Category Archives: Fertility

Peanuts are looking really good now. We are between pegging and developing seeds at this time. We are on our second and third fungicide applications across the county. We are starting to see evidence of caterpillars. I saw some three corner alfalfa hoppers yesterday as well.

UGA Extension Fertility Scientist Dr. Glen Harris wrote a good piece of information on timing nutrients in peanuts. (Since I already wrote about applying landplaster, I moved the calcium to the bottom since it is a lot to read.)

Timing is everything right? Well, that’s not exactly true when it comes to applying these fertilizer nutrients on peanuts. Rate, source and placement, to round out the “4Rs” of fertilizer management, are important too. When it comes to timing though, if you are too early or too late you could come up short on providing these key nutrients to peanut.

Nitrogen – If peanuts are inoculated or in a short rotation, they should not need any nitrogen fertilizer. This includes putting nitrogen in a starter fertilizer or spraying foliar nitrogen. However, in the case of an inoculation or nodulation failure, nitrogen fertilizer will be recommended as a “rescue” treatment. The timing for fixing this problem is critical and should be detected and fixed around 30 days after planting or soon thereafter. It only takes 60 lb. N/A to fix the problem. Yes, peanuts normally fix more N than that, but recent research as shown that 60 lb. N/A is enough. Split applications and rates up to 180 lb. N/A yielded no more peanuts than the 60 lb. N/A treatment. Ammonium sulfate also seems to be the product of choice in this situation.

Developing seed (R5 Reproductive Growth Stage)

Boron – Since boron is important for pollination and fruiting, the recommended timing for B applications on peanuts is early bloom. And since it is a micronutrient that foliar feeds well, the recommended practice is to include boron with early fungicide sprays. Can you apply boron to the soil at planting? Yes, but this timing may be considered too early since like nitrogen, boron can be highly mobile in soils, i.e. leach out and not be available later when needed. And how late is too late to apply boron? Again, since peak pod fill for peanuts occurs 60 to 90 days after planting, once peanuts are 80 days old or older, the chances of applying boron and getting a yield increase decrease dramatically. And what about rate? The UGA recommendation for B on peanuts is 0.5 lb. B/A. This can be applied in one application or split into 2, 0.25 lb. B/A applications. Rates higher than 0. 5 lb. B/A in a single application can cause burn to the foliage. Rates less than 0.25 lb. B/A, for example 6 ounces of a 5 % liquid B that only provides 0.025 lb. B/A, are considered ineffective and not economical.

Boron burn on peanuts

Calcium – The two most common ways of supplying calcium to the pegging zone of peanut are lime at planting and gypsum (calcium sulfate) at early bloom. Again, timing of applying these two is critical and is linked to the solubility of calcium in these materials. The calcium in lime is not as soluble as the calcium in gypsum so it must be applied earlier to give it time to get in the pegging zone. Applying lime at early bloom is too late.

What about applying gypsum at planting? I get this question all the time. While in some years you could probably get away with this, in other years, like this year for example, applying gypsum at planting would have been too early and not a good idea. Heavy rains on sandy soils can actually “leach” (dissolve and move downward) the calcium right past the pegging zone (top 4 inches). If you applied gypsum too early or if you got 4 to 6 inches of a “leaching rain” soon after application, then you may consider reapplying the gypsum.

Of course, you may want to take a hard look at if you needed gypsum in the first place by looking at your calcium levels and the calcium to potassium ratio in a soil sample from the pegging zone. And what if you are about 60 days after planting and don’t want to run over lapped vines and discover you need some calcium? The period from 60 to 90 days after planting is considered “peak pod fill” and research has shown that applying 10 gal/A of calcium chloride thru the pivot with irrigation water can provide some much needed calcium to developing pods. This treatment will not raise the soil test calcium levels like lime or gypsum will but can be effective.

And what about foliar feeding calcium? The answer for timing of that one is easy…never! Calcium simply does not translocate form leaves to developing pods plus you could never get enough calcium to the pods from a quart per acre foliar calcium even if it did work.

We have been fortunate in our county with adequate rainfall – in most areas anyway. Peanut crop is looking good, we have set pods and kernels are developing in our oldest peanuts. With many questions concerning mixing chemicals, and foliar fertilizers, here is an update on current peanut condition from UGA Extension Agronomist Dr. Scott Monfort:

We tend to think July is the half way mark for the season but the truth is we have a long season ahead of us due to the late plantings throughout the state. There are many acres that are lapped and are setting pods while others are barely 8 to 10 inches wide and are struggling to grow. The good news is a majority of the crop looks good with a large part of the area receiving some rains over the last couple of weeks. However, there are many dry areas that need rain. In some of these areas, a few peanuts have stopped growing and blooming as well as showing signs of elevated leaf burn (with some leaf scorch) as a result of applications of different combinations of adjuvants, herbicides, fungicides, and foliar fertilizers being made in extremely hot and dry conditions (mid to upper 90’s and bright sunny days). A few of these fields have lost more than a third of their leaves. Growers should use caution regarding potential burn as a result of these applications but it’s not something you can eliminate due to weeds and diseases need to be addressed.

Foliar Fertilizer?

I have noticed foliar fertilizers being recommended in these situations to turn the dry land field around. The problem is, the peanuts have shut down due to lack of moisture and are not going to recover until they receive rain. The use of the foliar fertilizer is only costing the growers money and adding to the excessive foliar burn. The best thing to do is to not add these products to their fungicide or herbicide applications under these conditions. Growers can also limit burn by not spraying during the middle of the day (again this might not be an option as growers have a lot of acres to cover).

Leaf Scorch – Dr. Scott Monfort

Former UGA Peanut Agronomist Dr. John Baldwin always said, “If it don’t rain, it don’t matter.” We are putting out landplaster in peanuts now to supplement calcium. If we don’t have enough calcium, we get “pops”. This usually happens more in dryland fields as we also need water to move the Ca through the roots. Peanut plants absorb calcium through the roots (and transported upward in xylem) and not translocated through the leaves. Once peanuts begin to peg, the peg and developing pod passively absorb Ca directly from the soil. This is why we need high levels of Ca in the pegging zone. Ca must be available in a water soluble form and is why gypsum or landplaster is recommended to apply at early flowering. We also need rain very bad. Thankfully, we are getting some today.

UGA Fertility Specialist Dr. Glen Harris has more to say about different types of Ca:

“The more they stay the same! When we switched from growing small-seeded Georgia Green to large-seeded Georgia 06G we really thought we would need to increase our gypsum or calcium recommendations. But after years of research we concluded that the recommendations didn’t need to change. You can still use a pegging soil sample (3 inches deep, next to the peanut row soon after emergence) if you have at least

1. 500 lb/a of soil test calcium AND
2. Calcium to potassium ratio is 3:1 or better

In this case, you don’t need to apply gypsum. If you do not meet EITHER of these requirements then you need to apply 1000 lb/a gypsum at early bloom.  Also, all peanuts grown for seed should automatically receive this gypsum application regardless of soil test calcium levels.

There are a number  of different gypsum or landplaster fertilizers currently available. Chemically they are all calcium sulfate, and the good news is that we have tested these too. They are all comparable as far as providing calcium to the pegging zone of a peanut. Probably the most commonly used is technically called Flue Gas Desulfurized or FGD gypsum and is a byproduct of scrbbing sulfur gas out of smokestacks at coal burning power plants. I call this “smokestack” gypsum although a lot of growers refer to it as “synethetic” gypsum. There is also the old ‘wet bulk” phosphogypsum (a by-product of the phosphorous fertilizer production), and the naturally mined USG 500 among others.

The lime method can also be used to provide calcium to the pegging zone of peanut but a few things:

1. This method should only be used when you also need a soil pH adjustment, otherwise use gypsum if you need calcium.
2. Both dolomitic or calcitic lime can be used. Some people think you HAVE to use calcitic but this is not true.
3. The lime method does not work as well as gypsum under dryland conditions during years of normal rainfall. We have good replicated field data to support this too.

We have also been testing putting calcium chloride though the pivot at peak pod fill (60-90 days after planting). This method has a fit when you are on the borderline of needing some calcium. The benefits are you can apply this yourself and you do not have to run over the vines. One disadvantage compared to gypsum or lime is that this method with not build your soil test calcium levels basically at all.”