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Important Differences in Fertilizer Materials Containing Sulfur and Zinc

Important Differences in Fertilizer Materials Containing Sulfur and Zinc published on No Comments on Important Differences in Fertilizer Materials Containing Sulfur and Zinc

by J Stevens, Associate Professor and Extension Soils Specialist

As of recent, I have become aware that there are some fertilizer dealers who might be unaware of some of the differences in the fertilizers they are handling and selling to producers. Let’s take Sulfur and look at it first.

The use of sulfur in soil fertility programs has become more routine. The most common chemical forms of sulfur used in fertilizers are sulfate-sulfur and elemental sulfur. However, these two forms of sulfur react quite differently in the soil. It’s very important to understand the differences between sulfate-sulfur and elemental sulfur in order to use these two forms in the most effective manner possible.

Plants can only absorb sulfur through their root system in the sulfate form. Thus all soil sulfur must be converted to a sulfate in order to be utilized by plants. For the most part, sulfates move freely with soil moisture, especially in the upper part of the soil profile. This is very much like nitrate-nitrogen in soils. As a result, sulfate levels frequently increase with increasing depth in the soil profile. Like nitrates, sulfates can leach in sandy-textured and silt loam  soils.

Elemental sulfur is totally unavailable to plants. Plant roots cannot absorb elemental sulfur. Elemental sulfur is inert and is water insoluble. When elemental sulfur is added to a soil, it has to be converted to the plant-available sulfate form through the activity of soil bacteria. The rate at which this conversion takes place is the determining factor regarding the effectiveness of elemental sulfur as a fertilizer source of sulfur. This transformation of elemental sulfur to the plant-available sulfate form is a slow process often taking months to be accomplished. Thus, for most crops in the initial sulfur fertilization, a sulfate fertilizer like Ammonium sulfate is recommended and elemental sulfur is not.

Now, let’s look at Zinc, specifically zinc sulfate and zinc oxysulfate.  Most of the formulations of these two products contain 35.5 – 36% zinc. Among the inorganic zinc sources on the market, the most common sources are sulfates, oxides, and oxysulfates. Zinc sulfate is essentially 100% water soluble, while the Zinc oxides are essentially insoluble in a single crop year, thus unavailable to the crop to be planted. Many agronomists consider the oxides to be ineffective as a fertilizer source. Oxysulfates are a mixture of sulfates and oxides, with varying proportions of sulfates and oxides. The solubilities of the oxysulfates vary considerably, from 0.7 to 98.3%. The effectiveness of these can be highly variable. Low solubility materials may have some value in a long-term build up program, however, when immediate results are the goal, highly soluble fertilizers are the best choice. It is suggested that in order to be effective, a Zinc fertilizer should be at least 50% water soluble.

I’ll leave you with a few questions to ponder; Are you using sulfur and/or zinc in your soil fertility program? Are you soil testing to determine if your crops could benefit  from adding one or both of these nutrients? If you are applying sulfur and/or zinc, have you ever considered which form is being field-applied?  The answers to these questions could lead you toward a better soil fertility program and enable your crops to improve their yields as they come closer to reaching their genetic potential.

If you have any questions on this article or would like to discuss your soil fertility program, please feel free to contact me by email ,  telephone, 318-308-0754 cell, or text.

Soybeans Planting Underway Throughout Louisiana

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by Dr. Ronnie Levy, Soybean Specialist

Louisiana is projected to plant a little over one million acres of soybeans in 2012.    Strong exports and demand for soybeans continue and soybean acres may increase throughout the planting season.  The acres planted will probably be limited by weather.  If the weather is favorable, we could see up to 1.1 million acres of soybeans planted.  Each year seems to present different problems for production, hopefully this will be the year without one. 

 In Louisiana approximately 60% of the acres are planted to maturity group IV’s and 35% of the acres to maturity group V’s.  The remaining 5% is planted to maturity group III’s and VI’s.  Then trend has been toward maturity group IV’s.

 Soybean planting got started early this year with a few acres being planted in late March.  As planting continues to progress, the question always arises – What is the optimum plant population?

 Too dense a plant population reduces yields, encourages diseases and lodging and increases seed cost.  When calibrating planters, use seed per foot as your guide rather than pounds of seed per acre.  In the following table, the estimated pounds per acre should be used only to calculate how much seed to buy.  Because of varietal difference in seed size, as well as seasonal variation within lots of the same variety, planting rates can be misleading if expressed in pounds per acre.  The following rates are recommended:


Row Width






Row Foot

Row Foot


in 1000s
































 When planting is delayed until June 15 or later, the amount of vegetative growth that the plant produces becomes more critical.  It is important to choose varieties that grow rapidly in a short time.  When blooming starts, most vegetative growth ceases in determinate varieties.  When planting late, seeding rates should be increased to compensate for reduced vegetative growth.


Precision Ag – Variable Rate Applications

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by Dennis Burns

ANR Agent Tensas Parish

Recently I was talking to a producer who wanted to learn about making variable rate applications of nitrogen. The first question he asked was: “How much was am I going to save by making the application variable rate?” My response was not what he expected. I said “Don’t look at it as saving money, but as making money.” By matching the optimum nitrogen rate to the corresponding soil/production zone, crop use efficiency is highest and the potential profit from the nitrogen application is maximized.

To make a variable rate nitrogen application, a producer has to define the application zones. This can be based on soil types, Veris Ec soil zones, yield maps, producer knowledge or a combination. The producer’s knowledge of the field along with a yield goal helps determine the nitrogen rate assigned to each zone. The total amount applied to a field with a variable rate application may not be much different than if a producer had gone with a single rate, but by putting the correct rate in the right area the field doesn’t have areas with over or under applications of nutrients.

Soil Sampling is an essential part of variable rate applications, whether it is grid sampling or zone sampling. Each method would benefit from the addition of yield map data to the analysis. Yield maps over several crops and several years can help define the potential yield and profitability of a field. It can also assist with the definition of productivity zones for a field. This is especially obvious when a cropping history is developed over several years.

Variable rate applications of lime, P, K, and other essential nutrients need to be applied in areas defined by the sampling pattern (grid or zone). Variable rate applications of other nutrients is the most cost effective and efficient method for supplying crop needs. Variable rate also allows a producer to match fertility needs to the current crop’s needs. Supplying/maintaining fertility levels enhances the nitrogen efficiency and use by the crop.

The most useful piece of precision ag equipment a producer can own is a yield monitor. A yield monitor gathers the information from the field with which a producer can evaluate how well fertilizers, varieties, etc. performed. Verification strips of a nutrient, nitrogen rate, or another input can be used as a comparison for the rest of the field. Analyzing the results as whole strips and soil/production zones allows a producer to determine the most productive/economical practices to use on their farm.

Precision agriculture, its use, the results, and the incorporation of the practices into a farming operation is a long term process which can enhance the productivity of a farm. For more information or assistance with precision ag applications or yield data on your farm, contact Dennis Burns at 318-267-6709 or R.L. Frazier at 318-267-6714.


Wheat Insect Update

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By Sebe Brown

Extension Entomologist, LSU AgCenter

I have had some reports of armyworms and leaffooted bugs in commercial wheat fields.   True armyworms are primarily an early season (spring) pest with a strong preference for grass crops.  Usually greenish in color with orange strips running down the lateral edges of the body, true armyworms typically feed at night and during overcast days.  During the day, true armyworms can be found under debris and thatch on the soil surface.  In Louisiana infestations normally occur in April, but with the unseasonably warm weather, early infestations from a multitude of pests can be expected.  Scout for this pest during the early morning, late evening or look for larvae on or under the soil surface.  Larvae feed on the foliage of wheat plants from the base and gradually work their way up towards the flag leaf.  Once the wheat has reached milk stage, the plant can tolerate greater levels of defoliation and see little to no yield loss. However, if armyworms begin to feed on or clip the wheat heads substantial yield losses can occur.  Thresholds for Louisiana are 5 or more larvae per square foot with foliage loss occurring.  True armyworms can be controlled with pyrethroids.  If an application for armyworms is justified, use enough carrier to adequately penetrate the wheat canopy.  Applications made during the late morning or afternoon may miss some armyworms in thatch or near the soil surface when direct sunlight and warm temperatures are abundant.

 Leaffooted bugs are similar to stink bugs with regards to their piercing sucking mouth parts and foul odor excreted when they are disturbed.  These insects are characterized by flattened leaf like expansions arising from the hind legs and a white strip running across the central part of the back.  Leaffooted bugs are very flighty and can easily migrate in and out of wheat fields from adjacent weed hosts such as thistle.  Flights of this pest can come from adjacent fields where burndown applications have been recently applied removing their primary host.  Louisiana currently does not have a threshold for these pests and control can be quite difficult with pyrethroids.  This insect is a minor pest of wheat.  However, if your wheat is lodged with them and they have not migrated out of your field within a few days or been blown out by the torrential down pours this spring, a pyrethroid application can be made.  If an application is deemed necessary, a high label rate of a strong pyrethroid should be used.  

 Aphids seem to be less of a problem this season than in previous years. The threshold for green bugs in wheat is 300-800 aphids per linear foot in wheat 6-16 inches in height.  Pyrethroid applications made for other pests such as true armyworms can effectively suppress populations of green bugs.  Many of the fields I have scouted have high numbers of natural enemies. These beneficial insects provide a free service in reducing aphid populations; however, aphids have the ability to outnumber their natural enemies in a short time frame.

 With fungicide applications going out, tank mixing a pyrethroid in while covering ground is an option if insect pests have begun to be a problem.  However, a jar test to assess fungicide/insecticide compatibility may be necessary prior to application.

 For more information concerning insect pest management, contact your local LSU AgCenter parish agent, LSU AgCenter specialist, or your agricultural consultant.



Wheat Disease Update

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by Boyd Padgett, Ph.D., Plant Pathologist, LSU AgCenter

I have received a few reports of leaf and stripe rust in commercial fields; however, not at high levels. I have not observed any rust in producer fields in Northeast and Central Louisiana. In my tests around the state (Dean Lee, Red River, Ben Hur, and Macon Ridge), I have observed leaf rust at low levels in my tests located at the Macon Ridge Research Station, at moderate levels at Ben Hur, and stripe rust at low levels in tests at Dean Lee.  These tests are intentionally planted to SUSCEPTIBLE varieties, and are not representative of producer fields planted to resistant varieties. I have also observed powdery mildew in tests located at Ben Hur and the Red River Research Station. This disease is not considered to negatively impact wheat produced in Louisiana. However, if the disease is active (high incidence and severity) and present on the flag leaf prior to heading a fungicide may be justified. I HAVE NOT SEEN THIS SENARIO IN THE PAST 15 YEARS.

 Producer fields: If rust incidence and severity is low (no pustules on the flag and confined to the lower canopy not active), most plants are fully headed (not flowering), and the variety is rust resistant, a fungicide is probably not needed.

Fungicides are justified if the wheat is at flag leaf to early heading and rust is active (spores are easily seen on the lower canopy). The following conditions are necessary for leaf and stripe rust development.

 Stripe rust development is most aggressive when nighttime temperatures are 50 to 65oF in the presence of intermittent rain or dews. However, development can occur when temperatures are near freezing up to 70oF.  Initial infections on seedling wheat may not have the characteristic striping pattern that occurs on more mature plants.  Seedling infections often occur in ‘thumb-sized’ clusters on the leaves, as opposed to a random distribution that occurs with leaf rust.    Infections may appear as linear rows of small yellow to light orange pustules (stripes) on the lower leaves during late winter or early spring. Striped patterns are typical of infections in older pants.  If conditions remain favorable for development, pustules may cover the entire upper leaf surface, as well as portions of the head. A lifecycle (infection to reproduction) can be completed in 7 to 10 days when conditions are optimum for development.

 Leaf rust is usually evident later in the season than stripe rust. This is because the leaf rust pathogen requires warmer temperatures for development than stripe rust. Initial symptoms of leaf rust begin as light yellow spots, usually on the lower foliage. As the disease develops, small pin-point pustules form on the upper leaf surface. Pustules are brick or dark red and occur randomly on the leaf. Similar to stripe rust, pustules can cover the entire leaf surface if conditions remain favorable for development. The disease develops optimally when nighttime temperatures are 50 to 70oF and leavers remain wet for 6 to 8 hours. Similar conditions will favor the development of leaf and glume blotch caused by Stagonospora and Septoria, respectively.

 For more information concerning wheat disease management, contact your local LSU AgCenter county agent, LSU AgCenter specialist, or your agricultural consultant.

Preparing for the upcoming season using precision ag equipment

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By Dennis Burns & R.L. Frazier

Now is the time to get fields and crops organized for the upcoming season.  When it comes to field names and numbers, consistency is the key to success.  Analyzing yield data or documenting production practices for multiple years makes it virtually a requirement.  Other information such as crops, variety names, chemicals, fertilizers, equipment, etc. can be entered now in preparation for use.  This information can be entered using desktop programs (e.g. APEX, Farm Works, SMS) and copied to the data cards which go in the equipment on the tractors, sprayers, and harvesters.  Or it can be entered directly into the equipment if one of the desktop programs is not available.  Along with these card entries, make a reference notebook with maps and other information that can stay with each tractor, sprayer, harvester, and other equipment.  Time spent now getting data prepared and organized will help keep field operations moving smoothly with fewer glitches to hinder data analysis after the tasks are finished.  For more information or assistance with this or other precision ag applications please contact Dennis Burns (318-267-6709) or R.L. Frazier (318-267-6714) with the LSU AgCenter.

LSU AgCenter Establishes Blog Site for Row Crops Newsletter and Updates

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by John S. Kruse 

LSU AgCenter researchers and specialists have created a new avenue for obtaining the Crops Newsletter. Articles published in the Louisiana Crops Newsletter can now also be found at Many constituents have expressed their preference for the easy, article-by-article access provided by a website and it is our goal to make science-based information available in forms that are user-friendly. For those that prefer to continue to receive the Newsletter in the current pdf form, rest assured that we will continue to send it out in this form as well. We look forward to serving your needs and hope you enjoy this additional way of accessing the Newsletter.

The LSU AgCenter Explores Biofuels as an Alternative Crop for Growers

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Authors:  John Kruse, Michael Blazier, Richard Vlosky, Vadim Kochergin, Glenn Hughes, Dek Terrell, Paul Darby, Roger Smithhart

Research scientists and extension specialists from the LSU AgCenter are participating in federally-funded research and extension efforts to explore the potential that biofuel crops may hold for Louisiana producers.   These efforts have great potential to expand the energy production portfolio of Louisiana.  An ambitious five-year study will involve growing and selecting cultivars of energy cane (sugarcane varieties with characteristics better suited for biofuel production than conventional sugar production) and sweet sorghum well-adapted to Louisiana.  Agronomic practices such as planting rates and dates as well as fertility will be developed for these crops.  Processes for converting these crops into an array of biofuels and biochemicals are being developed in partnership with collaborators in the biofuels industry. Louisiana is particularly well-suited to develop biomass crops due to its climate, well-developed agricultural and energy infrastructure, and central location within the U.S.

In another study, a team of researchers led by Dr. Richard Vlosky submitted a survey to producers in Pointe Coupee, Concordia, Catahoula, Tensas, Madison, Richland, West Carroll and East Carroll Parishes, as well as several counties in Mississippi’s Delta region. The purpose of the survey was to gauge initial interest in producing biofuel crops, as well as find out what factors are important to making it a success. Well over 700 surveys were returned, providing a solid sample to study the responses.  Roughly 60% of the respondents farmed less than 250 acres and 40% farmed more than 250 acres. Thirteen percent of the respondents farmed over 1000 acres, providing a good cross-section of producers. When asked their overall opinion of using biomass for bioenergy, two thirds of the respondents were somewhat or extremely positive. Only 17% were pessimistic that a bioenergy market will be competitive relative to conventional energy markets.

When growers were asked about their perceptions of biofuel crops, 56% felt that economically viable technologies already exist for converting biomass to bioenergy and half of all respondents believed that agricultural biomass transportation can be conducted with existing equipment. When it came to on-farm equipment needs, 43% believed that some sort of specialized equipment would be necessary to get the job done.  A plurality (41%) neither agreed nor disagreed with the statement that converting agricultural biomass to bioenergy is a simple process that can be done at most agricultural processing facilities, and almost a third were not sure if agricultural biomass requires utilizing the entire crop as well as residual feedstock. These responses strongly indicate that growing biofuel crops is a new frontier for most producers, so agronomic education will be critical to its successful adoption by growers.

The majority of producers surveyed were clearly willing to give biofuels the benefit of the doubt when it comes to potential impact on the environment, with roughly three-fourths of respondents believing that raising a biofuel crop would not negatively impact wildlife, air and water quality, or soil quality. The majority of growers surveyed felt that government had a clear role to play in the development of this potential market. Two-thirds of respondents felt that tax credits should be given to landowners, harvesters, and companies that produce and utilize biomass for bioenergy. Well over half believed that subsidies should be provided as an incentive to companies for selling biomass residues from agricultural operations. Over 60% agreed that incentive programs should be provided to defray the costs of establishing biomass crop species and that secured loans should be provided to develop and construct commercial-scale bio-refineries. Almost three quarters of responding growers specifically saw a lead role for research institutions such as theLSU AgCenterwhen they agreed that grants should be awarded for research and development capable of advancing biomass production technologies. When it came down to individual participation, the jury is still out: When asked, “Would you be willing to participate in management activities specifically geared toward biomass production from your agricultural land?” the response was virtually evenly split, with 49% saying “No” and 51% saying “Yes.”

The fact that half of responding growers were willing to participate in bioenergy feedstock production and the high percentage of neutral responses to many of the questions indicates that many producers would benefit from additional information. It was also concluded that a gap exists between the desire to utilize agricultural biomass and the current viability of bio-based markets. The survey seems to reveal that a biofuel-based crop production system in Louisiana is still in its infancy, and that many producers are open to the idea of making it part of their production systems. They just need more information before they can make a decision.



Fall Fertilizer Applications – Are They Worth It?

Fall Fertilizer Applications – Are They Worth It? published on No Comments on Fall Fertilizer Applications – Are They Worth It?

ByDonna S. Morgan, Associate Area Agent, Louisiana Master Farmer Program

Traditional methods of applying fertilizer to cropland primarily include fall applications of Phosphorus (P) and Potassium (K), which are usually broadcast, and then may be incorporated if conditions permit. Nutrients are then left on the soil surface, or slightly beneath, for 6-7 months prior to planting of the crop. Soybeans, for example, are categorized as legumes and therefore fix their own nitrogen, but do require adequate amounts of P and K, if soil tests results recommend it (this is based on soil type and texture, soil pH, previous crops, and other variables). A medium soil type (such as a silt loam or clay loam) would normally require the application of 200#/acre of 0-18-36. If these nutrients are applied this far in advance of planting, is it really beneficial to the crop and to the environment to do so? What happens to the nutrients during typical, heavy winter rainfall events? What if the soil has a high pH (such as those found in the Red River Alluvial soil class) and the Phosphorus becomes bound to the soil particles, thereby becoming unavailable to the plant when it needs it the most? Do you apply the nutrients anyway? Or is a spring application more beneficial? These are some of the questions that prompted a study at the Dean Lee Research Station to determine if fall and spring fertilizer applications, as well as the application methods, had any impact on agronomic traits, yield, and water quality.

 The Louisiana Soybean and Grain Research and Promotion Board funded a project titled “The Effect of Phosphorus and Potassium Application and Timing Methods in Soybeans on Yield and Water Quality”. This project was funded in 2011 and will continue through harvest in 2012.  Dr. Brooks Blanche, (former LSU AgCenter cotton and soybean agronomist), and J Stevens, LSU AgCenter state soil specialist, cooperated with me on this project to ensure accurate agronomic data would be collected and nutrient recommendations would be applicable to this project. This study was implemented in November, 2010 and included a fall broadcast treatment (FBT) of P and K, a spring broadcast treatment (SPT), a spring liquid injected treatment (SLI), as well as an untreated check (UTR). Included in these 12 plots were automatic water sample collectors, also known as ISCO samplers, which were programmed to collect 200 ml of runoff every 5 minutes for four hours. The fall and winter months produced fairly significant rainfall events, where several collections were able to be made. After spring treatments were applied and a Maturity Group V soybean (Pioneer 95Y01) was planted, a lengthy drought ensued, which severely limited the water quality data that was able to be collected and analyzed. Growing conditions were fair to good for most of the growing season, with the exception of the summer months. Stand counts, plant heights, tissue samples, and soil samples were collected throughout the growing season to determine if any differences were seen in high pH conditions with each treatment. The plot was harvested on September 21, 2011 with average grain yields ranging from 32-34 bushels per acre.

 Data collected was analyzed and results showed no statistical differences in yield, plant heights, plant stand populations, and soil and plant tissue P and K levels. Plants heights and stands all fell within acceptable ranges to maximize yields. Soil samples (regardless of timing of sample collection) showed higher levels of Phosphorus across all treatments and adequate levels for Potassium. Phosphorus levels in many of the fields at the Dean Lee Research Station have continued to increase because of the limiting crop removal rate with these nutrients being applied annually. Tissue samples collected at the R3 growth stage showed the plants had sufficient levels of P and K during that growing period. And even though the soybeans visually appeared healthy, yields were compressed across all treatments with the onset of lengthy dry conditions.

 Field variability, equipment failure, and lack of field runoff limited the water sample collections and make comparisons for each treatment difficult, to say the least. Analysis showed no differences in the amount of total Solids, total Phosphorus, and Phosphates that left the field during rainfall events. Even though 31 inches of rain fell from November, 2010 to September, 2011, the majority of events were not sufficient to cause high volumes of runoff from plots. Total Solid levels were high in every treatment, primarily because the field had been sub-soiled after the previous crop harvest, and was bare during the winter months. This was due to lack of residue, cover crop, and even natural vegetation during this time period.

 One statistical difference that was noted was the level of Potassium that left the field in water sample collections. The fall broadcast treatment levels were significantly higher than those of the untreated and spring broadcast. No differences were seen in fall broadcast and spring injected. At this point, conclusions cannot be drawn from one year of data collection, but it is a possibility that Potassium levels were higher in fall treatments due to the high volume of rainfall that occurred during that time period. Potassium is also very water-soluble and this may have affected the levels found in the sample collections. Additional replications of this trial would be needed in order to determine any trends in application timings or methods.

 Though this particular study, under these specific field and environmental conditions, proved no differences in most of the parameters, does not mean the information can’t be useful. If multiple years of data are collected, and no statistical differences are determined, wouldn’t that prove useful to a producer in his nutrient management plans? Variables such as post-harvest field conditions, fertilizer prices, cropping systems, and application equipment all affect when and how nutrients are applied. This also has an effect on how many nutrients enter the surrounding water bodies and contribute to water quality issues related to production agriculture. So answering the question, “Are they worth it?” is more complicated than a simple yes or no. Conducting studies such as this will not only help producers answer these questions to maximize their nutrients, but minimizing water quality and environmental impacts as well.