{"id":4073,"date":"2016-11-08T00:00:00","date_gmt":"2016-11-08T05:00:00","guid":{"rendered":"https:\/\/firstascentstaging.com\/iwm2019\/row-spacing\/"},"modified":"2023-08-07T10:28:36","modified_gmt":"2023-08-07T14:28:36","slug":"row-spacing","status":"publish","type":"page","link":"https:\/\/growiwm.org\/row-spacing\/","title":{"rendered":"Row Spacing"},"content":{"rendered":"\n
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Row Spacing<\/h1>\n\t\t\t
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The Importance of<\/strong> Row Spacing<\/span><\/h3>\n<\/div><\/div>
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The manipulation of row spacing is a conceptually simple management tactic that can have a sizable impact on weeds in some crops. Row spacing (along with seeding rate) determines the crop arrangement in a field, altering how fast the crop canopy closes (leaves from adjoining rows begin overlapping) and the ways in which weeds grow between crop rows. Weeds compete with crops for essential resources (sunlight, nutrients, water, and space); if they outcompete the crop this can lead to significant yield loss. Narrow row spacing reduces the time the crop needs to close the canopy, thereby providing rapid shading and decreasing weeds\u2019 competitive abilities and simultaneously decreasing the reliance on herbicides later in the season.<\/p>\n<\/div><\/div>

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What is the Critical Period for Weed Control (CPWC)?<\/span><\/strong><\/h3>\n<\/div><\/div>
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Row spacing and faster canopy closure are important factors for the Critical Period for Weed Control (CPWC). CPWC is the period of time that a crop must be kept weed-free to prevent yield loss. Crops that rapidly develop a dense canopy often have a shorter CPWC. Crops are typically most susceptible to weed competition during their early growth stages. Each crop has a different CPWC which depends on the intrinsic biology of the crop (or even the variety) and environmental factors. <\/p>\n<\/div><\/div>

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Highly competitive weeds that grow rapidly during this period can cause significant yield reduction even at low densities; wide-row spacing exacerbates the problem. For instance, soybean row spacing as wide as 36 inches is common for some parts of the US. With wider rows there is less shading of the ground and weeds densities are often higher; lack of crop shading allows weeds to grow taller and for relatively longer periods of time. Wide rows require additional weed control to compensate for reduced crop competition. <\/p>\n<\/div><\/div>

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Studies have shown that weeds must be managed early and during the CPWC to protect crop yield and decrease the number of seeds the weeds produce at maturity. Weed seed production can replenish the soil seedbank with new seeds, which can be a problem in the following years.<\/p>\n<\/div><\/div>

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Narrow Row Spacing<\/span><\/strong><\/h3>\n<\/div><\/div>
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Reducing row spacing is an effective way to increase the competitiveness of some crops. Though there are exceptions, narrow row spacing generally leads to faster canopy closure, thus increasing weed suppression. Early crop canopy formation blocks sunlight, decreases weed seedling emergence, and suppresses the growth of emerged weed seedlings. The CPWC can be shortened with narrow rows, which may reduce the reliance on herbicides and\/or improve overall weed control.<\/p>\n<\/div><\/div>

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Narrow rows for soybeans have been classified to be 15 inches (or less).  Narrow-rows for annual cereals are typically planted at 7 inches or less.<\/p>\n<\/div><\/div>

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A long-term study in wheat has demonstrated that narrowing row spacing from 6 or 9 inches to 4 inches increased wheat\u2019s competitiveness against goosegrass and gardencress. In narrow rows, both weed species produced less than five seeds per plant 60 days after wheat emergence (versus over 900 seeds per weed plant in wide row treatments). In addition, wheat yield was considerably greater in the narrower row treatments (Fahad 2015).<\/p>\n<\/div><\/div>

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Crop Species is Crucial<\/span><\/strong><\/h3>\n<\/div><\/div>
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A key consideration in choosing the spacing of crop rows is the nature of the crop species. Although research has revealed that narrow row spacing is beneficial for some crops, each crop varies in growth characteristics and CPWC. These physiological\/CPWC differences, along with agronomic practices, dictate the ideal row spacing for each crop. While narrow row spacing can reduce CPWC, it can sometimes reduce yield if plants are spaced too closely together due to competition between the crop plants themselves. There is also evidence that narrow rows may promote disease incidence in susceptible crops. It is therefore important to know the limits of each crop, and space accordingly both between and within rows. <\/p>\n<\/div><\/div>

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Narrow row corn and cotton have not shown to have a consistent benefit for weed control.  While narrow row corn has increased yield in some studies, its effect on weed competition is less clear.  Studies with cotton have shown some benefits for increased competition with weeds; however, production in narrow rows has led to an increase in trash (leaf and stem tissue) in harvested fibers.<\/p>\n<\/div><\/div>

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In-Depth Look: Soybean<\/strong> <\/span><\/h3>\n<\/div><\/div>
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Soybean row spacings of 30- to 36- inches are common in some regions of the country due to prevailing equipment setups and production practices, but planting in narrow rows can improve weed control. Soybean is the grain crop that consistently benefits from narrow row spacing. Its upright growth habit and numerous branches make it well adapted  to narrow row spacing, particularly that of 7.5 inch rows. Studies dating back to 1966 demonstrated row spacing of 10 inches reached 95% sunlight interception 17 days earlier than 30 inch rows; full canopy closure happened 40 days earlier in narrow rows (Shibles and Weber 1966). <\/p>\n<\/div><\/div>

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One of the most troublesome weeds in the eastern US is Palmer amaranth (Amaranthus palmeri<\/em>)  a pigweed species. Palmer amaranth is a highly competitive broadleaf weed, able to grow much faster than most soybean cultivars in warm regions. Worse still, a single plant can produce hundreds of thousands of seeds, thus increasing the size of the soil seedbank in a single season. <\/p>\n<\/div><\/div>

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Research indicates that 7.5-inch row spacing greatly affects Palmer amaranth, in particular, due to early canopy closure which blocks photosynthetic active radiation. In 7.5-inch soybean rows, it was found that Palmer amaranth emergence was decreased by 76% compared to fields with no soybean; while common cocklebur emergence was reduced by 33% (Jha 2017). Other species of pigweeds, common lambsquarters , and other weeds that are often found in soybean fields in the United States are similarly affected by soybean shading.<\/p>\n<\/div><\/div>

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Left to right: Palmer amaranth plants from plots planted with 7, 15, and 30-inch row spacing. Photo credit: Claudio Rubione, University of Delaware.<\/figcaption><\/figure><\/div>\n<\/div><\/div>
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