David Moseley, Davis, Jeff A., Stephenson, Daniel O., Brown, Sebe, Brown, Kimberly Pope, Foster, Matthew, Parvej, Md Rasel, Towles, Tyler, Dodla, Syam, Conger, Stacia
In this article:
|Pesticide Disposal Program|
|Reminder: Survey on Flood Irrigation Practices Still Open|
|Nitrogen rate and fertilization timing in corn production|
|Starter fertilizer in corn production: Is it needed?|
|Grain Sorghum Planting and Nutrient Management Tips|
|Pipe Planner Has New Look, Easier to Use|
|Soybean Insecticide Seed Treatment Decisions|
|Identifying Soybean Growth Stages|
Kim Brown, LSU AgCenter pesticide safety coordinator
The Louisiana Department of Agriculture and Forestry (LDAF) is sponsoring two opportunities to dispose of unwanted pesticides. These events are free to participants. Only pesticides may be disposed of at these events.
March 30, 2021 at the Old 3 Leagues Gin in Natchitoches, LA
April 1, 2021 at the Louisiana Department of Agriculture and Forestry in Monroe, LA
The events will run from 7:00 AM – 1:00 PM both days. People that would like to participate should contact their local county agent to get an inventory form. Please be sure to complete a pesticide inventory form and return to your local county agent prior to March 19th to allow for the disposal contractors to plan for the disposals.
For additional information contact LDAF or the LSU AgCenter.
Stacia L. Davis Conger, LSU AgCenter engineer
A NASS-style survey was created to help 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 using flood irrigation systems.
Click the link to access the flood irrigation survey.
The survey is 21 questions and will take an estimated 15 minutes to complete. This survey maintains anonymity of individual respondents and you may choose to discontinue participation at any time. Summaries of responses will be shared at extension and outreach events such as university field days, workshops, social media, and crop schools in the future.
We appreciate your willingness to participate in this timely research.Please direct all questions, comments, and concerns to Dr. Conger at firstname.lastname@example.org or (904) 891-1103.
Rasel Parvej, Syam Dodla, and Matthew Foster, LSU Agcenter scientist
Nitrogen is the most yield limiting nutrient for corn production. Corn requires nitrogen for amino acids, protein, and chlorophyll production. Chlorophyll is the key component for photosynthesis. Insufficient chlorophyll content results in reduced yield potential. A 200-bushel corn crop requires about 200 to 250 pounds nitrogen per acre i.e., roughly 1 to 1.25 pounds nitrogen per bushel corn harvested. The upper range is for clayey soils since corn production in clayey soils requires more nitrogen than sandy or silty soils due to nitrogen (ammonium ion) fixation between clay particles to a biologically unavailable form.
Nitrogen management in corn production is one of the biggest concerns for corn producers every year. Nitrogen is recommended to apply in 2 to 3 splits from planting to tasseling since it is very prone to loss to the environment via different loss mechanisms. Unfortunately, most corn producers in Louisiana apply the total nitrogen fertilizer in a single application as sidedress at or few weeks after corn emergence. A significant amount of this nitrogen in most years can be lost during the growing season through volatilization, denitrification, leaching, and/or runoff, resulting in corn yield loss. Volatilization loss is very high in hot and humid climates, common in Louisiana, and in alkaline soils (pH more than 7.0) if nitrogen fertilizer (especially urea but can be UAN as it contains 50% urea) is not incorporated within a few days after application. Denitrification loss is the main concern in poorly drained soils but can occur in any soil with excessive rainfall that creates water-logged anaerobic conditions. Leaching loss is high in high rainfall areas especially in sandy soils with low cation exchange capacity (CEC). In most years in Louisiana, excessive rainfall often occurs in the lower Mississippi Delta during the early growing season, resulting in saturated soils for several days, which accelerates nitrogen losses via denitrification, leaching, and/or runoff and reduces corn yield potential. Although researchers from the mid-South states have showed that it is possible to maximize corn yield by a single nitrogen application during the growing season in both silt loam and clay soils, for this to occur, the growing season must be ideal with moderate temperature and adequate and evenly distributed rainfall, which is seldom occurred in Louisiana. Since we cannot predict weather conditions during the growing season, a single application is, therefore, a risky nitrogen management plan for corn production in most years in Louisiana.
In general, a 200-bushel corn in silt loam soils requires about 10% (20 pounds) of the total nitrogen (200 pounds) from planting to V6 stage (6 visible collar leaves and plant is about 12-18 inches tall; Figure 1), 55% (110 pounds) from V6 to R1 (silking), and 35% (70 pounds) from R1 to R6 (maturity; Figure 2). On the other hand, corn initiates ear shoots and tassel and sets yield components such as kernel rows per ear and potential kernels per row at or little after V6 stage (Figure 2). Considering both nitrogen requirement and yield component development at different growth stages of corn, it seems like a nitrogen management plan should include nitrogen application in three splits with a small amount of nitrogen (1/4) at planting, most (2/4) at around V6 stage, and another small amount (1/4) at pre-tassel stage. However, most of the research showed that two applications (1/4 at planting and 3/4 at V6-8 stage) are good enough to maximize corn yield under normal conditions in most soils with medium to high CEC (>10).
Regardless of split application number, applying a small amount of nitrogen at or before planting would provide the corn plant enough nitrogen for setting maximum yield components at or after V6 stage. It would also provide a wide window of opportunity to sidedress nitrogen application during the growing season from V6 to V8 stage. For instance, having a pre- or at-planting nitrogen application would allow the producers to delay their sidedress application if missed at V6 stage due to rainfall and wet soil conditions. Unfortunately, pre- or at-planting nitrogen application is not very common in Louisiana corn production. Rather, most corn producers in Louisiana often use in-furrow starter fertilizer (ammonium polyphosphate 10-34-0 or 11-37-0 at a rate of 5 gallons per acre) to compensate corn nitrogen requirements during the early growing season. However, this starter fertilizer is not adequate to meet the early season nitrogen demand of about 30 pounds nitrogen per acre because a 5-gallon starter fertilizer (10-34-0) per acre provides 19.8 pounds phosphorus (P2O5) but only 5.8 pounds nitrogen. Corn nitrogen demand during the early season can only be met by applying nitrogen as broadcast (urea; 46-0-0) followed by incorporation before planting or as sidedress or dribbling (UAN; 32-0-0) at planting. Note that pre- or at-planting nitrogen rate should not exceed 45 pounds per acre for silt loam and 60 pounds per acre for clay soils and should not be applied in the seed furrow due to the likelihood of potential salt injury from ammonium-nitrogen.
Sometimes a 3rd application of nitrogen (around 45-50 pounds per acre) at pre-tassel stage (V12-V14; about 2 weeks prior to tassel) is beneficial especially for coarse-textured low CEC (<10) soils as well as for poorly drained soils that are very prone to water-logged conditions. This also helps protect corn yield losses in years with excessive rainfall during the early corn growing season, which increases nitrogen losses. Including a pre-tassel application in the nitrogen management program can help reduce nitrogen losses and ensure adequate nitrogen supply during the maximum nitrogen uptake period from V10 to grain-filling stage. Many land-grant universities including LSU AgCenter trials showed that pre-tassel nitrogen application can increase corn yield when part of the pre-plant and sidedress nitrogen are lost due to excessive rainfall during the early growing season. However, the need for a 3rd nitrogen application at or before tasseling should be based on crop growth, rainfall amount and soil conditions during the growing season, yield potential, environmental forecasts, reference strips (NDVI), and leaf tissue testing (leaf nitrogen concentration). To determine the need for a pre-tassel (V12 to 14) nitrogen application, a nitrogen reference strip can easily be established by applying a double rate of the total nitrogen in one corner of the corn field and/or leaf tissue sample can be collected from V10 to tasseling stage and analyzed for total nitrogen concentration. A detailed article regarding corn pre-tassel nitrogen application will be posted in April or May newsletter issues. Overall, an ideal nitrogen management program for over 200-bushel corn yield should include at least 30 to 45 pounds nitrogen at planting and remainder amount at V6 to V8 stage with or without 45 to 50 pounds nitrogen before tasseling based on NDVI reading from reference strips and/or leaf nitrogen concentration.
Figure 1. A V6 corn plant with 6 visible collar leaves (Source: Mississippi State University Extension; How to determine corn vegetative growth stages).
Figure 2. Corn seasonal nitrogen uptake (Source: Abendroth et al., 2011. Iowa State University Extension, Ames, IA).
Figure 3. Corn yield component development across growth stage (Source: University of Nebraska-Lincoln Extension; Cropwatch).
Rasel Parvej, Syam Dodla, and Matthew Foster, LSU AgCenter scientist
Starter fertilizer is also called “pop-up” fertilizer and usually applied in the seed furrow or in 2 by 2 band i.e., 2 inches side and 2 inches below the seed depth. Louisiana corn producers mostly use ammonium polyphosphate such as 10-34-0 or 11-37-0 as starter fertilizer and apply it in the seed furrow with their planter. These starter fertilizers mostly contain small amounts (10 or 11%) of nitrogen (N) and high amounts (34 or 37%) of phosphorus (P2O5). Some starter fertilizers may also contain small amounts of potassium (K2O), sulfur (S), and some micronutrients such as zinc (Zn), manganese (Mn), etc. Starter fertilizer is usually applied at a lower rate (5 gallons per acre) for in-furrow application due to the chance of salt injury from ammonium-nitrogen but can be applied at a higher rate (up to 10 gallons per acre) for 2 by 2 banding. Although adequate soil moisture at planting can reduce the likelihood of salt injury, high rates of nitrogen fertilizer is still not recommended for in-furrow application.
The main purpose of applying starter fertilizer is to help the germinating corn seedling to boost up early-season growth by easily accessible nutrients placed near the seeds, resulting in increased yield potential. However, corn grain yield response to starter fertilizer is very inconsistent with no yield response being common across mid-South and Midwest. Therefore, each year Louisiana producers often ask the same question whether they should apply starter fertilizer at corn planting. The most common extension answer is “it depends”. Mascagni et al. (2007) conducted 15 site-years research trials from 1991 to 2005 on starter fertilizer (10-34-0 or 11-37-0) for corn production in northeast Louisiana and found that starter fertilizer increased corn yield by 8 to 25 bushels per acre in only 5 out of 15 trials (Figure 1). They reported that the positive yield response to starter fertilizer came only from phosphorus but not from nitrogen. This was because 5 gallons of in-furrow starter fertilizer (10-34-0) contains 19.8 pounds phosphorus (P2O5) but only 5.8 pounds nitrogen (N) per acre, which is a very small amount to make any yield difference by nitrogen at planting. Note that corn requires 30 to 45 pounds nitrogen from planting to V6 stage (6 visible collar leaves and plant is about 12-18 inches tall); therefore, corn nitrogen requirement during the early season can only be fulfilled by applying N as broadcast (Urea; 46-0-0) followed by incorporation before planting or as sidedress (UAN; 32-0-0) at planting. The most important point that Mascagni et al. (2007) reported was that starter fertilizer increased corn yield only in coarse-textured soils such as sandy loam soils. They also reported that sandy loam soils were cold-natured soils with low organic matter content and nutrient holding capacity, where phosphorus deficiency symptoms were common during early corn growing season (mid-March to mid-April). However, they mentioned some benefits of starter fertilizer regardless of soil type and yield response such as improved early-season plant growth and 3 to 4 day earlier mid-silk stage along with earlier maturity. Therefore, based on the research conducted in Louisiana and other corn producing states, the following points need to be considered before making decision in using starter fertilizers.
Overall, starter fertilizer may only benefit corn yield in a very specific situation. If corn price is low and input cost is high, corn producers may not need to spend their money on using starter fertilizer in most fields. However, with high corn prices this year, starter fertilizer, if not too expensive, can be a cheap insurance for early corn planting in coarse-textured soils against the detrimental cold and wet weather conditions often experienced by Louisiana corn producers in March.
Figure 1. Corn yield response to starter fertilizer in research trials conducted by Mascagni et al. (2007) on Mississippi River alluvial sandy loam/silt soils at the Northeast Research Station in St. Joseph, Louisiana. [NS, not significant at the 0.05 probability level; Source: Mascagni (Rick), H.J., D. Boquet, and B. Bell. 2007. Influence of starter fertilizer on corn yield and plant development on Mississippi River alluvial soils. Better Crops. Vol. 91(2)].
Matt Foster and Rasel Parvej, LSU AgCenter scientists
Louisiana growers are expected to plant more acres to grain sorghum this year compared to previous years. Grain sorghum is a good option for dryland fields where productivity is marginal. It has a longer planting window and provides many benefits when used in a crop rotation with cotton and/or soybean.
Grain sorghum typically responds well to early planting but has less seedling vigor when compared to corn. The recommended planting window ranges from April 1 to May 1 in south Louisiana and April 15 to May 15 in north Louisiana. Soil temperature is the main factor influencing germination rate. When considering the ideal time to plant sorghum, the five-day average soil temperature should be at least 60 degrees Fahrenheit at the 2-inch depth and the seven-day forecast is for warm weather. Optimal temperature for quick germination and establishment of grain sorghum is near 65 degrees Fahrenheit.
Grain sorghum should be planted at a rate of approximately 75,000 seeds per acre. This is equivalent to five to six seeds per row foot on 40-inch centers, four to five on 30 to 36-inch centers, and three to four on 20-inch centers. If rows are 10 inches or less spaced, three seeds per row foot should be adequate. Sorghum can be grown in a variety of row widths, but research has shown that yield responds well to row spacing of 30 inches or less. Seed should be planted in adequate moisture no deeper than 2 inches. Optimum depth ranges from 0.75 to 1.5 inches deep. Sorghum seed varies in size from 12,000 (38 grams per 1,000 seed) to 18,000 (25 grams per 1,000 seed) seeds per pound. If using pounds per acre to plant, growers should be aware that populations can vary greatly (Table 1). Seeding rates should be based on seed per acre and not pounds per acre.
Grain sorghum is sensitive to low soil pH. The optimal soil pH for grain sorghum ranges from 5.8 to 6.5. Continued cultivation and the use of chemical fertilizers, especially those containing ammonium and sulfur, tend to decrease soil pH over time.
Nitrogen should be applied between 100 to 125 pounds per acre on upland soils and 125 to 150 pounds per acre on alluvial soils. Clay soils typically require a higher nitrogen rate compared to sandy/silty soils. A rough rule of thumb is to apply 1.12 pounds of actual nitrogen for each bushel of grain sorghum produced. Yield becomes less responsive to nitrogen as yield approaches 150 bushels per acre (Figure 1). The amount of applied nitrogen should be based on crop yield goal and the amount of residual nitrogen in the soil. All the required nitrogen can be applied before or at planting, but this increases the risk of fertilizer burn on seedlings and nitrogen losses through volatilization, leaching, or denitrification. Therefore, nitrogen is recommended to be applied in a split application with 50 to 75% before or at planting and the remainder no later than the 6- to 8-leaf stage.
Grain sorghum utilizes phosphorus and potassium during the early part of the growing season, so these nutrients should be applied pre-plant or at planting. Soil testing is recommended to determine phosphorus and potassium needs for each field. The soil-test-based fertilizer recommendation for grain sorghum can be found at the LSU AgCenter Website.
A 125 bu/A grain sorghum crop takes up about 23 pounds per acre sulfur with about 8 pounds per acre removed in the grain at harvest. When a soil test is utilized to determine if sulfur is needed, values of less than 12 ppm (Mehlich 3 extraction) suggests that additional sulfur may be needed. In this case, the typical recommended rate of sulfur is 20 pounds per acre in the sulfate form.
Table 1. Effect of seed size on planting rate and plant population when planting is based on pounds per acre.
|Seed weight grams/1,000 seed||38||25|
|Number seed per pound||12,000||18,000|
|Number of seeds @ 6 lbs/acre||72,000||108,000|
Figure 1. Grain sorghum yield response to nitrogen rate (Source: Mengel, Kansas State University).
Stacia L. Davis Conger, LSU AgCenter engineer
On February 19, Delta Plastics released the fourth and most recognizable update to their computerized hole selection software named Pipe Planner. This software uses hydraulic engineering principles to help irrigators select appropriate hole sizes for punching into lay-flat polytubing. Using this type of software can help with more accurate planning in terms of design and in-season management of both furrow and rice irrigation practices as well as improving efficiency, which includes water, energy, and labor savings.
The ultimate goal of this update was to streamline various previously cumbersome processes, provide better feedback concerning input errors, and convert to a responsive design for using the software on a mobile device. Irrigators can now access the website on their phone’s web browser to input field specifications while in the field. Though the look and feel of the website is different, the learning curve is small for those that utilized Pipe Planner previously. All pipe plans from previous years are still available and editable after the update.
Delta Plastics worked with NRCS Arkansas through a Conservation Innovation Grant (CIG) to conduct the work behind this upgrade. Thus, a new feature of Pipe Planner is the ability to report irrigation events as an exportable record for NRCS programs. Pressing the “Irrigation” button at the top of the screen opens a menu for this option. Inputs include start and stop times for calculating duration as well as selecting the irrigation scheduling method used to determine that irrigation was necessary.
While personally exploring the product on a mobile phone, the instructions that now appear at the bottom of the screen to help direct the user with the next steps of the process was a positive addition. Occasionally, rotating the screen by 90° was necessary to access all of the menu options at the top of the screen. At one point, the buttons along the left edge were obscured possibly due to the rounded edge of the phone’s screen but was quickly fixed by a refresh of the webpage without losing progress. The option to work with Pipe Planner on a computer is still available.
Though still a free software, access to Pipe Planner must now be accompanied by a verified purchase of of polytubing on an annual basis. When signing into Pipe Planner for the first time after the update, a window appeared that asked for my business address and the name of the distributor where pipe was last purchased. Access to the software was granted immediately but may be fully verified later.Pipe Planner is considered the best internet-based option for computerized hole selection due to its modern design and helpful technical support. The predecessor to Pipe Planner is a downloadable software called PHAUCET that can still be accessed from the NRCS Science and Technology Conservation Tools Software website. PHAUCET operates similarly to a DOS program with few educational resources available today. If you need help with either software, please contact your ANR extension agent or Dr. Stacia L. Davis Conger directly.
Sebe Brown, Jeff Davis, and Tyler Towles: LSU AgCenter entomologists
One of the most important decisions producers must make when planting soybeans in Louisiana is planting date. Soybeans have the utility to be planted in early March to late June. This wide variation in planting dates potentially exposes seedling soybeans to a multitude of insect pests that affect both above and below ground plant structures.
Optimal seeding dates for each maturity group planted in Louisiana are:
• Group III – April 15–May 10
• Group IV – April 15–May 10
• Group V – March 25–May 5
• Group VI – March 25–April 30
Soybean seedlings possess an exceptional amount of vigor and can tolerate a substantial amount of insect injury during the seedling stage. However, early planted soybeans may also encounter greater amounts of environmental fluctuations that affect air and soil temperature. Cool conditions can negatively affect vigor and under the right conditions stall plant growth and development. The addition of insect injury, to the aforementioned mentioned environmental conditions, increases stress the plant encounters resulting 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, threecornered alfalfa hopper, wireworms, grape colaspis, and thrips.
On the opposite end of the spectrum are soybeans planted late i.e. behind wheat or are late due to unforeseen circumstances such as inadequate or excessive soil moisture. These beans are more at risk for insect injury due to the potential for large insect populations to build in neighboring fields and generally more insects present in the environment. 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 threecornered alfalfa hoppers. Thus, an IST is a sound investment when soybeans are planted late.
However, soybeans during the recommended planting window, under optimal soil conditions and low pest densities will often not benefit from the addition of an IST. Insecticide seed treatments typically provide the most benefits when environmental conditions are sub-optimal as outlined in the prior paragraphs. With the current economic climate and many agricultural professionals looking at areas to cut inputs, justifying the use of IST on soybeans when planted under optimal conditions becomes harder to support. Saving the cost of an IST can go to making a stink bug application later season that may provide a greater economic return.
Outside of early or late-planted soybeans are situations where ISTs are justifiable. These include weedy fields with incomplete burn down applications, reduced tillage field arrangements, fields with historically problematic early insect pests (wireworms and/or threecornered alfalfa hoppers) and the use of a cover crop. Each field is unique and the use of ISTs as a blanket treatment over every acre may not be justifiable.
David Moseley, LSU AgCenter soybean specialist
Soybean development consist of vegetative and reproductive growth stages. The vegetative growth stages are from emergence to the onset of flowering and the reproductive stages are from the onset of flowering to maturity.
(R3-R6: Evaluated from one of the top four nodes which contain a fully developed trifoliate leaf)
Plants within the same field can simultaneously be at slightly different growth stages. To represent the entire field, examine multiple plants in different areas. To determine the growth stage of the field, more than 50% of the plants should be in or beyond a particular growth stage.
Correctly staging the soybean plants is important for making timely applications throughout the growing season. During the early vegetative growth stages (at approximately V3-V5) the roots can be examined for nitrogen fixing nodules. Checking the roots early in the vegetative growth period for adequate nodulation allows time to apply supplemental nitrogen if necessary. Identifying the reproductive growth stage is also important for timely agronomic practices such as applying pesticides and defoliants and for nutrient management.
Figure 1: A soybean plant at the VE growth stage. The cotyledons have emerged past the soil surface.
Figure 2: A soybean plant at the VC growth stage where the first true leaves (unifoliate leaves) are completely unrolled.
Figure 3: A plant at the V3 growth stage where the third trifoliate leaf has completely unrolled.
Figure 4: A soybean plant at the R1 growth stage where there is an open flower anywhere on the main stem.
Figure 5: A soybean plant at the R2 growth stage where there is an open flower at one of the two uppermost nodes on the main stem that contain a fully developed trifoliate leaf.
Figure 6: A soybean plant at the R3 growth stage with a pod that measures 3/16 of an inch on one of the top four nodes which contains a fully developed trifoliate leaf.
Figure 7: A soybean plant at the R4 growth stage with at least one pod that measures 3/4 of an inch at one of the top four nodes which contain a fully developed trifoliate leaf.
Figure 8: Soybean pod and seed development from the beginning pod stage (R3) to maturity (R8).
Figure 9: Soybean pod development from beginning pod (R3) to maturity (R8).