Perennial rice


Perennial rice are varieties of long-lived rice that are capable of regrowing season after season without reseeding; they are being developed by plant geneticists at several institutions. Although these varieties are genetically distinct and will be adapted for different climates and cropping systems, their lifespan is so different from other kinds of rice that they are collectively called perennial rice. Perennial rice—like many other perennial plants—can spread by horizontal stems below or just above the surface of the soil but they also reproduce sexually by producing flowers, pollen and seeds. As with any other grain crop, it is the seeds that are harvested and eaten by humans.
Perennial rice is one of several perennial grains that have been proposed, researched or are being developed, including perennial wheat, sunflower, and sorghum. Agronomists have argued that increasing the amount of agricultural landscapes covered at any given time with perennial crops is an excellent way to stabilize and improve the soil, and provide wildlife habitat.
Perennial rice breeding was initiated at the International Rice Research Institute, Philippines and are currently being developed at the Yunnan Academy of Agricultural Sciences, People's Republic of China, and other institutions, but are not yet available for distribution.

Perennial and annual rice

Domesticated Asian rice, Oryza sativa is a short-lived plant. Most cultivars die after producing seeds, though some can regrow and produce a second crop under favorable conditions. In regions with mild climates, two or three crops of rice may be grown each year. Except for ratoon crops, this means that the dead stalks must be removed, the soil cultivated, and new seed sown every few months.
In contrast, the wild ancestor of Asian rice, Oryza rufipogon, often lives for many years, setting seed each year and spreading vegetatively. In addition to these perennial types, some O. rufipogon populations are annuals or intermediate in lifespan.
Other wild species in the genus Oryza are also perennial. While perennial Oryza rufipogon spreads vegetatively by above-ground stems, O. longistaminata, O. officinalis, O. australiensis, O. rhizomatis spread by underground stems.

Potential benefits

Reduced soil erosion

Farm fields, especially those in the humid tropics, that have been cleared of vegetation or recently plowed are highly vulnerable to soil and nutrient loss through wind or water erosion, soil compaction, and decline in soil organic matter and microbial biomass.
Eroded fields become less productive and the soil particles and dissolved nutrients cause environmental problems downstream, including hypoxia in oceans and rivers and the silting of reservoirs and waterways.
Perennial plants regrow quickly after being harvested, re-establishing a protective cover. The fields do not need to be plowed after the initial planting.
Researchers at The International Rice Research Institute believed that perennial rice would "improve the sustainability of food production in the hilly uplands and downstream."

Reduced rate of deforestation

A high-yielding, nutritious, perennial cereal could allow poor farmers around the world to produce food on a plot of land indefinitely. Currently, many subsistence farmers clear plots in the forest for their crops. Once the soil and its nutrients have washed away, the plot is abandoned and a new piece of forest is slashed and burned. Forest may eventually regenerate on the abandoned plot, or weedy grasses may dominate. Environmental impacts of this cropping system include loss of biodiversity, carbon dioxide emissions, increased runoff and decreased rainfall. Deforestation could be reduced by practices that conserve soil productivity

Other potential benefits

  • Drought resistance: Annual rice has a shallow root system and is very drought susceptible. A long-lived plant has time to develop a deep and extensive root system making it theoretically capable of accessing more moisture than an annual plant. Tilled soil dries out more quickly than untilled
  • Resist weed invasion: Weed pressure has increased in upland rice systems as the fallow period has shortened. Ecologist Jack Ewel wrote: "Weeds are widely recognized as a major impediment to continuous cropping in the humid tropics, and fields are often abandoned more because uncontrollable weed populations are anticipated than because of declining fertility or pest buildups." Grassland restoration with perennials results in fewer annual weeds and perennial grasses, sown at appropriate densities, can out-compete even perennial weeds once they are established.
  • Plant nutrition: While shallow rooted species, such as rice obtain most of their nutrients from the topsoil, deep rooted perennials can obtain significant proportion of their phosphorus from the subsoil. "Deep roots are especially important in nutrient-poor substrates because they increase the volume of soil exploited by the vegetation".
  • Reduce the need for transplanting, weeding, and other backbreaking labor.
  • More efficient use of applied fertilizer

    Potential disadvantages

  1. Improved habitat for pests. If fields are not left bare for a portion of the year, rodents and insects populations may increase. Burning of the stubble of perennial rice could reduce these populations, but burning may not be permitted in some areas. Furthermore, rodents and insects living underground would survive burning, whereas tillage disrupts their habitat.
  2. Makes crop rotation more difficult. Crop rotations with perennial systems are possible, but the full rotation will necessarily take longer. The slower pace of rotation—compared with annual crops—could allow a greater buildup of pathogens, pests or weeds in the perennial phase of the rotation.
  3. Builds soil organic matter at the expense of plant productivity. In the absence of tillage, and in soils with depleted organic matter, crops with large root systems may build up organic matter to the point that nearly all of the soil nitrogen and phosphorus is immobilized. When this happens, productivity may decline until either the organic matter builds up to a level where equilibrium is reached between nutrient mineralization and nutrient immobilization or fertilizer is added to the system.
  4. Hydrological impacts. Perennial plants may intercept and utilize more of the incoming rainfall. than annual plants each year. This may result in water tables dropping and/or reduced surface flow to rivers.
  5. Reduced nutrient delivery to downstream farms. Wide replacement of annual with perennial plants on agricultural landscapes could stabilize soils and reduce nitrate leaching to the point that the delivery of sediment and dissolved nitrogen to downstream landscapes could be reduced. Farmers in these areas may currently rely on these nutrient inputs. On the other hand, other water usage sectors might benefit from improved water quality.

    Target environments for perennial rice

Upland rice

is grown on more than in the highlands of southern China and across southeast Asia. Because it is grown on steeply sloping soil without terracing, severe erosion results, and a given patch of land can economically produce rice for only a year or two before it must be allowed to return to natural vegetation—only to be cleared and re-sown to rice a few years later. Population increase and agricultural intensification is reducing the fallow period. This is a potent recipe for soil degradation. Were rice a perennial rather than an annual species, its continuously living roots and thick cover of vegetation would prevent such erosion, just as a planting of grass can prevent a roadside slope from washing away. Perennial rice could produce critically needed food year after year on the same plot of land without degrading the soil.

Rainfed paddy rice

38 million ha of rice lands are terraced but unirrigated. This cropping system produces about 17% of world rice.
While upland rice production systems were the initial target for the perennialization of rice, the perennial habit may prove to have benefits in paddy systems where erosion is less of a concern. Faced with drought one year and flooding the next, "...the rainfed rice farmer can usefully be thought of first as a manager of risk and uncertainty." Given the erratic moisture, many farmers do not use purchased fertilizers. With deforestation, manure may be used as cooking fuel making fertility a key problem. Where fertilizers are purchased, flooding can result in fertilizer runoff contaminating water systems.
Rice with deeper roots, as would be predicted with perennial rice, could exploit the moisture and nutrients in a greater soil volume than short-rooted types. The perennial habit could reduce the uncertainty of planting and transplanting with erratic rainfall patterns. Rhizomes would simply lie dormant until temperature and moisture conditions were adequate for emergence.

Irrigated paddy rice

Irrigated rice is very productive and this production method must be fairly sustainable, as it has been practiced in China for millennia. However, high yielding rhizomatous rice varieties may still have some advantages, according to Dr. Dayun Tao
  • Fixing hybrid vigor: The first generation hybrids between two particular lines or individuals may be exceptionally good, but may be almost impossible to re-create. If the exceptional individual was perennial and rhizomatous, millions of genetically identical plants could be made from pieces of the rhizomes.
  • Expediting the production of inbred lines: Even if the final propagule for the farmers' fields is hybrid seed, not hybrid clones, the parents of exceptional F1 hybrids could be immediately clonally propagated if they were rhizomatous. These genetic replicas could be maintained indefinitely and crossed afresh each year to produce new F1 hybrid seed. Normally, re-creating parents using sexual reproduction requires many generations of inbreeding.
  • Ratoon cropping: In some environments, additional grain crops could be harvested each year if the plants ratooned quickly. Shoots growing from the mature plant can reach the reproductive stage more quickly than shoots growing from seed. Transplanting seedlings is faster than sowing seed, but still requires time and labor-intensive field preparation and, of course, a large supply of labor for transplanting.
Other benefits can be imagined in this environment:
  • Reduce the need for transplanting, weeding, and other backbreaking labor. Because of migration to cities, many rural parts of Asia actually suffer from severe labor shortages.
  • More efficient use of applied fertilizer