Soybean Production In Arkansas Chris Tingle Extension Agronomist Soybeans
First planted in the United States in 1765. • Primarily grown as a forage crop. • Around 1910 the benefits of soybean oil & soybean meal were recognized. • Soybean acreage increased throughout the 1920’s and 1930’s, but primarily use was still forage.
Today, soybeans are used for in many items and these uses are growing daily.
In 2003, Arkansas planted 2.9 million acres (ranks 9th nationally). Record yield average: 34 bu/acre (1994 & 2002) In 2003, Soybean production in Arkansas had $545 million.
5.3 to 7 million bushels 4.1 to 4.8 million bushels 2.8 to 3.9 million bushels 1 to 2 million bushels < 1 million bushels In 2003, Arkansas planted 2.9 million acres (ranks 9th nationally). Record yield average: 34 bu/acre (1994 & 2002) In 2003, Soybean production in Arkansas had $545 million.
Approximately 1.74 million acres is produced using some form of irrigation. In 2003, approximately 2.47 million acres were produced using Roundup Ready Technology.
A 45 bu/a soybean crop can remove up to 180 lbs of nitrogen. Soybeans can supply their nitrogen needs through root nodules. These nodules contain soil bacteria (Rhizobium spp.) that allow the use of N2 (80% of the earth’s atmosphere).
Soybeans are photoperiod sensitive plants. Soybeans are recognized as “short-day” plants (i.e. the length of dark period induces a photoperiodic response). Based on a wide range of sensitivity, different maturity groups of soybeans are available. These maturity groups are geographically specific.
Determinate vs. Indeterminate Determinate varieties are generally associated with MG V-IX. These types complete over 80% of vegetative growth prior to bloom. Indeterminate varieties are associated with MG 000-IV. These types will undergo vegetative and reproductive growth simultaneously.
1. Northeast Arkansas (1): Groups IV, V, or VI 2. Southeast Arkansas (2): Groups IV, V, VI, or VII 3. Southwest Arkansas (3): Groups IV, V, VI, or VII 4. Arkansas River Valley (4): Groups IV, V, or VI 5. Northwest Arkansas (5): Groups IV or V
Soybeans are annual plants. -depending on soil temperature/moisture can emerge from 5-12 days -first true leaves are unifoliate
Soybeans develop compound leaves (called trifoliates). -develop a well defined root system
Stage No. Abbreviated Stage Title Description V-E Emergence Cotyledons above the soil surface V-C Cotyledon Unifoliate leaves unrolled sufficiently so the leaf edges are not touching V-1 First-node Fully developed leaves at unifoliate nodes V-2 Second-node Fully developed trifoliate leaf at node above the unifoliate nodes V-3 Third-node Three nodes on the main stem with fully developed leaves beginning with the unifoliate nodes Vn nth-node n number of nodes on the main stem with fully developed leaves beginning with the unifoliate nodes Soybean Vegetative Growth Stage Descriptions
V-3 Three nodes on the main stem with fully developed leaves beginning with the unifoliate nodes
V-6 Six nodes on the main stem with fully developed leaves beginning with the unifoliate nodes
R-1 (Beginning Bloom) One open flower at any node on the main stem
R-2 (Full Bloom) Open flower at one of the two uppermost nodes on the main stem with a fully developed leaf
R-3 (Beginning Pod) Pod 3/16 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf
R-4 (Full Pod) Pod 3/4 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf
R-5 (Beginning Seed) Seed 1/8 inch long in a pod at one of the four uppermost nodes in the main stem with a fully developed leaf
R-6 (Full Seed) Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf
R-7 (Beginning Maturity) One normal pod on the main stem that has reached its mature pod color
R-8 (Full Maturity) 95 percent of the pods have reached their mature pod color; 5-10 days of drying weather are required after R8 before the soybeans have less than 15 percent moisture
Soybean Reproductive Development Time Table *some indeterminate varieties undergo R1 and R2 stages simultaneously
Planting Practices Based on the different maturity groups, soybeans have a wide range of planting dates. In Arkansas we have three different production systems. 1. Early-Season Production System 2. Full-Season Production System 3. Double-Crop Production System
Early-Season Soybean Production System Typically consists of planting indeterminate MG III & IV’s and in some cases determinate MG V’s in April. This type of production system makes up about 25-30% of state’s acreage each year. Recommended planting dates:
Full-Season Soybean Production System This is the state’s largest production system and usually comprises 5-60% of the acreage. Higher yields (usually above 50 bu/a) are often achieved. However, due to increased irrigation expenses, these systems may not always be the most profitable. Recommended planting dates:
Double-Crop Soybean Production System Each year, producers will plant some of their soybeans following wheat. This type of system allows the producer to harvest two crops within a single year. Recommended planting dates:
Row-Spacing Based on the different maturity groups and wide range in planting dates, soybeans can be produced under a variety of row-spacings. Typical row-spacings in Arkansas can range from 7.5” to 38”. Research indicates that higher yields can be achieved with row-spacings less than 20”.
Row-Spacing • The row-spacing used can have a direct impact on soybean height. • Soybeans produced on narrow rows (usually less than 20”) grow taller than those produced on wider rows. • This can be desirable when planting an early maturity group later in the season. • Taller plants may also cause lodging problems with sensitive varieties.
Plant Population Recommended soybean plant populations are based on the type of production system used. Early-Season (irrigated or dryland) 130,000 plants per acre Full-Season/Double-Crop (irrigated) 100,000 plants per acre Full-Season/Double-Crop (dryland) 80,000 plants per acre
Effect of Soybean Population on Yield (3-Year Average)
How To Determine Seeding Rate First we must determine the row width factor. This is a number based on the row spacing used. For example, a producer using a 38” row spacing would do the following: 38”/12”= 3.167 ft Now by using algebra, we can determine what determine how many row-feet are in one acre. 3.167 (x) = 43,560 ft2 (square feet in one acre) Where x = 13,754 ft Now determine how many seed per foot the planter is planting and multiply by 13,754 ft: 15 seed per foot x 13,754 ft = 206,315 seed Now it is doubtful that all seed will survive so by using the general rule that “80 percent of the seed will germinate/emerge and 90% of those emerged will survive” , you can determine the approximate plants per acre. 206,315 seed x 0.80 =165,052 will germinate 165,052 x 0.90 = 148,556 plants per acre
How To Determine Plants per Acre You may from time to time be asked to determine if a soybean stand is adequate for yield. By using some of the same formulas we used earlier, this can be determined. First we must determine the number of plants per acre. This can be accomplished two ways. Usually for wider rows (30-38”), it is easier to determine the number of plants per row feet and calculating the plants per acre. Like the previous problem, let’s assume a producer using the Early-Season Soybean Production System is using a 38” row spacing and has a final plant stand of 9.5 plants per foot. Is the plant stand adequate? Determine how many row feet are in one acre by: 38”/12” = 3.167 ft 3.167 ft (x) = 43,560 ft2 (square feet in one acre) X = 13,754 ft Now multiply the number of plants per foot counted by 13,754 ft 9.5 plants per ft x 13,754 ft = 130,663 plants per acre Yes, the plant stand falls within our recommendations.
How To Determine Plants per Acre The previous method may not be as desirable for narrow rows. In these instances, you will need to determine the number of plants per square foot. These can be easily done with a number of items (PVC square, hula-hoop, etc.) as long as you know or can calculate the square footage the plants lie within. For example, Suppose you have a PVC square that measures 10 ft2, and you count 30 plants per 10 ft2. How many plants per acre is this field? 30 plants per 10 ft2 / 10 = 3 plants per ft2 Then by multiplying 3 plants per ft2 by 43560 ft2 (square feet in acre) you can determine that the plant stand is 130,680 plants per acre. Helpful Formulas and Numbers To remember 43,560 ft2 in one acre Area of circle = 3.142(diameter) Remember to always take multiple measurements in a field and calculate an average.
Helpful Resources Arkansas Soybean Handbook(MP-197) Available on-line at the following web address: http://www.uaex.edu/Other_Areas/publications/HTML/MP197/default.asp -Also available in print and on CD
Soybean Update and SOYVA Computer Program -Variety selection aids updated each year -The Early-Season and Conventional Soybean Update Publications and SOYVA are available on-line at the following web address: http://www.aragriculture.org/cropsoilwtr/soybeans/varietyyields/default.asp -Soybean Updates are also available in print Helpful Resources