Domesticating Intermediate Wheatgrass for Sustainable Grain Production

Scientists and farmers working with pasture and agroforestry systems have long recognized the benefits of perennial crops that live for many years and do not require annual reseeding. Although some livestock production can be shifted to pasture-based perennial systems, humans depend upon grain. Decades of research have demonstrated that extensive planting of annual grain crops is inherently unsustainable. Although in the past plant breeders have had difficulty finding a role in sustainable agriculture, perennial grain breeding is a promising opportunity to transform agriculture. Intermediate wheatgrass (IWG) has potential to be the first widely grown perennial grain crop providing food for humans. More than 10 years of breeding IWG for grain production has already been completed, and methods for growing IWG are available. Long term outcomes of IWG grown in diverse cropping systems would include soil conservation, reduced nutrient leakage from fields, reduced pesticide application, reduced farmer input costs, and improved quality of life for society as a whole through improved natural resource conservation and wildlife protection. The next critical step toward widespread use of IWG is the expansion of a breeding program functioning within a community of practice consisting of farmers, researchers, millers, and bakers.

In two cycles of plant breeding, we doubled seed size of IWG and its average seed yield per head. In on-farm trials we identified key limitations for establishment and production, enabling greater success in later years. Experimental milling and baking produced promising results. Due to increased knowledge of the crop, additional research is beginning at institutions throughout the country.

Introduction:

Annual grain crops comprise a large and essential portion of the human diet, but the large-scale production of grains required to meet human food needs inevitably results in soil erosion, nutrient loss and subsequent contamination of waters, and pesticide contamination. Organic and no-till practices are among the most sustainable approaches to small grain production. However, organic systems depend on tillage for weed control and can experience soil loss through erosion and nitrogen loss through leaching into groundwater. No-till small grain systems require herbicides and often allow leaching of high levels of nitrogen into groundwater. Unfavorable weather and other uncontrollable factors often disrupt methodologies that rely on cover crops, rendering such approaches unreliable. As a perennial small grain crop, IWG would drastically reduce nitrogen loss by leaching, soil loss through erosion, and the need for tillage or herbicides for weed control. This potential comes at a time when farmers’ input costs are at an all-time high (especially that of nitrogen fertilizer, much of which escapes the root systems of annual grains), and nitrogen contamination of ground and surface waters is a serious issue facing society. Intermediate wheatgrass is an obvious choice for domestication because 1) a population is available that has already experienced a decade of selection for grain production by a joint Rodale Institute–USDA project, 2) it is widely adapted, and 3) cultural techniques have been developed in the forage-grass seed industry.

In Kansas, 60% of gross farm income comes from the sale of grain crops (USDA-NASS, 1997). Globally, more than two-thirds of all cropland is dedicated to annual grain crops (FAO, 2003). Although land currently producing grains fed to livestock could be converted to pasture, annual crops grown for human consumption will remain important in the North Central Region and internationally. In 2004, wheat was planted on 29 million acres in the North Central Region, producing 1.1 billion bushels worth $3.7 billion (USDA-NASS, 2004). A sustainable supply of small grains is critical—the average American consumes about 83 kg of wheat per year (FAO, 2002).

Although soil erosion has been recently reduced in the U.S., most of the improvement has come through taking land out of grain production rather than improving production practices. Conversion of highly erodable land to perennial cover (CRP) reduces soil erosion by an average of 17.2 tons acre-1 year-1, whereas better management of annual crops had only reduced erosion by 2.8 tons acre-1 year-1 between 1982 and 1992 (Uri, 2001). In other words, conversion to perennials is up to six times as effective at controlling erosion as is improved management of annual crops. Despite progress, soil erosion remains a major problem, causing the U.S. an estimated $37.6 billion in social costs annually (Uri, 2001).

The most effective means of reducing erosion in grain production is no-tillage practices. Unfortunately, these practices depend heavily upon pesticides for weed and disease control. The pesticides that are required in order to reduce erosion from annual crop fields have potential to harm both humans and animals. Recent findings suggest that deformities and population declines of amphibians have been due to pesticide exposure (Sparling et al., 2001; Hayes et al., 2002). In humans, pesticides have been linked to profound learning disorders (Guillette et al., 1998), childhood leukemia (Reynolds et al., 2002), birth defects, shifts in sex ratios (Garry et al., 2002), and reduced sperm counts and quality (Swan et al., 2003). According to a study by the Centers for Disease Control and Prevention (CDC) of chemicals in 9,282 people across the U.S., at least one pesticide was detected in every person studied and the average person carries a mixture of 13 of the 23 pesticides analyzed (Schafer et al., 2004). Clearly, a non-chemical approach to reducing erosion in grain fields is needed, and perennial grain crops are an attractive solution.

Globally, only about 30-50% of applied nitrogen fertilizer is taken up by annual crops (Tilman et al., 2002). Due to the lack of year-round vegetative cover, annual cropping systems can lose five times the water and 35 times the nitrogen to leaching as perennial systems (Randall et al., 1997). Not only is lost nitrogen economically wasteful, nutrients lost from annual cropping systems can pollute ground and surface waters, endangering aquatic biodiversity thousands of kilometers distant (Burkhart and James, 1999; Turner and Rabalais, 2003). Some perennials can be fertilized at a rate of 200 kg N ha-1 yr-1 and lose only 1 kg N ha-1 yr-1 to leaching (Andrén et al., 1990; Paustian et al., 1990).

The large number of funded SARE grants directed toward expanding use of perennial systems, such as pastures, is a testimony to the importance of perennials to sustainability. Perennial grain crops promise to bring the inherent sustainability of pasture systems (erosion control, nitrogen use efficiency, freedom from pesticides, and reduced input costs) into the millions of acres currently planted to annual grain crops in the North Central Region.

Intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D.R. Dewey) is a perennial cool season grass, originally from Eurasia, but long cultivated in North America for hay and forage (USDA-NRCS, 2004). The seed is hulled, resembling a small, slender oat seed, although free-threshing (naked) seed is present in most samples.

At least twelve improved forage varieties of IWG are currently available, enabling this crop to be grown from Washington to Pennsylvania, and Alberta to Texas. This highly palatable species frequently out-yields other cool-season forage species (Sleugh et al., 2000;USDA-NRCS, 2004), especially on fertile, well-drained soil with adequate moisture (Lawrence and Warder, 1979). Although IWG responds well to inputs and prime soils, it is also considered to be tolerant to drought, episodic flooding, acid soil, saline soil, fire, and cold (USDA-NRCS, 2004).

One reason IWG is so widely grown is that the seed has good germination and the seedlings are vigorous (USDA-NRCS, 2004). It can be planted in either the spring or the autumn in many regions, and establishes well using both no-till and conventionally prepared seedbeds (Saskatchewan Agriculture and Food, 2005;USDA-NRCS, 2004).

An explanation for the productivity and stress-tolerance of IWG across many environments is its tremendous capacity for root growth. The NRCS reports that after 5 years of growth, there may be up to 7000 lb/acre of IWG roots in the top 8 inches alone(USDA-NRCS, 2004). Even on mine spoils with no topsoil present, IWG root systems reached 20 inches (the greatest depth examined) in less than six months(Mc Ginnies and Nicholas, 1980) and at The Land Institute, one-year old plants typically produce vigorous root systems down to 72 inches and by 18 months they can exceed 120 inches (Jerry Glover, personal communication). In experiments with various ratios of mine spoils and topsoil, IWG root production always exceeded that of winter wheat (Mc Ginnies and Nicholas, 1980) and IWG exhibited strong, deep rooting even on zinc-contaminated soil (Palazzo et al., 2003).

Although not native to North America, IWG has been grown here since the 1930s, has been well-documented, and has shown no tendencies to become weedy or invasive (USDA-NRCS, 2004). It co-exists well with native plants and has no known negative impacts on wild or domestic animals (USDA-NRCS, 2004). The NRCS considers this to be a good species for building and stabilizing soil and for providing cover for nesting birds (USDA-NRCS, 2004).

Herbicides are the most commonly used pesticide globally, making up about 45 percent of the dollar value of all pesticides sold (Yudelman et al., 1998). This major category of pesticide could be sharply reduced if cropping systems could be made less invasible by weeds. Prairie restoration (planting herbaceous perennials) has been shown to reduce weed biomass by 94% (Blumenthal et al., 2003). Possible mechanisms of weed reduction in stands of perennial grasses include greater aboveground biomass throughout the season (which reduces light availability to weed seedlings), establishment limitation, presence of mutualists or antagonists, and the strong competitive effects of perennial grasses. Darwent and Elliot (1979) found that when planted in narrow rows, IWG can have a “pronounced effect” on dandelion growth. As expected, there was much less suppression of dandelions when IWG was planted in wider rows. Similarly, high-density IWG populations were able to control the invasive knapweed, but successful establishment of IWG required a very high seeding rate (Sheley et al., 1998). In general, cool season grasses have been able to out-compete weeds such as quackgrass and bindweed only when planted densely (Darwent and Elliott, 1979). In wide rows, weeds frequently invade cool season grasses unless there is cultivation between the rows (Darwent and Elliott, 1979;USDA-NRCS, 2004).

In South Dakota, soils cultivated for 50 years have typically lost 40% of their original organic matter (White et al., 1976). Farmers striving toward sustainability have typically inherited soils with similarly depleted organic matter and have a vital interest in rebuilding that organic matter. In a six-year study, IWG added 1.5 more tons/ha of soil organic carbon (SOC) than continuous wheat, and 3 tons/ha more than a wheat/fallow system. IWG has built SOC even in low-input situations (Bremer et al., 2002).

Intercropping grasses with legumes is a strategy for reducing the need for inputs of nitrogen-rich manure or compost. Adding legumes to grasses often has other benefits: increased forage yield, better seasonal distribution of forage, reduced weed invasion, reduced soil erosion, and improved stand longevity (Berdahl et al., 2001; Karnezos and Matches, 1991; Schultz and Stubbendieck, 1982; Sleugh et al., 2000). Sleugh et al. (2000) found that IWG mixed with kura clover, alfalfa, or birdsfoot trefoil gave greater yields than stands of pure IWG, even though the pure grass stands were fertilized and the mixtures were not. IWG mixed with alfalfa did especially well, yielding more than three times the forage as pure grass. Although legumes frequently come to dominate grasses in such mixtures (Berdahl et al., 2001), IWG has been found to be more competitive with legumes than other grasses (Schultz and Stubbendieck, 1982; Sleugh et al., 2000). Even IWG, however, is eventually out-competed by alfalfa, probably due to alfalfa’s deep taproots (Berdahl et al., 2001; Berdahl et al., 2004; Sleugh et al., 2000).

Moore et al. (1995) found that even modest plant breeding work on IWG produced improved strains with potential for significant impact on animal productivity. They concluded that existing cultivars have not been genetically narrowed; each contains enough genetic variation for continued plant breeding. Breeders have found significant genetic diversity for forage-related traits including yield (Vogel et al., 1986; Vogel et al., 1993), digestibility (Vogel et al., 1993), in-vitro dry matter digestibility (IVDMD) (Vogel et al., 1986), and resistance to leaf-spot (Helminthosporium sativum) (Karn et al., 1989; Krupinsky and Berdahl, 1982).

Improved pasture crops often have low, unreliable seed yield, making forage seed expensive. Therefore, forage breeders and agronomists have been interested in methods for increasing the seed yield of IWG. Knowles (1977) used recurrent mass selection to develop lines with more than twice the potential for seed yield. Importantly, he also found that breeding exclusively for seed yield did not lead to a reduction in forage yield. He determined that the yield of plants in their second year was predictive of their long-term yield, while first-year yields were not. It is therefore important to wait until the second year to select for seed yield, but not necessary to measure seed yields for many years. Confirming existing theory, he showed that controlled intercrossing of the selected plants gave greater improvement per cycle than open pollination. Selection following poly-cross progeny testing gave a greater increase per cycle than mass selection but a lower rate of increase per year since each cycle took longer.

Agronomists determined that growing IWG in wide rows greatly increased seed yield per hectare. Wide row spacing also reduces the effect of drought on seed yield and even allows certain intercrops such as flax and oats to be grown with relatively small reduction in IWG seed yield (Saskatchewan Agriculture and Food, 2005). The NRCS (USDA-NRCS, 2004) recommends planting in 24-36 inch rows, cultivation between rows, and occasional use of a sod ripper to restore productivity. Managed in this way, a stand can produce seed economically for 7-10 years. Spring burning of stubble has been found to increase subsequent seed yields and reduce some pest populations in IWG seed fields (Schaber, 1994). Saskatchewan Agriculture and Food (Saskatchewan Agriculture and Food, 2005) has published instructions for determination of correct moisture content and machinery settings for combine harvesting of IWG seed.

In the 1980s, Peggy Wagoner at The Rodale Institute identified IWG as the most promising perennial cool season grass for development as a perennial grain (Wagoner, 1990). Out of 100 species evaluated, IWG came the closest to meeting the following criteria for a perennial, mechanically-harvested grain: seed flavor, easy threshing, large seed, synchronous seed-set, shatter-resistance, strong erect seed stalks, seed heads held higher than the foliage, seed head and stalk dry-down at maturity, and a hardy perennial habit (Wagoner, 1990).

In addition to plant breeding, researchers at The Rodale Institute experimented with organic practices for raising IWG as a grain crop (Wagoner, 1989; Wagoner, 1990). After trial-and-error, they found that IWG could be reliably established in rotation following a small grain. Seed was drilled in narrow rows (7 inches) with white clover or birdsfoot trefoil instead of IWG every third row. IWG did not perform well following a legume, because weeds were better able to exploit the released nitrogen than were the IWG seedlings. Even without irrigation or manure, yields of IWG interplanted with a legume were similar to those obtained by conventional forage seed producers.

An economic analysis of IWG production for grain in North Dakota showed that while yields are less than yields of annual crops, the input costs are also likely to be less (Watt, 1989). In this analysis of likely costs and prices, an IWG grain stand persisting for 8 harvests would need an average annual harvest of 500 lb per acre for the break-even price to equal wheat. The usual yield range for forage varieties of IWG is 100-600 lb/acre. Yields of 800-950 lb/acre have been reported (Gardner, 1991; Ross, 1962).

Becker et al. (1991) found no evidence of toxicity or antinutritional compounds; the nutritional value of uncooked IWG grain was equivalent to wheat. Cooking increased the nutritional value of both grains. IWG grain had higher protein, fat and ash content than wheat, but lower carbohydrates. Products made with both types of flour had similar shelf-lives. No problems were encountered stone- or impact-milling IWG kernels. Tempering the grain to 15% moisture improved roller-mill endosperm flour yield. As expected, IWG flour is higher in bran and lower in starch than wheat flour. Hulls can be readily removed from most seeds with simple mechanical processing.
Because IWG grain contains poor baking quality gluten, it cannot be used on its own to make raised products. In addition, its high fiber content makes its whole-grain dough viscous and weak. However, bread made with 15%, banana bread made with 50%, and cookies and muffins made with 100% IWG were highly rated in a taste-test. Simply boiling IWG kernels for 20 minutes made a rice-substitute that had good texture and flavor (Becker et al., 1991).