Soybeans
Planting Guidelines for Mississippi

Management of production practices is essential to ensure profitable production of soybeans. Timeliness and management continue to be of utmost importance, and many of these decisions involve no added costs but add significantly to yield and profit potentials.

Tillage

Costs vary, depending on the type of implement used in field preparation and the type tillage system being considered. In general, only enough tillage is needed to control existing weeds. Tillage may be essential to prepare a seedbed, incorporate herbicides, and control weeds, but this depends entirely on your management decisions. Too much tillage can be costly, dry out the soil, damage the soil's physical condition, and delay planting, which could lead to lower yields. Sometimes little or no tillage is required, a practice that works extremely well on the heavy clay soils. Burndown chemicals let you substitute chemical weed control for tillage. Heavier soils are well suited for this practice, and by minimizing tillage, you can better manage these soils.

Seed Selection

Crop production begins with the seed, so there is no substitute for good planting seed. Good seed will produce strong seedlings; they will emerge faster, more uniformly, and grow off quicker than do seed of lesser quality. Good seed ensure seed free from weed seed, varietal mixtures, and other crop seeds. Buying Mississippi Certified Seed is one way to be assured of obtaining seed that meet these criteria.

Most soybean seed will be labeled 80 percent germination unless problems arose during the previous year and quality has been affected. Ordering or buying seed early is a step that helps ensure your chance of getting the highest quality seed available. Even though seed may be labeled 80 percent, Mississippi seed laws allow for tolerances in testing germination. A lot of seed may germinate 95 percent but be labeled only 80 percent. Ask for the actual germ, or conduct your own test to determine actual germination.

A vigor test is another way to determine seed quality. Accelerated aging and tetrazolium tests (TZ) help determine seed quality. Vigor tests tell that seed are alive and how they should perform under stress. The tests can be conducted at most seed labs and are essential if growers are saving seed.

Seed size is not an indication of performance but more of a factor in determining seed rate. Varieties differ in seed size, and yield potential is not related to seed size; recent field research at Mississippi State University has reaffirmed this fact.

Seed Treatment with Fungicides

High-quality soybean seed planted in warm, moist soil generally do not require fungicidal protection. Under good planting conditions, yields will seldom be influenced by fungicides. However, many growers apply a fungicide as insurance against unfavorable seedbed conditions, seed rots, and seedling disease.

Seed treatments are beneficial under several conditions, including (1) when planting seed that germinate below 80 percent, (2) when planting in fields with a history of seedling disease problems, (3) when planting early or late (cooler and warmer soils), and (4) when planting into surface residue or nonrotated fields. Seed treatments can be beneficial if one of these situations exists, but several studies in Mississippi have shown no yield benefit from the use of seed treatments when soybeans are planted under optimum conditions.

In recent years, a shift toward earlier plantings has raised a lot of questions about seed treatments. Current information was developed around optimum plantings; earlier plantings probably could benefit from the use of a seed treatment.

Several fungicides are available for use as seed treatments. Liquid formulations give a more uniform coating, whereas dry powders may be less uniform in coverage and accumulate in the bottom of seed hoppers. Treated seed cannot be used for livestock feed or sold at the oil mill; therefore, avoid pretreatment of large quantities. The biggest question facing producers is what to use. Certain conditions favor different seedling diseases. When and what product to use depends greatly on time of planting, the 5-day weather forecast, and history. Seed treatments are only insurance and under certain conditions are not needed. Consult your county Extension agent, agricultural supplier, and Extension Information Sheet 1167, Soybean Seedling Diseases, for data on current fungicides labeled for seed treatment.

Planting Dates

Before the early 1990's, approximately one-third of the Mississippi soybean crop was planted later than the recommended planting dates. Most years this is too late for best production, but exceptions do exist. Planting behind a receding flood or adequate rainfall late in the season can make later plantings successful. Drought tolerance in soybeans is not available; plantings depend on seasonal rainfall or supplemental water. By planting on time, growers can add significantly to their yields.

Planting dates can be in two categories, optimum and acceptable. The optimum time frame is when the fastest, most uniform emergence will occur. Acceptable dates are broad, and plantings can range from early April to mid-July and be successful. Even though soybeans are photoperiod sensitive, the maturity of a variety is not shifted forward as much due to early planting as if planted late. To spread your risks, vary maturity groups rather than spacing planting dates.

Soybean seed germinate and emerge faster with soil temperatures of 68 to 86 degrees Fahrenheit and 50 to 55 percent seed moisture. Given this fact, good seed-to-soil contact is essential; under these conditions, soybean seedlings should emerge in 5 to 7 days. Soil temperatures of 55 °F allow germination to begin, but emergence will be slow. Once temperatures reach 65 °F, emergence should be fairly rapid.

Early season soybean production has increased in acreage over the last several years due to grower success. The interest in early planting of earlier maturing varieties has really changed the picture regarding soybean plantings. Earlier maturing varieties commonly referred to as Group IV's have allowed growers to increase yields by avoiding late summer weather patterns that are typically hot and dry. Although Group IV's are not drought tolerant, this avoidance is the best option available.

Even though early maturing varieties have increased in popularity, they are not essential. Just using early planting of maturity Group V can improve yield levels as well. Planting date recommendations once encouraged later plantings, but new genetics, temperature requirements for germination, and the potential increase in yields from earlier plantings have shown a need to change from what was once practiced. A real opportunity exists to plant soybeans earlier than is traditional, and given soybeans' abilities to handle weather extremes (cool weather), growers need to capitalize on this option by planting a portion of the soybean crop before cotton. For many growers, this could mean planting an entire soybean crop early.

Most of Mississippi's soybeans are grown on low-lying, poorly drained soils. Drainage is a major concern when planting early on these soils, since they normally will be wet and likely will remain wet just below the surface. Two ways to avoid some of the problems of saturated soil are planting on beds and/or treating seed with fungicides that fight Pythium.

Premature flowering was a concern in the 1970's and 1980's. The MG V and later varieties that were grown then apparently were more photoperiod sensitive than are varieties grown today. About 80 percent of the state's soybean crop is planted to varieties in MG's IV and V. To take full advantage of the increased yield potential from early planting, you should plant these varieties in mid-April. Plantings at this time may take 10 days to 2 weeks to emerge, but evidence shows this longer emergence period does not cancel the effect from the earlier planting.

There is no apparent advantage to planting early maturing varieties earlier than about April 10. However, in the future, growers may move planting dates even earlier if earlier maturing varieties are developed that will provide sufficient vegetative growth. A lot of interest has been expressed about planting full-season varieties early, but planting date information is incomplete. Tests should answer this question, but it appears many of the new varieties are not as photoperiod sensitive as are older varieties. Just taking advantage of timely planting, not necessarily using Group IV's, can contribute to increased yields.

Late planting dates are usually the most damaging to yields. Yield losses are variable, but after mid-June, yields decline rapidly. Potential yield loss of 2 to 2½ percent per day for late planting after June 15 can be expected. Late-planted soybeans have more limited root systems and cannot withstand long periods of drought. Near-ideal rainfall distribution is needed if late plantings are to succeed. Late plantings are also more likely to require insect control. Planting in narrow rows and irrigating can minimize the loss in yield due to late planting.

Because of weather, large acreage, limited equipment, and other management considerations, it may not be possible to plant your entire acreage in the ideal time frame (April 20-May 10). In general, yields will be positively affected by planting earlier than this period vs. the negative effects on yield from planting later. If there is a likelihood you cannot plant the entire crop during the optimum time, it is better to begin planting early rather than risk late planting.

Row Spacing

Soybean varieties adapted to Mississippi can produce high yields over a range of row spacings and plant populations. If you use timely planting and good varieties, no research evidence in Mississippi that shows an advantage for any row spacing (of 30 inches or less). Generally row spacings less than 30 inches will yield more than 38- to 40-inch rows. Soybeans planted in wide rows can be adequately irrigated and can produce yields equivalent to narrow rows. Higher yields are more consistently achieved in narrow rows, with later plantings. If narrowing row spacing is to improve yields, it is more likely to occur when you already use high levels of technology and management. Short-statured early varieties should be planted in rows of 30 inches or less, but tall-growing MG V varieties planted in April will yield the same when planted in wide or narrow rows. Make the final choice of row spacing after considering variety, weed problems, equipment capabilities, comparative costs, and how the system will fit into an overall farm plan.

Wide rows (36 to 40 inches) - These are considered conventional widths and fit with most other row crops grown in Mississippi. This width makes it convenient to interchange equipment for use with other crops. Advantages of wide middles are easy cultivation and easy chemical weed control with directed sprays. Canopy closure is more important in these row spacings and should be achieved soon after final weed control application and/or irrigation initiation. This canopy closure should occur before late-emerging weeds from irrigation or rainfall have a chance to gain access to needed light.

Narrow rows (15 to 30 inches) - These widths are more intermediate spacings preferred by the majority of soybean producers. Advantages over wide rows include quicker shading and more complete ground cover when planting late. There are more rows per acre to compete with weeds compared to wider rows. Advantages of narrow rows over drilled plantings include the use of a planter for planting to allow better control of seeding rates and depth, the ability to cultivate, and the ability to use directed sprays. When planting large acreage over a wide range of planting dates and soil types, narrow rows are a good compromise between wide rows and drills. They allow greater flexibilty.

Drilled planting (6 to 14 inches) - Many growers refer to this as "broadcast planting" or "solid seeding." Advantages of narrow row spacings include rapid ground cover, less total equipment, lower labor requirements, and the ability to plant more efficiently on steeper slopes and in small fields. Some indications of reduced erosion on sloping fields are evident. Late-planted soybeans generally are not reduced in yield as much with narrow rows.

Weed control is the biggest disadvantage of row spacings too narrow to cultivate and/or direct spray herbicides. Herbicide choices are numerous, and all treatments must be broadcast over the top. Lodging may become a bigger problem because of the greater difficulty in controlling seeding rates within desirable limits. Herbicide management becomes much more critical because of rapid canopy closure. The increased costs of herbicides and seed often more than offset cost savings for labor and equipment.

Plant Population and Seeding Rates

Soybean plant populations can vary considerably without affecting final yield. It is best to plant enough seed to ensure your final stand is within a range considered optimum. Suggested plant populations for several row widths are listed in the table at the end of this publication. For a detailed discussion of seeding rates and plant populations, refer to Extension Publication 1194, available at your county Extension office.

Seeding rates can be refined under good planting conditions. Plant based on seeds per foot of row, not pounds per acre. Pay attention to seeding rates, since growers tend to overplant. Using plants per foot of row will help eliminate overplanting when variations in seed size exist. Calibrate planters before planting to ensure actual seeding rate.

Depth of Planting

Soybean seed require relatively high levels of moisture for germination. Soybeans must absorb 50 to 55 percent of their weight to swell and germinate; ironically, this is the same moisture level at which soybean seed are considered physiologically mature. Place the seed in firm, moist soil about 1 to 1½ inches deep in sandy or silty soils up to 2 inches in clay soils. Planting in dry soils and waiting for a rain to bring them up is not advised. It is generally better to delay planting until there is adequate moisture at the desired seeding depth. Double disks or narrow sword openers that allow a minimum of soil disturbance while giving good seed-to-soil contact are preferred. Seeds should be well covered to prevent drying out and to reduce the risk of herbicide injury. Gently firming soil around the seed without excessive packing is important. If soil crusting occurs, a rotary hoe can aid in seedling emergence.

Soybeans can be produced profitably, and a major factor influencing this profitability is attitude. If soybeans were grown on better soils, high yields would be achieved consistently. Although growers do not grow the bulk of soybeans on these soils, they must evaluate each field to determine crop needs and the limiting factors.

Soybeans do not require a high degree of management, but they often can benefit from more than they receive. Variety selection and planting dates are the two most important production inputs you need to address.

Publication 1289
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director