture Research and Education Program.1994. Potato systems cut costs. SARE 1994 Project Highlights.
2. SARE. 1992. Project No. LW-91-29 Development of sustainable potato production systems for the Pacific Northwest. Annual Report. University of Idaho, Aberdeen, ID.
3. Luna, J.1993. Crop rotation and cover crops suppress nematodes in potatoes. Pacific Northwest Sustainable Agri culture 5(1): 4-5.
4. Santo, G.S. 1994. Biology and management of root-knot nematodes on potato in the Pacific Northwest. Advances in Potato Pest Biology and Management St. Paul, MN: APS Press. Pp.193-201.
5. Davis, J.R. et al.1994. The influence of cover crops on the suppression of Verticillium wilt of potato. Advances in Potato Pest Biology and Management St. Paul, MN: APS Press.
6. Al-Khatib, K. and R. Boydston. 1994. Weed control with rapeseed and white mustard as green manure. Pacific Northwest Sustainable Agriculture 6(1):4.
7. Lanfranconi, L. E. et al. 1993. Grain residues and weed control strategies in reduced tillage potatoes. Weed Technol. 7(1) 23-28
8. Mojtahedi, H. et al. 1993. Managing Meloidogyne chitwoodi on potato with rapeseed as green manure. Plant Disease 77(1): 42-46.
9. Oregon Tilth, 1993. Sustainable Potato Farming The Farmers' Side of the Story. Video. (Produced by Paul Thiers.)
Citation : Huntsinger, Teresa, 1995, "Sustainable potato production", Vol. 15, No. 2, Summer 1995, pp. 4-5.
Copyright © 1995 Northwest Coalition for Alternatives to Pesticides.
Reprinted with permission.
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