Volume 11, Issue 8 - September 2021

David Moseley, Stephenson, Daniel O., Harrison, Stephen A., Price, III, Paul P, Padgett, Guy B., Foster, Matthew, Parvej, Md Rasel, Deliberto, Michael, Tubana, Brenda S., Wang, Jim Jian, Conger, Stacia

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Estimating the Forgone Revenue from Harvesting Dry Soybeans

Michael Deliberto, LSU AgCenter economist

When soybeans are delivered to the elevator, any difference between actual and desired moisture content can potentially result in lower producer revenue. For example, soybeans testing over 13% moisture are assigned a penalty that is shown directly on the scale ticket. Soybeans testing under 13% moisture are accepted by the elevator with the assumption that 60 pounds of soybeans constitutes a bushel. So, by definition, a standard bushel of soybeans weighs 60 pounds at a moisture level of 13%. Given that 13% of the weight is comprised of moisture that leaves 87% (52.2 pounds) as dry matter.

If dry matter weight remains unchanged at the standard 52.2 pounds, the wet basis weight for any moisture content can be calculated. If the moisture content were reduced to 11% (89% dry matter), the wet basis weight of the soybeans would be 58.65 pounds. For each 52.2 pounds of dry matter delivered at 11% moisture, the producer forgoes revenues of 1.35 pounds of paid weight had they been sold at 13% moisture (60 - 58.65 pounds).

It is standard practice for buyers to assume 60 pounds of soybeans constitutes a bushel when soybeans are at or below 13% moisture. When beans are below 13%, the difference in water content is made up for by an equal number of pounds (wet basis) of soybeans. In Table 1, the wet basis weight of a bushel of soybeans represents the 52.2 pounds of dry matter plus the water content to bring the moisture to the stated level. The table represents the pounds of soybeans per bushel being substituted for water when the moisture content is below 13%. The revenue foregone (lost) is an estimate of the potential extra profit the producer could realize if the beans had been harvested at 13% moisture instead of at lower moisture levels (assuming a 60 bushel per acre yield and selling price of $12.00 per bushel). For example, harvesting soybeans at a moisture content of 9% would result in lost revenue of $31.65. However, given the year-over-year increase in the price of soybeans, the revenue foregone (lost) from harvesting dry soybeans can be substantial especially on highly productive fields. Table 2 estimates the foregone revenue for an imposed increase in the yield per acre assumption at a selling price of $12.00 per bushel. For example, assuming a field yield of 70 bushels per acre, the revenue lost by harvesting soybeans at 9% is estimated to be $36.92.

Table 1. Foregone revenue by not harvesting soybeans at 13% moisture.

Item Description

13%*

12%*

11%*

10%*

9%*

Wet Weight of a bushel

60.00

59.32

58.65

58.00

57.36

Pounds Lost

0.00

0.68

1.35

2.00

2.64

Revenue Lost

$0.00

$8.18

$16.18

$24.00

$31.65

*Moisture content (%) at Harvest

Table 2. Foregone revenue by not harvesting soybeans at 13% moisture for varying yield levels.

Varying Yield Levels

13%*

12%*

11%*

10%*

9%*

Revenue Lost at 60 bu/ac yield

--

$8.18

$16.18

$24.00

$31.65

Revenue Lost at 65 bu/ac yield

--

$8.86

$17.53

$26.00

$34.29

Revenue Lost at 70 bu/ac yield

--

$9.55

$18.88

$28.00

$36.92

*Moisture content (%) at Harvest

The background information presented in this report was adapted from the University of Nebraska- Lincoln Institute of Agriculture and Natural Resources: Dorn, T. Harvest Soybeans At 13% Moisture. January, 2009.

LSU AgCenter Conducts Soybean Variety Trials and On-farm demonstrations

David Moseley, LSU AgCenter soybean specialist

One of the most important decisions a soybean producer makes every year is variety selection. The LSU AgCenter conducts an Official Variety Trial (OVT) and Core-block demonstration plots to provide unbiased data to assist in variety selection. The OVT and core-block demonstrations are planted throughout the state to collect performance data in different environments. It is important for a producer to consider how varieties perform in an environment similar to their own and how varieties perform in multiple environments. Varieties that perform consistently well across multiple environments and years could be considered to have more performance stability.

Official Variety Trial

The 2021 OVT includes 125 varieties entered by 12 seed companies and two university soybean breeding programs. The varieties consist of several different herbicide technologies, and the maturity groups range from 3.8 to 6.0. The trial is replicated at seven research stations across the state in different soil types including fine sandy loam, silt loam, silty clay and clay. At each location, the varieties are replicated four times.

On-farm Demonstration Plots

In addition to the OVT, the LSU AgCenter collaborates with soybean producers to evaluate soybean varieties directly on farms. For the core-block demonstration program, the LSU AgCenter parish agents cooperate with producers to plant, maintain, and harvest strip trials submitted by seed companies and university soybean breeding programs. These demonstrations provide valuable yield data from local growing conditions and agronomic practices. In some cases, observations from these large plots can result in identification of varieties that are resistant to a number of soilborne maladies.

In 2021, 8 seed companies and one university soybean breeding program submitted varieties to be evaluated in the core-block demonstrations. Twenty demonstrations were planted across 12 parishes. The demonstrations were divided by maturity group (MG). A demonstration consisted of varieties with a MG of 3.7 to 4.4; 4.5 to 4.9; or 5.0 to 5.6. The number of varieties submitted for each MG were four (MG 3.7 to 4.4), twelve (MG 4.5 to 4.9) and nine (MG 5.0 to 5.6).

The LSU AgCenter also conducted a nematode resistant screening demonstration in two parishes. Nematode assays before and after harvest and yield data will be collected to help determine if a variety can be tolerant or resistant to high nematode pressure. An aerial view of the nematode resistant screening in Concordia parish shows possible differences in the effect of nematode pressure among the varieties (Figure 1).

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Figure 1. An aerial view of a soybean variety nematode screening demonstration in Concordia parish (Photo by Wil Miller).

Variety Testing Results

The performance data from the OVT and core-block demonstrations will be published by the LSU AgCenter in the annual soybean variety testing summary. Maturity date, height, lodging and disease reaction information from the OVT will also be included. The 2021 OVT results will be published following harvest to assist with 2022 variety selections and planting decisions. The variety publication for the 2021 growing season can be found at 2021 Soybean Variety Yields and Production Practices.

More information on LSU AgCenter variety testing can be found in the Louisiana Agriculture Magazine Vol. 64, No. 1, Winter 2021.

Potential Nutrient Losses from Burning of Corn Residue

Matt Foster, Rasel Parvej, Michael Deliberto, LSU AgCenter Scientists

With corn harvest finishing up around the state, many questions have been coming in regarding residue management. Corn produces more biomass than most row crops in Louisiana and the leftover residue after harvest is often perceived as a problem that needs to be removed by fire. However, crop residue plays an important role in successful crop production. One of the most important benefits from crop residue is the improvement of soil organic matter that is limited in many southern soils. Organic matter reduces soil erosion and positively contributes to soil microbes, nutrient availability, soil water holding capacity, and the formation and stability of soil aggregates.

Crop residue also has value as a nutrient source. Generally, corn stover for every bushel of grain yield contains 0.45 lbs of nitrogen (N), 0.10 lbs of phosphorus (P2O5), 0.60 lbs of potassium (K2O), and 0.06 lbs of sulfur (S) (Table 1). Therefore, the stover of a 200-bushel per acre corn crop would contain 90 lbs N/acre, 20 lbs P2O5/acre, 120 lbs K2O/acre, and 12 lbs S/acre.

When crop residue is burned, approximately 100% of N and 80 % of S will be lost upon combustion. In theory, phosphorus and potassium are not lost during combustion, but substantial loss can occur from the smoke or ash. This loss usually occurs when ash floats away during the burn event or is moved away from the field by wind or rain after the burn event. If the remaining ash isn’t immediately incorporated into the soil, up to 80% of phosphorus and potassium could be lost. Excessive removal of crop residues can eventually result in soil nutrient and organic matter depletion and more fertilizer inputs. While the nutrients lost can be replaced, the loss of soil organic matter is not so easy to improve overnight.

When considering the nutrient concentrations present in the stover of a 200-bushel per acre corn crop and the percentage of potential losses, approximately 90 lbs N/acre, 16 lbs P2O5/acre, 96 lbs K2O/acre, and 9.6 lbs S/acre could be lost after corn residue is burned. Based on current fertilizer prices, the total estimated dollar value of the nutrient loss would be $113/acre for a 200-bushel corn crop.

Preserving the soils for future generations should be a top priority for producers. Therefore, we encourage producers to let corn residue naturally decompose during the winter months instead of burning it. One option to manage corn residue is to bush hog it and re-hip the bed. Soil cover will accelerate microbial decomposition of corn residue.

Table 1. Pounds of nutrient removal from corn grain and stover for every bushel of corn grain yield (Rasel Parvej, LSU AgCenter; personal communication).

Nutrient

Grain (pounds per bushel of grain yield)*

Stover (pounds per bushel of grain yield)*

N

0.67

0.45

P2O5

0.35

0.10

K2O

0.25

0.60

S

0.07

0.06

*Corn nutrient removal from the grain or the stover for every bushel of corn grain yield.

Soil Liming and Lime Qualities

Rasel Parvej, Brenda Tubana, Jim Wang, LSU AgCenter Soil Scientists

After receiving a soil test report, the first thing that needs to be checked is soil pH. Soil pH is the most important soil quality component that greatly influences soil nutrient availability. Most nutrients are highly available at the soil pH of 6.5 (Figure 1). Therefore, soil pH needs to be adjusted to the target pH either by applying lime for low pH (<6.0) soils or by elemental sulfur for high pH (>7.5) soils. Increasing soil pH by liming is a more common practice than decreasing soil pH by elemental sulfur. The following things need to be considered before a making liming decision.

Soil Liming:

  • The rate of lime depends on the initial and target soil pH and the buffering capacity of the soil (buffer pH, ability of a soil to resist the change of pH). If the soil buffering capacity and the difference between initial and target soil pH are low, lime rate would be low. However, for soils with high buffering capacity (low buffer pH), lime rate would be high even for a small change of soil pH. Clay soils have higher buffering capacity and require greater amount of lime for each unit increase of soil pH than silt loam soils. Note that the LSU AgCenter Soil Testing and Plant Analysis Lab does not run buffer pH but indicate the unit change of soil pH with the addition of maximum 3 tons of lime and let the farmers decide how much they would like to spend, assuming higher than 3 tons lime may be too expensive.
  • The target soil pH should be determined based on the crop to be grown. For example, soybean is more sensitive to low soil pH than corn and cotton. The target soil pH should be set at 6.3 for soybean and 6.0 for corn and cotton. Lime is required if the target soil pH is 0.2 unit more than actual soil pH.
  • Lime takes at least 6-9 months, depending on liming materials, to react with the soils and raise soil pH. Therefore, lime should be applied uniformly and incorporated by tillage in the fall.

Lime Qualities:

  • The quality of liming materials is very important to raise soil pH. There are two qualities of liming materials: purity and particle size. The purity of a liming material is determined in relation to pure calcium carbonate (CaCO3), calcitic limestone, which is rated as 100% (molecular weight of pure calcium carbonate is 100) and this rating is called calcium carbonate equivalent (CCE). The rate of lime recommended by soil testing labs is based on pure calcitic limestone with 100% CCE. So, the actual lime application rate should be adjusted based on the CCE of the liming materials. For example, if the CCE of the liming material is 80% and the recommendation is 2-ton lime per acre, 2.5-ton lime (2-ton/0.80) per acre should be applied.
  • Another lime quality is the particle size, which is the fineness factor of liming material and is expressed as the percentage of liming material that passes through various sized screens. The higher the percentage of liming material that passes through the larger size screen (i.e., smaller hole), the greater the fineness factor would be. Finer particles are more efficient in neutralizing soil acidity (increasing soil pH) by reacting quickly with soils due to greater surface area or soil contact. However, the liming materials should have a good distribution of particle sizes with both smaller and larger particles so that smaller particles can raise the soil pH quickly and larger particles can have a long-term control in neutralizing soil acidity. According to current Louisiana recommendations for ground lime, 90% of liming materials should pass through a 10-mesh sieve, 50% should pass through a 60-mesh sieve, and 20% should pass through a 100-mesh sieve.
  • Both purity (CCE) and particle size (fineness factor) of the liming material are expressed together as effective CCE (ECCE) or effective neutralizing value (ENV). The higher the ECCE or ENV of the liming material the more efficient it is in increasing soil pH. Like CCE, the actual lime rate also needs to be adjusted with the ENV of the liming material if the recommendations are based on ENV. For example, if the ENV of the liming material is 60%, but the recommended lime rate is based on standard calcium carbonate with 90% ENV, 1.5-ton (0.9/0.6) lime should be applied for every 1-ton of lime recommended. Note that the lime recommendations from LSU AgCenter Soil Testing and Plant Analysis Lab is based on 50% ECCE or ENV.

Rasel pH Picture1png

Figure 1. Soil pH and nutrient availability [Source: Reitsma et al. (2011). Chapter 2: Soil fertility. In: Alternative practices for agronomic nutrient and pest management in South Dakota. Edition: I. South Dakota State University, College of Agriculture and Biological Sciences]

Soil Sampling and Testing in Fall

Rasel Parvej, Brenda Tubana, Jim Wang, LSU AgCenter Soil Scientists

Soil sampling for nutrient analysis and fertilizer recommendations is a very common phenomenon after summer crop harvest in the Fall. The following things need to be considered before soil sampling and testing.

Soil Sampling:

  • Soil should be tested at least once in every 2-4 years or once in a complete crop rotation.
  • Soil sample should be taken at the same time of each sampling year and at a constant depth of 0-6 inch with a soil probe or auger.
  • At least one sample should be taken for every 10 acres of land for zone sampling and 2.5 acres of land for grid sampling. Both zone and grid sizes depend on spatial variability of the field. More soil samples are needed per unit area for highly variable fields. Therefore, soil type and color, past management, and a yield map should be considered to determine the actual zone and grid sizes.
  • Each soil sample should consist of 15-20 subsamples (i.e., 2-3 subsamples per acre for zone sampling and 6-8 subsamples per acre for grid sampling). However, more subsamples are needed for fields that received fertilizer banding and/or manure spreading in the past. Subsamples should be taken in a zigzag pattern within each zone or grid.
  • Scrap the thin layer of soil surface before inserting the soil probe or auger. For furrow irrigation system, each sample should be taken from the shoulder of the bed (4-6 inch apart from crop row). However, for any field, each sample should not be taken from fertilizer bands, manure or lime stockpiles, wet spots, fence rows, and from an area that is too small to manage separately. All subsamples should be mixed thoroughly in a clean plastic bucket. Remove stones, roots, stems, trash, and other debris from the mixed soil samples.
  • Each soil sample should be placed in a separate plastic bag with clear labelling that includes farm name and location, sampling date and depth, previous crop, and expected crop to be grown and sent immediately to the soil testing lab for routine soil analysis.

Soil Testing:

  • Soil samples should be tested in a certified soil lab (e.g., LSU AgCenter Soil Testing and Plant Analysis Lab, Baton Rouge) that uses appropriate soil extraction methods for the state. Soil-test-based fertilizer recommendations in Louisiana are based on Mehlich-3 soil exaction method for soil sample collected from 0-6-inch depth.
  • Soil samples should be analyzed in the same lab each year to create a historic record.

Soil Test Interpretation for Fertilizer Recommendations

Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter Soil Scientists

Soil test results should be interpreted based on the critical soil test nutrient concentration. The critical concentration is defined as the soil test nutrient concentration below which crop response to added fertilizer is expected and above which is unlikely. Critical nutrient concentration varies with crops, soil types, and states. Therefore, soil test results should be interpreted with crop, soil type, and state specific critical nutrient concentrations that are derived from correlation and calibration research. Usually, soil scientists from every land-grant university develop their own critical soil test nutrient concentrations for each crop of that state. So, it would be better to analyze soil samples in the state soil testing lab and obtain fertilizer recommendations.

Fertilizer recommendations should be based on critical soil test nutrient concentration and fertilization philosophies. There are three main fertilization philosophies: sufficiency, buildup and maintenance, and cation saturation ratio. In the sufficiency approach, used by most land-grant universities including LSU AgCenter, fertilization is only recommended if the soil test nutrient level is at or below the critical level and the fertilizer rate is determined based on expected crop yield increase. This approach is called “fertilize the crop”. In the buildup and maintenance approach, also known as “fertilize the soil”, fertilization is almost always recommended unless the soil test level is very high. The buildup part of this approach is used for soils with nutrient concentration below the critical level and the fertilizer rate is determined based on sufficiency rate plus some extra rate to raise the soil test nutrient concentration above the critical level. The maintenance part is used for soils with nutrient concentration above the critical level and the fertilizer rate is determined based on the expected nutrient removal rate by the crop to maintain soil test nutrient concentration at the same level. The cation saturation ratio is not very accurate and economic in recommending fertilizer. In this approach, fertilizer is recommended based on the cation ratio mainly calcium (Ca), magnesium (Mg), and potassium (K) on the cation exchange site. The most used ratio is 65% Ca, 10% Mg, 5% K, and 20% others.

Care should be taken using buildup and maintenance philosophy for K fertilization in coarse-textured soils with low cation exchange capacity (CEC <10) such as loamy sand to silt loam soils. Potassium is highly prone to leach down to the soil profile with excessive rainfall in low CEC soils. So, building up soil test K level in coarse-textured low CEC soils may not be feasible and economic. Please visit the LSU AgCenter website for detailed soil-test-based fertilizer recommendations for each crop.

The soil-test-based fertilizer recommendations mainly include phosphorus (P) and K which can be applied in fall especially for fine-textured soils (clayey soils) with high CEC (>20). For coarse-textured low CEC soils (sandy to silt loam soils), it is better to apply all fertilizers in spring or at planting. There is a misconception about spring application of P (TSP) and K (Potash) that both fertilizers require a long time to dissolve and become available for plant uptake. Many studies showed that spring application of both fertilizers is better than fall application in increasing crop yield especially for soils that are highly prone to nutrient loss via leaching, runoff, and erosion. For more information, please read Fall vs. Spring Phosphorus and Potassium Fertilizers Application.

Surface Irrigation Survey

Stacia L. Davis Conger, LSU AgCenter engineer

Please complete this survey on surface irrigation practices in Louisiana. To access the survey, use the QR Code or the Flood (Surface/Gravity) Irrigation Survey website.

QR code_Stacia_2021 Sept LA Crops Newsletterjpg

Figure 1. A QR code to access the Flood (Surface/Gravity) Irrigation Survey.

Time to plan for management of glyphosate-resistant Italian ryegrass

Daniel Stephenson, LSU AgCenter Extension Weed Scientist

In April of 2021, I wrote an article entitled “Ryegrass control: We are not faring well. ”If you missed it, it can be found here Ryegrass control: We are not faring well (https://www.lsuagcenter.com/articles/page1617844075389).In that article I pointed out that the major issue I had discussed with producers, parish agent, consultants in March and April was how bad the Italian ryegrass was. Well, it is time to develop a plan to manage the issue so we are not repeating this situation in 2022.

A glyphosate-resistant Italian ryegrass management plan is divided into three options. This plan was developed by our friends at Mississippi State University because Italian ryegrass became a problem for them many years before it reached Louisiana and LSU AgCenter weed scientists believe the plan fits Louisiana’s needs.

Fall (late October through November):

Italian ryegrass emerges predominately in the fall, which makes this option the best time to implement a management strategy. Therefore, residual herbicide application or tillage in late October through November. Based on Mississippi State’s data, the choice of residual herbicide depends on the crop to be planted in the spring.

Spring crop to be plantedFall management strategy/residual herbicide
Corn/Grain sorghumDual Magnum at 1.33 to 1.67 pints/A Or double disk
CottonDual Magnum at 1.33 to 1.67 pints/A or Trifluralin at 3 pints/A or double disk
SoybeanDual Magnum at 1.33 to 1.67 pints/A or Boundary at 2 pt/A or Trifluralin at 3 pints/A or double disk
RiceCommand at 2 pt/A (currently not labeled, but the LSU AgCenter is supporting a label for fall use) or double disk

*Tank-mix paraquat at 0.5 to 0.75 lb ai/A plus surfactant with all residual herbicide applications listed above.

The primary complaint with the fall application of residual herbicides is erosion or bed integrity. An option is to seed a cereal cover crop and apply Dual Magnum or Zidua postemergence two weeks after cover crop emergence. Again, this is the best option.

Winter (mid-January through mid-February):

Implementation of this strategy requires scouting for emerged Italian ryegrass, particularly if a residual herbicide application or tillage occurred in late October through November. Regardless of the crop to planting, clethodim at 0.125 lb ai/A plus surfactant can be applied if emerged ryegrass is found. This application must be made 30 days before planting corn, grain sorghum, or rice. This option should be seen as an addition to the Fall plan.

Over the past years, Louisiana producers have attempted to tank-mix clethodim in their normal burndown program applied in January through February. This has led to disasters for many.2,4-D and dicamba can antagonize clethodim, thus reducing Italian ryegrass control, but this antagonism can be overcome by increasing the rate of clethodim to 0.125 lb ai/A. Oftentimes antagonism is only a part of the problem. Most of the time, Italian ryegrass is too big at application and received a sublethal dose of clethodim. There have been times that a big ‘glug’ of clethodim did not kill Italian ryegrass.Is this potential resistance to clethodim, which has been discovered in Mississippi? Potentially.Was the ryegrass just too big at application in the first place? Probably.

The clethodim labels warn against or says “do not” do what we have been doing. For example, we should be tank-mixing 1% v/v AMS with clethodim and crop oil. Spray volume should be 15 gpa by ground and 5 gpa by air. The next statement is a big one. “Do not apply to grasses that have tillered, formed seedheads, or exceeded recommended stage.” The proper targeted size is 2 to 6 inch Italian ryegrass. As Dr. Jason Bond, Mississippi State Extension Weed Specialist, pointed out, ryegrass reaches 2 to 6 inches in the fall. So, our current practice of tank-mixing clethodim with our burndown application in January/February is the wrong thing to do.

Spring (March):

Waiting until the spring to manage Italian ryegrass is a repeat of 2020 and 2021.However, if no management plan was implemented in the fall/winter and now you have large, multi-tillered Italian ryegrass, then two applications of paraquat at 0.75 to 1 lb ai/A 10 to 14 days apart is your only herbicide option. Tank-mixing atrazine at 1 lb ai/A (corn and grain sorghum), metribuzin at 4 oz/A (soybean), or diuron at 0.75 lb ai/A (cotton) to the first paraquat application with increase efficacy.

As many of you know from experience, paraquat is not that great at controlling Italian ryegrass in the spring. Paraquat will burn it brown, possibly kill it after two applications, but a producer will have to deal with the biomass that can hamper planting and early-season crop growth.

Implementing a management plan for glyphosate-resistant Italian ryegrass is a must. Let’s not repeat history. If you have any questions, please contact your local county agent. Thanks and have a great day.

Wheat Variety Performance and Production Practices in Louisiana

Stephen Harrison, Boyd Padgett, Trey Price, LSU AgCenter Scientist

Wheat acreage increased in 2021 compared to 2020. The season started off well but deteriorated in many parts of the state. The freeze in February and wet weather during portions of the year negatively impacted production. Wheat prices are currently high and there will probably be more interest in planting wheat this fall. Growers should be wary of planting varieties that do not have proven performance and are not shown to be adapted to Louisiana. When possible, choose adapted high yielding varieties with resistance to Fusarium head blight (scab). Also plant in fields that are well drained.

In an effort to assist producers, agents, and consultants in variety selection, the LSU AgCenter continues to evaluate varieties in official trials located on seven experiment stations. To access the complete 2021 Variety Performance Trial publication, go to the following website: 2021 Small Grain Performance Trials (https://www.lsuagcenter.com/profiles/aiverson/articles/page1629210681934).

Variety selection:

Choice of varieties for planting is a crucial management decision that sets the stage for yield potential and input costs. While grain yield is the most important factor, test weight, disease resistance, and heading date are important considerations as they also impact economic return.

Test weight is important because low test weight results in dockage at the elevator. Heading day is a function of cold requirement (vernalization) and day length (photoperiod) response that determines when a variety heads out. Some varieties head very late or not at all in south Louisiana due to a long vernalization requirement or photoperiod response, while those same varieties may perform better in north Louisiana or Arkansas. Varieties that fully vernalize but head out late due to long photoperiod requirement perform poorly in south Louisiana due to grain fill during hot weather. By contrast, early heading varieties may yield poorly in north Louisiana due to late spring freeze damage. Vernalization and photoperiod response are the primary reasons for dividing Louisiana into North and South regions.

Early-heading and maturing varieties permit earlier harvest and more timely planting in a double-crop system, while later-heading varieties guard against damage from a late spring freeze and can be planted earlier in north Louisiana. Early-heading varieties should be planted in the second half of the recommended planting window to reduce the likelihood of spring freeze damage. Lodging resistance helps guard against reduction in test weight and yield loss that results when near-mature heads come in contact with the ground.

Disease resistance protects yield and reduces input costs. Disease susceptibility is very important in terms of yield and profitability. Reactions for naturally-occurring diseases are also listed for each variety. Fusarium head blight (FHB) epidemics were severe during the 2020 seasons due to environmental conditions favoring infection during flowering. There are no varieties fully resistant to FHB, but some have high to moderately high to moderate levels of resistance. It should be noted that varieties less susceptible to disease may not always be the highest yielding, especially if disease pressure is not present. However, in high disease pressure situations, these varieties produce higher yields than susceptible varieties and enhance profitability by saving the costs of fungicide applications.

Crop management:

Planting dates for Louisiana wheat depend on location and variety. For southern and central Louisiana, optimum planting dates range from November 1 through November 30. The optimum planting for northern Louisiana is slightly earlier, ranging from October 15 through November 15. Early-heading varieties should generally be planted after the mid-date, while late-heading varieties can be pushed a little on the early side of the planting window. The weather in north Louisiana is cooler in the fall and early winter, which slows growth and prevents excess winter growth. It is important that the wheat crop be well-established and fully tillered before the coldest part of the winter. Additionally, because of the cooler conditions, the threat from fall pests (Hessian fly, army worms and rust) is decreased earlier in the fall compared to south and central Louisiana. While these dates are the optimum planting window averaged over years, the timing will vary in some years depending on weather patterns. Additionally, if wheat cannot be planted within these optimum windows, planting later than the optimum window is usually better than planting too early. Early planting can result in greater insect and fall rust establishment and also makes plants more prone to spring freeze injury due to excessive fall growth and development. Planting too late (more than 14 days after the optimum window) can result in significant yield loss due to slow emergence, poor stands from seed rotting and a decreased tillering period, which results in fewer and smaller heads.

Wheat can be planted by broadcasting seed and incorporation into the soil; however, it is preferred that the seed be drilled. Drilling the seed increases the uniformity of depth and uniform emergence. Use recommended planting rates for drilled wheat (60 to 90 lb/A) or broadcast wheat (90-120 lb/A) of quality seed into a good seedbed with adequate moisture. This higher seeding rate should be used under conditions in which good germination or emergence is not expected, as occurs with late-planted wheat or heavy, wet soils. Late-planted seed should be planted at a higher seeding rate using a drill to ensure rapid, adequate and uniform emergence.

Good surface drainage is critical to successful wheat production. Saturated fields lead to diseases such as root rots and downy mildew, reduced tillering and vegetative growth, and decreased root development and nutrient utilization. Yields in wheat fields suffering from waterlogging stress are greatly reduced. Fields with marginal drainage should be ditched to ensure that water stands for a minimum time after heavy rainfall.

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 soil type and rainfall after applications. Timing of 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 and increased lodging potential, as well as a higher probability of spring freeze damage from early heading. If the wheat crop is following soybeans, soil residual or mineralized 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 optimum, 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 top dress 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 February. However, first spring fertilizer application should be applied prior to first node (Feekes 6) in order to ensure optimum head development, tiller retention and head size. Crop N stress around jointing (Feekes 6) will result in yield losses. 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 as soon as possible 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. Oftentimes, early spring sulfur (S) deficiencies are mistaken for N deficiencies and additional S is not applied. Because sulfur is mobile, similar to N, the application solely in the fall may not be adequate. Supplemental applications of S with spring N applications are often warranted.

For further questions or comments contact:

Steve Harrison, Small Grain Breeder, sharrison@agcenter.lsu.edu

Boyd Padgett, Wheat Extension Specialist/Plant Pathologist, bpadgett@agcenter.lsu.edu

Trey Price, Extension Research Plant Pathologist, pprice@agcenter.lsu.edu

9/17/2021 2:27:49 PM
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