Timing N, Ca, and Boron On Peanuts

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.

Advertisements

Leave a comment

Filed under Fertility, Peanuts

Comments are closed.