D.H. Putnam1, E.S. Oplinger2, J.D. Doll2, and E.M. Schulte2
1Center for Alternative Plant & Animal Products, Minnesota Extension Service, University of Minnesota, St. Paul, MN 55108.
Amaranth, an ancient crop originating in the Americas, can be used as a high-protein grain or as a leafy vegetable, and has potential as a forage crop. Grain amaranth species have been important in different parts of the world and at different times for several thousand years. The largest acreage grown was during the height of the Aztec civilization in Mexico in the 1400's. The past two centuries grain amaranth has been grown in scattered locations, including Mexico, Central America, India, Nepal, China, and Eastern Africa. Research on amaranth by U.S. agronomists began in the 1970's, so optimum production guidelines and uniform, adapted varieties have not yet been fully developed.
A few thousand acres of amaranth are commercially grown in the United States, and markets for that small acreage are fragile but developing each year. Acreage has increased during the 1980s. Growers are advised to begin with a few acres, and to have a contract or identify buyers before planting the crop.
Grain amaranth has been used for food by humans in a number of ways. The most common usage is to grind the grain into a flour for use in breads, noodles, pancakes, cereals, granola, cookies, or other flour-based products. The grain can be popped like popcorn or flaked like oatmeal. More than 40 products containing amaranth are currently on the market in the U.S.A.
One of the reasons there has been recent interest in amaranth is because of its useful nutritional qualities. The grain has 12 to 17% protein, and is high in lysine, an essential amino acid in which cereal crops are low. Amaranth grown at Arlington, WI in 1978 had protein levels of 16.6 to 17.5%. The grain is high in fiber and low in saturated fats, factors which contribute to its use by the health food market. Recent studies have linked amaanth to reduction in cholesterol in laboratory animals.
Little is known about the production and utilization of amaranth as a forage. The leaves, stem and head are high in protein (15-24% on a dry matter basis). A Minnesota study (1 year) on amaranth forage indicated a yield potential of 4-5 tons/acre dry matter, with crude protein of the whole plant at 19% (late vegetative stage) to 11-12% (maturity) on a dry basis. A relative of grain amaranth, redroot pigweed, (Amaranthus retroflexus), has been shown to have 24% crude protein and 79% in vitro digestible dry matter. Pigweeds are known nitrate accumulators, and amaranth responds similarly. Vegetable amaranths, which are closely related, produced 30 to 60 tons/a of silage (80% moisture) on plots in Iowa. In areas where corn silage yields are low due to moisture limitations, grain amaranth may become a suitable silage alternative after further research.
The two species of grain amaranth commonly grown in the U.S. are Amaranthus cruentus and Amaranthus hypochondriacus. Grain amaranths are related to redroot pigweed, but are different species with different characteristics and have not become weeds in fields where they have been grown. The grain amaranths have large colorful seed heads and can produce over 1000 pounds of grain per acre in the upper Midwest, though a portion of this grain yield may be lost in harvesting.
Grain amaranth plants are about five to seven feet tall when mature, and are dicots (broadleaf) plants with thick, tough stems similar to sunflower. The tiny, lens-shaped seeds are one millimeter in diameter and usually white to cream-colored, while the seeds of the pigweed are dark-colored and lighter in weight.
Amaranthus is a widely adapted genus, and can be grown throughout the Midwestern and Western U.S. Grain amaranth is reportedly drought-tolerant, similar to sorghum, provided there is sufficient moisture to establish the crop. Amaranth responds well to high sunlight and warm temperatures. Early season frost damage is not a problem because the crop is not sown until late May or early June. However, frost plays an important role in the harvest of the crop. Since amaranth is an annual crop native to the southern latitudes of North America, it does not mature completely in the upper Midwest's short growing season. A frost is usually necessary to kill the crop so that the plant material will be dry enough to harvest.
Seeds are very small, so it is important to have a fine, firm seedbed. Seedbed preparation can be done with a field cultivator or disk; followed by cultipacking or spiketooth harrow and planting, preferably using a planter with press wheels. Seeds should be planted no more than 1/2 inch deep, depending on soil texture and surface moisture at planting time. Heavy textured soils should be avoided. If crusting is a problem, rotary hoeing at a slow speed may be helpful. Poor emergence, as low as 50%, is not uncommon, Since seeds are shallow planted, there is potential for them to wash out on sloping ground.
The crop is usually sown in late May or early June when the soil temperature is at least 65°F, and after early weed flushes have been controlled.1
An optimum plant population has not been established, but one-half to two pounds of seed per acre is considered suitable (approximately 600,000 seeds per pound). Row spacing should be based on the cultivator equipment available. A number of planter types have been used successfully to deal with the small seeds of amaranth. Approaches that have proven successful include: using a vegetable planter with a small plate appropriate for carrots or celery; installing special amaranth seed plates in a sugar beet planter; using the in-furrow insecticide application equipment as a planter; or using a standard grain drill. Grain drills are not recommended due to problems in controlling seeding rate and depth, but they can be used if the amaranth seeds are diluted with a "carrier" like ground corn. A mixture suitable for drilling consists of one-half pound of amaranth with four and one-half pounds of ground corn. Set the drill for a seeding rate of five pounds per acre.
Little data are currently available on the pH and fertility requirements of amaranth. Amaranth is adapted to soils that are slightly acidic to slightly basic (pH 6.5 to 7.5). Consideration of the pH requirement of rotational crops should also influence the lime recommendation for amaranth.
The fertility requirements of amaranth appear to be intermediate between small grains and corn and probably are similar to sunflower. Soil P and K should test in the medium to high range (30 to 75 lbs. P and 160 to 240 lbs. K per acre, depending on subsoil fertility group). Test the soil and apply any corrective P2O5 or K2O recommended on the soil test report.2
Maintenance fertilizer equivalent- to crop removal should be applied to maintain soil test P and K levels. A crop yielding 1200 lbs/a grain will remove about 36 lbs of N, 7 lbs of P, and 6 lbs of K per acre and various amounts of calcium and magnesium and micronutricnts. However, amounts greater than those are needed to sustain high yield levels. Requirements are higher when amaranth is harvested for silage because virtually the entire above-ground portion is removed. For example, the total N uptake of the amaranth plant is about 90 lbs/a. Suggested maintenance recommendations are 75 lbs N, 25 lbs P2O5 and 40 lbs K2O per acre. If soil organic matter exceeds 5%, apply 50 lbs N/A, if less than 1.5% organic matter, use 100 lbs N/A. Credits for a preceding legume crop and use of manure should be subtracted from these recommendations.
Uniform varieties of grain amaranth have not yet been fully developed. Available material consists of selected lines which vary in their uniformity and degree of adaption to temperate latitudes. Researchers at the Rodale Research Center in Pennsylvania and the USDA Plant Introduction Station at Ames, Iowa, have done significant work in developing amaranth varieties and cataloging germplasm. Rodale Research Center has distributed a number of lines including some that have been grown successfully in Minnesota (e.g. K343, K266, and K432). University of Minnesota trials'at Rosemount from 1977 to 1989 showed yields from 300 to 3800 lbs/a for the 20 lines tested. Amaranth seed is also available commercially (see Table 1).
Table 1: Sources of grain amaranth seed.1
American Amaranth, Inc., P.O. Box 196, Bricelyn, MN, 56014 (507-653-4377)
Terrance Cunningham, R.R. 1, Box 255 Twin Lakes, MN, 56089 (507-852-3465)
Johnny's Selected Seeds, Albion, ME, 049 10 (207-437-4301)
Nu-World Amaranth, Inc., P.O. Box 2202 Naperville, IL, 60540 (312-369-6819)
Calvin Oliverius, P.O. Box 25, Albin, WY, 82050 (307-246-3270)
Plants of the Southwest 1812 Second St., Santa Fe, NM 87501 (505-983-1548)
Soaring Eagle Seeds, P.O. Box 94, Shawmut, MT. 59078 (406-632-4528)
1This is a partial listing and does not imply endorsement of the seed quality.
1. Mechanical: Since amaranth is not planted until late May or early June, many weeds will already have emerged. These early weeds must be controlled by tilling the field prior to planting. Grain amaranths grow slowly during the first several weeks after planting, so three or four cultivations may be needed during this period to control weeds. Once the amaranth plant is about a foot tall, it begins to grow rapidly and is very competitive with weeds. Two species of weeds which are especially competitive with amaranth are lambsquarter and pigweed. Fields with high populations of these weeds should not be used for amaranth production. Since grain amaranth seeds do not undergo dormancy, and because plant growth is not vigorous early in the season, it is unlikely that grain amaranth will be a weed problem in succeeding crops.
2. Chemical: No herbicides are labeled for use with amaranth.
Researchers and growers have observed little in the way of major disease problems. Further problems may develop as the acreage of amaranth increases. Damping-off of young seedlings can be a problem under some conditions, caused by Pythim and Rhizoctonia and stem canker, caused by Phorma or Rhizoctonia.
Tarnished plant bug, flea beetle, and amaranth weevil, are potentially significant insect pests of amaranth. The insect most likely to affect yields is the tarnished plant bug, (Lygus), a sucking insect which often reaches high populations in the seed head during the critical seed fill stage. Flea beetles damage young leaf tissue. The adult amaranth weevil feeds on leaves, but the larval stage is more damaging because they bore into the central tissue of roots and occasionally stems, causing rotting and potentially lodging. It is currently unknown whether our insect control measures are cost-effective, but significant loss of yield and quality due to Lygus damage has been observed.
Harvest is the most critical stage in grain amaranth production. Without careful harvest techniques, it is possible to lose or damage the majority of the seed. A killing frost must occur before harvest followed by a week of good drying weather (there are no approved desiccants for amaranth). If the stems and leaves are too wet, the seeds become sticky and adhere to the inside of the combine as well as the straw discharge. Shattering during the cutting process can also cause losses, so adjustments should be made to minimize shattering of the heads. When reel heads are used it may be helpful to remove several reel bats or raise the height of the reel. Row headers perform better than reel heads for combining amaranth. High cylinder speed can damage grain and reduce germination and popping volume. Conventional combines can be used if fitted with appropriately-sized separator screens.
Grain handling and storage plans should be developed before harvest begins. It is important to clean the grain to remove plant and foreign material which will increase the chance of molding. Cleaning can be done using a 1/16 inch screen top, and a 1/23 inch screen, 22 × 22, or 24 × 24 wire mesh on the bottom. A gravity table can be used to separate particles of the same size but of different weight, such as the dark pigweed seeds. Maximum moisture for storing the grain is approximately 11%. Small amounts of grain can be dried by blowing air across the amaranth; heated air may be necessary at certain times. The optimum way to store the grain after cleaning and drying is in wooden storage bins or in heavy duty (4 or 5 ply) paper bags. University studies at Rosemount, Minnesota showed average test weight of 63 pounds per bushel.
University of Minnesota trials at Rosemount conducted from 1977 to 1989 showed yields from 300 to 3800 lbs/a on hand-harvested plots. Realistic yields from combine-harvested plots range from 600-1500 lbs/a.
Perhaps the greatest problem facing the development of amaranth as a crop is finding markets. The crop has only been grown commercially during the 1980's, and the markets are. still very small. The primary market for amaranth is the food industry, where it is used in 40-50 products. A farmer entering the market with grain from several hundred acres of amaranth could cause a surplus and drastically lower prices. For this reason amaranth should be grown only after identifying a market for the crop, and preferably after arranging a contract with a buyer.
Farmers have marketed their crop in a number of ways. Some sell small bags of the whole grain or flour mail-order to consumers. Many of these purchasers are allergic to wheat products. Other growers sell to local or regional health food stores or restaurants. There are also a few who buy grain from the farmers and market it to the larger health food companies. Companies that have developed grain amaranth products include Health Valley Natural Foods, Arrow Mills, Walnut Acres, Nu-World Amaranth, and American Amaranth, Inc.
lAmaranth seedlings are very sensitive to frost; the crop should be sown after all danger of frost is past.
2Until further studies on amaranth fertility needs are completed, nitrogen recommendations for sunflower are reasonable approximations. Amaranth is very responsive to nitrogen application, but can lodge severely under high nitrogen soil conditions.