Pepper, Gary E.

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ItU.NIVERSITY OFILLINOIS LIBRARYAT URBANA-CHAMPAIGNAGRfCULTUR^Digitized by the Internet Archivein 2011 with funding fromUniversity of Illinois Urbana-Champaignhttp://www.archive.org/details/narrowrowsoybean1161peppCIRCULATING COPYILTURfc UBRARYNarrow-Ro#^d^%eahsWhat to ConsiderG. E. PepperUniversity of Illinois at Urbana-ChampaignCollege of Agriculture • Cooperative Extension ServiceCircular 1161In 1977 nearly half of the soybean producers in Illinois used rows spaced36 inches or wider. Many producers probably sacrificed yields becauseof this wide spacing. According to much research in the Middle West, arow width narrower than 36 inches will probably help to improve soy-bean yields.The term "narrow row" is not associated with any particular width.No single width is ideal, since many factors affect the way soybeans-respond to row space. Moreover, what seems narrow to one producer mayseem wide to another. Thirty inches, for example, may appear narrow toproducers using 38 inches but wide to those using 15 inches.Potential Yield IncreaseThe main reason for planting soybeans in narrow rows is the poten-tial yield increase. The increase is due primarily to the quicker develop-ment of a full canopy in narrow rows and to the reduced competitionbetween plants within the rows.The sooner a canopy develops enough to fully shade the soil andintercept all available sunlight, the earlier in the season the plants mayreach maximum production. As shown in Table 1, soybeans in narrowrows can shade the soil in fewer days than those in wide rows. Table 1also indicates that a relatively high plant density helps to shade the soilsooner. Illinois soybean fields typically have 100,000 to 160,000 plantsper acre.When soybean plants are redistributed in narrow rows, the spacebetween plants in the rows is increased, cutting down competition be-tween plants. Up to a point, reduced competition improves a plant'syield by reducing lodging and increasing the number of pods per plant.Too little competition, however, is not desirable. Pods may form toonear the ground and side branching may increase, so that harvesting ishindered. Competition needs to be great enough to prevent these undesir-able effects.Yield increases will vary from one producer to the next. The amountof increase from narrow rows depends on variety, planting date, andother management practices.Effect of Soybean Variety on Narrow-Row YieldsWe do not yet have a method of predicting how a variety will respondto a reduction of row width. We do know, however, that not all varietieswill respond the same. Variation in response among several varieties isseen in Table 2. Inconsistent yield increases when these varieties aregrown in narrower rows seem to suggest some varietal influence, but thereason for this is not fully understood. Any given variety can also beexpected to have variable responses to narrower rows from year to yearor from one location to another......bC^hL^X^'5One possible exi)lanatiun for differences in response is related tocanopy size. When planted in narrow rows, small-canopied crop plantshave greater yield increases than plants with large canopies. Relativelyearly-maturing soybean varieties generally have smaller canopies thanfull-season varieties. In central Illinois, varieties from maturity groupsI and II should usually be more responsive to narrow rows than varietiesfrom the later maturity groujis III and IV.Table 1. — Days Needed for HawkeyeSoybean Canopy to Shade the Soilaf Various Row Widthsand Plant PopulationsRow width, inchesP'^"^^/^"^^ 10 20 40days26,136 " 81 69 7852,272 63 60 61 78104,544 53 55 57 66209,088 47 49 52 66" The soil was never completelyshaded.Source: R. Shibles and C. Weber,Iowa State University.Table 2. — So/bean Yield Increases Obtained in Several Studiesof Narrow Row Widths\'ariety,maturity groupRow widths,inchesYield increasewith narrowerwidth, pet.LocationCorsoy, II 7 vs. 30Williams, III 7 vs. 30Elf, III 7 vs. 30Williams, III 7 vs. 30Weils, II 7 vs. 34Amsoy 71, II 7 vs. 34Woodworth, III 7 vs. 34Corsoy, II 8 vs. 30Wells, II 8 vs. 30Corsov, II 8 vs. 40Wiihams, III 8 vs. 40Amsov 71, II 15 vs. 38Williams, III 15 vs. 38Kent, IV 15 vs. 38Corsov, II 28 vs. 39Amsoy, II 28 vs. 3913.415.7Urbana, 111.,19763.01.4Urbana, III.,197622.018.03.0West LafayetteInd., 1975-76Elwood, 111.,197615.61.9Hartsburg, 111.,197642.831.0Carbondale,111., 19777.86.3Ames, Iowa,1974In trials at three locations, earlier maturing varieties did generallyrespond more favorably to narrow rows than did those maturing later(Table 2). However, the earlier varieties may not necessarily producethe highest absolute yields on any one farm even when grown in thenarrow row widths.Varieties such as Elf, which have small canopies due to determinategrowth, may respond quite positively to narrow rows. In trials at Urbana,Elf showed a definite yield increase when row width was decreased(Table 3). Williams, a larger canopied variety, had a much smaller yieldincrease.The data for both Williams and Elf also illustrate that the largestyield increases are associated with the first reduction in row width, thatis, from 32 to 20 inches. This suggests that producers currently using36- and 38-inch rows have a very good chance of increasing their yieldsby simply reducing row widths to 30 inches.Narrower rows do not always result in yield increases (Table 2),but neither do they reduce yield if reasonable stands of soybeans areachieved in narrow rows and if the environment for soybean productionis favorable.Rate and Date of SeedingSome producers think they must greatly increase the seeding ratewith narrow row widths. This is a misconception. Even if you doublethe number of rows per acre, doubling the seeding rate is both unneces-sary and undesirable. Remember that plants are redistributed in nar-rower rows and hence are farther apart within the row. For example,the plants are II/2 to 2 inches apart in 30-inch row widths, but 3 to 4inches apart in 15-inch rows. Be prepared, however, to increase plantnumbers if the soybean canopy at your current population does not com-pletely intercept the sunlight relatively early in the season. Yields standa far better chance of improving the sooner the canopy is complete.At 30- to 40-inch row widths, populations of 100,000 to 150,000plants per acre at harvest are usually adequate for top yields from mostvarieties commonly grown in Illinois. Rows spaced 7 to 10 inches apartmight possibly benefit from populations of 150,000 to 175,000 at harvest.Consider the canopy size when choosing the best population for yourfields. Plant short varieties such as Elf at slightly higher populations thantall, full-canopied varieties such as Williams.Yields are usually highest when soybeans are planted in May. If soy-beans follow wheat in a double-crop program, they cannot be seededuntil late June or early July, so yields will be reduced. The amount ofyield reduction can be minimized, however, by planting in narrow rows.Late-planted beans are quite responsive to narrow widths because theydevelop smaller canopies than early-planted beans. The later the plantingTable 3. — Yields of Large- and Table 4. — Effect of Planting DateSmall-Canopied Soybeans at and Row Width onThree Row Widths Soybean YieldsRow Large Smallwidth, canopy canopyinches (Williams) (Elf)bu/A8 52.7 53.720 52.6 53.632 50.8 48.4PlantingdateRow width,inches Yield24 40increaseMay 21. . .May 31. . .June 23. ... 41.0.42.5. 37.0bu/A38.539.031.02.53.56.0Source: J. S. Beaver and R. R. Source : J. Pendleton, R. Bernard,Johnson, University of Illinois. and H. Hadley, ARS-USDA andUniversity of Illinois.date, the greater the response to narrow rows (Table 4). However, thehighest absolute yields usually result from the combination of narrowrows and a May planting date.EquipmentMechanical planting, cultivating, and harvesting of soybeans arestandard practices. But an obvious problem develops when a producerdecides to use a row width too narrow for standard field equipment. Fewrow planters can be adjusted to widths of less than 20 inches. Unitl)]anters can be used on a tool bar and adjusted to relatively narrow rows,but this requires investment in a number of unit planters. Producerswho want to avoid this expense can use a grain drill, if available, as analternative method. The drill should be equipped with a slow-speedmeter drive. Otherwise, the drill meter adjustment will probably restiltin many split soybean seeds. A harrow or other tillage tool should beplaced in front of the drill to eliminate tractor wheel tracks and to levelthe soil (Figure 1). Failure to do this will normally reduce the uni-formity of the stand.Cultivation for weed control is impossible when tractor tires arewider than the row spacing. This problem can be solved by using askip-row planting pattern in which a wider space is left every few rowsto accommodate the tractor tires. Because most of the field is plantedin narrow rcnvs, yield increases can still be obtained when skip rows areused. Figure 2 illustrates a skip-row arrangement using 15-inch rowsand 30-inch tire spaces.In most cases, harvesting narrow-row soybeans with currently avail-able combine headers is relatively free of problems. However, producerswho purchase a row crop header for their combine will have to fit theirrows to the dimensions of the header, that is, to a minimum of 30 inches.Figure 1. Press-wheel drill (top; and end-wheel drill (bottom) in tandemwith packer mulcher. (Photos courtesy of R. Nave, ARS-USDA and Univer-sity of Illinois.)Weed ControlWeed control is helped by the rapidly developing canopy and the con-sequent early shading of the soil in narrow-row soybeans. Althoughshading alone does not give total control, it does help suppress weedgrowth. This suppression, along with proper selection and applicationof herbicides, will improve total weed control.When narrow rows prevent cultivation for weed control, a preplantor preemergence herbicide for grasses is essential. Grasses are often theworst weed problem in soybeans, but to date postemergence herbicidesfor grass control in soybeans are only in the experimental stage. Forbroadleaf control, use preemergence, preplant-incorporated, or post-emergence herbicides. To prevent plant damage from equipment opera-tions, apply postemergence herbicides while the plants are still small.Late application can of course be made aerially.Choose the system that gives the greatest probability of successfulcontrol. For additional protection, plant narrow-row soybeans only infields where you know from past experience that weed problems are15"It—i30" 15"If Jl30"\^ Wide Spacefor Tractor Tires/15"K—iFigure 2. Skip-row pattern with 15- and 30-inch widths for planting narrow-row soybeans. This arrangement allows spaces wide enough to accommodatethe tractor tires for mechanical weed control.manageable. It would be unwise, for example, to plant in a field with ahistory of severe johnsongrass or morningglory problems.With the skip-row method of planting, you can use mechanical cul-tivation, as well as herbicides and shading pressure from the crop, tohelp control weeds. If skip rows are used, then the methods used forweed control are essentiallv the same as those for wider rows.Good Management NecessaryThe recent trend toward growing soybeans in row widths of 30inches or less is backed up by considerable research. Provided that othermanagement i)ractices are adec^uate, the changeover to narrower rowscan i)ossibly increase yields. The narrow row is simply another manage-ment tool to be used after the crop is being well managed in traditional,wider rows. Yield increases are generally greatest for the first reductionin row width; increases become smaller as the width becomes narrower.So with good management, many producers now using 36- to 38-inchwidths will probably have better yields by planting at 30 inches, andwidths of even less than 30 inches may, in some cases, lead to improvedyields.This circular was prepared by G. E. Pepper, Extension agronomist, Univer-sity of Illinois at Urbana-Champaign. The position is funded by the IllinoisSoybean Program Operating Board.Urbana, Illinois August, 1978Issued in furtherance of Cooperative Extension Work, Acts of May 8 ancJ June 30, 1914, incooperation with the U.S. Department of Agriculture. JOHN B. CLAAR, Director, CooperativeExtension Service, University of Illinois at Urbana-Champaign. The Illinois Cooperative Ex-tension Service provides equal opportunities in programs and employment.lOM—7-78—39949—SW''kon^'isf^^-ifi.

Narrow-row soybeans : what to consider / 1161

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