The U.S. has been the leading commercial producer of grain amaranth in recent years, although production has been less than 2000 ha annually since U.S. farmers started growing the crop in the early 1980s. Most U.S. production has been in the upper Midwest and Great Plains, particularly western Nebraska, with widely scattered fields in other parts of the U.S. Amaranth grain species are widely adapted, and have good potential for moisture limited areas. Other species of amaranth have been domesticated primarily for leafy vegetable or ornamental use.
Amaranth's development in the U.S. has benefitted by the formation of private companies that have focused exclusively or in part on amaranth products, and have done much of the work to build public awareness of the crop. The Amaranth Institute, a small non-profit organization of scientists, growers, and agribusiness, has also supported development of the crop through information exchange, promotional activities, and annual meetings.
This paper provides an overview of some of the history, characteristics, uses, and market dynamics for amaranth, and includes a summary of 12 field studies and 2 controlled environment studies with amaranth carried out in Missouri by the author during the period 1990-1994. Information concerning amaranth germplasm and amaranth grain characteristics can be found in previous review papers on amaranth (Kauffman 1992ab; Stallknecht and Schulz-Schaeffer 1993).
The most significant historical use of amaranth as a grain crop was in central Mexico during the Aztec civilization (the Aztec name for amaranth was huahtli). Amaranth was both an important food grain for the Aztecs, and a part of their religious practices. Annual grain tributes of amaranth to the Aztec emperor were roughly equal to corn tributes. The reasons for decline in amaranth production following Spanish conquest of the Aztecs in the 1500s are not well understood. Amaranth was significantly used in Aztec religious ceremonies, and some have speculated that the Spanish conquistadors discouraged production of amaranth as part of their overall efforts to suppress the Aztec culture and religion.
Although the production of amaranth in Latin America diminished dramatically subsequent to Spanish rule, the positive attributes of the crop led to its adoption in other areas of the world. By the 1700s, amaranth had spread throughout Europe for use as a herb and ornamental. In the late 1800s, amaranth was reportedly being grown in mountain valleys of Nepal and parts of east Africa. During the 20th century it has been grown in China, India, Africa, and Europe, as well as North and South America.
Although the U.S. has been the leading producer of grain amaranth used in retail food products, the largest production area in the last decade is believed to have been in China (the Chinese amaranth production is reportedly based on cultivars developed by the Rodale Research Center in Pennsylvania). The main Chinese use of amaranth is reportedly to feed the forage to hogs, rather than harvesting the grain.
The small but gradually growing market for amaranth as a food grain is based on its nutritional characteristics, and to some extent, its historical interest as the "lost crop of the 'mystic' Aztecs." The nutritional characteristics are indeed positive, with protein content ranging from 12%-17%, and a well balanced amino acid profile, including a relatively high amount of lysine. Amaranth is also high in fiber, and low in saturated fat. The amaranth grain can be popped or flaked, and works well in mixes with flours of other grains, including for extrusion processing.
Although amaranth leaves have been used in both human and livestock diets, little is know about the potential of grain amaranth species for livestock use. When the leaves, stem, and head are used for forage, the product will range from 15% to 24% protein. Palatability is not well known. Within the available amaranth germplasm are genotypes that show potential for significant forage production, but more research in this area is needed.
Amaranth, like most grains, has potential for use in industrial products. The oil fraction of the grain is unusually high in squalene, a chemical that sells for thousands of dollars per ton. However, the percent of squalene in the grain is still small, and may not be economical to extract. Greater promise lies with the starch fraction of the grain. Amaranth, like quinoa (Chenopodium quinoa), has very small, micro-crystalline starch granules, about one-tenth the diameter of maize (Zea maize) starch. The physical characteristics of the starch grains have been cited as being of potential value for both industrial and food product uses, though none has been commercialized to date.
Amaranth costs of production are modest, being similar to sorghum. Costs are kept low particularly because fertilizer needs are minimal, and registered pesticides are not available. Although seeding rates are low (1 to 2 kg/ha), seeding costs can be above average (up to $20/acre, or $50/ha) if certified seed is used. Farmers use either certified seed, or, for lower cost, bin run seed. Planting and cultivation costs are equivalent to other grain crops since the same equipment can be used, with some modifications to a planter to handle the small seed size. The other cost that can be high is in the harvest and post-harvest phase. While properly equipped and adjusted grain combines can effectively harvest amaranth, such modifications do add to production costs, from a few hundred to a few thousand dollars. More notably, distance to market is a significant factor for most amaranth producers, since there are only a few amaranth processors and delivery points in the United States (outside of direct marketing). Most growers are faced with shipping the crop hundreds of kilometers by truck, which can lead to a sizable shipping cost for the grain, as opposed to hauling the grain a few kilometers to the local grain elevator. Growers may also experience higher cleaning and handling costs with amaranth than with other grain crops. Altogether, cost of amaranth production per hectare can be expected to be in a range of +/-20% that of maize, with the variability mainly coming from postharvest handling and shipping costs.
The factor that has buoyed the success of amaranth to-date is the relatively high price of the grain ($0.90 to $1.00/kg), which has been up to 10x higher than maize and up to 5x higher than wheat on a per weight basis. Unfortunately, this high price received by farmers has also been a major factor in limiting use of the grain to "health" food products that sell for a premium, or to use as a tiny fraction of a multi-grain mainstream product. Discussions by the author with one major food processor and retailer indicated that for amaranth to gain broader use in the food marketplace, it would have to be sold for about 1/3 to 1/2 of its current price (still a premium compared to other grains), be available in adequate supply (i.e., more production area), and have broader consumer recognition and demand. Certainly amaranth is subject to the same price fluctuations as most grains, when supply overwhelms demand. If amaranth is to ultimately have a much larger and steadier market demand, it will have to follow the path of higher yields and lower prices.
The predominant source of amaranth cultivars used in the past decade in the United States was the Rodale Research Center in Kutztown, Pennsylvania. Initial breeding was done by Charles Kauffman, with followup work by Leon Weber (Kauffman and Weber 1988). Weber served as the initial distributer of lines for regional testing. Coordination of the regional test was later carried out by Dan Putnam (1990-91), then at the Univ. of Minnesota, followed by R.L. Myers (1992-94) at the Univ. of Missouri. The current regional test coordinator is David Baltensperger at the Univ. of Nebraska. A summary of the regional variety trial results for the period 1985 to 1993 was published in the 1994 annual issue of Legacy, newsletter of the Amaranth Institute (Myers 1994).
Early utilization research with amaranth focused on the grain's nutritional characteristics (Teutonico and Knorr 1985; Breene 1991; Bressani et al. 1992). More recently, work has been conducted on the potential industrial uses of amaranth, and on potential health benefits from amaranth in the diet. The industrial use research has focused on the starch or squalene content of the seeds. The health implications of consuming naturally occurring tocotrienols in amaranth has received preliminary evaluation. Recent food utilization research has included extrusion processing of the grain. Only a few studies have evaluated amaranth cultivars for forage use, and no substantive research has been done on the potential of amaranth grain as a livestock feed.
Plant height and lodging were increased by addition of N fertilizer, factors which negatively affected harvesting. Mature plant population and seed weight were unaffected by nitrogen fertilizer rate. Yield compensation was due to higher seed numbers per plant, rather than changes in seed weight, which is a trait that usually held true in other studies on amaranth management (there are differences in seed size between varieties, however).
The study had been intended to go for 8 years, but it was terminated after 4 years due to funding cuts, which limited the conclusions that can be drawn. Still, there were some clear findings. For all of the rotations, amaranth had no noticeable allelopathic effects on the following crop, and amaranth crop residue did not present a physical problem for planting and stand establishment of the following crop. Residue levels from amaranth after a winter of decomposition in Missouri are more than soybeans, but less than maize. There did not appear to be any disease or insect accumulation in amaranth grown continuously in this study, but plants were not systematically sampled for disease, nor were insect populations closely tracked. The most obvious problem occurring with continuously planted amaranth was volunteer plants from the previous season(s). Amaranth volunteers are readily controlled in maize and soybeans with tillage and herbicides, but the degree of volunteers in a new amaranth plot led to ragged stands, and also allowed pigweed (a weedy relative of grain amaranth) to build up. Mechanical cultivation to control volunteer grain amaranth and pigweed in a new stand helped, but did not deal with in-row problems. In this rotation study, amaranth planted as a double crop did not perform as well as in a later study that focused on double crop systems.
At all three locations, amaranth was successfully established and harvested as a double crop. Amaranth plant height was reduced following winter crops versus fallow, and establishment no-till into wheat residue was difficult, but possible, with the planting equipment available. In two out of the four site-years, amaranth yielded better after fallow than after wheat or canola. Amaranth yields after wheat versus canola were not different in any of the site-years. Double crop amaranth yields ranged from a low of 500-700 kg/ha at Portageville, where lodging was a problem, to a high of 1849 kg/ha following fallow at Columbia in 1993. In two of the four site-years, amaranth yielded 1200 kg/ha or better following wheat and canola, which would provide a substantial profit at current amaranth prices. The top yielding double crop was sunflower, with yields of 1500 to 3000 kg/ha, followed by soybeans, with 600 to 2100 kg/ha. However, amaranth would have provided the greatest profit in this study.
Amaranth intercropped with cowpea in alternate row fashion had a higher land equivalent ratio (better yield response) than cowpea-millet, but for other row arrangements the intercrop systems were similar. Millet generally outyielded amaranth: amaranth in 2-row strips yielded 973 to 1791 kg/ha, compared to 1750 to 3964 kg/ha for millet; when monocropped, amaranth yields were 1089 to 1591 kg/ha, versus 1849 to 3718 kg/ha for millet. When no nitrogen was applied, amaranth yields were higher in alternate row intercrop with cowpea than when grown as a monocrop, so N and/or other resource complementarity was occurring. An overall conclusion from the study was that amaranth and cowpea can be effectively intercropped, as a variation on the pearl millet and cowpea intercrop system common in parts of Africa.
Overall, Austrian winter pea outperformed the other cover crops, boosting amaranth yields an average of two-fold versus the control plots (from about 600 to 1200 kg/ha). Pea produced the most biomass, and had the highest level of inorganic N during July sampling of the upper soil profile. Amaranth grown after pea and hairy vetch were taller and had higher vigor ratings compared to rye and control plots. On the negative side, lodging was increased in plots following pea. Rye had the expected effect of reducing amaranth vigor compared to control plots. This reduction in vigor was partly, but not completely, offset by the addition of N fertilizer. Surprisingly, amaranth following rye had much higher stand populations in late season than those in control plots or following legumes. It is possible that the reduction in vigor caused by rye also reduced self-competition among amaranth plans, in turn reducing the amount of self-thinning of plants that normally occurs in an amaranth stand.
This study was also the first attempt at planting amaranth no-till in Missouri, an approach later used in double crop studies as well. In this instance, where amaranth was planted following control of growing cover crops by chemical burn down and mowing, no-till establishment worked reasonably well. Seed zone moisture for the amaranth can be helped or hindered by the use of cover crops, depending on rainfall timing preceding amaranth planting.
One non-chemical method of controlling Lygus in cotton has been to plant strips of alfalfa through the cotton fields, using selective mowing to keep parts of the alfalfa in bloom, and thus attracting Lygus. This system of alfalfa strips was duplicated in 1991 and 1992 in amaranth test plots to evaluate its effectiveness at controlling Lygus in amaranth (Clark and Myers 1995). 'Plainsman' amaranth was planted in plots 18 m wide, alternating with 6 m wide strips of alfalfa in a replicated design. Regular sweep net insect surveys were made in the center and edge of alfalfa strips, and at varying distances from the alfalfa into the amaranth strips. Insect counts were made at several times during the season to determine the buildup of Lygus in the two crop strips.
Alfalfa did attract a high percentage of the Lygus relative to amaranth early in the season. However, once amaranth began flowering, the Lygus populations built-up in the amaranth instead, and it was clear the alfalfa did not provide effective control.
When planted in early June in Missouri, inflorescences will begin to emerge by late July, in a pattern that is daylength sensitive for the available cultivars. Anthesis begins to occur after an inflorescence is only partially formed, and continues for parts of the inflorescence until the grain "head" reaches full size (typically 20 to 30 cm top to bottom). Seed development is thus not simultaneous within a head. Seeds that form early begin shattering well before all the seeds on a head are mature, but the seed heads are compact enough to hold most shattered seed in the head, provided strong wind or rain does not occur. (Note: nonshattering germplasm has been identified by D. Brenner, Plant Introduction Station, Iowa State Univ., Ames.) Seeds change in appearance from a glossy, or translucent appearance, to a dull, or opaque appearance as they mature (see research discussion on seed development and maturation).
In states such as Nebraska, North Dakota, and Minnesota, where most amaranth has been commercially grown, amaranth is normally killed by frost before it has a chance to naturally senesce. Plants killed by frost can be harvested a week or so later, depending on drying conditions, which can improve the opportunity to combine the crop before too many seed fall to the ground. However, in more southern areas, such as Missouri, the crop will normally senesce and dry down in Sept., before the first hard frost (in central Missouri, average frost date is end of Oct.). With current cultivars, the plants will turn a medium brown in the grain head and leaves during senescence, then drop almost all leaves. Once senescence begins, stalk strength declines, and plants are more susceptible to stem breakage from high winds.
Because relatively little has been known about many aspects of amaranth growth and development, a series of studies at Univ. of Missouri over a five year period sought to evaluate amaranth's germination requirements, seedling vigor, response to moisture stress, and seed development and maturation. These studies are briefly described below.
In 1991, heads were collected and threshed from replicated plots near Columbia, Missouri. Comparisons were made of seed appearance (translucent vs. opaque), seed weight (fresh and dry), and seed germination, for three cultivars ('Plainsman', D136, and K256), two planting dates (June 3 and 21), and three sampling dates. The samples were taken at approximately two week intervals. In 1992, a more limited sampling was done of 'Plainsman', D136, and 'Amont'.
Results indicated the percent of opaque seeds increases as the plant ages. The dry weight of the opaque seeds was higher than translucent seeds, and opaque seeds were generally lower in percent seed moisture at time of sampling. Based on this data, it was clear that opaqueness in amaranth seed is a suitable indicator of maturity. However, opaqueness was not an exact measure of physiological maturity (physiological maturity is defined as the point when seeds reach maximum dry weight, and generally coincides with the seeds being developed enough to germinate). Opaque seeds did have a higher percentage of germination than translucent seeds, but some seeds rated as translucent were still able to germinate.
Other characteristics of opaque seeds were noted which distinguished them from translucent seeds. Opaque seeds are harder and more brittle. It was also noted, under microscopic examination of seed cross sections, that opaque seeds have a perisperm with a white, fine granular appearance inside, as opposed to the glossy, more globular perisperm appearance of translucent seeds.
Response to sandy soils. Eight different grain plots were planted into replicated plots in the Missouri River bottoms near Jefferson City in 1994. The intent of this field test was to evaluate the relative performance of traditional and alternative grain crops on newly created sandy soils versus 'regular' alluvial soil in the river valley. The sand deposits were the result of record flooding along the Missouri river in 1993, which covered approximately 150,000 ha of bottomland fields with 15 cm or more of sand. A site was selected that had sand ranging in depth from 30 cm to 120+ cm.. Two adjacent field areas were used, one with "shallow" sand (30-45 cm) and one with "deep" sand (>75 cm). A nearby plot of ground with no sand deposits was chosen as a check plot area, and designated as "regular" soil (silty loam topsoil, formed as floodplain alluvium).
The eight crops chosen were soybeans and sorghum as traditional crops, and sunflowers, pearl millet, cowpeas, mung beans (Vigna radiata), amaranth, and sesame (Sesamum indicum) as alternative crops. Crops were selected on the basis of their suitability for planting in early summer, and expected tolerance for moisture limited conditions created by sandy soil conditions.
Stand establishment of all eight crops was good in the regular soil plot area. In the sandy plots, establishment was delayed by dry conditions until the first rainfall, which came a week after planting. Only amaranth germinated prior to rainfall, which was rather remarkable considering the very low moisture content in the seed zone of the sand. After rainfall, emergence was slow for some crops due to inconsistent planting depth in the sand. Ultimately, good stands were obtained of all crops except sunflowers and amaranth, which had partial stands. The partial stands of amaranth were probably due to the very dry seed zone conditions when the seed was planted, and began to germinate. Although some amaranth seedlings became established, other seeds probably only imbibed water, or barely sprouted, before running out of moisture. The other crop seeds which sat idle until the first rainfall a week after planting, had much more moisture available during establishment. The tendency of amaranth seeds to imbibe moisture and start germinating even under rather limited moisture conditions has been noted in regular field plots, and is somewhat of a problem, occasionally leading to ragged stands, where some plants emerge quickly, and others emerge later after rainfall, or not at all.
It was expected that tap-rooted crops like sunflower and amaranth would do well under the soil conditions of this study, where flood-deposited sand was layered over silt loam soil. However, both sunflower and amaranth tap-roots were found to go only as deep as the wetting front in the sand. Relatively modest rains of 1 cm or less would wet the sand down to about 10-15 cm. The tap-roots would go that deep, then turn sharply at a right angle (running parallel to the surface) as if they had hit an impermeable barrier. The relative advantage of the pearl millet and sorghum (grass) crops was their ability to send out a mass of fibrous roots laterally that could capture a larger portion of the rainfall that had occurred. The tap rooted crops (sunflowers and amaranth) would likely have been much more successful if early rainfall had wetted the sand all the way through to the underlying silt loam, allowing the tap-roots to reach that depth. It was noted that weedy amaranths (pigweed), established themselves quite successfully from rainfalls that occurred during the month preceding the test planting on June 14 of amaranth and the other grains. Pigweed was the dominant weed by far in the newly deposited sand areas, which overall were surprising free of weeds in the first year after flooding (weed seed probably floated off while the sand dropped out of flood waters as a heavy material; the sand was deepest near levy breaks).
Response to soil rooting depth. In 1994, a study evaluating response to rooting depth was planted at the Univ. of Missouri Agronomy Research Center, Columbia. The same 8 crops as in the sand test above, plus foxtail millet (Setaria italica), were planted into a unique constructed plot area that had been created in a previous field test. The site consisted of 6 x 60 m soil pits running parallel to each other, and separated by about 4 m. The pits had been dug out to varying depths and bottom-lined with a heavy grade, impermeable black plastic. On top of the plastic was laid a small drain tile. The pit was then filled with top soil to the surface level. Thus, the deepest pit was filled with about 94 cm of topsoil, which is certainly a better root zone through that depth than the regular soil profile of that site, with topsoil down to only about 20 cm, and somewhat of a claypan underneath. Not surprisingly, some of the crops planted on the 94 cm deep plot (thus with 94 cm of topsoil) actually had better vigor and more height than those planted on the regular soil, at least until moisture stress became limiting in early Aug.
The crops were planted in replicated 3 m wide strips across the field perpendicular to the direction of the soil pits, creating plot units 3 x 6 m in size. The soil depths varied from 33 to 94 cm (Fig. 2).
The rainfall pattern in May through August at the test location was conducive to gaining some valuable insights into the response of these crops to moisture deficiency. During May and early June, there was adequate rainfall to establish the crops to a height of 30-60 cm. From late June through early Aug., there was a dry spell broken only by a couple of minor rainfalls of about 2 mm each. During this dry spell, crops began to wilt, first in the shallow plots, then successively in the deeper and deeper plots marching across the field. By early Aug., after almost no rain for almost 6 weeks, even the crops on 94 cm of topsoil were affected, some severely. By contrast the crops on the undisturbed soil showed no wilting or other obvious adverse affects from the dry conditions.
The progressive wilting across the field in successively deeper soils was no surprise, but provided a chance to observe wilting patterns in some crops, including amaranth, for which little information is available. What was surprising was the way amaranth dealt with moisture stress compared to eight other grains. Before the test, it was presumed that amaranth would not fair particularly well in shallow soils, based on the idea that amaranth is tap-rooted like sunflower (sunflower gets its drought tolerance by sending its tap-root down deeply, as opposed to being efficient in water use). It was a complete surprise that amaranth was the first of the nine crops to show wilting symptoms. The wilting pattern of amaranth was quite dramatic, with plants going from full turgor one day to completely limp (leaves hanging straight down) the next. However, after almost 10 days of the plants in the shallow plots being completely wilted, the amaranth plants made a stunning recovery to full turgor and apparent health (no leaf lesions or brown leaf edges) after a small rainfall of 2 mm. This pattern repeated itself in deeper plots, after further dry conditions, and another 2 mm rainfall several days later. In contrast to amaranth's ability to rebound so completely from wilting, sunflower had substantial leaf tissue death, as did other crops, even though they were wilted for fewer days than amaranth, and perked up to some extent after the small rains. These observations indicated amaranth may owe part of its reputed drought tolerance to an ability to shut down transpiration through wilting, then recovering easily when moisture is available.
Amaranth was not noticeably affected by moisture limitation in the deepest plot (94 cm), unlike soybean, which used up the moisture available in the profile and completely died by mid-Aug. (soybeans on adjacent regular soil were seemingly unaffected by the dry conditions). Sunflower wilted severely in the 94 cm plots before rain finally came in mid-Aug. In other words, amaranth ran out of moisture first in 33 cm of soil, but for some reason was better able to get by on the moisture in 94 cm of soil than crops such as sunflowers and soybeans. This would seem to indicate amaranth has some water use efficiency compared to those other crops, at least during later stages of growth.
There is still much to be learned about amaranth's water use patterns, especially if the crop is to be promoted for moisture-limited agricultural areas around the world. The only other significant evaluation of amaranth water use in the United States was conducted by Henderson et al. (1992) in North Dakota. Neutron probes were used to evaluate seasonal water use in four grain amaranth cultivars. Data indicated amaranth water use extended down to about 1.2 m under their soil conditions (Prosper, North Dakota), with no cultivar differences in water use. Total water use was typically about 27-32 cm in 1990-91, but was half of that during 1992, which was an unusually cool season with limited plant growth.
Markets remain relatively small and undeveloped, in part because there is a general lack of familiarity with amaranth in the public and private sector. To achieve a higher level of market penetration, amaranth will have to become more publicized, prices will have to fall (although a premium could still be commanded), and availability will have to be increased. Distance to buyers is a problem for many current amaranth growers. Special markets such as the starches or other seed components could lead to increased marketing opportunities.
On the positive side, amaranth is widely adapted, tolerant of dry conditions, and diverse germplasm is available for breeding to improve the crop. Amaranth has relatively good yield potential for a high protein grain crop, especially considering the lack of breeding with the crop. It can be grown successfully with conventional grain crop equipment, usually with only minor modifications, and has a production cost comparable to other grain crops. The colorful appearance of the crop and its colorful history continue to generate interest in the crop, and its good nutritional characteristics combined with its variety of potential uses illustrate the importance of continued work with this "rediscovered" crop.
|Fig. 1. Grain amaranth research plots at Colombia, Missouri.||Grain heads, or inflorescences, are fully developed at this stage of the season, in late Aug.|
Fig. 2. Cross section diagram showing how restricted root zones of varying depths were developed by digging pits or trenches across a field, with the bottoms lined with impermeable plastic, and then backfilled with topsoil. Pits ran 60 m east-west, and were 6 m wide. Crops were planted north-south perpendicular to the length of the restricted root zone areas. In the undisturbed soil, a claypan is prevalent in the B horizon.