Soybeans:Guidelines

GUIDELINES: SOYBEAN PRODUCTION

STATISTICS

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OUTLINE OF MANAGEMENT ACTIVITIES

Cultural Practices

_____ Test soil for nutrient status and pH every year. Maintain records of test results and fertilizer applications. _____ Roots will not grow into dry soil and will not survive in excessively wet soils. _____ Through a symbiotic relationship with Rhizobium, soybeans are able to produce most of their own nitrogen. _____ Do not till or plant when soil is too wet. _____ Rotate soybeans with corn, small rains or forages for good control of diseases.

Pesticide Management

_____ Use approved and registered pesticides according to label. _____ Maintain application records including date, location, applicator, target pest, pesticide name, EPA registration number, formulation, rate and number of acres treated are maintained. _____ All sprayers are calibrated at the start of the season. _____ Minimize pesticide drift. _____ Develop and implement a resistance management plan. _____ Select pesticides which will preserve natural enemies of pests. _____ Use separate sprayers for herbicides and insecticides. _____ Check sprayer(s) calibration at least once during the season. _____ Recalibrate each sprayer as needed. _____ Maintain records of planting dates for treated fields. _____ Keep records of stage of crop of treated field. _____ Use water-sensitive spray cards to test coverage of leaf surfaces.

Insect Pest Management

_____ Scout "SUSPECT INSECTS" .. Seedling Pests .. Cutworms .. Darkling Beetle .. Seedcorn Maggot .. Foliage Pests .. Aphids .. Armyworms .. Corn Earworm .. Cucumber Beetles .. Empoasca Leafhoppers .. Leafminers .. Loopers .. Saltmarsh Caterpillar .. Silverleaf Whitefly .. Spider Mites .. Thrips .. Pod Pests .. Lygus Bugs .. Stink Bugs .. Weevils

_____ Keep a scouting record. _____ Identify control measures and implement according to thresholds.

Disease Pest Management

_____ Identify major diseases. _____ Keep a scouting record. _____ Identify control measures and implement according to thresholds.

Weed Pest Management

_____ Scout "SUSPECT WEEDS" .. barnyardgrass (Echinochloa crus-galli) .. bindweed, field (Convolvulus arvensis) .. canarygrasses (Phalaris spp.) .. foxtail, yellow (Setaria pumila) .. goosefoot, nettleleaf (Chenopodium murale) .. groundcherries (Physalis spp.) .. johnsongrass (Sorghum halepense) .. knotweed (Polygonum spp.) .. lambsquarters, common (Chenopodium album) .. lettuce, prickly (Lactuca serriola) .. mallow, little; cheeseweed (Malva parviflora) .. mustards (Brassica spp.) .. nettles (Urtica spp.) .. nightshade, black (Solanum nigrum) .. nightshade, hairy (Solanum sarrachoides) .. nutsedge, yellow (Cyperus esculentus) .. oat, wild (Avena fatua) .. pigweeds (Amaranthus spp.) .. puncturevine (Tribulus terrestris) .. purslane, common (Portulaca oleracea) .. shepherd's-purse (Capsella bursa-pastoris) .. smartweed, water (Polygonum amphibium var. emersum) .. sowthistle (Sonchus spp.) .. thistle, Russian (Salsola tragus) .. tomatillo (Physalis philadephica) .. velvetleaf (Abutilon theophrasti)

_____ Prepare weed maps in mid-to-late season, indicating significant weed species and their location. _____ Use last year's scouting records to begin this year's scouting. _____ Base all herbicide rate, selection and spot or strip sprays on weed survey results. _____ Weeds may be controlled by cultivation, with no herbicide applied. _____ Use reduced rates of herbicide through banding of herbicides and cultivation. _____ Do not use herbicides of the same class on the same field in succeeding years. (Use crop rotation and corresponding herbicide selections.) _____ Prevent weeds within the field, alleys and roadways from going to seed. _____ Use an experimental plot to test different weed management techniques and record the results.

Weather and Crop Monitoring

_____ Monitor weather and crop parameters _____ Keep daily records.

Date: - Min/max temperatures: - Rainfall: - Hours of leaf wetness: - Stage of tree development (by cultivar, weekly):

CROP DEVELOPMENT

The growth and development of soybean plants are very dependant upon the environmental conditions in which they grow. The dry weight within the plant, consisting of everything but water, determines the growth and development. Yields are determined by how the plant interacts with its surroundings. As the environment changes so does the plant's development and the overall yields are determined by these conditions. In order to create the best possible growing environment, the soil must be properly tilled and fertilized, the varieties most suitable for the area must be planted, and weed and insect infestations must be tightly controlled.

Varieties

Soybean varieties are classified by their form and structure, growing habits, and for the requirements necessary to initiate floral or reproductive development. They are also classified into two separate groups: indeterminate and determinate growing habits. The difference between the two varieties is that indeterminate plants continue their vegetative growth after the flowering begins, and determinate varieties do not.

Maturity

For soybean plants to reach maturity, they must be able to effectively use the growing season, which varies from region to region. The time between growth stages, seasons, plant height, number of leaves, planting dates and patterns will all vary according to varieties but the overall development pattern will be the same.

Stages of Development

Soybeans grow in two separate stages labeled the vegetative and reproductive stages. The vegetative stages are those in which the plant is increasing its overall mass and fully developed leaves form. The reproductive stages are those in which the plant flowers and produces pods. The amount of time that plants remain in these stages depends upon the variety. The maturity of leaves often determines the stage in which the plant may be growing. The unifoliolate leaf node is the first from which to begin counting upward to identify upper leaf node numbers and the simple leaves are produced on opposite sides of the stem. All other true leaves formed by the plant are trifoliolate (compound) leaves borne on long petioles, and are produced singularly and alternately on the stem.

(Reference: How a Soybean Plant Develops, Special Report No. 53, Iowa State University)

Vegetative Stages and Development

Germination and Emergence

When the seed is planted, the first thing to emerge is the primary root which bores deep into the soil to anchor itself and the seed to which it is attached. After this occurs, the cotyledonary node extends itself upward pushing through the soil surface and begins to open the cotyledons, exposing the epicotyl. The epicotyl contains most of the growing tissues such as the young leaves, stem, and growing point. Shortly before emergence, lateral roots begin to grow out from the primary root offering more support for the entire plant. The cotyledons hold the necessary nutrient and food reserves for the young plant as it is emerging and for about 7-10 days thereafter. At that time, the plant will rely upon fertilizer to supply the nutrients that it will need for optimal growth. Soybeans should be planted 1-1 1/2 inches below the soil surface, but never deeper than 2 inches. When the seeds are planted too deep, the weak seedlings have a difficult time pushing through the crusted soil and the soil will be cooler preventing good germination rates. Fertilizer should be placed either slightly to the side or below the seeds so that the seedling will have access to the nutrients, but should not be directly below the seed as the fertilizer can burn the young plant. Weeds compete for nutrients, water and sunlight and need to be effectively controlled. Proper tilling, herbicide use, and crop rotations are all effective measures for controlling weeds.

V2 Stage (second node)

When the plants are about 6-8 inches tall and have about three nodes with leaves, the plant's roots will normally become infected with a bacteria called Rhizobium japonicum which forms round or oval growths called nodules on the root surface. The bacteria is extremely important since it is the main source of nitrogen supply to the plant. The bacteria is able to convert non-available nitrogen gas into nitrogen products that the plant can use. Healthy, nitrogen fixing nodules are pink or red on the inside. Nitrogen fertilization is not necessary and will not increase yields. Also, when the plants are about 6-8 inches tall, the lateral roots are growing rapidly and are found about 6 inches below the soil surface making cultivation of weeds a little more complicated. Whatever method of weed control is being used, it should not be too deep as it can disrupt the root system.

V3 and V5 Stages (third and fifth nodes)

As the plants are about 10-12 inches tall and have six nodes with leaves, axillary buds begin to form between the main stem and a leaf petiole. These axillary buds are similar in nature to the main stem growing point and may develop into a flower cluster, pods, or remain inactive. As the auxillary buds begin to develop, the plant takes on a much fuller and bushier appearance and develops flower clusters called racemes. A raceme is a short, stem-like structure that produces flowers and pods along its length. Because the plant has the ability to grow more leaves from the axillary buds, this acts as a great defense to the plant from damages such as hail. The axillary buds also have the ability to grow new branches or produce new flowering clusters in the event that the stem apex is severed or broken.

V6 Stage (sixth node)

Plants that are 12-14 inches tall have reached their final growing phase and have seven nodes with leaves and unfolded leaflets. The cotyledons may have fallen from the plant at this time. The lateral roots are growing very close to the soil surface and all cultivating must be shallow.

Reproductive Stages and Development

There are four parts in the reproductive stages of soybean development. They are flowering, pod development, seed development, and plant maturation. The plant will still continue to produce vegetative growth while the reproductive stages are occurring. Remember, the general timing of all stages will vary amongst the several different soybean varieties.

R1 Stage (beginning bloom)

The first reproductive stage begins when the plants are 15-18 inches tall and 7-10 nodes are fully developed. The flowering begins on the third to sixth node of the main stem and progresses upward and downward. The branches begin flowering a few days later. Flowering on a raceme occurs at the base and extends to the tip. Root growth also increases during this time and secondary roots and root hairs may grow above ground within the top 0-9 inches of soil.

R2 Stage (full bloom)

Plants in the secondary reproductive stage are 17-22 inches tall and will begin to store more total mature dry weight and nutrients. This accumulation initially begins in the leaves, stems, petioles, and roots, but will gradually shift to the pods as seeds. As the plants produce more dry weight, more energy is required, which means that more nodules are being formed on the roots to increase the amount of nitrogen fixation that is taking place to meet all of the plant's requirements. The long lateral roots begin to penetrate deeper into the soil at this time instead of remaining so close to the topsoil levels.

R3 Stage (beginning pod)

Plants in the beginning pod stage are 23-32 inches tall and often show signs of developing pods, withering flowers, open flowers and flower buds all on the same plant at the same time. The pods continue to grow producing more dry weight and are about 3/16 inch long on the uppermost nodes of the main stem. Yield is determined by three separate components, which include the total number of pods per plant, the number of beans produced per pod, and the weight per bean. The environmental conditions in which the plant is growing greatly determines the overall yield potential. Plants that are stressed due to high temperature or moisture deficiency will produce lower yields than those that have grown where these conditions could be controlled. About 60-75% of all soybean flowers do not contribute to the overall yield because they are lost to abortion before the flowers develop into pods or are aborted during the pod stage. Much research is being done to determine how to take full advantage of the plant's potential. At this time, the best alternatives are good fertilization practices, narrow rows, proper planting rates, sufficient irrigation, and good weed control.

R4 Stage (full pod)

When the plant is at the full pod stage, the pods are about 3/4 inch on the main stem and the plant is about 28-39 inches tall. The pod will continue to rapidly grow and begin to produce seeds. Because of this rapid growth, many of the older pods will have reached their length and width and spend the rest of their energy developing seeds. There is no other developmental period when stress on the plant is so harmful to the seed yield.

Stage (beginning seed)

During this stage, the seeds are about 1/8 inch long and the plant is about 30-43 inches tall. The seeds are rapidly growing and redistributing the dry weight and nutrients within the plant to the seeds. Seed yields depend upon the rate of dry weight accumulation in the seeds and the length of time that dry weight accumulates in the seeds. During this time, the need for water and nutrients is great and the plant should not be stressed because of these possible deficiencies.

R6 Stage (full seed)

At this stage, the plants have reached their maximum height at about 31-47 inches tall and the seed or bean fills the pod on the older stems. The growth rate of the beans is still very rapid but the plants rate of dry weight and nutrient accumulation begins to decline. Nearly all the plants energy is being used to fill the pods with dry weight and nutrients. The older leaves on the plant may also begin to turn yellow and begin to fall off the plant. This senescence will continue gradually to the newest leaves on the plant.

R7 Stage (beginning maturity)

During this stage, the oldest pods begin to reach maturity and dry weight ceases to accumulate in the pod. As the seed matures, it loses its green color and appears yellow to brown. The seed also contains about 60% water and has all the necessary plant parts to begin the next generation of soybean plants. As the pods mature, they generally will not abort, but under stressful conditions they may produce small seeds. At this stage, stress does not play as big a factor in the overall yield as it did in earlier stages.

R8 Stage (full maturity)

When the seeds have reached full maturity, they will have lost their green pod color and contain less than 15% moisture. Many plants will have lost their color, but still need 5-10 days of drying weather before they lose their moisture and can be harvested. Harvesting soybeans at the proper time is crucial and ideally should occur when the seeds contain about 13% moisture. If the moisture levels are too high, some yield will be lost to molding; however, if the moisture levels are too low, the seeds may shatter or split, also reducing yields. Plant densities of the plant are also a major consideration to the overall harvest and yield. If the plant density is too thick, lodging occurs and the plants are more difficult to harvest. Plants that are not very dense cause low pod set and branching which is difficult to harvest because the pods are too low and can't be harvested mechanically. Reducing losses can be as simple as driving at a proper speed, and checking concave clearance, cylinder speed, sieves, and air velocity. Be sure reel speed and ground travel are synchronized to minimize sickle-bar shatter loss.

Summary

The growth of soybeans is divided between two stages: the vegetative and reproductive stages. During the vegetative phase, the plant produces mass and the structural development takes place. During the reproductive phase, the plant begins to produce pods and seeds. The plant has the ability to produce its own nitrogen supply through bacteria on the roots called Rhizobium japonicum. As the plant ages and the energy is filling the pods, the plant produces less nitrogen to avoid unnecessary top growth. Root growth is greatly influenced by the environmental conditions in which the seed is planted. The soil must be well prepared and fertilized and the weeds in the area must be controlled to avoid unwanted competition.

GROWTH REQUIREMENTS

There are three different growth stages that occur with soybeans, which include preflowering, flowering, and podset. Preflowering is when the seedling is trying to emerge and grow enough to anchor itself into the soil to add stability to the plant to support the other growth stages. It is largely dependent upon depth of planting, soil moisture and temperature conditions. The flowering stage is initiated by day length. This stage lasts for about 2-3 weeks and occurs about 6-8 weeks after the plant emerges. Shortly after flowering, the dry weight of the seeds begins to increase and accumulates for about 3-4 weeks. Nutrient uptake also occurs as the seeds are accumulating dry weight. At maturity, the seeds contain approximately 75% of the nitrogen and phosphorus and about 60% of the potassium that is taken up by the plant.

Climate and Soil Requirements

As with other crops, soybeans require proper fertilization and climatic conditions to produce satisfactory yields. However, because soybeans have the ability to produce nitrogen through nodules, they can out perform other crops if unfavorable climatic and soil conditions are present.

Nutrient Requirements and Uptake by Plants

Soybeans require all major and minor nutrients associated with plants; however, the most important are nitrogen, phosphorus, and potassium. The plants produce enough nitrogen through nitrogen fixation to sustain the plant, but will need additional applications of phosphorus and potassium. A soil test will determine the amount necessary and when to apply or reapply all minerals. Environmental conditions will also affect how well nutrients are absorbed. The soil must be moist so that the nutrients can move up into the plant through the roots, but too much water inhibits growth and can damage roots. Late in the reproductive season, plants will not be affected by additional fertilizer treatments, so it is essential that they are properly fertilized throughout the growing season, otherwise yields will be small.

FERTILIZATION

The amount of nutrients needed for proper growth and development are often not available to the plant and need to be added to the soil, usually through fertilizers. However, it should not be implied that the plant will use all of the nutrients added to the soil. It is not necessary to add nitrogen to the soil because the nitrogen is fixed through the nodules on the roots. The soil should be properly prepared to encourage the desired bacteria to grow. Most soils will need to have phosphorous and potassium added to the soil because not enough is available to support the plants. Often lime will need to be added depending on the soil pH. A soil test should be taken to determine if other micronutrients are deficient and the rates at which they need to be applied.

Economics of Soybean Fertilization

Direct fertilization is probably the single most factor that will increase yields from an economic standpoint. Fertilizer increases the nutrient supplying capabilities and consistently increases net returns per acre. Other factors include selecting higher yielding varieties and changing cultural practices such as narrow rows.

Soil Requirements

Soybeans are heavy users of nitrogen, potassium, and phosphorus. They will use more than twice the fertilizer that corn will use. Soybeans are especially sensitive to potassium deficiency, so the soil must have potassium that can be available to the plant. This is probably because soybeans have shallower, less extensive root systems.

Potassium and Phosphorus

Applications of potassium fertilizer offer the most consistent increases of soybean yield and profit of all the nutrients applied. Soybeans that have an adequate potassium supply are less susceptible to soybean cyst nematode, pod and stem blight, gray moldy-seed, and purple-stain. Phosphorus fertilizer also increases the overall yield and profit, but not at the same rate as potassium. Phosphorus applications can reduce the amount of diseased and shriveled seed which will increase the overall yield profit. Both of these nutrients perform better when applied together as opposed to applied separately.

Nitrogen Fertilizer

There is not enough research to indicate that applying additional rates of nitrogen fertilizer will increase the yield of the plant. In most circumstances, the root nodules will be able to fix the appropriate amount of nitrogen for the plant. But, if the soil has not properly been prepared to encourage the Rhizobium japonicum bacteria, then nitrogen fertilizer is the only other option.

Conclusion

Most research indicates that soybeans perform best if they have been directly fertilized using a complete N-P-K fertilizer rather than applications of P or K.

CULTURAL PRACTICES

The following is a list of common cultural practices which will increase the success of the soybean crop. Have the soil tested and follow all fertilizer and/or lime recommendations, do not till or plant when the soil is too wet, plant in the recommended time period for the area and select varieties of seed that are adaptable to the area, plant in narrower rows, do not over or underplant the rows (about 10 seeds per foot in 40-inch rows, 8 seeds in 30-inch rows, 6 seeds in 20-inch rows, and 3-4 seeds per foot in rows less than 10 inches apart), do not plant too deep (1-1 1/2 inches is optimum), control all pest problems, and harvest at the appropriate time to avoid any additional losses.

ROTATION

Rotating the crops is very beneficial to soybeans. This is one of the best ways to control pathogens that infect the plants because it deprives them of a host plant to carry over between soybean crops. Soybeans perform best when on a rotation program with corn, small grains, or forages.

VARIETY SELECTION

Selecting varieties that are most adaptable to the area is extremely important in achieving high yields. Also, select varieties that are resistant to Phytophthora root rot and nematodes, if they are a problem in the area.

Common soybean seeds (H. F. Schwartz; Colorado State University)

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Edamame soybean seeds (H. F. Schwartz; Colorado State University)

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SEED QUALITY

Using good quality seed will increase the overall yield. Make sure that the germination rates are high and use seed treatments to protect them from soil-borne diseases and insects that attack seedlings.

TILLAGE

Avoid working in the soil when the conditions are too wet and avoid making too many trips through the field. The soil needs to be as light as airy as possible and not compacted. Shallow tillage is adequate to incorporate pre-plant herbicides into the soil and does not stir or compact the soil too much.

PLANTING

Planting Date

It is extremely important that the seeds are planted around the optimal date of planting because the overall yield will significantly decline if they are planted too late. This date will depend upon the plants growing habits, its maturity rate, and field conditions.

Planting Depth

It is recommended that seeds be planted about 1-1 1/2 inches below the soil and not any deeper. This ensures that the seeds can push through the soil surface and achieve a high rate of germination.

Inoculation

Inoculation is generally not necessary unless soybeans are new to the field. If so, use a slurry inoculant for soybeans right before planting.

Row Width

Research indicates that soybeans perform best when planted in narrower rows, especially varieties that are indeterminate.

Fertility

Soybeans perform best when properly fertilized and the soil conditions are right. Most plants do best when the soil pH is at least 6.0; soils with a lower pH often suffer from manganese and molybdenum deficiencies. Manganese can be applied either as a spray or in a band in the soil. Molybdenum can be applied in a seed treater.

Weed Control

Controlling weeds is extremely important because they compete with the soybeans for water, nutrients, sunlight, and space. When they are not controlled, there will be an overall yield decrease.

Summary

To have a successful crop it is essential to consider all production factors and incorporate them into the decisions that will effect the crop. Good crop management will lower unit cost of production and increase profits.