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,Wagoner, P. (1990)Perennial grain development: past efforts and potential for the future. Critical reviews in plant sciences. 9(5):381-408 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.Reviewed in Cox, T.S., et al. (2002) Breeding Perennial Grain Crops. Critical Reviews in Plant Science. 21(2):59-91..
Perennial rice breeding was initiated at the International Rice Research Institute, PhilippinesInternational Rice Research Institute, 1988. pp. 66 in IRRI toward 2000 and beyond. IRRI, Manila, 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 AsianAfrican rice, Oryza glaberrima is another domesticated rice. Its ancestor is strictly annual. The vast majority of the rice grown in the world—even in Africa—is Asian rice so, henceforth, "rice" in this article will refer only to Asian rice. rice, Oryza sativa is a short-lived plant. Most cultivars die after producing seeds, though some can regrow (ratoon) and produce a second crop under favorable conditions.Chauhan, J.S, B. S. Vergara, and F.S.S. Lopez. 1985. Rice ratooning. IRRI Res. Paper Ser. 102. IRRI, Manila, Philippines 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.Kush, G.S. 1997. Origin, dispersal, cultivation and variation of rice. Plant Mol. Biol. 35:25-34 In addition to these perennial types, some O. rufipogon populations are annuals or intermediate in lifespan.Morishiima, H., Y. Sano, and H.I. Oka. 1984. Differentiation of perennial and annual types due to habitat conditions in the wild rice O. perennis. Plant Syst. Evol. 114:119-135
Other wild species in the genus Oryza are also perennial. While perennial Oryza rufipogon spreads vegetatively by above-ground stems (stolons), O. longistaminata, O. officinalis, O. australiensis, O. rhizomatis spread by underground stems (rhizomes).
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.Pimental, D., et al. (1987) World agriculture and soil erosion. Bioscience 37:277-283.
Perennial plants regrow quickly after being harvested, re-establishing a protective cover. The fields do not need to be plowed after the initial planting.Glover, J.D. (2005) The necessity and possibility of perennial grain production systems. Renewable Agriculture and Food Systems. 20:1-4
Researchers at The International Rice Research Institute (IRRI) 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.Tinkera, P.B. (1996) Effects of slash-and-burn agriculture and deforestation on climate change. Agriculture, Ecosystems & Environment. 58(1):13-22 Deforestation could be reduced by practices that conserve soil productivitySanchez, P., et al. Approaches to mitigate tropical deforestation by sustainable soil management practices. In, Soils on a warmer earth: effects of expected climate change on soil. Scharpenseel, H.W., et al., eds. Volume 20 of Developments in soil science. 1990 Elsevier pp 211-220
Other potential benefits Drought resistance: Annual rice has a shallow root system and is very drought susceptible.Bernier, J. (2008)Breeding upland rice for drought resistance. Journal of the Science of Food and Agriculture. 88(6):927-939. 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 untilledBlevins, R.L., et al.(1971) Influence of No-tillage on Soil Moisture. Agronomy Journal. 63:593-596 Resist weed invasion: Weed pressure has increased in upland rice systems as the fallow period has shortened.Roder, W., Phengchanh, S. and Keoboulapha, B. (1997) “Weeds in slash-and-burn rice fields in Northern Laos”. Weed Research 37: 111-119. 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."Ewel, J.J. (1986) DESIGNING AGRICULTURAL ECOSYSTEMS FOR THE HUMIDTROPICS. Annu. Rev. Ecol. Syst. 17:245-71 Grassland restoration with perennials results in fewer annual weedsBlumenthal, D. M., N. R. Jordan, and E. L. Svenson (2003) Weed control as a rationale for restoration: the example of tallgrass prairie. Conservation Ecology 7(1): 6. [online] URL: http://www.consecol.org/vol7/iss1/art6 and perennial grasses, sown at appropriate densities, can out-compete even perennial weeds once they are established.Darwent, A. L., and C. R. Elliott (1979) Effect of Grass Species and Row Spacing on Dandelion Establishment and Growth. Canadian Journal of Plant Science 59:1031-1036 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
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. 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. 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. 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. 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 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,Crosson, P. (1995)Natural resource and environmental consequences of rice production. In Fragile Lives in Fragile Ecosystems Proceedings of the International Rice Research Conference 13–17 February 1995. International Rice Research Institute, Los Baños, Laguna, Philippines http://books.irri.org/9712200736_content.pdfValentin, C., 'et al'.(2008)Runoff and sediment losses from 27 upland catchments in Southeast Asia: Impact of rapid land use changes and conservation practices. Agriculture, Ecosystems and Environment 128:225–238 PDF available 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.de Rouw, A, Soulileuth, B., Phanthavong, K., Dupin, B., 2005. The adaptation of upland rice cropping to ever-shorter fallow periods and its limit. In: Bouahom, B., Glendinning, A., Nilsson, S., Victor, M. (Eds.), Poverty reduction and shifting cultivation stabilisation in the uplands of Lao PDR: technologies, approaches and methods for improving upland Livelihoods – Proceedings of a workshop held in Luang Prabang, Lao PDR, January 27–30, 2004. National Agriculture and Forestry Research Institute. Vientiane, Lao PDR, pp. 139–148.PDF available 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.Schmit, V., 1996 Improving sustainability in the uplands through the development of a perennial upland rice, pp. 265-273 in Upland Rice Research in Partnership, Proceedings of the Upland Rice Consortium Workshop, edited by Piggin C., B. Courtois, V.Schmit. 4–13 January 1996; Padang, Indonesia.
Rainfed paddy rice 38 million ha (26%) of rice lands are terraced but unirrigated. This cropping system produces about 17% of world rice.