Michael J. Mulvaney UF/IFAS Cropping System Specialist, and Glen Harris UGA Soil Specialist
With the frequent rains this summer, it’s been wet. You may not have been able to get into fields for timely topdress fertilizer applications on your cotton. If you’re still within 60 days of planting, nutrient demand has been low, so you still have an opportunity to apply granular fertilizer, particularly nitrogen (N) and potassium (K). However, some of our early-planted cotton has reached the third week of bloom, and nutrient demand are much higher during this time. Questions have come in about the possibility of foliar fertilization to address this issue.
Can I apply foliar fertilizer by pivot?
Not effectively, no. The amount of water applied by pivot essentially washes the fertilizer off the leaves, making this essentially a soil-applied fertilizer. And if the soil is saturated, cotton will need to recover somewhat before it can effectively take up foliar applications.
What can I do to determine if my crop is nutrient stressed?
Petiole testing and leaf tissue testing are good ways to track the nutrient status of cotton. However, petiole and tissue testing should be done at intervals throughout the season, so that you can track how the crop is doing. A “one-and-done” tissue test won’t help you track nutrient levels over time, and may provide a snapshot of the field, but without referencing previous tests, these can be of limited value since wide variation in nutrient levels exist among cultivars. In addition, remember that K can be taken up as “luxury consumption,” which can confuse interpretation of tissue K results. That said, during early bloom, I like to see 3.5-4.5% N (35,000-45,000 ppm NO3-N), 1.5-3.0% K (15,000-30,000 ppm), and 20-60 ppm boron (B) in leaf blades from vegetative branches collected representatively from the field. (Vegetative branches are identified as those at nodes before fruiting branches, where the first position of the branch is not reproductive, Fig. 1). If you’re below these values at this time of year, a supplemental foliar application may be appropriate. After blooming, petiole tests are a better indicator of nutrient status in cotton because leaf blade nutrients are shunted to reproductive tissue, and leaves are often damaged by disease.
Figure 1. Vegetative branches are those branches prior to reproductive branches, where the first node on the branch is not a square. Leaves from these branches can be useful for tissue testing prior to boll set, although periodic petiole testing throughout the season is better for tracking nutrient status in cotton. Leaves from vegetative branches are better than those from reproductive branches because there are fewer flowers/reproductive parts that serve as nutrient sinks from leaves. Image from www.soilcropandmore.info/crops/cottoninformation/pgd/hacpg.htm.
Can I get enough nutrients on cotton using foliar fertilizer during peak demand?
Foliar fertilization should be considered supplemental fertilization as part of a sound fertility management program. If you applied 1/4 to 1/3 of N and K at planting, along with all of the required P, this is likely enough to hold you over until you can get back into the field. In this case, you may be able to foliar feed until you can get in with ground spreaders.
However, if you didn’t apply any N or K at planting, you are not likely to meet demand during peak production using foliar applications. (Remember, peak K demand in cotton is up to 3 lbs K/ac per day.) This is partly why we recommend applying 1/4to 1/3 of N and K at planting – as a mitigation strategy for late applications due to weather. I am often asked if split applications result in increased yield. The answer is no, not always. The reason we recommend split applications is in large part for cases such as this, where you can’t get in the field on time for topdressing. But if you’ve applied part of your fertility early, you should have enough nutrients to hold you over until you can apply topdress applications. If you need both N and K, potassium nitrate (KNO3) can be applied alone or in combination with urea. (The use of KCl is not recommended because of the high salt index.) The main problem here is application volume and rates. High rates can burn leaves, particularly with urea, and low volumes will not likely apply enough nutrients to make a difference.
What about micronutrient foliar fertilization?
Foliar feeding micronutrients is effective, but deficiencies should be addressed prior to bloom. Indeed, liquid applications (including by pivot) of micros are more effective than granular applications because of the small amounts applied. Suppose you were to spread granular B at 1 lb/ac, prills would end up tens of feet apart, which doesn’t do the plants in between any good. Liquid applications of micro-nutrients ensure that they are uniformly distributed in the field. Identification of micronutrient deficiencies is best accomplished with a tissue test (again, prior to bloom).
Will adjuvants help?
Probably not. Research has shown increased uptake with adjuvants, particularly with K applications, but this does not commonly increase yield. If it makes you sleep better, feel free to use an adjuvant though. It probably won’t hurt anything except your wallet, and even then the damage won’t be too great. Just don’t expect a yield boost.
Take a stand. Just make a recommendation, will you?
If you have a sound fertility management program, additional foliar fertilizer applications are unlikely to help. If you need a rescue treatment for micros, foliar fertilization is a good idea. If you need a rescue treatment for macros (N-P-K), I remain skeptical that foliar applications will help. If you’re managing 3 bale/ac cotton, more attention to fertility and disease will be critical. If you’re managing 1 bale/ac cotton, the extra expense of foliar fertilization won’t be worth it. Response to foliar K is unlikely, if soil test K is adequate or greater than 125 ppm K.
Managing 3 bale/ac cotton requires more attention to detail than managing 1 bale cotton.
It’s only February, but it will be April before you know it. That means it is time to start planning for peanut and cotton planting season.
If you’re a peanut grower, you’re placing your orders for GA-06G now. Which is great – it’s a cultivar that sets a high bar for disease resistance and yield potential. You probably should continue to plant most of your acreage to GA-06G. But consider planting some acreage with other cultivars as well, just to test them out. There are a few promising cultivars on the market, such as GA-13M and GA-12Y. 12Y has excellent tomato spotted wilt virus (TSWV) resistance with high oleic oil, and although it may be susceptible to Rhizoctonia limb rot, it has yielded nearly as high as 06G. Consider planting smaller acreage to newer cultivars to see how premiums play out, and test if they work well in your situation.
Some growers int the area say they don’t like the high oleic cultivars, because of their reduced disease resistance, but in the end, they may yield as well as 06G, even if they don’t retain leaves as well. Be smart. Don’t let looks fool you. Keep your eyes on the ledger sheets. Even if they don’t look as good in the field, they may improve your bottom line – but you won’t know unless you try them. The key here is to start with small acreage, essentially doing your own variety testing on your farm. It really doesn’t cost that much to plant a few passes of different cultivars. Just make sure you keep records of what you planted where, and have a weigh wagon at the end of the season. Check out the reulsts from the variety and fungicide testing trials conducted in Jay for more information. (Remember that propiconazole restrictions are still in place for exported peanuts.)
The same applies to cotton cultivars. In this area, we’ve seen an increase in planting of “stovepipe” varieties that have more erect growth and lap the middles later in the season, which may reduce target spot incidence, an increasingly problematic disease in the Southeast. In some fields in west Florida, I didn’t see lapping of rows until early August last year, which may present weed control challenges, but also increase airflow in the canopy – corresponding with very low target spot incidence last year. I would encourage growers to try small acreage of different cotton cultivars to see which cultivars work best for their conditions – and let me know what works for you. Be sure to check out the 2017 cotton variety trial data, as well as previous years’ data for cotton variety selection. And again, start with small acreage first to see how cultivars respond in your microclimate and soil conditions.
Early-season conditions for cotton and peanut
Current predictions call for a 40-50% chance of above normal temperatures in the next 6 weeks.
They also call for a 40-50% chance below normal precipitation probability over the next 6 weeks.
If those predictions become reality, higher temperatures coupled with lower precipitation, that means you cannot afford to delay planting. Make sure you have your seed ordered early and plant in the early part of the planting window, to take advantage of warmer temperatures, but try to time planting ahead of rainfall, if you don’t have irrigation. If you’ve had white mold issues, make sure you have a good white mold control program in place to get the product to the crown of the plant where it is needed. This might mean night spraying, or trying a “canopy opener” spray rig that increases product application where it’s needed at the soil-plant interface.
Urea prices remain near 5-year lows, but it’s usually worth a phone call to your local suppliers to see who has the best prices in your area. This year I am finding that differences in nitrogen prices are smaller than in previous years, hovering around $400/ton for bulk urea.
Even though nitrogen (N) is relatively cheap right now, fertilizer is still the highest operational cost for cotton and corn production. Use it wisely. Split applications of N. Incorporate urea with water or tillage. A 2×2 placement of N with phosphorous (P) will increase P uptake, particularly during the early season when temperatures may be cooler, because the roots won’t have to “look” for it.
Average operating costs for cotton in the South:
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Average operating costs for peanut in the South:
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Average operating costs for corn in the South:
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Your peanut fields are harvested and you’re probably waiting for those last few bolls to bust open to finish cotton harvest. After that, it’s time to soil test!
Fertilizer expenses are 46% of your total operational costs in corn in the South. That number is 24% for cotton, and 15% for peanuts. Fertilizer is the single greatest operational cost for corn and cotton in the South, so it’s worth soil testing to manage your soil fertility carefully.
If you had nematode problems this year, you should consider submitting samples for nematode analysis as well. If you wait until winter or early spring, nematode populations will decline, and won’t provide an accurate estimation of populations in your fields. More information on nematode sampling is at this link: Sampling Instructions for Nematode Assays.
[important]Not sure what crop you’ll plant next year? You can still soil test. If you change your mind about crops, you can call the lab and they’ll re-run the recommendations using your soil test values for whatever crop you decide to plant next year. There is nothing to be gained in waiting to soil sample. You can download the UF/IFAS soil test form at this link: Commercial Producer Soil Test Form[/important]
When to zone your fields
Not all fields are uniform. If you have a non-uniform field, consider zoning it. Zoning only pays when there is significant variability in your field. Wet areas, low-yielding areas, sandy parts of the field are all factors when you’re considering zoning your field. If you pay a contractor to grid sample your field, take the time to pencil in areas that you feel should perform better. Many contractors or fertilizer suppliers will be able to spread fertilizer for you and help you design a zoned field, if needed. When they zone, you should be at the table to make sure the zones make sense. No one knows your fields like you do.
Field A is uniform and should not be zoned. Field B is highly variable. It makes sense to consider zoning Field B. Be at the table when zones are created to make sure the zones make sense.
Some contractors and fertilizer suppliers have air-boom applicators they can use on your fields. These increase uniformity and limit overlap, and can even spread cover crop seed as well. Often, these come with GPS guidance and section control. You may find that it pays to have them spread your fertilizer for you, saving you time and diesel.
An air-boom applicator available for hire can spread fertilizer and cover crop seed, and may save you time and diesel. An air boom applicator limits overlap and increases uniformity.
Don’t just focus on lime & macronutrients
Plants need more than just the macronutrients: nitrogen, phosphorous, and potassium (NPK). When is the last time your soil tested for sulfur?
Don’t ignore the secondary or the micronutrients. When applying micronutrients, it is recommended to use a liquid formulation, because the spread is more uniform than if they are applied as a granular fertilizer. For example, if you apply two lbs./acre of boron as a granular, you’ll end up with one granule here and another way over there, which won’t help your crop much. A liquid application ensures more uniform application of the micronutrients.
For more information, please read the following UF/IFAS publications:
Michael J. Mulvaney, UF/IFAS Soil Specialist & Glen Harris, UGA Soil Specialist
If you’re like me, you’re watching this rain and wondering where your nutrients are in the soil profile. The Jay FAWN station has recorded almost 20″ of rain so far in June. Last week we talked about peanut gypsum application, but this week we’d like to talk about cotton.
If you applied at-plant N, you might want to re-apply some of it, if you’ve had leaching rainfall events this season. For BMP purposes, you should document the amount of rainfall to show that leaching likely occurred on your soils. If you only apply one application at first square, you likely haven’t applied any N yet this season – so there’s still time for you.
To see if you are N deficient, there are commercial cotton petiole tests available from public and private labs in the Southeast. See http://aesl.ces.uga.edu/FeeSchedule/Complete.pdf for more information. You can also sample representative areas for the youngest fully mature leaf (without petiole). The leaf tissue N should be in the range of 3.5 to 4.5% N for sufficiency.
Those of you on deep sand or soils with no subsoil clay within the top 20 inches should think about K as well. Modern cotton cultivars have higher K demand than N demand, and K is susceptible to leaching, particularly on very sandy soils. If you are on deep, sandy soils, you probably already know that you should split your K applications at planting and topdress. Cotton K demand can exceed 3 lbs K2O per acre per day during flowering. Peak K demand comes during flowering and boll set, so K deficiency during this period can lead to boll shed, reduced lint quality, and/or reduced yield.
K deficiency in cotton shows up as bronzing of leaves and is affiliated with increased Stemphylium disease, as seen below.
Potassium deficiency in cotton appears as bronzing of the leaves. Photo: M. Mulvaney
Oftentimes, we have sufficient soil K according to soil test results, but drought conditions leads to a lack of K in soil water and the plant can’t take it up. There is still plenty of time for that to happen. But so far this year, it’s likely to be the opposite problem on deep, sandy soils: K has leached from the rooting zone after you’ve taken your soil samples.
Boron also leaches easily from sandy soils. If you are concerned about boron, and you are making a fungicide application at first bloom for Target Spot control, you can consider adding 0.3-0.5 lbs B as a tank mix. Boron deficiency in cotton is more evident in younger leaf tissue and shows up as stunted or disfigured terminal growing points and shorter, thicker petioles with “coon tailing” visible on the petioles.
Boron deficiency in cotton with “coon tailing” visible on the petioles. Photo credit: Darrin Dodds & Bobby Golden, Mississippi State University
For more information related to this subject, use the following publication link:
Soil calcium in the pegging zone of peanuts can be increased by adding gypsum at early bloom without raising soil pH. Credit: Glenn Harris
Area farmers have had numerous challenges to deal with already in this growing season. With so much rain over the past two weeks, many farmers have had their production schedule wrecked. Questions have been coming in about a wide range of crop issues, because wet fields have delayed management practices. One that has been repeated numerous times this week is, “What to do if you have not applied gypsum yet to your peanuts and your fields are still wet?”
Dr Glenn Harris, UGA Soil Specialist, makes the following suggestion related to answering this key question:
If you’re worried about missing a gypsum application due to all the rain this year, you should look at your soil Ca test results. UGA research shows that there is no yield response to additional Ca applications, if initial soil test levels are above 250 mg Ca/kg soil (same as ppm). However, if peanut seed is being grown, a gypsum application is needed regardless. Of course, it would be preferable to get a gypsum application down if you can.
Injection of CaCl during peak pod fill (60-90 days) is an option for peanuts under a pivot, if growers are concerned about replacing Ca leached out of the pegging zone. My recommendation is to apply 10 gal/a. In my research I applied it at 75 days after planting. It may not sound like a lot of Ca per acre, but unlike lime and gypsum it is 100 % available.
Gypsum should be applied to peanuts at this stage of growth, and is especially critical for non-irrigated peanuts. Photo by David Wright