Perennial grain

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Roots of intermediate wheatgrass, a perennial grain candidate compared to those of annual wheat (at left in each panel) 4 Seasons Roots.jpg
Roots of intermediate wheatgrass, a perennial grain candidate compared to those of annual wheat (at left in each panel)

A perennial grain is a grain crop that lives and remains productive for two or more years, rather than growing for only one season before harvest, like most grains and annual crops. While many fruit, nut and forage crops are long-lived perennial plants, all major grain crops presently used in large-scale agriculture are annuals or short-lived perennials grown as annuals. Scientists from several nations have argued that perennial versions of today's grain crops could be developed and that these perennial grains could make grain agriculture more sustainable. [1] [2] [3] [4]

Contents

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 Millennium Ecosystem Assessment [4]

The 2005 Synthesis Report of the United Nations’ Millennium Ecosystem Assessment program labeled agriculture the “largest threat to biodiversity and ecosystem function of any single human activity.” [4] Perennial grains could reduce this threat, according to the following logic:

Crop development

Thinopyrum intermedium (intermediate wheatgrass) first year nursery. A 4000-plant breeding nursery in the first year. Thinopyrum intermedium is being domesticated as a perennial grain crop. Thinopyrum intermedium first year nursery.JPG
Thinopyrum intermedium (intermediate wheatgrass) first year nursery. A 4000-plant breeding nursery in the first year. Thinopyrum intermedium is being domesticated as a perennial grain crop.
Thinopyrum intermedium harvest. Individual plants of Thinopyrum intermedium are tied into bundles to be cut and threshed in order to select the plants with the highest yield and largest seed. Wheatgrass harvest.jpg
Thinopyrum intermedium harvest. Individual plants of Thinopyrum intermedium are tied into bundles to be cut and threshed in order to select the plants with the highest yield and largest seed.
Thinopyrum intermedium crossing block. Thinopyrum intermedium selected for high grain yield and large seed size planted in a crossing block. Thinopyrum intermedium crossing block.JPG
Thinopyrum intermedium crossing block. Thinopyrum intermedium selected for high grain yield and large seed size planted in a crossing block.

The current agricultural system is predominantly composed of herbaceous annuals. Annual systems depend heavily on tilling and chemical applications, like pesticides and fertilizers, and thus contribute to sustainability issues like erosion, eutrophication and fossil fuel use. The development of perennial grains could improve the sustainability of agriculture. [8] [9] [1] [5] In contrast to annual systems, perennial systems involve plants with deep, long lived roots. A perennial system is not dependent on tilling and could reduce the dependence on chemical applications, build soil health, and sequester carbon. [1] [8]

Annual crops have been domesticated for nearly 10,000 years, whereas no commercial perennial grains have yet been developed. It is unclear exactly why perennial grains were not domesticated alongside annual grains during the agricultural revolution. [10] [11] Annuals may have been more predisposed to domestication for several reasons. For one, wild annuals were likely easier targets for early domestication efforts because they generally have greater single-year yields than wild perennials. Because the fitness of annual plants depends on the reproductive output of a single year, annuals naturally invest heavily in seed production (typically the product of interest for agriculture). In contrast, perennials have to balance seed production with overwinter survival in any given year and thus tend to produce lower yields per year. [11] Second, annual plants have a shorter generation time, facilitating faster gains through the artificial selection process. [11] Third, early agriculture used tilling to clear fields for the following year's crop and the practice of annual tilling, which clears the soil of existing plants in preparation for new ones, is not compatible with perennial grains. [11] Finally, once annual grains were domesticated there was a reduced incentive to pursue the domestication of new perennial grains. [11]

If the limitations of early domestication efforts explain the lack of perennial grains, there may not be an insurmountable physiological barrier to high yielding perennials. For instance, the trade off between survival and yield in perennials should primarily be observed in the plant's first year when they are establishing root structures. In subsequent years, perennials may actually benefit from having a longer growing season and greater access to soil resources due to pre-established root systems ( which can also reduce reliance on fertilizer). [12] However, even if physiological limitations limit resource allocation to seed production in perennials, their yields may still be comparable to or exceed annual grain yields due to improved resource acquisition and higher overall biomass. [11]

While perennial crop domestication could alleviate some of the sustainability issues caused by reliance on annual crops, the gains may still be fundamentally limited by general agricultural practices. Producing grain on scales large enough to meet the world demand depends on the conversion of massive tracts of native grassland to agriculture, regardless of the perennial or annual nature of the crop. [10]

Methods

To capitalize on the potential benefits of perennial crop domestication, the domestication process needs to be accelerated. Serious efforts to develop new perennial grains began in the 1980s, largely driven by Wes Jackson and The Land Institute in Salina, Kansas. [13] Approaches to perennial crop development generally fall under three main methods: perennialization, de novo domestication, and genetic manipulation. These methods are not mutually exclusive, can be used in tandem and each present their own challenges.

Perennialization

Hybridizing existing annual crops with perennial wild relative is a common approach to perennial crop development. This approach aims to conserve the important agronomic traits that have been developed in annual grain crops while converting the plant to a perennial life cycle with well-developed long-lived root systems. [14] [15] However, perennialization is not without challenges.

For one, plants produced through hybridization are often infertile so successful breeding of plants beyond the F1, or initial hybrid generation is rare. [16] Second, perennial traits are often polygenic (controlled by multiple genes) so conferral of a perennial lifecycle to domesticated annual crops depends on a full suite of genes being transferred to the hybrid offspring from the perennial parent. In contrast, yield traits are generally less polygenic so single genes can have positive effects on yield. [17] [14] Thus, perennial crop development through hybridization may be more effective if the goal of hybridization is to introduce increased yield to perennials rather than introducing perenniality to annual crops. [14]

Accelerated domestication

Accelerated domestication (also called de novo domestication) of perennial wild plants provides another avenue for perennial crop development. [18] This approach involves selection of wild herbaceous perennials based on their domestication potential, followed by artificial selection for agronomically important traits like yield, seed shattering (the tendency of seeds to fall off the plant or stay attached until harvest), free-threshing seeds (the tendency of seeds to easily detach from the chaff) and plant height. [9] [15] Pipelines for domestication, like those developed by researchers at The Land Institute, have established criteria for evaluating the potential of candidate species to be successful for domestication programs—e.g. high variability and heritability of agronomically important traits—and also guide what traits should be focused on during breeding efforts. [17] [19] Extensive lists of potential candidate species can be found in Wagoner & Schaeffer [1]  and Cox et al. [14]

Domesticating new perennial species has a couple of major drawbacks. For one, wild perennial grains have very low yearly yields compared to domesticated annuals so breeding efforts have to make up a lot of ground before perennial grains are commercially viable. This problem is exacerbated by the fact that many candidate species are polyploid (i.e. they have extra sets of genetic material). Polyploidy makes it harder to breed undesirable alleles out of the population and create uniform plants that grow and mature simultaneously for easy harvest. [12]

Genetic methods

Several genetic methods can help the perennial crop development process. Genomic selection, a method of predicting plant traits based on analysis of their genome, shows promise as a method to accelerate selection of plants in domestication programs. [15] If adult plant phenotypes can be predicted from the genomes of young plants, plants can be artificially selected at an earlier age, reducing time and resources needed to identify individuals with desirable traits. [20] Transgenics and gene altering can add or target “domestication genes” and their orthologs (genes with similar sequences and functions) in perennial plants. Domestication genes have known effects on traits that are relevant to domestication, and have been discovered in annual crop species. Genome sequencing indicates that many orthologs also exist in perennial species that may be useful targets for genetic alteration. [17]

Current applications of genetic manipulation are limited because the genomes of many candidate species have not been sequenced. Furthermore, methods of genetic manipulation have not yet been optimized in most candidate species. [14] [17] Despite these limitations, there have been rapid gains in the development of genetic techniques and these methods are likely to be a useful aid for the development of perennial crops in years to come. [17] [15]

Advantages

Several claims have been published: [6]

  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. [21]
  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. [3] 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. [22] [23] A similar phenomenon is seen in unfertilized fields harvested for wild hay. [24] 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.” [25] 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) and it can be stored (unlike fruit) for consumption during the winter or dry season.
  5. Reduced Soil erosion U.S. Forest Service et al. cite perennial grasses as a preventative for soil erosion. [26] Perennials of all kinds establish thick root systems which tie up soil and prevent surface erosion by wind and water. Since water runoff is slowed, it has a longer time to soak in and enter the groundwater system. Net water inflow into streams is marginally reduced due to groundwater infusion, but this also reduces high flow rates in streams associated with fast-flowing water-based erosion of streambeds. .
  6. Increased wildlife populations U.S. Forest Service et al. cite slower release of water into streams, which makes water levels more consistent instead of alternating between dry and flash-flood situations common to deserts. Consistent water levels contribute to increased wildlife populations of fish, amphibians, waterfowl, and mammals dependent upon a consistent water source. [26]
  7. Reduced weed competition - Minimizing tillage and herbicide applications.
  8. Improved soil microbiomes - Perennial grain crops may nurture beneficial soil microbiomes, as the frequent soil disturbance required in annual crop production is disruptive to these microbiomes.
  9. Sequester more carbon - It is hypothesized that perennial grains may sequester more carbon, due to better landscape management, and maintaining more cropland in production. [27] [23]

Potential disadvantages

  1. Does not address food security today. Perennial grain crops are in the early stages of development and may take many years before achieving yields equivalent to annual grains.
  2. Makes crop rotation more difficult. Crop rotations with perennial systems are possible, but the full rotation will necessarily take longer. For example, a perennial hay crop [28] like alfalfa is commonly rotated with annual crops or other perennial hay crops after 3–5 years. 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. [3] 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 sectors might benefit from improved water quality.
  6. 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 grains 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.

Perennial grains in the marketplace

Kernza, an intermediate wheatgrass, has been under development for use as a grain crop since the 1980s. Since 2001, the nonprofit organization The Land Institute's Dr. Lee DeHaan has led development of the crop, coining the trademarked name Kernza in 2009. [7]

Recently, work on Kernza has rapidly expanded to include more than 25 lead scientists in diverse fields working on three continents. This international team has developed growing techniques and dramatically improved traits such as shatter resistance, seed size and yield, enabling the crop to now be produced and marketed at a small scale. US Institutional Kernza research partners now include the University of Minnesota, the University of Wisconsin, Madison, Cornell University, Ohio State, Kansas State, and numerous international universities in Canada and Europe, including the University of Minnesota, Lund University, and ISARA. [29]

As the first perennial grain crop grown across the northern United States, researchers hope that Kernza will help dramatically shift agriculture practice, making croplands multifunctional through the production of both food and ecosystem services. [1]

The Land Institute developed the registered trademark for Kernza grain to help identify intermediate wheatgrass grain that is certified as a perennial using the most advanced types of T. intermedium seed.

The cultivar of perennial rice 23 (PR23) is used for a new rice production system that is based on no-tillage. [30]

See also

Related Research Articles

<span class="mw-page-title-main">Agriculture</span> Cultivation of plants and animals to provide useful products

Agriculture encompasses crop and livestock production, aquaculture, fisheries, and forestry for food and non-food products. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to live in cities. While humans started gathering grains at least 105,000 years ago, nascent farmers only began planting them around 11,500 years ago. Sheep, goats, pigs, and cattle were domesticated around 10,000 years ago. Plants were independently cultivated in at least 11 regions of the world. In the 20th century, industrial agriculture based on large-scale monocultures came to dominate agricultural output.

<span class="mw-page-title-main">Cereal</span> Grass that has edible grain

A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize. Edible grains from other plant families, such as buckwheat and quinoa are pseudocereals. Most cereals are annuals, producing one crop from each planting, though rice is sometimes grown as a perennial. Winter varieties are hardy enough to be planted in the autumn, becoming dormant in the winter, and harvested in spring or early summer; spring varieties are planted in spring and harvested in late summer. The term cereal is derived from the name of the Roman goddess of grain crops and fertility, Ceres.

<span class="mw-page-title-main">Rice</span> Cereal (Oryza sativa)

Rice is a cereal grain, and in its domesticated form is the staple food for over half of the world's human population, particularly in Asia and Africa, due to the vast amount of soil that is able to grow rice. Rice is the seed of the grass species Oryza sativa or, much less commonly, O. glaberrima. Asian rice was domesticated in China some 13,500 to 8,200 years ago, while African rice was domesticated in Africa some 3,000 years ago. Rice has become commonplace in many cultures worldwide; in 2021, 787 million tons were produced, placing it fourth after sugarcane, maize, and wheat. Only some 8% of rice is traded internationally. China, India, and Indonesia are the largest consumers of rice. A substantial amount of the rice produced in developing nations is lost after harvest through factors such as poor transport and storage. Rice yields can be reduced by pests including insects, rodents, and birds, as well as by weeds, and by diseases such as rice blast. Traditional rice polycultures such as rice-duck farming, and modern integrated pest management seek to control damage from pests in a sustainable way.

The following outline is provided as an overview of and topical guide to agriculture:

<span class="mw-page-title-main">Intensive farming</span> Branch of agricultire

Intensive agriculture, also known as intensive farming, conventional, or industrial agriculture, is a type of agriculture, both of crop plants and of animals, with higher levels of input and output per unit of agricultural land area. It is characterized by a low fallow ratio, higher use of inputs such as capital, labour, agrochemicals and water, and higher crop yields per unit land area.

<span class="mw-page-title-main">Agronomy</span> Science of producing and using plants

Agronomy is the science and technology of producing and using plants by agriculture for food, fuel, fiber, chemicals, recreation, or land conservation. Agronomy has come to include research of plant genetics, plant physiology, meteorology, and soil science. It is the application of a combination of sciences such as biology, chemistry, economics, ecology, earth science, and genetics. Professionals of agronomy are termed agronomists.

<span class="mw-page-title-main">Sustainable agriculture</span> Farming approach that balances environmental, economic and social factors in the long term

Sustainable agriculture is farming in sustainable ways meeting society's present food and textile needs, without compromising the ability for current or future generations to meet their needs. It can be based on an understanding of ecosystem services. There are many methods to increase the sustainability of agriculture. When developing agriculture within sustainable food systems, it is important to develop flexible business process and farming practices. Agriculture has an enormous environmental footprint, playing a significant role in causing climate change, water scarcity, water pollution, land degradation, deforestation and other processes; it is simultaneously causing environmental changes and being impacted by these changes. Sustainable agriculture consists of environment friendly methods of farming that allow the production of crops or livestock without damage to human or natural systems. It involves preventing adverse effects to soil, water, biodiversity, surrounding or downstream resources—as well as to those working or living on the farm or in neighboring areas. Elements of sustainable agriculture can include permaculture, agroforestry, mixed farming, multiple cropping, and crop rotation.

<span class="mw-page-title-main">Polyculture</span> Growing multiple crops together in agriculture

In agriculture, polyculture is the practice of growing more than one crop species together in the same place at the same time, in contrast to monoculture, which had become the dominant approach in developed countries by 1950. Traditional examples include the intercropping of the Three Sisters, namely maize, beans, and squashes, by indigenous peoples of Central and North America, the rice-fish systems of Asia, and the complex mixed cropping systems of Nigeria.

<span class="mw-page-title-main">The Land Institute</span> American nonprofit organization

The Land Institute is an American nonprofit research, education, and policy organization dedicated to sustainable agriculture, based in Salina, Kansas. Their goal is to develop an agricultural system based on perennial crops that "has the ecological stability of the prairie and a grain yield comparable to that from annual crops".

<span class="mw-page-title-main">Perennial</span> Plant that lives for more than two years

In botany, a perennial plant or simply perennial is a plant that lives more than two years. The term is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs, which are also technically perennials. Notably, it is estimated that 94% of plant species fall under the category of perennials, underscoring the prevalence of plants with lifespans exceeding two years in the botanical world.

<span class="mw-page-title-main">Agroforestry</span> Land use management system

Agroforestry is a land use management system that integrates trees with crops or pasture. It combines agricultural and forestry technologies. As a polyculture system, an agroforestry system can produce timber and wood products, fruits, nuts, other edible plant products, edible mushrooms, medicinal plants, ornamental plants, animals and animal products, and other products from both domesticated and wild species.

<i>Distichlis palmeri</i> Species of flowering plant

Distichlis palmeri is an obligate emergent perennial rhizomatous dioecious halophytic C4 grass in the Poaceae (Gramineae) family. D. palmeri is a saltwater marsh grass endemic to the tidal marshes of the northern part of the Gulf of California and Islands section of the Sonoran Desert. D.palmeri is not drought tolerant. It does withstand surface drying between supra tidal events because roots extend downward to more than 1 meter where coastal substrata is still moist.

<span class="mw-page-title-main">Energy crop</span> Crops grown solely for energy production by combustion

Energy crops are low-cost and low-maintenance crops grown solely for renewable bioenergy production. The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas. The fuels are burned to generate electrical power or heat.

Upland rice is a variety of rice grown on dry soil rather than flooded rice paddies.

<span class="mw-page-title-main">Weed</span> Plant considered undesirable in a particular place or situation

A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals. Plants with characteristics that make them hazardous, aesthetically unappealing, difficult to control in managed environments, or otherwise unwanted in farm land, orchards, gardens, lawns, parks, recreational spaces, residential and industrial areas, may all be considered weeds. The concept of weeds is particularly significant in agriculture, where the presence of weeds in fields used to grow crops may cause major losses in yields. Invasive species, plants introduced to an environment where their presence negatively impacts the overall functioning and biodiversity of the ecosystem, may also sometimes be considered weeds.

<i>Thinopyrum intermedium</i> Species of flowering plant

Thinopyrum intermedium, known commonly as intermediate wheatgrass, is a sod-forming perennial grass in the Triticeae tribe of Pooideae native to Europe and Western Asia. It is part of a group of plants commonly called wheatgrasses because of the similarity of their seed heads or ears to common wheat. However, wheatgrasses generally are perennial, while wheat is an annual. It has gained the Royal Horticultural Society's Award of Garden Merit as an ornamental.

<span class="mw-page-title-main">Perennial rice</span> Varieties of rice that can grow season after season without re-seeding

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 crops are a perennial plant species that are cultivated and live longer than two years without the need of being replanted each year. Naturally perennial crops include many fruit and nut crops; some herbs and vegetables also qualify as perennial. Perennial crops have been cultivated for thousands of years; their cultivation differs from the mainstream annual agriculture because regular tilling is not required and this results in decreased soil erosion and increased soil health. Some perennial plants that are not cultivated as perennial crops are tomatoes, whose vines can live for several years but often freeze and die in winters outside of temperate climates, and potatoes which can live for more than two years but are usually harvested yearly. Despite making up 94% of plants on earth, perennials take up only 13% of global cropland. In contrast, grain crops take up about 70% of global cropland and global caloric consumption and are largely annual plants.

<i>Silphium integrifolium</i> Species of flowering plant

Silphium integrifolium is a species of flowering plant in the family Asteraceae. Its common names include rosinweed, whole-leaf rosinweed, entire-leaf rosinweed, prairie rosinweed, and silflower. It is native to eastern North America, including Ontario in Canada and the eastern and central United States as far west as New Mexico.

De novo domestication is a process where new species are genetically altered to meet human needs, such as agriculture or companionship. It is performed both by farmers and scientists, and can be done through traditional selective breeding or modern biotechnological methods. Targets for de novo domestication are often species that have never been under cultivation, but may also include wild relatives of already domesticated species.

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  23. 1 2 Culman SW, Snapp SS, Ollenburger M, Basso B, DeHaan LR (May 2013). "Soil and water quality rapidly responds to the perennial grain Kernza wheatgrass". Agronomy Journal. 105 (3): 735–44. Bibcode:2013AgrJ..105..735C. doi:10.2134/agronj2012.0273.
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  26. 1 2 "Chapter 10 – Water Quality Management for National Forest System Lands in Alaska" (PDF). FSH 2509.22 – Soil and Water Conservation Handbook. United States Forest Service, division of United States Department of Agriculture.
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  29. ↑ "Kernza® Grain & Perennial Agriculture". The Land Institute. Retrieved 2017-12-14.
  30. ↑ Zhang, Yujiao; Huang, Guangfu; Zhang, Shilai; Zhang, Jing; Gan, Shuxian; Cheng, Mao; Hu, Jian; Huang, Liyu; Hu, Fengyi (2021-01-01). "An innovated crop management scheme for perennial rice cropping system and its impacts on sustainable rice production". European Journal of Agronomy. 122: 126186. doi: 10.1016/j.eja.2020.126186 . ISSN   1161-0301. S2CID   225122362.
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