Volume 11, Issue 1 - February 2021

David Moseley, Stephenson, Daniel O., Foster, Matthew, Parvej, Md Rasel, Towles, Tyler, Harrison, Stephen A., Brown, Sebe, Padgett, Guy B., Tubana, Brenda S., Dodla, Syam, Conger, Stacia

Louisiana Crops Newsletter Plain Banner.

Calling All Irrigators! An Open Survey on Flood Irrigation Practices

Stacia L. Davis Conger, LSU AgCenter scientist, and Saleh Taghvaeian, Oklahoma State University scientist

We are asking for your help!

Flood irrigation plays an important role in supplying food, feed, and fiber demands in the US, but has received much less attention in recent decades compared to sprinkler and drip irrigation methods. According to the most recent data, 91% of Louisiana’s irrigated acreage falls into the category of surface irrigation.

In effort to assess and prioritize the research needs of our producers, a NASS-style survey was designed about flood (a.k.a. surface or gravity) irrigated croplands, including those under furrows, borders, or basins. Information from this survey will be used to guide researchers, extension specialists, and county agents and advisors at land-grant universities in designing and developing their future educational and outreach projects to better serve farmers on water management in flood irrigation systems.

This survey does NOT ask or record any private or personal identifier information. NO individual response will be shared. All responses will remain anonymous. Summaries of responses will be shared through extension events and outreach venues, such as university field days, workshops, social media, crop schools, and various other events in the near future. The survey is 21 questions in length and will take an estimated 15 minutes to complete. You may choose to discontinue participation at any time.

To participate, please access this survey.

We appreciate your willingness to participate in this timely research. Please direct all questions, comments, and concerns to Dr. Conger at sdavis@agcenter.lsu.edu or (904) 891-1103.

Freeze Injury on Wheat

Boyd Padgett and Steve Harrison, LSU AgCenter Scientist

The impact of freezing temperatures (24oF) on wheat varies dramatically depending on the growth stage the crop is in when it occurs (Table 1). Temperatures are projected to dip into the teens and 20s in central and north Louisiana for several days beginning February 11th. Fortunately, wheat is very tolerant to freezing temperatures (12oF) prior to jointing (F6) since the growing point is still below ground. Freezing temperatures on pre-jointing wheat may result in leaf injury only but this is superficial, and the plants should resume normal development (Figures 1-4). However, damage can be severe beginning at jointing depending on the temperature and duration of the freeze event.

Most oat varieties are less tolerant of cold weather than wheat and there is substantial variation among oat varieties for degree of cold tolerance. Oat varieties will sustain more leaf injury than wheat in general. However, oat varieties still in juvenile growth stages (similar to wheat) with growing points below the soil surface should be protected. Where leaves are significantly damaged by cold the plants should survive and regrow with no significant impact on yield. If oats are growing upright with nodes visible above ground, these tillers may be killed. It is still pretty early in the crop cycle and those varieties have time to put up secondary tillers and recover.

Growers should wait about a week after the freeze event to assess potential damage in order for damaged tissue to become discolored and wilted.

For more information on freezing temperatures on wheat and oats contact your local county agent or specialist.

Table 1 is taken from Kansas State publication C-646

Similar information can be found at this Agrilife publication.

A good explanation of wheat growth stages can be found at University of Kentucky publication called Identifying Wheat Growth Stages.

Table 1. Injury Symptoms of Wheat Resulting from Freezing Temperatures

Growth Stage

Approximate injurious temperature (two hours)

Primary Symptoms

Yield Effect

Tillering

12 F (-11 C)/

Leaf chlorosis; burning of leaf tips; silage odor; blue cast to field

Slight to Moderate

Jointing

24 F (-4 C)

Death of growing point; leaf yellowing or burning; lesions, splitting, or bending of lower stem; odor

Moderate to severe

Boot

28 F (-2 C)

Floret sterility; head trapped in boot;
damage to lower stem; leaf discoloration;
odor

Moderate to severe

Heading

30 F (-1 C)

Floret sterility; white awns or white heads;
damage to lower stems; leaf discoloration

Severe

Flowering

30 F (-1 C)

Floret sterility; white awns or white heads;
damage to lower stems; leaf discoloration

Severe

Milk

28 F (-2 C)

White awns or white heads; damage to lower stems; leaf discoloration;
shrunken, roughened, or discolored kernels

Moderate to severe

Dough

28 F (-2 C)

Shriveled, discolored kernels; poor germination

Slight to moderate


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Figure 1. Tip burn on wheat seven days after below freezing temperatures (about 20 F).

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Figure 2. Tip burn on wheat seven days after below freezing temperature (about 20 F).

Freeze_injury_Fig_3jpgFigure 3. Freeze injury (silvery colored streaks) on wheat seven days after below freezing temperatures.

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Figure 4. Freeze injury (silvery colored streaks) on wheat seven days after below freezing temperatures.

Wheat Fertilization

Boyd Padgett, and Steve Harrison, LSU AgCenter scientist

Nitrogen (N) fertilization of wheat can be a challenging aspect of production. Total N application should normally range from 90 to 120 pounds per acre, but this will vary depending on the previous crop, soil type and rainfall after application(s). Timing N application depends on several factors. The wheat crop needs adequate N in the fall and early winter to establish ground cover and properly tiller; however, excessive levels of fall N can result in rank growth which increases lodging potential, as well as a higher risk to spring freeze damage due to early heading. If the wheat crop is following soybeans, soil residual or mineralizable N should be adequate for fall growth, and no pre-plant N is needed. However, if the wheat crop follows corn, sorghum, rice or cotton, the application of 15 to 20 pounds of N per acre would typically be beneficial. Where the wheat crop is planted later than the optimum date, additional N may be necessary to ensure adequate fall growth prior to winter conditions. If the wheat crop did not receive a fall application and appears to be suffering from N deficiency in January, the initial topdress N application can be made early to promote additional tillering. Early spring is when the majority of N for the wheat crop should be applied. There is no universal rule on how early spring N should be applied. Each field should be evaluated based on tillering, stage of development, environmental conditions and crop color. A crop that has good growth and good color should not need N fertilization prior to erect leaf sheath (Feekes 5), usually sometime in early to mid-February. However, first spring fertilizer application should be applied prior to first node (Feekes 6) to ensure optimum head development, tiller retention and head size. Crop N stress around jointing (Feekes 6) will result in yield loss. Any additional N applied following flag leaf typically contributes very little to crop yield. Splitting topdress N into two or three applications is common in Louisiana production systems due to the increased risk of N losses often associated with heavy rainfall and our long growing season. Splitting N typically occurs by applying fertilizer N at or just prior to jointing with a second application occurring 14 to 28 days later. About 50 percent of the topdress N is normally applied with the first split, but this may be decreased if the first split is put out early and plants are not well enough developed to take up that much N.

Phosphorus, K, and micronutrients should be applied in the fall based on soil test reports. All fertilizers applied as well as lime should be incorporated into the soil prior to planting. Required lime should be applied pre-plant because it takes time for the lime to begin to neutralize the acidity of most soils. The application of sulfur is a growing concern in Louisiana production systems, with increasing deficiencies appearing every year. Early spring sulfur (S) deficiency is sometimes mistaken for N deficiency and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall will not be adequate. Supplemental applications of S with the first spring N applications are often warranted.

Managing weeds in corn

Daniel Stephenson, LSU AgCenter Extension Weed Scientist

Managing weeds in corn can be divided into three phases, preplant, in-crop, and post-harvest, but I’ll save the post-harvest phase until later in the year. Preplant is otherwise known as burndown. We suggested applying a burndown herbicide 4 to 6 weeks prior to planting. Typically, glyphosate at 1 to 1.25 lb ae/A is the first component with either 2,4-D at 0.5 to 1 lb ae/A and/or dicamba 0.25 to 0.38 lb ae/A in a tank-mix. Sometimes LeadOff or Valor are included to provide some residual control. Regardless of what you apply, fields need to be completely weed free prior to planting corn. Emerging corn is sensitive to weed competition; therefore, corn yield can be lost if fields are not weed-free.

If glyphosate-resistant Italian ryegrass is an issue, clethodim cannot be applied within 30 days of planting…which, based on history, we are within 30 days of planting. Therefore, to manage glyphosate-resistant Italian ryegrass, your only option is paraquat at 0.75 to 1 lb ai/A tank-mixed with atrazine at 0.5 lb ai/A followed by another paraquat application at the same rate 10-14 days later. If glyphosate-resistant Italian ryegrass is still alive after corn has emerged, little to no herbicide options are available to help.

Corn planting date influences when you should apply a herbicide treatment. If corn is planted late February through the first two weeks of March, herbicides can be applied either preemergence behind the planter or postemergence before 12-inch tall corn. If corn is planted during the last two weeks of March or later, then a two-pass program, preemergence followed by a postemergence application, is needed. The choice of herbicide applied is not that difficult. Based on data, weed control following a tank-mix glyphosate, atrazine, and Dual Magnum is like many higher priced treatments. The only caveat is if morningglory is known to be a problem. Then, products that contain mesotrione, Halex GT for example, are the better choice. My research just does not justify spending a significant amount of money for early-season weed control in corn.

Please call your local county agents if you need assistance. Also, my number is 318-308-7225 and my email is dstephenson@agcenter.lsu.edu.Good luck.

Tips for Successful Corn Establishment

By Matt Foster, LSU AgCenter Corn Specialist

With corn planting just around the corner, many factors should be taken into consideration before deciding to plant. Early planting is a key component of successful corn production; however, a rapid and uniform stand is critical in achieving a productive crop. Even though corn seedlings are extremely vigorous, they can be affected by adverse conditions. Therefore, it is very important to plant when conditions are favorable.

Three factors that can influence corn establishment are soil temperature, soil moisture, and planting depth.

Soil Temperature and Moisture

Soil temperature is the main factor influencing seedling growth rate. Cool soils (below 50 degrees Fahrenheit) can impede germination and seedling growth. Good germination and emergence can be expected once the soil temperature at a 2-inch depth reaches 55 degrees Fahrenheit by 9 a.m. for three consecutive days. This normally occurs in late February and March in Louisiana. In most years, the planting window for south Louisiana is Feb. 25 to March 20. For north Louisiana, it is generally March 10 to April 1.

Adequate and uniform soil moisture is needed in the seed zone for proper corn establishment. Adequate moisture is usually defined as soil that is not too dry and not too wet. Excess soil saturation can kill corn seedlings, limit aeration, and hinder root development. Uneven soil moisture in the seed zone can lead to uneven seedling emergence and is generally a result of different soil types, tillage patterns, and inconsistent seeding depth. Closely monitoring soil temperature and moisture prior to planting will help ensure a healthy corn stand.

Planting Depth

Typical planting depth recommendations are 1.5 to 2.5 inches. However, optimal depth can be slightly adjusted based on soil type and moisture conditions. Corn should never be planted less than 1.5 inches deep, as this can lead to root development issues (Figure 1) and increased susceptibility to herbicide and insect injury. Deep planting can expose seed to cooler and wetter soils and delay emergence, thus leading to stand issues. Planting corn at a target depth of 2 inches is recommended because this ensures proper seed-to-soil contact and strong nodal root development.

Good seed-to-soil contact promotes uniform and rapid imbibition of water and leads to even emergence. Successful stand establishment is dependent on a good nodal root system. The first set of nodal roots are usually visible by the V2 leaf stage and are dominant by the V6 leaf stage. The nodal roots are a vital structural component of the plant and are responsible for the majority of nutrient and water uptake. A well-developed nodal root system helps reduce early season lodging and rootless corn syndrome. Fine tuning your planting depth will help optimize your emergence and stand.

Best of luck during the upcoming planting season.

Foster_Fig_1_corn_nodal_root_systempng

Figure 1. Corn plant with a strong nodal root system (left) and a corn plant without nodal root development (right). The plant on the left was planted 2 inches deep and the plant on the right was planted 1 inch deep. LSU AgCenter Photo

Early Season Corn Insect Considerations

Sebe Brown and Tyler Towles, LSU AgCenter Entomologists (adapted from Leonard and Baldwin 2008)

Pre-Plant Pest Management Decisions

Burndown herbicides typically are applied 30-45 days prior to planting the crops. Complete control of all weed species within in the field and on the surrounding field borders is necessary to eliminate alternate host plants of insect pests. Fields should be scouted at the time of planting to ensure the seedbeds are essentially weed-free. The presence of heavy plant residue following burndown applications or any green vegetation on the seedbeds can create a favorable environment for arthropod pests. Incomplete termination of some weed species provides a refuge for insect pests until crop seedlings become available. Even at planting, a herbicide application or modified tillage treatment may be warranted to ensure a clean seedbed and remove alternate hosts of arthropod pests.

In addition, heavy residue from previous crops (corn, sorghum, and soybean) covers the soil surface and mediates soil temperature and moisture levels. This, in turn, increases the probability of insect pests such as corn earworm, corn borers, or stink bugs successfully over-wintering in those fields. Identifying these problems early provides producers with the information necessary to modify their insecticide use strategies at the time of planting.

At-planting and surface-applied insecticide applications should be used to manage cutworms if winter vegetation was not terminated well in advance of planting, if incomplete kill of winter weeds occurred, if any freshly emerged vegetation is observed on the seedbeds at the time of planting, or if cutworms are observed in high numbers on plants in the field or along field borders. The most common insecticides used for this application includes any pyrethroid. The lowest application rates have proven to be effective preventative treatments when applied properly. Producers should apply a broadcast treatment or in a wide band over the seed furrow. Cutworms exist below the soil surface feeding on root tissue and may not be exposed to the insecticide if only part of the seedbed is treated.

At-Planting Pest Management Decisions

Soil insecticides such as Counter 15G, Lorsban 15G, and Aztec 2.1G were the standard insecticide treatments applied either in the seed furrow or at-planting to control seed and seedling pests in corn. However, Gaucho 600FS, Cruiser 5FS and Poncho 600FS have become standard as seed treatments have replaced granular and liquid soil-applied insecticides on considerable acreage. Regardless of the product(s) used, an at-planting insecticide treatment is essential for optimal seedling development. Producers should not reduce seeding rates below recommended levels when using at-planting insecticide treatments. Lower than optimal plant populations cannot consistently tolerate injury from seedling insect pests and recover to produce maximum yields.

Post-Emergence and Reactive Pest Management Decisions

Generally, corn seed treatments, at existing rates, will exhibit enough residual efficacy for corn seedlings to develop beyond the susceptible stages to many above/below ground insect pests. However, when soil temperature is below 55ºF delayed germination and uneven emergence can increase the susceptibility of corn seedlings to arthropod pests. For producers using herbicide-tolerant crops, the co-application of foliar insecticides with post-emergence herbicides are a cost-effective practice when controlling above ground pests. However, there are no rescue treatments for below ground insect injury and seedling protection is critical when planting corn in sub-optimal conditions.

As conservation tillage systems continue to evolve, IPM strategies will need to adapt to address emerging pest issues. Pest managers and producers should scout fields and identify those situations that may result in pest problems. These fields should be considered “high risk” and managed with preventative pest management methods. An effective IPM strategy for field corn pests should include weed-free seedbeds well in advance of planting, optimal application dates and rates of cultural practices, and discriminate use of preventative and reactive chemical control strategies for pest problems.

Most of the extension IPM recommendations do not recognize general differences in insect management recommendations between conventional and conservation tillage systems. However, to improve the overall success of insect pest management in conservation tillage systems, crop advisors and producers should timely apply broad-spectrum herbicide treatments to control winter vegetation not only within the field but also on field borders. Many of these insect pests are highly mobile and crop advisors should scout field borders and adjacent fields to observe potential refuges for these pests. Fields should be scouted regularly during the season and treated only as needed based on insect density and changes in plant development. Agronomic practices that enhance rapid seed germination and promote seedling growth should be used to reduce that period of time that plants are susceptible to insect pests. Chemical control strategies are effective against field corn insect pests, but the application method, product rate, and treatment timing must be adjusted for the requirements of each individual field. Seed treatments and soil applied insecticides are critical inputs in conservation tillage systems for field corn. Crop advisors and producers should recognize the potential for unidentified pest problems, intensify scouting practices, and use all available resources to make an informed decision on the appropriate management strategy.

Southern row crop producers have incorporated significant changes in field corn production systems to decrease input costs and improve profits. These changes can significantly influence arthropod pest diversity and density as well as overall pest status. Conservation tillage systems or components of those systems have widespread acceptance among producers. However, several of those practices including reduced tillage and winter cover crops have also been demonstrated to increase problems with some insect pests. There are numerous insect pests are capable of injuring field corn annually across the Southern Region, but only a select few are directly affected by a change in tillage systems. Most of these are associated with seed germination and seedling development. There are, however, other pests that can be indirectly affected by conservation tillage production systems and occur as problems later in crop development. These indirect effects are the result of production systems that influence changes in the landscape across an entire farm or farm region. Fortunately, the impacts of insect pest problems have been minimized with the tools, technologies, and production practices that are now available. The purpose of this report is to identify some common insect pest problems associated with conservation tillage systems for field corn and propose general IPM strategies to address those problems.

The following table summarizes field corn pest problems common to the MidSouth. The ranges of these effects are highly variable and depend on the environment of the local landscape and the production practices applied to individual fields.

Table 1.Common Pest Problems in Mid-South Field Corn

Insect

Effecta

Description of Problems

Southern Corn Rootworm

0 to +++

Fields to be planted to corn that contain winter weeds such as henbit is attractive to adults that lay eggs in the soil. The larvae hatch and feed on corn seeds and roots.Timely vegetation management can reduce the impact of these pests.

Seed Corn Maggot

0 to +++

Adults prefer to lay eggs on fields with decaying crop residue. Wet soil conditions and cool temperatures can slow seedling development and make plants more susceptible to injury

Beetles

0 to +

Wireworm and carrot beetle larvae as well as sugarcane beetle adults may be serious pests of seedlings in fields with heavy crop and winter vegetation residue.

Cutworms

+ to +++

Cutworms can overwinter in no-tillage fields.The adults of some species prefer to lay eggs in fields with dense weeds, winter cover crops, or heavy crop residue. As pre-plant vegetation is destroyed, larvae feed on crop seedlings to survive.

Slugs

0 to +++

Winter vegetation and crop residues in wet soil conditions favor slug populations and seedling injury.

Chinch Bug

+ to +++

Plant residue provides a favorable habitat for these insects.Chinch bugs prefer fields with surface vegetation which makes control with foliar insecticides difficult.

Corn Borersb

0 to +++

Several species of borers overwinter in corn stubble.Con-till can increase overwintering survival and subsequent problems in corn.

Stink Bugs

0 to +

Con-till fields usually have little effect on bug pests.Delayed herbicide applications can increase population in fields. Poor control of spring weeds such as marestail or primrose can increase populations.Vegetation management surrounding fields is critical to bug IPM.

Corn Earworm

0

Winter survival of heliothine populations can be increased in con-till fields. Little economic injury occurs except for seed producers.

a“+++” Substantial increase in pests; “+” =Some increase; “0“ =No effect; “-“ = Decrease in pests.
bBorer pests include Southwestern corn borer, sugarcane borer, and European corn borer
.

Fall vs. Spring Phosphorus and Potassium Fertilizers Application

Rasel Parvej, Brenda Tubana, Syam Dodla, David Moseley, and Matthew Foster, LSU AgCenter Scientists

For corn and soybean production in Louisiana, producers mainly supply macronutrients such as nitrogen (N; for corn only), phosphorus (P), potassium (K), and sometimes sulfur (S). To meet these nutrient demands, organic and/or inorganic fertilizers are often applied onto the soil surface at or before planting. Nitrogen is mainly applied for corn and the recommendations depend on yield goals and soil types. For P, K, and S fertilizations, soil-test-based fertilizer recommendations are used. Fertilization is recommended if soil-test nutrient concentrations fall below the critical level. The critical nutrient level is defined as the range of soil-test nutrient concentration below which crop response to added fertilizer is expected, within which is uncertain, and above which is unlikely. In general, the critical soil-P and K concentrations for both soybean and corn production in Louisiana range from 21 to 35 ppm P (42 to 70 lb P/acre) for all soil types and 98 to 141 ppm K (196 to 282 lb K/acre) for silt loam, 142 to 264 ppm K (284 to 528 lb K/acre) for clay loam, and 142 to 317 ppm K (284 to 634 lb K/acre) for silty clay soils. Detailed soil-test-based fertilizer recommendation for row crop production in Louisiana can be found at the LSU AgCenter (Variety Trials and Production) website.

For P and K fertilization, Louisiana producers mostly use triple superphosphate (TSP; 0-46-0) for P and muriate of potash (MoP; 0-0-60) for K and apply both fertilizers mostly in the fall rather than in the spring. One of the main reasons for fall application is due to wet soil conditions or limited application time in the spring. However, lots of producers believe that they must apply both TSP and MoP in the fall since both fertilizers are rocky materials (TSP is originated from phosphate rock and MoP is from potash ore) and require long time to dissolve and become available for plant uptake. Practically, both fertilizers are water soluble and can rapidly release nutrients, regardless of application time, when dissolve with adequate soil moisture and/or rainfall/irrigation water. Many studies showed that spring application of both TSP and MoP fertilizers is either equal to or better than fall application in increasing crop yield especially in soils that are highly prone to nutrient losses via leaching, runoff, and/or erosion.

In 2019-2020, we evaluated the effect of P and K fertilizer application timings on soybean and corn yields at the Macon Ridge Research Station (MRRS) in Winnsboro and Northeast Research Station (NERS) in St. Joseph, LA (Fig. 1-2). The trials were conducted in silt loam soils at both locations. The soil-test P and K concentrations across all sites were either below or within the critical level except for the corn trial at the NERS where soil-test P and K concentrations were above the critical level. As expected, both corn and soybean yields responded positively to both fall and spring fertilization at sites with soil P and K concentrations below or within the critical level and did not responded at site with soil P and K concentration above the critical level (corn at NERS; Fig. 1). Although both corn and soybean yields were not significantly different between fall and spring P and K application, our one-year preliminary results showed that there was a trend of getting numerically higher yield (~3 bu/acre soybean and ~8 bu/acre corn) from spring P and K application compared to fall application especially in silt loam soils with P and K concentrations below or within the critical level.

Overall, both fall and spring fertilization have advantages and disadvantages. Fall application may help save critical time in the planting season but reduces available quantity of applied nutrients due to losses through leaching, runoff, erosion, or soil fixation. Although our one-year study showed no significant bump in yield between fall and spring P and K application, the following factors need to be considered in making decision regarding fertilizer application time.

  • The rapidity of P and K fixation to unavailable forms usually increases with the decrease of soil-test P and K concentrations. For example, soils with deficient P and K will fix applied P and K more rapidly than soils with sufficient P and K. Therefore, fertilizers should be applied in the spring at or near planting in P and K deficient soils to ensure maximum nutrient availabilities during the time of rapid plant uptake.
  • Soil P availability is maximum between soil pH 6.0 and 7.5. Fertilizer-P is fixed to unavailable forms as aluminum phosphate when soil pH falls below 5.5 and as calcium phosphate when soil pH exceeds 7.5. Therefore, fertilizer-P should be applied in the spring as close to planting as possible for fields with low (pH <5.5) or high (pH >7.5) soil pH to ensure maximum fertilizer-P availability for plant uptake.
  • Spring application of fertilizer-P and K should be considered for coarse-textured soils with very low cation exchange capacity (CEC <10) such as loamy sand to sandy loam (sometimes silty loam) soils where nutrient leaching and soil erosion are common, and nutrient deficiencies are often observed.
  • For soils that are very prone to waterlogged/flooded conditions, fertilizer-P and K should be applied in the spring at or near planting since the alternating flooding (anaerobic) and non-flooding (aerobic) conditions decreases soil nutrient availability and increases losses.
  • Fall application of P and K should be considered for soils with nutrient concentration within (medium) or above (sufficient) the critical level, where fertilizers are mainly applied to replace soil nutrients that are removed by harvested grains to maintain the same level of soil nutrient level. In addition, fertilizer-K should be applied in the fall in fields that have long history of chloride (Cl) toxicity problems and are poorly drained. Since K fertilizer (MoP) mainly consists of KCI, fall application will allow enough time to decrease Cl toxicity by reducing Cl accumulation from fertilizer KCl through winter and early spring rainfall.

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Fig. 1. Corn grain yield response to fall vs. spring P and K fertilizer application time.

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Fig. 2. Soybean yield response to fall vs. spring P and K fertilizer application time.

Planting Considerations for Soybean

David Moseley; Boyd Padgett; Sebe Brown; Daniel Stephenson; Rasel Parvej, LSU AgCenter scientists

The optimum planting dates for soybean in Louisiana range from mid-April until mid-May. Late March plantings are often possible; however, caution should be taken as soybean seed can be damaged during cool temperatures and saturated soils that often occur in North Louisiana. In addition, yield potential declines for planting dates outside the optimum window.

Row Spacing

There has been a lot of discussion regarding the advantages and disadvantages to planting soybean with narrow (e. g. 7.5 or 15 inch rows) vs. wide row spacing (e.g. 38 or 40 inch rows). One advantage in narrow row spacings is the canopy closure occurs faster which will increase light interception by soybean leaves. Greater light interception can result in increased yield through photosynthesis and help decrease weed pressure. In addition, a closed canopy will help minimize moisture loss through evaporation. However, there can be a few disadvantages associated with narrow rows. One possible disadvantage is that there may be poor seed-to-soil contact when using precision drills, especially in no-till or cover crop production systems. Also, a dense canopy will reduce sunlight penetration and air movement which can lead to an increase in disease risk and decreased fungicide penetration into the lower canopy. Planting on raised beds (typical in 38 and 40 inch rows) help reduce plant injury from saturated soil conditions. Using GPS to create spray lane tracks in narrow row production systems minimize damage to plants in late season field applications. Previous research from the LSU Agcenter has shown up to a six bushel per acre yield increase with narrow row compared to wide row spacings. However, the yield response was inconsistent over multiple years.

Optimum Seeding Rates

The planter should be calibrated using seed-per-foot instead of pounds of seed per acre. Varieties vary in seed size; therefore, seed-per-foot will be more accurate than pounds of seed per acre. The table below, adapted from the 2021 Soybean Variety Yields and Production Practices are recommended seed- per-foot at various row spacings (Table 1).

Table 1. LSU AgCenter Recommended Seeding Rates

Row Width (Inches)

Seed per Row Foot

Plants per Row Foot

Population in 1,000s

36 – 40

8 – 9

6 – 8

78 – 104

30 – 32

6 – 7

4 – 5

78 – 104

20 – 24

5 – 6

4 – 5

104 – 130

7 – 10

4 – 5

3

104 – 130

Broadcast

5 – 6/sq. ft.

3/sq. ft.

150

Late Planting

6 – 7/sq. ft.

4/sq. ft.

200

When planted in mid-April to mid-May, recommended soybean seeding rates range from approximately 120,000 – 130,000 seeds per acre with a final stand of approximately 104,000 to 113,000 plants per acre. This planting rate and final stand require an 87% establishment rate of seedlings. This rate of survival would likely require optimum planting conditions. Therefore, if planting under less than favorable conditions seeding rates may need to be increased. In a population trial conducted at the Dean Lee Research station in 2019, there was no significant reduction in yield with planting rates between 75,000 to 175,000 seeds per acre (Figure 1).



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Figure 1. Population Trial at the Dean Lee Research Station in 2019.

In 2020, there was a population trial planted on May 6 and on June 1 at the Dean Lee Research Station. In this trial, there was a yield reduction when planting 75,000 seeds per acre at the May 6 planting date and at 100,000 seeds per acre at the June 1 planting date (Figure 2). Rainstorms occurred within five days after both planting dates, likely causing compaction leading to a reduced stand. Studies have shown that seeding rates should be increased when planting outside the optimum window. Final plant stand was 61 and 54% of the planted seed population for the May 6 and June 1 planting date, respectively. This reduction in final stand was likely the cause of yield reduction.


Moseley_Fig_2_2020_pop_trialpngFigure 2. Population Trial at the Dean Lee Research Station in 2020.

The population trial in 2020 consisted of three varieties, six seeding rates, and two planting dates (Figure 3). Variety A had the highest yield averaged across all planting rates and dates. This data suggest variety A was able to compensate better for a low stand count. Selecting a variety that has high yield potential across multiple locations and years can be a good indicator the variety can compensate for adverse conditions.


Moseley_Fig_3_2020_var_by_pop_by_PD_trialpng

Figure 3. Variety by Planting Rate Trial at the Dean Lee Research Station.

Planting Conditions

Soil temperatures should be above 60 degrees Fahrenheit before planting. Soybean seed should not be planted when soil temperatures are below 50 degrees Fahrenheit as the seedlings can be damaged during the rapid water imbibition stage. Make sure that there is a favorable weather forecast for at least 48 hours after planting to avoid soil temperatures below 50 degrees Fahrenheit. Planters should be inspected to ensure good seed-to-soil contact. Seeds should be planted between 1 to 2 inches deep depending on soil moisture conditions. Soybean seed emergence is sensitive to compaction and saturated soils, therefore, favorable soil conditions and proper planter settings are critical for optimum soybean germination and stand establishment. Wet soil conditions at planting could lead to the compaction of the seed furrow side walls limiting outward root growth. The most important day in a seed's life is the day it is planted. Plant into the most favorable conditions possible to limit the possibility of replanting and yield reductions.

Nutrients

For soybean, nutrient availability is greatest in a soil pH range from 6.2 to 7.0. If lime is required, it should be applied and incorporated into the soil in the fall of the year. This mixing of the soil with the lime and fall application allows time for the lime to react with the soil acidity. If soil pH is below 6.2, a molybdenum seed treatment is recommended. Molybdenum is an essential nutrient for nitrogen fixation in soybean. However, if a soybean inoculant is to be used in conjunction with a molybdenum seed treatment the seed should be treated the day of planting. Using a soybean seed inoculant is recommended if the field has not been planted to soybean within 3 years. Soil samples should be tested every 3 years from fields to determine nutrient replacement and lime needs. For a 55 bushel per acre crop, soybean utilize approximately 5.2 lb N, 1.0 lb P2O5, and 3.4 lb K2O per bushel. Approximately 4 lb N, 0.8 lb P2O5, and 1.4 lb K2O per bushel is removed from the field when the grain is harvested. This equates to 220 lb N, 44 lb P2O5 and 77 lb of K2O removed per acre for a 55 bushel per acre soybean crop. Proper fertility management is critical for producing optimum soybean yields.

Seed Treatments

Seedling diseases are usually not an issue when soybean is planted into favorable soil condition and weather. When poor weather conditions occur after planting a base fungicide seed treatment can help ensure stand establishment. Seedling diseases are most problematic in cool and wet soils. Diseases associated with cool to warm, saturated soils are root rots, and preemergence and post emergence damping off caused by: Pythium, Fusarium, and Rhizoctonia. Diseases associated with 60 degrees Fahrenheit and higher and saturated soils are Phytophthora root rot and some Pythium species.

Soybean seedlings can tolerate a substantial amount of insect injury during the seedling stage. However, early planted soybeans may encounter greater amounts of air and soil temperature fluctuations. Cool conditions reduce seedling vigor (also nutrient uptake is reduced) and plant growth may become arrested under the right conditions. Adding insect injury, to the aforementioned environmental conditions, increases plant stress and can result in loss of stand and yield potential. Therefore, the inclusion of an insecticide seed treatment (IST) provides growers a risk management tool when soybeans are planted early. The primary insect pests of early planted soybeans are bean leaf beetles, three-cornered alfalfa hopper, wireworms, grape colaspis and thrips.

As a general rule with all agronomic crops, the later the crop the more insect pressure that will be encountered throughout the season. This is particularly evident when soybeans are planted into wheat stubble. Wheat stubble is favorable for the development of three-cornered alfalfa hoppers. Thus, an IST is a sound investment when soybeans are planted late.

Early-Season Weed Control

Planting soybean in a weed-free field is very important. Obviously, an application of herbicides for control of winter vegetation (burndown) 4 to 6 weeks prior to planting is the primary method producer’s use. However, issues could arise if fields scheduled for soybean receive a burndown application greater than 6 weeks before planting. When that occurs, a second burndown application may be needed to control newly emerged weeds. Another option is to apply paraquat at 0.5 lb. ai/acre plus 0.25% v/v nonionic surfactant or 1% v/v crop oil concentrate at planting. To help maintain the soybean weed-free during and after emergence for at least 3 weeks, a residual herbicide should be applied preemergence. It can be tank-mixed with the paraquat applied at planting if needed. However, the choice of residual herbicide is not a ‘one size fits all’ scenario because weed spectrum dictates residual herbicide choice. Data has shown that maintaining soybean weed-free for the first 5 weeks after emergence will help ensure maximum yield can be attained. A great program to achieve is one that contains a residual herbicide applied preemergence followed by a postemergence application of a residual herbicide tank-mixed with a non-selective herbicide 3 to 4 weeks after emergence.

LSU AgCenter Specialists

Specialty Crop Responsibilities Name Phone
Corn, cotton, grain sorghum Agronomic Matt Foster 225-621-5799
Soybeans Agronomic David Moseley 318-473-6520
Wheat Agronomic Boyd Padgett 318-614-4354
Pathology Cotton, grain sorghum, soybeans Boyd Padgett 318-614-4354
Pathology Corn, cotton, grain sorghum, soybeans, wheat Trey Price 318-235-9805
Entomology Corn, cotton, grain sorghum, soybeans, wheat Sebe Brown 318-498-1283
Weed science Corn, cotton, grain sorghum, soybeans Daniel Stephenson 318-308-7225
Nematodes Agronomic Tristan Watson 225-578-1464
Irrigation Corn, cotton, grain sorghum, soybeans Stacia Davis Conger 904-891-1103
Ag economics Cotton, feed grains, soybeans Kurt Guidry 225-578-3282
Precision ag Agronomic Luciano Shiratsuchi 225-578-2110
Soil fertility
Corn, cotton, grain sorghum, soybeans Rasel Parvej 479-387-2988


2/19/2021 4:13:22 PM
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