**7. Organic farming and crop rotations**

Organic farming has embraced crop rotations as its backbone to success. Crop rotation is practiced with what appears to be, much more intensity than most conventional farming systems with particular emphasis on sustainability. A crop rotation plan and accompanying records for a field and/or farm are required for certification as an organic farming operation (Johnson and Toensmeier, 2009). Organic farming and its use of crop rotations could be summed up in part, as the employment of proven crop management practices prior to the advent of pesticides and processed fertilizers. This is not to say that improvements on those rotation systems have not occurred. Most have been modified to accommodate mechanization and most other time saving ideas. But, yields may be lower. Maeder et al., (2002) reported on a 21 year study in Europe that crop yields on organic farms were generally 20% lower. However, there was an offsetting decrease of 34% in fertilizer expense, a 53% reduction in energy costs, and a 97% decrease in pesticides. Reganold et al., (1987) reported a comparison of the long-term effects (40 years) of conventional farming to organic systems found that organic farms had significantly higher levels of soil organic matter than conventional systems, greater top soil depth, higher polysaccharide content, and less soil erosion. Clark et al., (1998) reported that over an eight year period of applying organic crop rotation practices that soil organic matter had increased 2% over a comparable field that used conventional practices in a two-year rotation scheme.

A major challenge to organic crop production is control of weeds. Weed management has been identified by producers as the principle problem in organic farming (Walz, 1999). The advent and subsequent extensive use of herbicides after World War II altered crop production practices, especially crop rotations. Conventional crop farming today usually involves two- or three-crop crop rotations as have been previously mentioned with a heavy reliance on herbicides to at least reduce or eliminate weed problems. Regardless of the type of farming system used, conventional or organic, weeds are a constant annual drag on achieving maximum yields of high quality produce. Nave and Wax (1971) reported a reduction in soybean seed yields of between 25% to 30% compared to weed free plots due to

will develop rotation schemes and select species based upon the crop's ability to extract nutrients and water from the soil. Some organic producers include vegetable crops into their operations due to these species tendency to extract nutrients and water from shallow depths then follow with a cereal that generally feeds to greater soil depths. Species selection is also made on the basis of weed, insect, and disease control. Delate and Hartzler (2003), states that rye has allopathic properties and is often used as a winter cover crop following corn to aid in weed control in preceding soybean or oat crops. Sustainability through the natural preservation of soil fertility is paramount to the organic farmer and makes the selection of species an important part of the operation. Organic crop production makes as

Interest in using lignocellulosic biomass to produce ethanol is gaining in popularity. Lignocellulosic biomass production mainly involves growing and harvesting plants generally not used for food or feed. Woody species such as willow (*Salix*. spp.) and poplars (*Populus* spp.) (Matthew et al., 2010) and grasses such as switchgrass (*Panicum virgatum*), big bluestem (*Andropogon gerardii),* reed canarygrass (*Phalaris arundinacea*) are several sources of lignocellulosic biomass that have shown to be useful in ethanol production (Hill, 2007). Rotation schemes for growing lignocellulocsic crops are, for the most part, still in development. Production of these materials for biofuels though is being done mostly on land not suitable for extensive corn and soybean production thus relieving pressure to grow more hectares of these crops to satisfy the conventional and biofuels markets. Worldwide it is estimated that about 1% of crop land or about 11-12 million hectares are being used to grow biofuels (de Fraiture et al., 2008). Raghu et al., (2006) points out that some of the traits favorable to producing a lignocellulosic crop such as being a C4 photosynthetically, lacking pests, rapid early season growth, and long canopy duration can also tend towards them being invasive. This would not work well in a rotation scheme with most conventional crops. Currently lignocellulosic crops contribute little to current U.S. transportation biofuel

much use of natural pest control, including crop rotations, as is possible.

suppliers but will likely provide the great share of ethanol in the near future.

schemes and the tillage of soils that are not well suited for cultivation.

In the United States, debate is underway concerning the use of corn as a primary source of fuel ethanol. Also, soybean oil is being blended with diesel to extend it. Diversion of these crops for biofuels is believed to increase food prices for consumers as the competing interest of food and fuel vie for the available supply. There is also concern that the increased demands for these grains will negatively impact crop rotations, particularly those that help conserve soil, water, and plant nutrients. One of the primary reasons corn and soybean are currently popular for biofuels over lignocellulosic crops is the comparatively short time to harvest maturity. Most of the lignocellulosic crops require three to five years to reach harvest maturity(Hill, 2007), compared to one year for corn or soybean. Though corn and soybean are regularly rotated with one another, history has shown that a substantial increase in the price received for any crop can encourage monocultures at the expense of proven rotations and their accompanying benefits. The expanded use of corn and soybean as biofuel could diminish the inclusion of small grains and/or forage crops in rotation

Besides lignocellulosic crops, the harvesting of crop residues for ethanol production has been considered. Perlack et al., (2006) has reported that nearly 7.0 X 1010 kg of corn stover

**8. Biofuels production and crop rotations** 

the presence of one smooth pigweed (*Amaranthus hybridus* L.) per 30 cm of row and that yield losses from stubble, lodging and stalks were more than double in pigweed and giant foxtail (*Setaria fabric* Herrm.) infested plots compared to weed free plots. Weeds compete with a crop for water, light, and soil nutrients directly reduce yields. Some species have alleopathnogenic effects upon certain crops, reducing their growth and yield or in extreme cases causing their death. Weeds can harbor insect pests or serve as alternate hosts to plant diseases that further reduce yields and produce quality. They can add off-flavors to crop products or in some cases provide toxins to produce, rendering it unhealthy to consume. Weeds present during harvest can also damage the crop being harvested. Ellis et al., (1998) reported increases in damaged soybean seeds by 8.2% to 11.1% with the presences of a plant per m of row of any of five common weed species found in the Mid South. In organic farming, crop rotations are vital to controlling weed growth. Teasdale et al., (2004) evaluated the weed seed dynamics of three organic crop rotations and found that seedbanks of smooth pigweed and common lambsquarter (*Chenopodium album* L.) were usually lower following a hay sward in a four-year rotation or wheat in a three-year rotation than following soybean in a two-year rotation prior to being planted to corn. However, annual grassy weed seedbanks prior to corn planting were generally higher following the hay sward of the four-year rotation than the wheat of three-year rotation or the soybean of the two-year rotation. Porter et al., (2003) also found that weed control in organic corn and soybean were better when they were part of a four-year rotation of corn-soybean-oat-alfalfa compared to a two-year corn-soybean scheme.

Nitrogen is probably the most important of the macro-nutrients in crop production. Libraries at all major agricultural universities have a seemingly endless supply of research articles and texts pointing out the importance of adequate N-fertility in the growth and development of every crop important to humankind. In organic crop farming, and increasingly in conventional cropping systems, the use of crop rotations that supply ample supplies of N to non-leguminous cereals is an important management strategy. Prior to the escalating energy prices and the increasing cost of manufactured N-fertilizer sources, the use of legumes that fix atmospheric N by *Rhizobium*-legume symbiosis, especially clover species, as green manures or cover crops had diminished sharply. Even prior to World War I legumes would almost always be seeded for a green manure crop preceding corn (Heichel and Barnes, 1984). In organic farming, where the emphasis is to refrain from using manufactured N-fertilizer, green manure crops or cover crops are a vital source of N for much of their production. Lupwayi et al., (1998) reported that microbial diversity was greater under wheat preceded by red clover manure or field peas (*Pisum sativum* L.) than under continuous wheat. Long-term crop rotation research in Iowa has shown very little or no increase in corn yields from plots receiving N-fertilizer compared to those following one or two years of an alfalfa- bromegrass- red clover meadow (Voss and Shrader, 1984).

Species selection for organic crop rotations is probably more thought out than for conventional crop rotations. As explained earlier, conventional crop rotations are heavily influenced by market price of the various commodities available to be grown. Though commodity price is important to practitioners of organic farming it is not the primary driving force in making species selections. Baldwin (2006) states that organic farmers face the challenge of practicing crop rotations by defining systems that maintain farm profits while improving soil quality and preserving the environment. Frequently organic farmers

the presence of one smooth pigweed (*Amaranthus hybridus* L.) per 30 cm of row and that yield losses from stubble, lodging and stalks were more than double in pigweed and giant foxtail (*Setaria fabric* Herrm.) infested plots compared to weed free plots. Weeds compete with a crop for water, light, and soil nutrients directly reduce yields. Some species have alleopathnogenic effects upon certain crops, reducing their growth and yield or in extreme cases causing their death. Weeds can harbor insect pests or serve as alternate hosts to plant diseases that further reduce yields and produce quality. They can add off-flavors to crop products or in some cases provide toxins to produce, rendering it unhealthy to consume. Weeds present during harvest can also damage the crop being harvested. Ellis et al., (1998) reported increases in damaged soybean seeds by 8.2% to 11.1% with the presences of a plant per m of row of any of five common weed species found in the Mid South. In organic farming, crop rotations are vital to controlling weed growth. Teasdale et al., (2004) evaluated the weed seed dynamics of three organic crop rotations and found that seedbanks of smooth pigweed and common lambsquarter (*Chenopodium album* L.) were usually lower following a hay sward in a four-year rotation or wheat in a three-year rotation than following soybean in a two-year rotation prior to being planted to corn. However, annual grassy weed seedbanks prior to corn planting were generally higher following the hay sward of the four-year rotation than the wheat of three-year rotation or the soybean of the two-year rotation. Porter et al., (2003) also found that weed control in organic corn and soybean were better when they were part of a four-year rotation of corn-soybean-oat-alfalfa

Nitrogen is probably the most important of the macro-nutrients in crop production. Libraries at all major agricultural universities have a seemingly endless supply of research articles and texts pointing out the importance of adequate N-fertility in the growth and development of every crop important to humankind. In organic crop farming, and increasingly in conventional cropping systems, the use of crop rotations that supply ample supplies of N to non-leguminous cereals is an important management strategy. Prior to the escalating energy prices and the increasing cost of manufactured N-fertilizer sources, the use of legumes that fix atmospheric N by *Rhizobium*-legume symbiosis, especially clover species, as green manures or cover crops had diminished sharply. Even prior to World War I legumes would almost always be seeded for a green manure crop preceding corn (Heichel and Barnes, 1984). In organic farming, where the emphasis is to refrain from using manufactured N-fertilizer, green manure crops or cover crops are a vital source of N for much of their production. Lupwayi et al., (1998) reported that microbial diversity was greater under wheat preceded by red clover manure or field peas (*Pisum sativum* L.) than under continuous wheat. Long-term crop rotation research in Iowa has shown very little or no increase in corn yields from plots receiving N-fertilizer compared to those following one

or two years of an alfalfa- bromegrass- red clover meadow (Voss and Shrader, 1984).

Species selection for organic crop rotations is probably more thought out than for conventional crop rotations. As explained earlier, conventional crop rotations are heavily influenced by market price of the various commodities available to be grown. Though commodity price is important to practitioners of organic farming it is not the primary driving force in making species selections. Baldwin (2006) states that organic farmers face the challenge of practicing crop rotations by defining systems that maintain farm profits while improving soil quality and preserving the environment. Frequently organic farmers

compared to a two-year corn-soybean scheme.

will develop rotation schemes and select species based upon the crop's ability to extract nutrients and water from the soil. Some organic producers include vegetable crops into their operations due to these species tendency to extract nutrients and water from shallow depths then follow with a cereal that generally feeds to greater soil depths. Species selection is also made on the basis of weed, insect, and disease control. Delate and Hartzler (2003), states that rye has allopathic properties and is often used as a winter cover crop following corn to aid in weed control in preceding soybean or oat crops. Sustainability through the natural preservation of soil fertility is paramount to the organic farmer and makes the selection of species an important part of the operation. Organic crop production makes as much use of natural pest control, including crop rotations, as is possible.
