Planting Practices
No one set of planting practices is best suited for all situations. Each location, year and set of growing conditions will alter planting recommendations. Planting date, planting depth, inoculation, seeding rate and row width must all be adjusted for specific conditions and taken into consideration for other production practices.

Planting Date
Planting on time is necessary to obtain enough plant growth and development for good yields. If planting is delayed beyond the optimum date, yields are reduced. Likewise, planting too early can reduce yields because of poor stands caused by cool soil temperatures or because day lengths are too short, causing plants to flower early and have reduced vegetative growth. Generally, however, planting soybeans too early will not be a problem in Kentucky because low soil temperatures will prevent early plantings.
The main factor governing initial planting dates in Kentucky is soil temperature. Although soybean germination can occur at 55°F, it will be slow and emergence will require almost 3 weeks, too long for the seed and seedling to remain in the soil. It is best to plant soybeans after the soil temperature has reached a minimum of 65°F or above, which will permit rapid germination and emergence within 7 days. Soil temperatures of 65°F at planting depth are normally reached by May 1 in the western half of the state and by May 10-15 as you proceed to the eastern and more northern portions of the state.
The optimum planting period in Kentucky occurs from early May to mid-June (June 10-15). Several planting date studies conducted in Kentucky over several years, show a 1 1/2%/day yield loss (1/2-1 bu/acre depending on yield level) can be expected when planting is delayed past June 10-15 (Figure 1). If plantings are made beyond mid June, a mid- to full-season variety for a given area should be used since the plants will produce more vegetative growth and have the potential for higher yield. However, if plantings are delayed beyond the first part of July, an earlier maturing variety should be used to ensure that the crop matures before a freeze occurs.
Although maturity dates are affected by planting date, there will not be an equal relationship between differences in planting date and those in maturity for a given variety. In general, a 3 day delay in planting brings only a one day delay in maturity. At later planting dates, a 5 day delay in planting equals about a one day delay in maturity. Thus, if your goal is to stagger harvest maturity dates, selecting varieties with different maturities will be more satisfactory than staggering planting dates. Remember, maturity date is governed more by variety because the soybean is photoperiod (day length) sensitive.

Planting Depth
Planting depth can greatly influence soybeans' ability to emerge and establish a uniform stand. Ideal planting depth depends on soil texture and moisture. Plant the seed deep enough to be in moist soil but no deeper than necessary. Planting soybeans too deep is a frequent cause of poor stands. The ideal planting depth for best emergence is 1 to 11/2 inches under most conditions.
Avoid planting deeper than 2 inches if possible because at deeper levels emergence is delayed, seedling vigor is reduced, and it is harder for a soybean seedling to break through a crust that may have formed. Varieties also differ in their ability to emerge from greater depths. As a result, although all soybeans emerge slowly when planted deep, the ability to emerge successfully differs among varieties.
Soil type will also influence soybeans' ability to emerge from deep plantings. Heavy rains can cause hard crusts to form on fine-textured, heavy soils. When this happens, it is harder for deep planted soybeans to break the crust. In such cases, the seedlings may completely deplete the food stored in their cotyledons before they emerge and eventually die. The most severe damage resulting from a soil crust is the breaking of the hypocotyl arch during emergence, resulting in a reduced stand. When crusts develop, rotary hoeing may help emergence.
Various conditions can dictate slightly different planting depth recommendations.

•Sandier soils are often droughty and not susceptible to crusting, so soybeans can be planted slightly deeper (2 inches) for good emergence.
•Heavier soils which often crust should have soybeans planted shallower (1 to 1 1/2 inches).
•Soybeans should also be planted shallow (about 1 inch) when planted into cool, moist soils early in the growing season.
•If soils are dry, producers tend to plant deeper so that the seed will be in moist soil. However, delaying planting is better, if not too late. Wait for moisture rather than planting deep.
•With certain herbicides, planting as deep as recommended by the manufacturer may be necessary to reduce possible crop injury.

Inoculation
The soybean plant is a legume and capable of supplying nitrogen for its growth through a symbiotic nitrogen fixation process with certain bacteria (rhizobia) in the soil. These bacteria form nodules on soybean roots and extract nitrogen from the air for the plant to use. If soybean plants are well-nodulated with effective nitrogen-fixing bacteria, this condition will supply the soybean's nitrogen requirement and no additional nitrogen as a fertilizer will be needed. Thus, it is very important that the soybean plant have effective nodulation for good nitrogen fixation. The safest way to ensure good nodulation is to inoculate the soybean seed with the proper bacteria. Only Brady rhizobium japonicum has been shown to effectively nodulate and fix nitrogen with soybeans.
Many different kinds and brands of inoculant are available to the grower. The oldest type and most commonly used is the peat-based material which is applied to the seed before planting. In recent years, oil-based inoculants have become commercially available as well as granular-type inoculants, which are soil applied in the row at planting. Choice of inoculant should be based on cost, ease of application and planting equipment.
There are several methods of applying the inoculant to the seed. Thorough mixing of the rhizobia inoculant with the seeds in the manner recommended by the manufacturer is important. Methods include slightly wetting the seeds, applying the inoculant in a dry form on the seeds, or use of a sticking agent.
Remember that inoculants contain live organisms and should be handled carefully to retain their viability. Keep them in a cool, dry place until use. Over-exposure to sunlight, excessive heat or drying will impair or destroy the bacteria's effectiveness, so inoculate the seed just before planting to retain viability. Rhizobia's viability on unplanted seeds is only a few hours. Further, since the bacteria do not survive indefinitely in the inoculant package, use fresh supplies. Most companies put an expiration date on the label.
Fungicides and molybdenum can impair the rhizobia bacteria's viability. Therefore, it is not advisable to use inoculants that were pre-mixed with molybdenum or fungicides. If a fungicide and/or molybdenum is needed, purchase and apply them separately to the seed before inoculation. To ensure the bacteria's viability, seed having been inoculated and treated separately with molybdenum and/or fungicides should be planted immediately and not stored for more than a few hours.
Soybean rhizobia are not native to the soils of the U.S. and were most likely introduced through use of commercial inoculants. When soybean nodules decay, the rhizobia are released to the soil where some remain viable for a number of years. These "naturalized bacteria" living in the soil are as capable of infecting soybean roots as those provided in inoculants. In fact, most nodules of soybeans that are grown in fields with a recent soybean history arise from naturalized rhizobia, even though the seed may have been inoculated.
Should soybean seed be inoculated every year since most soils contain naturalized rhizobia? Although yields are not always increased, many growers routinely inoculate their seed as a good, inexpensive practice to ensure that efficient nitrogen-fixing bacteria are present.

Be sure to inoculate soybean seed to be planted under the following conditions:
•on new soybean land,
•on land where soybeans have not been grown in the past 3 to 5 years,
•on land where previously grown soybeans had poor nodulation.

Seeding Rates
Use soybean seeding rates that will result in optimum yield and favorable plant characteristics for the expected field environment. This statement implies that seeding rates (or plant populations) can vary and that several factors need to be considered in choosing a seeding rate (or final plant population). One of these considerations is the soybean plant's tremendous ability to compensate for variations in populations. Soybean yields are not seriously affected by variations in populations caused by having slightly more or fewer plants per acre than what may be considered optimum. In fact, stand reductions of as much as 50% could occur without significant yield reductions if the remaining stand were uniformly distributed.
However, excessively high or low seeding rates can cause problems for which the soybean plant cannot compensate and result in decreased yields. With high plant populations, yields may decrease because of increased lodging, plant competition and stress. With thin stands, yield losses may come from harvest losses due to low podding and branching and inadequate competition against weeds.
Soybean seeding rates should be based primarily on row width and seed size. Germination, soil conditions and specific situations should also be considered in determining the desired final stand.
In general, as row width decreases, the optimum seeding rate increases, for several reasons. First, in wide rows (30-40 inches), plants are more closely spaced within the row. Any increase in population would bring potential for more plant stress and lodging. As rows narrow, however, plants become more evenly distributed within the row and slightly higher populations can be supported without lodging and yield loss. Higher seeding rates are also recommended as row width decreases to compensate for potentially lower emergence rates, to provide insurance against irregular stands and to ensure a uniform canopy to aid in weed control.
Higher seeding rates for narrow rows, however, does not imply excessive seeding rates. Plants in narrow rows will also lodge, particularly in years of abundant rainfall and excessive vegetative growth, if seeding rate recommendations for these row spacing are exceeded. Narrow row populations above 200,000 plants/acre are considered too high for most varieties and situations.
Seed size is very important in determining the seeding rate since varieties vary widely in number of seeds per pound. A pounds-per-acre seeding rate for one variety may be incorrect for another. For example, planting 40 lb/acre of small seed (3600 seeds/lb) would be the equivalent of 60 lb/acre of larger seed (2400 seeds/lb) to achieve the same seeding rate (seeds/acre). Therefore, to recommend an overall seeding rate in lb/acre is impractical because of seed size differences. The only practical and sound guide that can be used is seeds per foot of row. With this approach, similar seeding rates are achieved, regardless of seed size, and problems due to over population or thin stands are avoided. However, if seed size and row spacing are known, the pounds of seed required per acre can be determined for a recommended number of seeds/ft of row.
Table 1 gives a soybean seeding guide. After selecting the seed size for your variety or seedlot and the row spacing you want, you can find the pounds of seed per acre to achieve the recommended number of seeds/ft of row. Example: A variety with a seed size of 2600 seeds/lb planted in 30 inch rows at 10 seeds/ft requires a seeding rate of 67 lb/acre. The lowest seeding rate for a given row spacing in Table 1 can be used to obtain adequate stands under good planting conditions (good seed bed conditions, adequate moisture or warm soil). Whereas, the highest seeding rate should be used for less than ideal conditions (poor seedbed conditions, dry or cool soil).
The average seed size of various varieties can be found in the Kentucky Soybean Performance Test Progress Report. These sizes can be used as a starting point. Remember, seed size can vary among seed lots, even for the same variety. Varieties can also vary in seed size from year to year depending on environmental conditions during growth and also screening procedures used during cleaning. Seed size information may be available on the seed bag or tag.

Table 1. Soybean Seeding Guide.

Seeds/Lb	Row Spacing (Inches)
	7		15		20		30		36
	Seeding Rate (Seeds/Ft of Row)
	2	3	5	6	6	8	8	10	9	11
	Lb of Seed/Acre
2000	80	110	85	105	78	104	70	87	65	80
2200	73	100	77	95	71	95	64	79	59	72
2400	66	93	71	88	65	87	58	73	54	66
2600	61	86	65	81	60	80	54	67	50	61
2800	57	80	61	75	56	75	50	62	46	56
3000	53	75	57	70	52	70	46	58	43	53
3200	50	70	53	66	49	65	44	54	41	49
3400	47	66	50	62	46	61	41	51	38	46
3600	44	62	47	58	44	58	39	48	36	44
3800	42	59	45	55	41	55	37	46	34	42
4000	40	56	43	53	39	52	35	44	33	40
4200	38	53	40	50	37	49	33	41	31	38
4400	36	51	39	48	35	47	32	40	30	36
Expected plants/ ft of row*	1.6-2.4		4.0-4.8		4.8-6.4		6.4-8.0		7.2-8.8
Expected plants/ acre*	119,000-179,000		139,000-167,000		125,000-167,000		111,000-139,000		104,000-128,000

*Assumes 80% emergence of planted seed, based on high quality seed and average to good conditions for establishment.

If seed size is unknown, a grower can determine seed size by the following method:
•Count out four 500-seed samples.
•Weigh each of the samples.
•Average the weight of the 4 samples.
•Divide 500 by the average weight.
•The result is number of seeds/lb.

Assume the following example:
1)500 seed sample weights = 0.18, 0.21, 0.19, and 0.18 lb. (if weighed in grams, 1 lb = 453.6 gms).
2)Average weight of the 4 samples = 0.19 lb.
3)500 seeds divided by 0.19 lb. = 2630 seeds/lb.

When a seeding rate has been determined from the guide in Table 1, adjust it for seed germination that is 85% or below. Multiply the seeding rate determined from Table 1 by the appropriate germination correction factor listed below to get the adjusted seeding rate.

SEEDGERMINATION
GERMINATION (%)CORRECTION FACTOR
851.2
801.3
751.4
701.5

Assume the following example:
1)Seeding situation:
--seed size = 2600 seeds/lb
--row spacing = 20 inches
--desired seeding rate -- 6 seeds/ft of row
--seed germination = 75%
2)Determine the seeding rate from Table 1 = 60 lb/acre.
3)Adjust the seeding rate for a seed germination of 75%: 60 lb/acre X 1.4 (correction factor) = 84 lb/acre.

*Therefore, an adjusted seeding rate of 84 lb/acre is needed to achieve 6 viable seeds/ft of row with a seed germination of 75%.

The germination correction factors listed above could also be used to directly calculate an adjusted seeding rate for seeds/ft of row rather than lb/acre.

Example:
1)Desired seeding rate = 6 seed/ft of row.
2)Adjust seeding rate for seed germination of 75%: 6 seeds/ft of row X 1.4 (correction factor)= 8.4 seeds/ft of row.

*Therefore, an adjusted seeding rate of 8-9 seeds/ft of row is needed to achieve 6 viable seeds/ft of row with a seed germination of 75%.

Planting too many seeds is probably more common than planting too few. Suggested seeding rates are designed to provide a higher seeding rate than what may be actually needed for a final plant stand to allow for potential seed or seedling losses.
Seeding rates lower than those suggested in Table 1 can be used, but remember that when aiming for top yields, you cannot afford to take a chance on having inadequate stands resulting from lower seeding rates. Too many factors can affect the final stand if you do not use a "buffer" rate. You can reduce seed costs by planting the lowest population needed for optimum yields; however, this practice can produce inadequate final stands if poor seed germination and vigor, seedling diseases, herbicide injury, insects, hail damage, cultivation, rotary hoeing and other pest problems result in additional losses. Further, thin stands do not compete adequately against weeds. Table 1 gives the recommended seeding rate for average conditions and allows tolerance for some of the problems just mentioned. If you reduce seeding rates, use only very high quality seed.
Since the seeding guide in Table 1 is based on average conditions, specific situations may need additional adjustments in seeding rate:
1)Increase seeding rate per acre by:
--10% for very early or very late planting
--10% for no-till
--10% for rough seedbeds
--10% for short season or thin line varieties
--25% for semi-dwarf varieties
--50% for broadcast seeding
--10% for soils that crust badly.
2)Decrease seeding rate per acre by:
--10% if lodging has been a problem
--5% if under ideal conditions
--5% if using high quality seed (90% or higher germination).

Recommended seeding rates only provide a starting point. Base actual seeding rates on experience and seeding conditions. Make seeding rate adjustments, if necessary, until desired stands are achieved for specific field conditions and previous stand problems have been alleviated, but only as long as yields are improved and not decreased.
Surveys indicate that most planters seed at rates different than those indicated by the charts that are provided by manufactures. Therefore, the most satisfactory method for obtaining a desired seeding rate is by "trial and error." Set the planter at a suggested setting, make actual seed counts over a measured distance and adjust if the rate is too high or low for the desired seed drop. Recheck the seeding rate whenever the variety, seed size or planting speed is changed.

Replanting
Soybean stands can be damaged or reduced by poor emergence, crusting, herbicide injury, hail, insects and diseases. However, soybeans also have a remarkable ability to adapt and compensate for damage and stand loss during vegetative stages of growth. The soybean plant has axillary buds at the lower nodes which are capable of developing into pod bearing branches if the need arises. These axillary buds are recovery sites if the terminal growing point is damaged and are also means of filling in for missing plants in thin stands. The plant compensates by producing more branches per plant, more pods per branch and/or more pods on the main stem.
When thin stands of soybeans occur because of poor emergence or plant damage early in the growing season, the grower must decide whether to keep the remaining stand or replant in the hope of a better stand and yield. When most of the stand is lost, replanting is realistic if the remainder of the growing season is adequate for soybeans to mature. However, when only parts of a stand are lost the decision whether to replant is more difficult.
When a stand loss occurs, first count the number of viable plants remaining. Figure 2 shows a generalized yield response of soybeans to a stand reduction. If more than 50% of the stand remains, replanting is probably not economical.
Of course, uniformity of the remaining stand will also affect the amount of yield reduction when 30-50% of the plants have been lost. If the stand is reduced as much as 50% of optimum, but the remaining stand is uniformly spaced, yield loss is usually not significant. Thus, recommended populations have a built-in safety factor.
However, when the remaining stand is not uniformly spaced (i.e. gaps occur in the row), yield reductions can occur. The yield loss from nonuniform stands is generally negligible unless the skips are large (2 ft or more) and they occur at less than 2/3 of normal stand. When less than 50% of the expected stand (Table 1 ) remains and replanting can be done before June 15, replanting is probably economical. Note that about 3-4 plants/ft of row in 30-inch rows equals a 50% stand. If replanting occurs after mid-June, you must also consider the inherent yield loss associated with late plantings (Figure 1). Also, you have no guarantee that replanted stands will be any better.
When deciding whether to replant, consider the cost of replanting (tillage, equipment, labor, seed and additional herbicide if needed) and balance it against the yield penalty for the existing stand loss. To make the final decision on whether to replant compare estimated yield from the present surviving stand against the estimated yield on the date of replanting plus the adjustment for the cost of replanting.

Row Spacing
In Kentucky the optimum row spacing is not the same for all situations. The most productive row width varies according to location, weed control practices, variety, planting date, production potential and environment.
Recent research from other states has shown a yield advantage for narrow row full-season soybeans (20 inch row spacings or less). Narrow rows seem to have a greater and more consistent yield advantage in the north but the advantage tends to decrease as you move south. These results can largely be explained by differences in growing season, varieties used (growth types), environment and planting date. Thus, Kentucky may be a transitional area for a consistent yield response to narrow row soybeans.
There are both pros and cons to narrow row soybeans. Factors favoring narrow rows are better light interception because of quicker canopy closure, higher pod height for more efficient harvesting, less lodging because plants are more uniformly spaced, suppression of late season weed germination and growth because of earlier canopy closure, surface moisture conservation because of earlier canopy closure, and a decrease in soil erosion because of more uniform plant distribution and earlier canopy cover which reduces rainfall impact. Negative factors include unsatisfactory control of troublesome weeds because cultivation is virtually eliminated, difficulty of obtaining uniform stands, additional equipment that may not have interchangeable use with other crops, and inconsistency of yield response.
Before 1970, row spacings of less than 30 inches had not shown a yield advantage in Kentucky for a full-season soybean crop. However, because of production technology improvements and development of higher yielding varieties, some of which were developed specifically for narrow rows, soybean row spacings have been reevaluated in Kentucky. This research indicates that planting date has an influence on the degree and consistency of response achieved with narrow rows. Therefore, to fully evaluate row spacing's effect on Kentucky soybean production, its effects on a full-season crop planted at optimum dates needs to be discussed differently from effects on double-cropped or late planted soybeans.
Full-season soybean crop--Recent research has shown that yield increases with narrow rows for a full-season soybean crop are possible in Kentucky (Table 2), mostly because of newer varieties with higher yield potentials and higher yield environments. The response to narrow rows for a full-season crop is still inconsistent as seen from Table 2 and ranges from a 0-32% yield increase. An obvious factor related to narrow row yield response is the yield environment potential. Small or non-existent responses exist at low yield levels, whereas the biggest responses occur in high yield environments (Table 2). Also, where large yield responses do exist, the biggest increase occurs when row spacing is narrowed to 20 inches or less with additional, smaller increases occurring as row spacing narrows to 10 inches or less (solid seeding). There seems to be no distinct yield advantage for solid seedings over 15-20 inch rows unless high yields are achieved.
The low yield environments of 1980 and 1983 (Table 2) resulted from limited rainfall during the growing season. Research has shown that soybeans in narrow rows use more water during vegetative growth period because of higher populations and more equidistant plant spacings. Thus, environments where water is limiting would be more detrimental to narrow row soybeans. In fact, any environmental condition which restricts the soybean plant's ability to respond, such as weed pressure, drought, low fertility or lodging tends to reduce or even eliminate the potential yield increase available with narrow rows.

Table 2. Response of Full-Season Soybean Crops to Narrow Rows.

Row Spacing (Inches)	Soybean Yield (Bushels/Acre)*
	1977	1978	1979	1980	1981	1982	1981-82	1983
8-10	54	44	70	24	43	40	66	18
16-19	50	45	64	26	44	40	--	20
30-33	41	44	54	23	41	36	54	22

*Data for each year has been averaged over varieties and/or locations.
All plantings occurred before June 8.

Not all soybean varieties respond in the same way to narrow rows, but in most years with most varieties, row widths of less than 30 inches will maximize yields. In general, varieties of mid-season or earlier maturity with a high yield potential, lodging resistance and narrow, compact canopies will respond more favorably to narrow rows, whereas tall growing, late maturing, large canopy types usually do not. Since the critical time for high light interception begins with the onset of flowering, the rule of thumb recommendation is that row width should be narrow enough to provide a closed canopy by time of flowering.
Narrow rows are a possible method for increasing yields, but other practices need to be at an optimum. Less than optimum practices may explain the failure to get consistent yield responses from narrow rows. If a grower is producing average or below average yields, other management inputs such as fertility, seeding rate, weed control, soil type or variety are probably limiting production and need to be improved or corrected before narrow rows are tried.
The following practices and/or situations are more likely to produce positive results when narrow rows are used for a full-season soybean crop:
1)A high-yield environment (yield potential above 40 bu/acre).
2)A high-yielding variety.
3)Semi-dwarf or short statured varieties (lodging resistant).
4)Narrow-line varieties or growth habit that do not permit canopy closure in wide rows by the time of flowering.

Late-planted Soybeans--Row width response changes considerably when soybeans are double-cropped or planted late. Research in Kentucky (Table 3) has shown that yields are increased by using narrow rows when soybeans are planted after the last optimum planting date (mid-June). As opposed to a full-season soybean crop, these yield increases for late-planted soybeans have occurred consistently across all varieties and yield environments (high and low yields). These results imply that plantings near mid-June or later, particularly with double-cropping, should be made in rows spaced 20 inches apart or less for highest yields. When soybeans are planted late, there is less vegetative growth associated with the shorter growing season, and as a result, soybeans will usually not produce a full canopy in wide rows before flowering. For this reason, and also to aid in weed suppression, row width should be reduced for late planted soybeans.

Table 3. Response of Late Planted Soybeans to Narrow Rows.

Row Spacing (Inches)	Soybean Yield (Bushels/Acre)*
	1971	1972-74	1976	1983
8-10	--	38	20	--
16-20	61	35	18	41
30-32	56	28	12	--
38-40	50	--	--	26

*Data for each year has been averaged over varieties. All plantings occurred after mid-June.

Successful narrow row soybean production depends on several factors, including:
•an adequate, uniform stand,
•productive varieties,
•effective weed control.

A uniform stand is important to achieve a full canopy and help suppress late season weed development. A smooth seedbed, whether conventional or no-till, is particularly critical if a drill is used. Most drills do not control planting depth and seeding rate as accurately as conventional unit planters. Depth control is important to achieve proper seed placement and avoid differences in seeding depth among units. Higher seeding rates are generally recommended in narrow rows, particularly solid seedings (10 inches or less), to compensate for potentially lower emergence and to provide insurance against irregular stands. Reduced emergence can result from: 1) less precise seed placement, and 2) the more widely spaced seeds being unable to break through the soil under serious crusting conditions.
Maximum yields in narrow rows are usually produced by varieties that also have high yields in wide rows. Possible exceptions are the semi-dwarf varieties which were developed specifically for narrow rows. Lodging resistance is also an important trait.
Early season weed control is important until the soybean canopy develops. Narrow rows are not recommended where weeds cannot be satisfactorily controlled with herbicides because it is difficult to cultivate narrow rows, particularly solid seedings. If weeds are not controlled, they may more than negate possible yield increases resulting from narrow rows. For certain weeds not easily controlled by present herbicides, row width should be determined by the width of equipment necessary for cultivation. Although weed control is a major constraint, recent improvements in herbicides have made growing narrow row soybeans more feasible. Weed control is essential before the canopy develops so that the canopy's shading effects can help suppress later weed development.
Some growers hesitate to adopt narrow rows because plants may be damaged by equipment needed for post-emergence spraying operations. However, solid seeded soybeans can be run over as late as growth stage V4 to V6 (30-40 days after planting) without an adverse effect on yield (Table 4). Although yields were lower in the run-over (damaged) rows, plants in adjacent rows compensated by producing higher yields.
Another available option is to use skip-row planting patterns so that you can use equipment without damaging soybeans. Skip-row systems usually consist of sets of 3 to 5 rows, 15 to 20 inches apart and bordered by a 30 inch wide middle to accomodate equipment tires. Soybeans in skip-row patterns usually produce yields comparable to those in uniform 15 or 20 inch rows (see Table 5). When using a skip-row system, any equipment should be able to accomodate the same number of rows and width of area or multiples of them.
The decision to switch to narrow rows will vary with different growers and will depend on:

•economic justification of new equipment or modification of present equipment,
•how the change would fit other crops on which equipment is used,
•level of weed infestation and control capabilities,
•present yield level and yield response expected,
•ability to do critical management practices on time.

Table 4. Effect of Run-over Time on Soybean Yields, Lexington, KY., 1980-81.

Plant Growth Stage When Run-over	Soybean Yield (Bu/Acre)
Check (not run over)	48.5
V2	48.2
V4	48.5
V2 plus V4	48.5
V6	49.4

Soybean row spacing was 9 1/2 inches.
 

Table 5. Effect of Skip-rows and Uniform Planting Pattern on Soybean Yields in Kentucky, 1980-81.

Variety1	Planting Pattern2	Yield (Bu/Acre)
Elf	Skip-row	48.5
	Uniform	46.8
Union	Skip-row	47.2
	Uniform	46.7

¹Union = indeterminate variety, Group IV.
Elf = determinate, semidwarf variety, Group III.
²Skip-row = alternating pattern of three 15" rows and a 30" skip.
Uniform = 15" rows.

Double-Cropping
Double-cropping (producing and harvesting 2 crops from the same land area in the same year) is an accepted practice in Kentucky. With soybeans, planting after small grains is the most popular double-cropping system. Most of the double-cropped soybeans in Kentucky are planted following wheat with a limited acreage planted following barley. A Kentucky Crop and Livestock Reporting Service survey found that 38% and 21% of Kentucky's total soybean acreage was double-cropped in 1983 and 1986, respectively. Double-cropping allows intensive use of land resources, spreads fixed or ownership costs, allows production and price risks to be spread over 2 crops and offers the possibility of increasing annual returns from the same crop acreage.
However, double-cropping is not always successful or economically profitable because it increases the risk of low soybean yields due to late plantings. Thus, it is important for soybean yield potential to be maintained or yield losses minimized for double-cropping to be profitable.

The following are key production and management techniques for improving the chances of success with double-cropped soybeans.

Timeliness
Timeliness is probably the single most important factor in determining double-crop soybean yields. The small grain crop must be harvested as soon as possible and the soybean crop planted immediately. Soybean planting date studies in Kentucky have shown an average yield loss of 1 1/2%/day for plantings made after June 10-15 (Figure 1). Normally wheat is harvested in Kentucky from mid June to early July. Thus, most double-cropped soybeans are planted after the date for optimum yields. However, several options are available to help plant soybeans earlier and minimize yield losses.
•Grow barley as the small grain--Barley, particularly the Barsoy variety, can be harvested 8 to 14 days earlier than wheat. If you grow barley, you can plant your soybeans before mid June without any yield loss (Table 6). Disease problems, winterkill and lack of cash markets have led to a decline in barley acreage during the last 10 years. If these problems are overcome, barley could be a prominent and profitable part of soybean double-cropping systems.
•Use of earlier maturing wheat varieties--Some wheat varieties are 4 to 6 days earlier in maturity than most of the varieties commonly being grown. Using them would allow soybeans to be planted a few days earlier. However, earlier wheat varieties may yield less than most of the other varieties and also are more subject to damage from late spring freezes.

Table 6. Effect of Cropping Systems on Soybean Yields. Princeton, Ky., 1972-75.

Soybean Cropping System	Planting Date1	---Soybean Yield2----
		Bu/Acre	%
Single-crop	May 21	51.3	100
Double-crop after barley	June 6	50.7	99
Double-crop after wheat	June 24	42.5	83

¹Four-year average, 1972-75.
²Average of two soybean varieties.

•Using wheat for hay or silage--Although most of the wheat crop is harvested for grain, cutting it as a silage or hay crop would permit soybeans to be planted before mid June. This alternative would be viable for grain producers with livestock.
•Direct combining of high moisture wheat--For farmers with drying facilities, wheat can be direct harvested with present-day equipment at moistures up to 20-25%. This procedure would improve the harvest date for wheat by 4 to 5 days. The minimal drying costs at this time of year should be easily made up in lessened risk and improved soybean yields.
•Swathing wheat--This relatively new practice in Kentucky has received considerable interest. With this method, the wheat is cut and swathed with a windrower at moistures as high as 40 to 42% without any loss in wheat yield. Above 42% m.c. the wheat is not physiologically mature and yields will be reduced if cut too early. When the swathed wheat has dried to a normal harvest moisture content, it is then harvested from the windrow using a combine with a pick-up attachment. Studies at the University of Kentucky (Table 7) found that swathing advanced wheat harvest, depending on the weather, from as few as 4 days and under good drying conditions to as many as 10 days. Soybeans were planted earlier as a result of swathing wheat and resulted in increased yields (Table 8).
Use of a side-delivery swather has the further advantage, as opposed to a center-delivery swather, of allowing soybeans to be planted immediately behind the swather. Thus, with this swathing procedure, soybeans are planted even earlier. The number of days gained in planting compared to using a center-delivery swather is equal to the length of time it takes for wheat to dry in the windrow. Regardless of weather conditions, by using a side-delivery swather and getting soybeans planted immediately, the soybean planting date is not determined by how fast wheat dries in the windrow.

Swathing may not be for every farmer. Each farmer needs to consider the economics of wheat swathing in relation to the equipment investment (swather and pick-up attachment), amount of wheat acreage involved and the potential for increased yields due to earlier soybean planting.

Table 7. Effect of Swathing Wheat on Advancing Wheat Harvest (Days Saved) Compared to Direct Combining (Check)¹

Location	Time Saved (Days)2
	1974	1975	1976
Lexington, Ky.	10	4	6
Purchase Area	9	4	4

¹Wheat was swathed at 41% moisture content.
²Determined from the time interval between the date the swathed wheat and the date the standing wheat (check) dried to less than 15% moisture content.
 

Table 8. Wheat Swathing and Soybean Double-Cropping Study, Princeton, Ky., 1975-77¹

Treatment2	Small Grains		Soybeans
	Days Saved3	Yield (Bu/acre)	Planting Date	% Yield4
Barley   (Soybean Check)	--	80	6-2	100
Swath 1   (above 45% m.c.)	8	42	6-9	102
Swath 2   (below 42% m.c.)	6	54	6-9	99
High Moisture   Direct Cut (18-25% m.c.)	4	51	6-12	92
Wheat Check   Direct Cut (13-15% m.c.)	0	51	6-21	80

¹All data averaged over a 3-year period (1975-77).
²Wheat moisture contents at cutting for swath 1 ranged from 48-52% and for swath 2 from 33-40%.
³Determined from the time interval between the date the swathed wheat and the date the standing wheat (check) first dried to less than 15% moisture content.
⁴% yield compared to planting made after barley.

•Interseeding soybeans in standing wheat--Two methods of interseeding are available:
--aerial seed soybeans into standing wheat before harvest,
--plant soybeans with either a drill or planter directly into the wheat before harvest.

However, interseeding is presently considered a high risk alternative in Kentucky because of problems with effective weed control; obtaining adequate stands, particularly with aerial seeding; and wheat damage from planting equipment. Current research in other states indicates that interseeding has potential if necessary management techniques are developed.

No-Tillage
Four out of every five acres of double-cropped soybeans were planted with no-tillage methods in 1986 according to a Kentucky Crop and Livestock Reporting Service Survey. No-till planting saves time and labor. Soybeans can be planted immediately behind the combine; thus saving one to two or more days that would have been used in land preparation with conventional tillage. No-till planting also conserves soil moisture which would be lost through tillage operations in preparing a seedbed. No-till soybeans have yielded as well or better than conventionally planted soybeans in double-crop tillage studies in Kentucky (Table 9). In these studies all tillage systems were planted on the same date to minimize planting date effects. However, the earlier planting date potential for no-till would favor an additional yield advantage.

Table 9. Yield Comparisons of Soybean Double-Crop Tillage Systems, Princeton.

Tillage System1	Soybean Yield (Bu/Ac)
	1976-78	1980-85
No-till	35	27
Minimum-till	35	26
Conventional	33	24

¹Planted following wheat harvested for grain.

Straw management is also important for no-tillage double-cropping. Using a straw chopper and/or spreader on the combine is recommended. Uneven distribution or bunching of the straw interferes with no-till planting and also reduces the effectiveness of herbicides being applied.
Refer to Cooperative Extension publication AGR-101, No-till Soybeans for further information on no-till soybean production.

Variety Selection
A good rule of thumb is to plant the latest maturity soybean variety that can safely mature before frost. This is generally a mid to full-season variety for a given area. Such varieties will give the most vegetative growth, height, canopy closure, weed suppression and yield. Early varieties for a given production area tend to be short, produce an incomplete canopy and are lower yielding. However, when planting extremely late (after the early part of July), the danger of a killing frost to a full-season variety, makes it necessary to use a variety that is earlier in maturity.

Row Spacing
Because of the shorter growing season and less vegetative growth achieved with double-crop soybeans, narrow the rows to at least 20 inches or narrower to whatever the planting equipment will allow. Not only will narrow rows increase yields of double-cropped soybeans, but the quicker canopy closure will help control weeds. Narrow rows have brought a consistent 3 to 7 bu/acre yield increase in Kentucky for plantings made after June 10th (Table 3).

Stand Establishment
Proper seeding rate is very important for double-crop soybeans. A uniform stand is necessary in late plantings to achieve a full canopy because of shorter plant height and less vegetative growth. Because of the risk of inadequate stands, poor weed control and lower yields, reduced seeding rates are not recommended for double-cropping. Seeding rates for various row spacings are given in Table 1.
Since emergence will tend to be lower for no-till plantings than in a well-prepared seedbed, increase seeding rates by 10% to ensure a satisfactory stand. Seeding rates should also be increased 10% for very late plantings(after late June).
Prompt germination and emergence is a matter of correct seed placement and soil moisture availability. Soybean seed should be planted 1 to 1 1/2 inches deep depending on soil moisture conditions. If the soil is too dry to support germination and emergence, wait until conditions improve to avoid poor stands and replanting.
The planter should have proper coulters to cut through the straw, seed openers for proper seed placement, and press wheels for firming soil around the seed for good, uniform stands in no-till.

Weed Control
One of the major reasons for unsuccessful double-cropping is poor weed control. Successful weed control in a double-cropping program begins with a good, uniform stand of small grain to help suppress weeds. It also involves knowing the potential weed problems in a field so that you can select proper residual herbicides.
A non-selective herbicide will also be needed in a no-till system to control existing vegetation. Proper pressure and volume depend on the vegetation present and the herbicides being used. Post-emergence herbicides may be needed later in the season to control escaped weeds.
For the latest herbicide recommendations, refer to Cooperative Extension publication, AGR-6, Chemical Control of Weeds in Kentucky Farm Crops, available from your county Extension office.

Fertilization
The best way to determine the fertilizer needed for small grains and soybeans in a double-cropping system is to have the soil tested. With double-cropping, 2 crops are being grown and harvested so nutrient needs are intensified. A soil pH of 6.2 to 6.8 and medium to high soil test levels for phosphorus and potassium are recommended for optimum growth and yield. Recent double-crop fertility research at the University of Kentucky indicates that the most efficient and economical way to manage fertilizer in a grain double-cropping system is to apply phosphate according to small grains recommendations and potash according to soybean recommendations. Adding together the phosphate and potash recommendations for each crop is not necessary or economical. For the latest soil test recommendations, see Cooperative Extension publication, AGR-1, Lime and Fertilizer Recommendations, available from your county Extension office.
Once you determine fertility needs, apply the phosphate and potash needed for both the small grain and soybean crops in the fall when seeding the small grain. Fall fertilization is practical since it avoids applying fertilizer during the soybean planting period when timeliness of planting is critical for optimum soybean yields.
There is less margin for error on the soybean production side of double-cropping. Soybean yields must be maximized if double-cropping is to be successful. Timeliness of operations is a key factor because of the increased demands for time, labor and equipment.

Suggested References and Related Publications
University of Kentucky Publications
1) AGR-1, Lime and Fertilizer Recommendations
2) AGR-6, Chemical Control of Weeds in Kentucky Farm Crops
3) AGR-80, Inoculation of Soybeans
4) AGR-101, No-Till Soybeans
5) AGR-111, Soybean Varieties
6) AGR-128, Soybean Production in Kentucky-Part I: Status, Uses and Planning
7) AGR-129, Soybean Production in Kentucky-Part II: Seed Selection, Variety Selection and Fertilization
8) AGR-131, Soybean Production in Kentucky-Part IV: Weed, Disease and Insect Control
9) AGR-132, Soybean Production in Kentucky-Part V: Harvesting, Drying, Storage and Marketing
10) 4B B-04PO, Kentucky 4-H Soybean Project
11) Kentucky Soybean Performance Tests (Annual Progress Report)

Other Publications
1) Modern Soybean Production (Available from American Soybean Association, St. Louis, MO) (For sale only)