Skip to content

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.

Current Weather Conditions May Affect Burndown Strategies

Current Weather Conditions May Affect Burndown Strategies published on No Comments on Current Weather Conditions May Affect Burndown Strategies

From: Daniel Stephenson, Ph.D (Weed Scientist), Sebe Brown (Extension Entomologist) and John Kruse, Ph.D. (Cotton and Feedgrain Specialist)

Historically, many corn producers in Louisiana desire to plant corn in February. LSU AgCenter weed scientists and entomologists suggest burndown applications occur 4 to 6 weeks prior to planting to prevent competition from weeds and to remove vegetation that may be infested with insect pests – collectively known as “breaking the green bridge”.

Fields intended for corn should have already received a burndown application; however, weather conditions during January and early February may have prevented herbicide applications. As an example, 14.5 inches of rain were recorded at the Dean Lee Research and Extension Center in Alexandria since January 1.

The wet fields prevented ground application of burndown herbicides. Also, there were only a few days since January 1 that an airplane was able to make these applications due to wind conditions. As a consequence, Louisiana producers may be faced with weedy fields that are intended for corn.

A failure to “start clean” can greatly influence corn yields. Data have shown that corn determines its leaf orientation very soon after emergence. Leaf orientation perpendicular to the planted row is desired for maximum light interception, which influences growth and yield potential. If a spiking corn plant perceives any competition from an adjacent winter weed, the leaf orientation will be altered, thus potentially reducing that corn plant’s ability to intercept enough light for maximum yield. Therefore, planting into a weed-free field is very important.

Focus on Weed Control

Traditionally, a burndown application of glyphosate plus 2,4-D has been the standard protocol. This treatment usually provides good to excellent control of many winter/spring annual weeds common in Louisiana fields.

When applied 4 to 6 weeks prior to planting, a producer has time to evaluate the efficacy of glyphosate plus 2,4-D and decide if an additional herbicide treatment is needed prior to planting. If a producer is prevented from applying the burndown application in a timely manner, then weed competition and insect pressure may be an issue for emerging corn. Henbit in particular may be a refuge for cutworms and spider mites.

If a field scheduled for corn has received a burndown application, then these fields need to be evaluated to determine if corn will be planted into a “clean” field.

If the weather has prevented a burndown application and a producer intends to plant corn within the next few weeks, several factors must be considered.

The first issue is the 2,4-D plant-back restriction, which is 7 days for corn. If you are within this window, then you should not apply 2,4-D, to prevent herbicide injury to the corn. Second, maximum efficacy of glyphosate will not be observed until 21 to 28 days after application, so glyphosate applied 7 to 10 days before planting may not provide acceptable weed control and may allow insect populations to survive.

If a producer is within 7 to 14 days of planting corn, he/she should consider the following burndown treatments:

  • Gramoxone SL at 1.5 qt/A plus atrazine at 1 lb ai/A plus 0.25% v/v nonionic surfactant.
  • Gramoxone SL at 1 qt/A plus Leadoff at 1.5 oz/A plus 0.25% v/v nonionic surfactant.

Gramoxone SL will provide control of existing weeds, but coverage is essential. Therefore, a minimum of 12 gallons of water per acre and flat-fan nozzles should be utilized to maximize coverage. Also, Gramoxone SL efficacy can be increased when the air temperature is high and cloud cover is minimal.

Atrazine or Leadoff will assist Gramoxone SL with control by providing residual activity on winter/spring weeds during the first few weeks after corn emergence – if beds are not disturbed at planting. However, if an organophosphate insecticide will be applied in-furrow when planting corn, then Leadoff cannot be applied or injury will occur.

Focus on Insect Control

At-plant bands or post-emergence pyrethroid applications can be used to control cutworms; however, the infestation needs to be detected early to minimize stand loss. Moist soils will help incorporate the application to improve efficacy on any cutworms that may be located below the surface.

Foliar insecticide applications can be applied in bands behind the planter in reduced tillage fields. At planting soil insecticides such as Lorsban 15G can be t-banded with corn to help control cutworms pre-emergence. Lorsban should not be planted in furrow due to possible phytotoxicity. It is important to note that the use of ALS inhibiting herbicides with organophosphates such as Counter and Lorsban have the ability to cause significant crop injury.

If producers used Leadoff in their burn down strategy then Counter should not be used at all, to prevent any negative effects between the two chemicals. Lorsban has greater crop safety than Counter when used in conjunction with ALS inhibiting herbicides.

Force 3G can also be used at plant to help protect against cutworms. Force 3G is a pyrethroid insecticide and the ALS interaction is not a factor. Counter is not effective for control of cutworms but useful for rootworms.

Planting corn into a weed-free field is a must to maximize yield. Regardless of when you apply a burndown treatment, a producer must strive to “start clean”.

Wheat: Cold Weather Means Risk

Wheat: Cold Weather Means Risk published on No Comments on Wheat: Cold Weather Means Risk

We are forecast to finally have some real winter over the next few days. Unfortunately, much of our wheat has already moved on to spring. Temperatures in Baton Rouge are forecast to reach 28–30 ˚F Saturday night. In Monroe (along I-20 in north Louisiana) temperatures are forecast to reach 22-24 ˚F, 18 ˚F at Greenville, MS, and 16 ˚F at El Dorado, AR.

The forecast has been in a state of flux over the past couple of days and it is hard to know what will really happen. I am pretty confident that we will have some freeze damage to wheat this weekend but it is difficult to predict how much. The good news is that it is still very early in the growing season, wheat has lots of time to recover, and wheat is a very resilient crop.

Wheat that is not jointed will not suffer anything more than superficial leaf burn at 20 ˚F. Our wheat has been growing very rapidly and there are lots of tender leaves that will have the tips burned, but this should not impact yield. Prior to jointing wheat is very tolerant of cold weather and damage is infrequent and superficial. Wheat becomes much more vulnerable to freeze damage as it progresses from first node to flowering. Hopefully we will have a cool February and not have to address that issue. There is really not much that can be done at this point. The chart below (borrowed from

shows the relationship between growth stage, temperature, and freeze damage. The months that correspond to the growth stages are appropriate for Kansas, not Louisiana. The growth stages are valid, except that tillering occurs all winter in Louisiana.





Wheat that has jointed (Feeke’s GS 6) will start to sustain significant damage around 24-26 ˚F. This damage can manifest in several ways. Stems can freeze on one side which weakens stems and can result in lodging at heading and poor grain fill due to inability to supply the developing head with adequate water and nutrients; or stems can completely freeze at the soft growing point resulting in loss of that tiller.

The link below is a good summary of spring freeze damage symptoms in wheat from our friends at Mississippi State. .

The amount of damage on tillered wheat will depend on temperature and duration of exposure. I suspect that most of the wheat in Louisiana will only sustain superficial damage. I do know that there are some fields that have one and maybe even two nodes showing and these will be hurt. It normally takes a couple of days after a freeze before symptoms are easily apparent. This comes in the form of dead and dying tissue; lodging and discolored tillers; and a distinct odor of rotting tissue. Again, we won’t know the extent of damage until early next week and there is still a lot of time for the plants to form new tillers and make a near-normal yield. I’m sure the internet will be abuzz with freeze damage discussions next week

Secondary Sidebar