The yield of these annual grains – cereals, oilseeds and legumes – continues to improve due to modern farming and seed development practices, but as valuable farmland is lost to soil erosion and salinity, or planted in biofuel or other non-food crops, the future production of annual grains may fail to satisfy the appetites of a growing population.

Scientists are now looking at ways to develop perennial grain crops which can match annual grain crops in yield, while preventing soil erosion, saving water and reducing the use of pesticides on agricultural lands. The successful development of productive perennial grain crops would lower the cost and reduce the energy needed to grow grain crops, while also reducing the environmental impacts associated with farming annual grains.

The Benefits of Perennial Crops

Annual grains live only one season, and therefore need to be planted every year. Early farmers took advantage of this by saving the best seeds from each year’s grain harvest and planting them the following season. In this way, grain crops could be improved over time. Perennial grains, which live year after year and do not require replanting, could not be as easily enhanced as annual grains.

Perennial grain crops have several distinct advantages over annual crops, however, which have agricultural scientists looking for ways to engineer perennials to produce the equivalent yield levels of annuals. The main benefits of perennial crops are:

Make more complete use of annual rainfall

Because perennial crops remain in the ground all year, their roots have access to all available rain water. The deeper roots of perennial crops are also able to tap deep-soil water reserves. Rainwater runoff is reduced because the soil is never left exposed; the thick grass catches and directs rain water down into the ground. Annual crops, compared to perennials, are relatively inefficient at capturing water and nutrients.

Reduce soil erosion

Annual grain crops have relatively shallow roots, about 12” in depth. Most of the plants’ energy is given to the above-ground production of large seeds. Perennial grains have extensive root systems which may grow as much as 8’ – 10’ in depth. This reinforces the soil much in the same way that rebar reinforces concrete, preventing the soil from breaking up and eroding.

Annual crops remain in the ground for only part of the year, leaving the soil exposed between crop plantings. The exposed topsoil is liable to runoff during rains, contributing to the erosion of croplands. With perennial crops, the soil is never left exposed to the elements. With deep roots, perennial crops prevent top soil from washing away, lessening the need for nitrogen fertilizer and reducing the amount of farm chemicals that pollute rivers and streams.

In high quality farmland, soils have a low to moderate risk of degradation under annual grain production, but this represents only about 12% of farmland worldwide. In marginal quality farmland, which represents about 33% of global land area and supports more than 50% of the world population, annual grain crops put soil at a high risk of degradation.

Do not require annual cultivation

The annual chore of ploughing under the stubble of previous crops and planting new seed is not necessary with perennial crops, which saves energy and labor costs for grain producers.

Reduce the need for pesticides and herbicides

When the soil is left exposed between crop rotations of annual grains, weeds are able to gain a foothold in the empty land. These weeds need to be controlled or eliminated with chemical treatments before planting successive annual crops. Healthy stands of perennial grains block weeds from becoming established by denying sunlight and ground space to weed seeds. Perennial crops save farmers the expense of buying and applying pesticides and herbicides, and reduce the impact of these chemicals on local watersheds.

Obstacles to the Development of Perennial Crops

Perennial grains have developed over millennia with strong traits which direct much of the plant’s energy into root development. Engineering perennial grains to produce large seeds, while retaining strong root growth, is a big challenge to agricultural scientists. The development of high yield perennials requires hybridization, genetic research and generations of successive plantings.

Earlier attempts to perennialize grain crops have fallen short of expectations, in part because the measure for success was the yield comparison of perennials versus annuals, without taking into consideration the environmental benefits of perennial cultivation. But even taking these benefits into consideration, yields from perennial crops need to be boosted to the approximate level of annual crops before producers can be expected to forego lucrative yields from annual crops and switch to planting perennial crops.

Recent advances in plant breeding and computational ability, however, offer researchers new opportunities to develop high-yield perennials. Plant breeders can use genetic modification to introduce new genes, to modify existing genes, or to interfere with gene expression in specific cases.

Seed suppliers, such as Monsanto, have a vested interest in annual grain crops since these crops require seeds to be purchased every year. And there is competition for limited federal funding for research, much of which is currently invested in improving the characteristics of annual crops. The USDA is financing some initial research into the genetic basis of perennialism and developing the genetics for breeding perennial crops, and has asked Congress for $1 million in fiscal 2012 for perennial grain or sunflower research at its own labs.

“Getting to the yields of today’s corn in central Iowa with a perennial corn will not happen quickly, but I do think it is possible,” said Ed Buckler, an Agriculture Department scientist at Cornell University in New York. “With prior technology, it would have taken 100-plus years. Now, I think we can do it in 20 years with a concerted effort.”

A serious effort to breed perennial corn crops would require spending $1 million to $2 million for five years to identify the genes necessary for perennialism, Buckler said. After that, $10 million to $20 million a year and dozens of scientists would be needed to breed a perennial corn that could eventually be commercialized, he said.

Progress and Promise

Deputy Agriculture Secretary Kathleen Merrigan sees the development of perennial grains as a promising way to produce food with less environmental impact.

“We’re interested in the development of perennial grains — big seeds, high yields,” she said at a recent food-policy conference in Washington. “These plants with deep roots to hold the soil in place and pick up water and nutrients year-round could reduce the demand for water over the more typical annual grain that produce a big harvest but die each year.”

And researchers are seeing progress. Initial cycles of hybridization, propagation and selection in wheat, wheatgrasses, sorghum, sunflower and Illinois bundleflower have produced perennial progenies with phenotypes intermediate between wild and cultivated species, along with improved grain production.

Today, with almost 70% of crop lands planted in annual grains, providing food security to growing populations across the globe will require a revolutionary breakthrough in food production. That breakthrough may come in the form of perennial grain crops.
References:
http://www.sciencemag.org/content/328/5986/1638.full.pdf?ijkey=jWkVC%2F8x0TeS2&keytype=ref&siteid=sci