Perennial grains

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

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.” 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
• 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.
• This "central dilemma" 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.

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)

Advantages of perennial crops

Several claims have been published :

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, the first cutting of alfalfa, a perennial legume crop, is typically done in the second week of June . Emergence of annual soybean seedlings from the soil does not reach 85% completion, on average, until June 12 in Minnesota, according to US Department of Agriculture statistics. 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 .
2. More conservative management of nutrients. Perennial plants use nutrients more efficiently, resulting in greater potential for long-term sustainable harvests. Some native tallgrass prairie meadows in Kansas have been harvested annually for 75 to 100 years with no substantial fertility inputs other than the limited inputs of nutrients from atmospheric deposition, weathering of parent material, and biological nitrogen fixation. Comparisons of soil nutrient contents maintained by five continuously cropped wheat fields to those maintained by adjacent native hay meadows on level bottomlands in north central Kansas illustrate the point. The wheat fields and native hay meadows, all harvested for approximately 75 years, currently yield similar amounts of nitrogen in the form of grain or hay. The wheat fields, however, have received approximately 70 kg of fertilizer nitrogen per hectare for more than a decade while no fertilizer has been applied to the hay meadows. Despite similar levels of nitrogen export and substantially different levels of nitrogen inputs, the hay meadows maintain significantly greater amounts of total soil nitrogen and carbon to a depth of one meter than do the annually cropped fields Phosphorus and potassium levels are similar for the two production systems despite annual fertilizer inputs to the wheat fields.
3. High biomass production. Perennials generally yield more aboveground biomass than do annuals, and some of it might be reallocated to grain production through breeding. Although those species currently being domesticated as perennial grain crops have low seed yields, their total aboveground productivity may be higher than that of annual crops with long breeding histories (DeHaan et al. 2005). Piper and Kulakow (1994) for example, reported a mean aboveground biomass for perennial sorghum hybrids that was 62 percent higher than that of their annual parent. However, the hybrids’ mean harvest index (ratio of seed yield to total aboveground biomass) was much lower than that of the annual parent. The carbon allocated for excess vegetative production (from a human point of view) in perennials is available for reallocation through plant breeding. A similar increase in harvest index was largely responsible for yield increases achieved in annual crops by the Green Revolution (Evans 1998).
4. Sustainable production on marginal lands. Because of increasing population pressure in many parts of the world, landscapes with a high risk of degradation under annual cropping are becoming increasingly important sources of food and income. 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.” Some perennial crops, such as perennial forages, are available for these landscapes, but increased global demands for grain will likely pressure farmers to plant grains (all of which are currently annual crops), not forages.

See also

• Perennial_rice
• Perennial_sunflower
• Plant breeding
• Hybrid (biology)
• Slash-and-burn agriculture
• Subsistence agriculture

External links

• Perennial upland rice takes root An article by Paul Cox in the New Agriculturalist.
• The Land Institute A scientific institute in Kansas, U.S.A. with several perennial grain breeding programs.
• the International Rice Research Institute (IRRI)