Volume 13, Issue 7 - September 2023

David Moseley, Stephenson, Daniel O., Hendrix, James, Majs, Franta, Miller, Donnie K., Wang, Jim Jian, Conger, Stacia, Parvej, Md Rasel, Tubana, Brenda S.

Louisiana Crops Newsletter Plain Banner.

Effective Soil Sampling and Testing Drive Precise Fertilizer and Lime Recommendations

Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter Soil Scientists; Jamil Uddin, LSU AgCenter Postdoctoral Researcher; James Hendrix, Conservation Agronomist, Northeast Region; Franta Majs, LSU AgCenter Soil Testing and Plant Analysis Laboratory Director

Article Highlights:

  • Soils from each field should be tested on a regular basis before making any fertilization decision.
  • Soil-test-based fertilizer recommendations for a particular crop should be obtained from the state soil testing lab since the recommendations vary with crop and state.
  • Soil testing is only reliable for phosphorus (P), potassium (K), sulfur (S), zinc (Zn), and lime recommendations.

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

Soil Sampling:

  • Soil should be tested at least once in every 2-4 years or once in a complete crop rotation.
  • Soil samples should be taken at the same time of each sampling year and at a constant depth of 0 to 6 inches with a soil probe or auger.
  • At least one composite sample should be taken for every 10 acres of land for zone sampling and 2.5 acres of land for grid sampling. The area associated with both zone and grid samplings depends on the spatial variability of the field. More soil samples are needed per unit area for highly variable fields. Therefore, soil type and color, topography, past management, and yield map should be considered to determine the actual zone and grid sizes.
  • Each composite soil sample should consist of 12-15 subsamples (i.e., 1-2 subsamples per acre for zone sampling and 5-6 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.
  • During sampling, the thin layer of soil surface should be scraped to remove any vegetation before inserting the soil probe or auger. For the furrow irrigation system, each sample should be taken from the top of the bed (4 to 6 inches apart from the crop row). However, for any field, soil samples should not be taken from fertilizer bands, manure or lime stockpiles, wet spots, fence rows, and from an area that is too small to be managed separately. All subsamples should be mixed thoroughly in a clean plastic bucket and stones, roots, stems, trash, and other debris should be removed from the mixed soil samples.
  • Each composite soil sample should be placed separately in a clean plastic or paper bag with clear labeling 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 the same soil extraction methods that were used to develop fertilizer recommendations for that state. Soil-test-based fertilizer recommendations in Louisiana are based on the Mehlich-3 soil exaction method for soil samples collected from 0-6-inch depth.
  • Soil samples should be analyzed in the same lab each year to create a historic record.

Soil Test Results Interpretation and Fertilizer Recommendations:

  • Soil test results should be interpreted based on recommendations developed from correlation and calibration research conducted across multiple site-years. Since soil-test-based fertilizer recommendations vary with crops and states, soil-test results for a particular crop of a particular state should be interpreted with that crop-specific recommendations developed by that state. Usually, soil scientists from every land-grant university develop their own recommendations for each crop. So, it is preferred to analyze soil samples in the state soil testing lab and obtain fertilizer recommendations from that state lab. Note that fertilizer recommendations obtained from different states' labs (public or private) may not be accurate and may often time higher than the actual need.
  • Soil testing is only reliable for phosphorus (P), potassium (K), sulfur (S), zinc (Zn), and liming recommendations. Therefore, soil-test-based recommendations for other nutrients from any soil test labs may not be accurate. Fertilizer recommendations for most micronutrients [Boron (B), Iron (Fe), Manganese (Mn), and Molybdenum (Mo)] depend on soil pH. In general, micronutrients except Mo is recommended for fields with pH higher than 7.5 and Mo is recommended specifically for soybean production in fields with pH less than 6.0 and no lime was applied in the previous Fall.

The Timing of Soil Sampling after Corn and Rice Harvest Impacts Fertilizer Recommendations

Rasel Parvej, LSU AgCenter Soil Fertility Specialist, and Jamil Uddin, LSU AgCenter Postdoctoral Researcher

Article Highlights:

  • Soil-test P and K concentrations fluctuate temporally from September through March and the degree of this temporal fluctuation depends on the previous summer crop.
  • Soil-test K concentration increases with time following the harvest of high-residue crops and peaks around late December.
  • It is better to collect soil samples in late December following high-residue crops to get higher soil-test values and save fertilizer input costs.

The amount of phosphorus (P) and potassium (K) fertilizer required for maximum crop yield is determined by routine soil testing. Most land-grant universities developed soil-test-based P and K fertilizer recommendations based on soil samples collected typically from late winter months (January-February) to before summer crop planting. However, the time for soil sampling from producer fields has recently changed greatly. Nowadays, crop consultants or farm-service reps prefer to collect soil samples mostly within a few weeks after summer crop harvest (August-November, depending on the type of summer crop) due to the chances of rain in the early to late winter months (December-January), increased number of soil collection over time, and use of ATV’s or autosamplers in dry soil conditions. Since soil-test P and K concentrations are reported to fluctuate spatially and temporally, the recent change in soil sampling time may influence the current soil-test-based P and K fertilizer recommendations for row crop production.

Recent research conducted on silt loam soils in Arkansas showed that soil-test P and K concentrations changed temporally from September through March and the temporal change was affected by the previous summer crop. Researchers from the University of Arkansas (Slaton et al., 2016) found that following rice harvest, soil-test P concentration remained constant across time, but soil-test K concentration increased gradually with time and peaked by 22 ppm (44 lb K/acre) in late December. Our 1-year preliminary data from 2022 showed that following the corn and rice harvest, soil-test K concentration increased up to 50 ppm (100 lb K/acre) in late December compared to early September mainly due to K leaching from crop residue (Figure 1). Corn straw releases around 60 lb K2O/acre and rice straw releases around 35 lb K2O/acre. However, soil-test K concentration decreased after late December with cold temperatures. High residue crops such as rice and corn hold a greater amount of K than P in vegetative plant parts and eventually release more K across time after harvest compared to a low residue crop such as soybean. Since K is not a part of the cell wall or any molecular structures, it is slowly being leached from crop residues by rainfall following harvest, resulting in increased soil-test K concentration in December-January compared to September-October and lower recommended fertilizer rates for samples collected in the late winter months. Therefore, it is better to collect soil samples in late December following the rice and corn harvest to get higher soil-test values and save fertilizer input costs. However, if the producers suspect having low pH and lime application for a particular field, soil sampling immediately after crop harvest will give enough time for lime to incorporate and increase soil pH to the targeted level.

Mehlich-3 soil potassium, straw potassium concentration, and amount of potassium leaching from straw across time after corn and rice harvest. Straw potassium concentration goes down over time and soil potassium concentration fluctuates up and down over time.

Figure 1. Mehlich-3 soil K concentration (a-b), straw K concentration (c-d), and amount of K leaching from straw (e-f) across time after corn (left) and rice (right) harvest for research trial conducted at LSU AgCenter – Macon Ridge and Northeast Research Station in 2022 to 2023 for corn–soybean and rice–soybean rotations.

Soil Liming Consideration Varies with Crop and Target Soil pH

Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter Soil Scientists; Jamil Uddin, LSU AgCenter Postdoctoral Researcher; James Hendrix, Conservation Agronomist, Northeast Region; Franta Majs, LSU AgCenter Soil Testing and Plant Analysis Laboratory Director

Article Highlights:

  • Liming depends on the target soil pH that varies with the crop, and lime is required if the target soil pH is 0.2 units more than the actual soil pH.
  • Lime should be applied followed by incorporation in the Fall since it takes a long time to raise soil pH.

After receiving the 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 making the liming decision.

Liming Consideration:

  • The rate of lime depends on the initial and target soil pH values as well as the buffering capacity of the soils (i.e., buffer pH, the ability of a soil to resist the change of pH). Lime rate would be low for soils with low buffering capacity (high buffer pH) and a small difference between initial and target soil pH values. However, for soils with high buffering capacity (low buffer pH), the lime rate would be high even for a small change of soil pH. Clay (fine-textured) soils have higher buffering capacity and require a greater amount of lime for each unit increase of soil pH than silt loam (coarse-textured) soils. Note that LSU AgCenter Soil Testing and Plant Analysis Lab does not determine lime requirement based on buffer pH but indicates the unit change of soil pH with the addition of a maximum 3 tons of lime per acre assuming higher than 3 tons of lime per acre may be too expensive and let the producers decide how much to apply based on their cost-benefit analysis.
  • 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 units more than the actual soil pH.

Application Time:

  • Lime usually takes long time, at least 6-9 months, to react with the soils and raise soil pH. However, lime reaction time with soils depends on the quality of liming materials, lime incorporation, soil temperature, and rainfall amount and distribution pattern. Therefore, lime should be applied uniformly and incorporated by tillage for till fields in the Fall.
  • For no-till fields, increasing soil pH by liming within a short period of time is difficult due to lack of incorporation. Therefore, soil pH needs to be monitored more often in no-till fields, if possible, each year. Also, special attention is required for fields with low buffering capacity that receive high rates of ammonium (NH4+) based fertilizers (urea, UAN, or ammonium sulfate) because ammonium fertilizer decreases soil pH. Producers should not let the soil pH go down too far from the target level for these types of fields.

The availability of nutrients increase or decrease depending on soil acidity and alkalinity.

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]

Lime Application Rate Depends on Lime Quality

Rasel Parvej, Brenda Tubana, and Jim Wang, LSU AgCenter Soil Scientists; Jamil Uddin, LSU AgCenter Postdoctoral Researcher; James Hendrix, Conservation Agronomist, Northeast Region; Franta Majs, LSU AgCenter Soil Testing and Plant Analysis Laboratory Director

Article Highlights:

  • Liming materials should have more than 80% CCE (calcium carbonate equivalent) and/or 50% ENV (effective neutralizing value) and the recommended lime rate should be adjusted based on these two qualities.
  • Finer lime particles are more efficient in increasing soil pH by reacting quickly with soils, but liming materials should have 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.

Lime Quality:

  • 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% (the molecular weight of pure calcium carbonate is 100 g) and this rating is called calcium carbonate equivalent (CCE).
  • Another lime quality is the particle size, also known as the fineness factor of liming material, and is expressed as the percentage of liming material passes through various-sized screens. The higher the percentage of liming material 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 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.

Lime Application Rate:

  • 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. Also, the actual lime rate 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 per acre 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.

Fall Phosphorus and Potassium Application Depends on Soil-Test Values and Soil Types

Rasel Parvej, LSU AgCenter Soil Fertility Specialist; David Moseley, LSU AgCenter Soybean Specialist; and Jamil Uddin, LSU AgCenter Postdoctoral Researcher

Article Highlights:

  • Fall application of P and/or K should be considered as a maintenance rate for medium to high P and K testing soils. For clayey soils, the fall application of P is suitable regardless of soil-test values.
  • In all other scenarios, it is advisable to apply fertilizer near planting in the spring.
  • Fertilizers applied in the fall must be incorporated by tillage or hipping the bed to minimize losses over the winter. Incorporation following spring application is also recommended, if possible.

Louisiana producers predominantly use triple superphosphate (TSP; 0-46-0) for phosphorus (P) fertilization and muriate of potash (MoP; 0-0-60) for potassium (K) fertilization. These fertilizers are typically applied during the fall rather than the spring. Fall application is primarily driven by factors such as wet soil conditions or limited time for application during the spring planting season. One common misconception regarding the spring application of both P and K fertilizers is that they require an extended period to dissolve and become available for plant uptake. In reality, both fertilizers exhibit high water solubility and can rapidly release nutrients, regardless of the time of application, provided there is sufficient soil moisture or access to rainfall/irrigation water.

Numerous studies, including research conducted in Louisiana, have demonstrated that spring application of both TSP and MoP fertilizers can yield equal to or better than fall application, particularly in soils that are deficient in nutrients and highly prone to nutrient losses through leaching, runoff, and/or erosion. However, when applying both fertilizers in the spring, it is crucial to incorporate them by re-hipping the planting bed (typically for 30-40-inch row spacing). This process helps bring most of the broadcasted fertilizers from the furrow back into the bed and reduces the potential loss of fertilizer-P and K from the furrow due to rainfall and irrigation water over time. This incorporation also increases the availability of fertilizer-P and K within the bed, closer to the plant roots, leading to improved P and K uptake and ultimately higher crop yields. Several key factors should be considered when deciding on the timing of P and K fertilizer application:

  • The rapidity of P and K fixation to unavailable forms typically accelerates as soil-test P and K concentrations decrease. This means that soils with insufficient P and K levels tend to immobilize applied P and K more quickly than soils with ample P and K reserves. Consequently, it is advisable to apply fertilizers in the spring, either at or close to planting, in soils deficient in P and K. This timing ensures optimal nutrient availability precisely when plants undergo rapid uptake.
  • The highest soil P availability occurs between soil pH 6.0 and 7.5. When the soil pH drops below 5.5, fertilizer-P becomes immobilized as aluminum phosphate, and when it rises above 7.5, it transforms into calcium phosphate, rendering it less available to plants. Consequently, for fields with low soil pH (<5.5) or high soil pH (>7.5), fertilizer-P should be applied in the spring near planting to ensure the greatest accessibility of fertilizer-P 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. However, for fine-textured soils with a high CEC (>20), applying P and K in the fall may not pose significant issues.
  • For soils that are very prone to waterlogged/flooded conditions, fertilizer-P and K should be applied in the spring, ideally at or around the time of planting. This is because the cyclic transition between flooded (anaerobic) and non-flooded (aerobic) conditions decreases soil nutrient availability and increases nutrient losses.
  • Fall application of P and K should be considered for soils that already have nutrient concentrations at or above the critical level (medium to sufficient), where fertilizers are primarily applied to replenish soil nutrients depleted by harvested crops. In addition, fertilizer-K should be applied in the Fall in fields that have a history of chloride (Cl) toxicity issues and are poorly drained. Since K fertilizer (MoP) mainly consists of potassium chloride (KCI), fall application provides ample time to decrease Cl toxicity by reducing Cl accumulation from KCl through winter and early spring rainfall.

LSU AgCenter Conducts Soybean Variety Trials and On-farm Demonstration Plots

David Moseley, LSU AgCenter soybean specialist

Article Highlights:

  • It is important for a producer to consider how varieties perform in an environment similar to their own and in multiple environments.
  • The LSU AgCenter conducts an Official Variety Trial (OVT) and Core-block demonstration plots to provide unbiased data to assist in variety selection.
  • The LSU AgCenter also conducted other on-farm demonstrations including variety evaluations (conventional and nematode resistance) and fertilizer applications (potassium and manganese).

Selecting the most adapted and high yielding varieties is one of the most important decisions a soybean producer makes every year. 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 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 2023 OVT includes varieties with maturity groups ranging from 3.7 – 5.8. The maturity groups are divided into sections including 3.7-4.4; 4.5-4.7; 4.8-4.9; 5.0-5.3; and 5.4-5.8, and there were 12; 22, 15; 10; and 12 varieties submitted to the maturity group sections, respectively, by nine seed companies and one University soybean breeding program. The varieties consist of several different herbicide technologies. 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 Core-block 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 2023, seven seed companies submitted varieties to be evaluated in the core-block demonstrations. Twenty-seven demonstrations were planted across 14 parishes. The demonstrations were divided by maturity group (MG). A demonstration consisted of varieties with a MG of 3.9 to 4.4; 4.5 to 4.9; or 5.0 to 5.8. The number of varieties submitted for each MG were five (MG 3.7 to 4.4), twelve (MG 4.5 to 4.9) and eight (MG 5.0 to 5.6).

Nematode resistance demonstrations were conducted again in 2023. A total of seven varieties from four seed companies were entered into the nematode resistance screening trial. Among the varieties, six were entered as resistant varieties and one was entered as a susceptible variety. The nematode resistant demonstrations were planted in three parishes (Tensas, Franklin, and Bossier) in fields known to have nematode pressure. Along with yield, nematode assays were taken near the R8 (mature) growth stage. To complement this trial, Dr. Tristan Watson (LSU AgCenter Nematologist) also conducted greenhouse trials to determine the level of resistance for each variety.

Conventional soybean variety demonstrations were conducted in Acadia, Bossier, Franklin, and Tensas parishes. The University of Missouri and a seed company entered a total of seven conventional varieties. For comparison, a glyphosate and dicamba commercial check was included in the demonstrations. Data from these demonstrations will help farmers who produce soybean in herbicide restricted habitats and who are looking for a potential premium from conventional soybean varieties.

In addition to the variety trials, a potassium demonstration was conducted in Beauregard parish on a light soil with very low potassium soil levels. Granular and foliar applications of potassium were applied at various times and rates (eight different applications). This data will help farmers understand best management practices to economically correct low potassium levels.

In 2023, an on-farm manganese trial was initiated in Catahoula parish. The trial was initiated in two fields covering a total of approximately 170 acres. There were 13 different treatments with different fertilizer formulations, rates, and timing applied. In addition to manganese, the treatments included different nutrients to help alleviate other deficiencies. Follow-up trials on the farm will be to examine different fertilizer rates and application timings for a better understanding of the most economical fertilizer program for those fields.

The parishes in which the soybean core-block demonstrations were located in 2023 are indicated in figure 1.

Variety Testing and On-farm Core-block Demonstration Results

The performance data from the soybean OVT and on-farm 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 2023 OVT results will be published following harvest to assist with 2024 variety selections and planting decisions. The variety publication for the 2022 growing season can be found at 2023 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.

The LSU AgCenter on-farm core-block variety demonstrations were planted in 14 parishes across Louisiana. Figure 1: 2023 soybean core-block locations

Scheduling Soil Tests Can Vary with Cropping Systems

James Hendrix, Conservation Agronomist, Northeast Region and Rasel Parvej, LSU AgCenter Soil Fertility Specialist

Article Highlights:

  • Issues with applications without soil tests
  • Cover crops can affect soil test results
  • Crops determine soil test timing
  • Proper sampling technique

Balancing soil nutrients to optimize production and profit is a basic management practice that should begin with a soil test.

Soil testing is a “best management practice” that can identify nutrient deficiencies and surpluses, nutrient availability for the crop to be grown and potential environmental concerns. Another benefit to soil testing is that it offers an idea of how well you came through the past growing season. Mid-range values indicate an adequate fertility program during the previous season. A buildup of nutrients may be caused by over-fertilization and result in high or very high soil test results. Nutrient buildups can lead to plant growth problems and environmental pollution.

Applying fertilizer or lime without a soil test can result in one of three things, two of which are bad.

1.You may apply more fertilizer or lime than is required, resulting in higher production costs and no increase in crop yield. The surplus buildup of nutrients may pose an environmental hazard.

2.You may apply less fertilizer or lime than you need, resulting in reduced yields or less than expected outcome.

3.You may accidentally get the rate and timing right, which provides the intended results.

Late fall and early winter soil testing are common in Louisiana, especially if you expect issues with pH that needs addressing prior to planting spring and summer crops. If lime is recommended, it should be applied several months in advance to reduce soil acidity to the desired level.

If soil nutrient recommendations are the major focus for soil testing, fall vs early spring soil testing can provide mixed results. After harvesting crops, substantial amounts of nutrients remain in the remaining crop residue left in the field. High residue crops such as corn and rice contain more K than P in the biomass. Corn residue from a 200-bushel crop can contain approximately 30 lb. P2O5 and 200 lbs. of K2O. Rice residue at the same yield can contain 15 lbs. P2O5 and 100 lbs. of K2O. Since K is not a part of the plant’s cell wall or other molecular structure, it can be leached from residues by rain events following harvest. This can result in higher soil-test K levels in December-January versus results from sampling in September-October. Research in Arkansas has shown that soil-test P and K concentrations change from September to March and the change was affected by the former crop grown. Soil testing for high residue crops such as rice and corn that was conducted in December-January revealed higher nutrient values, reducing fertilizer recommendations and costs.

If soil tests are to be conducted in the fall, the producer should consider the additional nutrients that are provided by the previous crop residue, as well as nutrients produced or scavenged by cover crops that were planted in the fall. Timing cover crop termination to maximize the objective(s) for planting while minimizing any negative impact to the crop following must also be considered. Residue from cover corps with a low C:N ratio, such as legumes break down and release nutrients quickly after termination but may leave the ground bare and vulnerable to erosion. Cereals can take several weeks to break down, releasing nutrients slower over time, but reducing the issue of erosion. Nutrient release and plant availability from the crop residue can be affected by many factors, such as the weather, soil properties, physical features, and tillage. Utilizing a suite of best management practices (BMPs) such as residue management, cover crop management, reduced tillage, etc. can boost nutrient availability for crops and minimize losses from erosion.

Research trials are currently being conducted at the Louisiana State University AgCenter – Macon Ridge and Northeast Research Stations to identify the optimal time to soil sample after corn, cotton, and soybean harvests. The 1-yr preliminary results showed that Mechlich-3 soil K concentration can be increased up to 50 ppm in late December compared to right after corn and rice harvest and corn and rice straw can release around 60 and 35 lb. K2O/acre, respectively from harvesting to mid-January.

For agricultural producers, the common sampling method is to pull a soil sample on at least every 10 acres. Large fields, especially with multiple soil types or yield issues need to be subdivided and identified accommodate this.

Ten to fifteen random samples from the surface down to a depth of six inches should be collected in a clean plastic container/bag and mixed thoroughly for each site sampled. Specify on each bag or container the sample location, collection date, irrigated or non-irrigated land and crop to be planted. Contact your local Parish Extension Office for sample boxes, costs and instructions for collection and shipment to the soil testing laboratory. A routine analysis includes soil pH, extractable phosphorus; sodium, potassium, magnesium and calcium, copper, sulfur, and zinc, lime/sulfur requirement soil texture and fertilizer recommendation.

Sampling technique is of major importance in analysis of a soil sample. Sample depth, if taken above or below the recommended six- inch level, can result in inaccurate results. Many people use a shovel to collect soil samples. This can result in a greater proportion of the sample originating from the top. Some trimming of the shovelful may be necessary so that all parts of the zero to six-inch depth are equally represented.

Using a soil probe for sampling avoids this problem. Contact your local extension office, as soil probes may be available for you to borrow. Usually, most of the phosphorus and potassium are in the upper six inches, thus taking samples below the six-inch level will cause results to appear lower than they actually are, resulting in a recommendation to apply these nutrients. On the other hand, taking a sample in soil at a depth of three inches may reflect abnormally high levels of phosphorus and potassium when they may be lower. Most university soil tests are calibrated based on a depth of six inches.

For more information, contact your local LSU AgCenter Extension Office.

Italian Ryegrass Management

Donnie Miller and Daniel Stephenson, LSU AgCenter Weed Scientists

Italian ryegrass has become one of the most common and problematic weeds infesting Louisiana crops. Research has shown that it can be competitive with most crops, in particular corn. This annual winter weed often requires only 7-10 days of temperatures below 90 degrees to germinate, but lack of adequate moisture is often the limiting factor delaying germination to October or November in Louisiana. Research has indicated that glyphosate and paraquat-resistant Italian ryegrass populations are present and ACCase resistance is suspected in Louisiana, therefore, producers are encouraged to closely monitor populations.

Management of Italian ryegrass can be divided into a fall, winter, or spring management timing. However, research has shown greater control when measures are initiated in the fall followed by a winter or spring herbicide application(s) if needed. Fields should be double-disked or treated with Command, Boundary, metribuzin, Dual Magnum or equivalent, Zidua, Anthem Flex, Anthem Max, or trifluralin in mid-October thru November. Please consult individual product labels for fall applied rates, precautions, and plant-back restrictions. Emerged Italian ryegrass will not be controlled by these products, therefore, should be tank-mixed with paraquat at 0.5 to 0.75 lb a.i./A if ryegrass has emerged. Preliminary research has shown that Reviton at 2 oz can provide fair control of small (1-2”) ryegrass, but not to the level of paraquat. Research has also shown that Dual Magnum or Zidua applied 2 weeks after emergence of a cereal rye cover crop to be very effective in managing Italian ryegrass. Regardless of which fall control measure is utilized, fields should be scouted in January/February and if Italian ryegrass has emerged, glyphosate, paraquat, or Select Max at 12 to 16 oz/A (or equivalent rate of 1, 2 or 3 lb clethodim formulation) should be applied.

Preplant applications of Select Max or any other clethodim formulation should be made at least 30 days before planting corn, grain sorghum, or rice. Producers are cautioned that addition of 2,4-D to clethodim may result in reduced ryegrass control. Multiple applications of Select Max or any other clethodim formulation are discouraged to prevent development of resistance to this herbicide. If no control measures are initiated in the fall or winter, paraquat at 0.75 to 1.0 lb a.i./A should be applied. Research has shown that the addition of atrazine (corn) at 1 qt/A, Metribuzin 75 DF (soybean) at 3 to 4 oz/A or equivalent rate of other metribuzin formulations, or diuron (cotton) at 1.5 pt/A will increase efficacy of paraquat on Italian ryegrass. Liberty can provide good control (not to the level of paraquat) but is much more effective in higher temperatures. Sequential applications should be based on careful scouting for emerged glyphosate-resistant Italian ryegrass.

If you have any questions, please contact your local parish agent or Donnie Miller at 318-614-4044 or Daniel Stephenson at 318-308-7225.

Cover Crop Planting Considerations

James Hendrix, Conservation Agronomist, Northeast Region and Dr. Donnie Miller, LSU AgCenter Weed Scientist

Article Highlights:

  • Weather related planting issues
  • Seeding rate decisions
  • Herbicide tolerances
  • Last minute crop decisions

Crop harvest and soil preparation for next year’s crop is continuing at a record pace due to the favorable harvest conditions in most of Louisiana. Producers planting covers this year have seen seed costs increase 10-12% this year due to supply and demand. Most have already purchased seed in late summer, and those that have not may see seasonal increases in prices due to the shorter supplies available if buyer demand is high.

Producers should consider several factors before planting covers too early this year. Even though the early planting dates for winter cover crops are approaching, the weather and soil conditions have not been favorable to get an early start planting. Drought conditions have plagued much of northeastern Louisiana, and the rains we have been blessed with have not been enough to assure cover crop germination and growth. Also, remember the fall armyworm. This summer has been abnormally dry and hot, the ideal environment for armyworm infestations. Keep in mind the issues that can be associated with early planting. If you plant early, remember to scout your fields.

Once the weather and soil moisture are favorable, hopefully by the end of September, plantings will begin. Producers should begin planting fields that will be planted to corn or grain sorghum next year, due to the short growing season to produce desired biomass.

Anyone planting cover crops under EQIP or any other contracts with seeding rate specifications must remember to use the seeding rates specified by the contract. Planting a cover crop mix, with two or more species, is based on a percentage of the seeding rate for each species. Before planting, contact your NRCS office for approval of the seeding rate for the mix. Producers not under contract can contact their local County Agent for assistance with seed mixes.

If you purchased seed based on planting next year’s cash crop, such as cotton, and have changed your mind to plant corn, you may face less than expected results from the cover crop and future crop’s yield. Selecting a cover crop species is based on specific objectives to be accomplished, and soil characteristics, environmental factors and the management practices of the past cash crop and next year’s crop should be considered. The timing of planting, termination, and residue management must coincide with the future crop’s planting and management practices, and still accomplish your objectives. Otherwise, your time and investment in utilizing cover crops in your production system can be frustrating and of little value.

Another factor in the decision to plant cover crops are the previous crop lay-by and post-harvest herbicide applications that must be considered. Residual herbicides can cause significant issues to germination and growth of some cover crops, so contact your extension agent or consult the herbicide label for tolerances.

Last, but not least, select the species and varieties of covers that are recommended for your area and will fit your production system. Study the species and varieties you plan to plant and contact your extension agent if you have any questions. Do not put yourself in a situation that can destroy your production system. One example has been planting pasture wheat as a cover crop. There have been multiple issues with termination that have caused serious problems with nutrient scavenging, residue management, and planting the following crop.

In conclusion, remember that legumes produce most growth during the spring, so planting early in fall can benefit establishment before winter freezes slows growth. Brassicas grow fast in the fall and can be terminated by freezing weather, so should be established early to benefit from nutrient scavenging and other benefits. Most cereals grow well in fall and spring, so the planting window is broader. Oats germinate faster than most cereals, but can be terminated during extreme winter temperatures, while cereal rye, triticale and wheat are more tolerant.

IT’S HERE! Drought Irrigation Response Tool Just Released

Stacia L. Davis Conger, Ph.D., State Irrigation Specialist, LSU AgCenter

We are overly excited to announce that the Drought Irrigation Response Tool (DIRT), our highly anticipated irrigation scheduling webtool, has been released to the public! This tool was created to assist with managing furrow irrigation strategies for corn, cotton, soybean, grain sorghum, and sugarcane (beta).

You can access the webtool by visiting www.lsuagcenter.com/dirt. There is a draft manual on the landing page that will be very helpful when navigating the application for the first time. The AgCenter does not save your personal log-in information, so logging in must occur using a third-party option. Options currently include Google or Facebook. Do you have another option to recommend? Let us know by emailing Dr. Conger directly (sdavis@agcenter.lsu.edu). She can work with AgCenter IT on accommodating new requests.

While we understand that your irrigation season may be over or wrapping up, you may want to use this opportunity to look at what the tool predicted for this past crop season and compare it to what you were able to accomplish this year. Familiarizing yourself with this option now can speed up the learning curve for the spring in case we have another dry year. And keep your eyes/ears open for when we schedule training sessions in the early spring!

LSU AgCenter Specialists

Specialty Crop Responsibilities Name Phone
Corn, cotton, grain sorghum Agronomic Trey Price
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 James Villegas
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 318-435-2908

9/21/2023 5:55:38 PM
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