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While many fruit, nut and forage crops are long-lived perennial plants, all major grain crops are annuals or short-lived perennials grown as annuals. Scientists from several nations have argued that perennial versions of todays grain crops could be developed and that these perennial grains could make grain agriculture more sustainable.

Rationale

Cultivation often has a negative impact on provision of [ecosystem] services. For example, cultivated systems tend to use more water, increase water pollution and soil erosion, store less carbon, emit more greenhouse gases, and support significantly less habitat and biodiversity than the ecosystems they replace

The Millenium Ecosystem Assessment [1]

The 2005 Synthesis Report of the United Nations’ Millenium Ecosystem Assessment program labeled agriculture the “largest threat to biodiversity and ecosystem function of any single human activity.” [1] Perennial grains could reduce this threat, according to the following logic:

  • Most agricultural land is devoted to the production of grain crops: cereal, oilseed, and legume crops occupy 75% of US and 69% of global croplands. These grains include such crops as wheat, rice, and maize; together they provide over 70% of human food calories [2]
  • All these grain crops are currently annual plants which are generally planted into cultivated soil.
  • Frequent cultivation puts soil at risk of loss and degradation.[1]
  • This "central dilemma" [3] of agriculture in which current food production undermines the potential for future food production could be escaped by developing perennial grain crops that do not require tilling the soil each year. No-till technology enables short-lived (annual) crops to be grown with less intense tillage, but perennial plants provide the most protection for the soil.[4]

A dense stocking of perennial plants-whether trees, shrubs, or herbs-in an agroecosystem increases the likelihood that the soil will be covered continuously, moderating oscillations in temperature and humidity that can damage the soil

J.J. Ewel (1986) [4]

Methods for developing perennial grains

Disadvantages of perennial crops

Advantages of perennial crops

Several claims have been published [3]:

  1. Greater access to resources through a longer season.Perennial plants typically emerge earlier than annuals in the spring and go dormant in the autumn well after annual plants have died. The longer growing season allows greater interception of sunlight and rainfall. For example, In Minnesota, annual soybean seedlings emerge from the soil in early June. By this time perennial alfalfa has grown so much that it is ready for the first harvest. Therefore, by the time a soybean crop has just begun to photosynthesize, a field of alfalfa has already produced about 40% of the season’s production [5].
  2. Greater access to resources through a deeper rooting zone. Most long--lived plants construct larger, deeper root systems than short-lived plants adapted to the same region . Deeper roots enable perennials to "mine" a larger volume of soil each year[6]. A larger volume of soil also available for exploitation per unit of cropland also means a larger volume of soil water serves as a reservoir for periods without rainfall.
  3. More efficient use of soil nutrients. Leaching of nitrogen from fertilizer has been found to be much lower under perennial crops such as alfalfa (lucerne) than annual crops such as maize [7]. A similar phenomenon is seen in unfertilized fields harvested for wild hay [8]. While adjacent wheat fields required annual inputs of fertilizer, the wild perennial grasses continued to produce nitrogen-rich hay for 75 to 100 years with no appreciable decline in productivity or soil fertility. Presumably, the larger root systems of the perennial plants and the microbial community they support intercept and cycle nutrients passing through the system much more efficiently than do the ephemeral root systems of crop plants.
  4. Sustainable production on marginal lands. Cassman et al. (2003) wrote that for large areas in poor regions of the world, “annual cereal cropping …is not likely to be sustainable over the longer term because of severe erosion risk. Perennial crops and agroforestry systems are better suited to these environments.” [9] Current perennial crops and agroforestry systems do not produce grain. Grain provides greater food security than forage or fruit because it can be eaten directly by humans (unlike forage) andit can be stored (unlike fruit) for consumption during the winter or dry season.

Potential Tradeoffs associated with domestication or perennialization

See also

References

  1. ^ a b c Cassman KG, Wood S. 2005. Cultivated systems. Pages 741-876 in Millenium Ecosystem Assessment, ed. Ecosystems and Human Well-Being. Washington (DC): Island Press.Chiras DD, Reganold JP, Owen OS. 2004 Natural Resource Conservation. Upper Saddle River, New Jersey: Prentice-Hall.
  2. ^ Glover, JD, Reganold, JP. 2010. Perennial grains: Food security for the future. Issues in Science and Technology. Winter 2010:41-47.
  3. ^ a b TS Cox, JD Glover,DL Van Tassel, CM Cox and LR DeHaan. 2006. Prospects for developing perennial grain crops. BioScience. 56:649-659"
  4. ^ a b Ewel, J.J. (1986) DESIGNING AGRICULTURAL ECOSYSTEMS FOR THE HUMIDTROPICS. Ann. Rev. Ecol. Syst. 17:245-71
  5. ^ CC Sheaffer, Martin NP, Lamb JAFS, Cuomo GR, Jewett JG, Quering SR. 2000. Leaf and stem properties of alfalfa entries. Agronomy Journal 92:733-739.
  6. ^ JD Glover, et al.2010. Increased Food and Ecosystem Security via Perennial Grains. Science 328:1638-1639.
  7. ^ Huggins, D.R., Randall, G.W., Russelle, M.P., 2001. Subsurface drain losses of water and nitrate following conversion of perennials to row crops. Agron. J. 93, 477–486.
  8. ^ [http://www.landinstitute.org/pages/Glover%202009%20AGEE%20InPress.pdf Harvested perennial grasslands provide ecological benchmarks for agricultural sustainability (2010) Jerry D. Glover, Steve W. Culman, S. Tianna DuPont, Whitney Broussard, Lauren Young, Margaret E. Mangan, John G. Mai, Timothy E. Crews, Lee R. DeHaan, Daniel H. Buckley, Howard Ferris, R. Eugene Turner, Heather L. Reynolds and Donald L. Wyse. Agriculture, Ecosystems & Environment. 137:3-12.]
  9. ^ KG Cassman, A Dobermann, DT Walters, H Yang. 2003. Meeting cereal demand while protecting natural resources and improving environmental quality. Annual Review of Environment and Resources 28:315-358.

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