Posts Tagged: Phosphorous
P a Simple Little P
It is such a simple little letter, P. It stands for the element phosphorus. It is often misspelled as phosphorous which is an adjective, but even in technical literature it is misspelled. But that's not the end. Phosphorus is an element that takes many forms called oxidation states. When it is in the form of phosphate or phosphoric acid, it is a fertilizer – H3PO4. But when it is in the form of H3PO3 or phosphonate or phosphonite or phosphite or phosphorous acid, it does not perform like a fertilizer. It acts more like a stimulant for a plant to fight off Phytophthora or Pythium. And it works well for avocado and citrus root rots, as well as citrus brown rot.
But a grower recently told me that there is no end of confusion about these two very different forms of P.
A recent article helps to clear up some of this confusion
http://www.spectrumanalytic.com/support/library/pdf/Phosphites_and_Phosphates_When_distributors_and_growers_alike_could_get_confused.pdf
and more if you are still interested
https://edis.ifas.ufl.edu/hs254
Sick avocado on the left and healthy on the right
root rot vs healthy
Phosphorous Acid Confusion
It is more than just the confusion about the effects of phosphonates, but also how to spell the words associated with the P atom. Phosphorus with an ending in “us” is the element we know as P, while Phosphorous with a “ous” ending is the adjective of P. So an acid containing Phosphorous acid is written H3PO3 while phosphoric acid is H3PO4. These are both strong acids and can hurt and cause damage if splashed on the skin. When either is reacted with calcium or potassium hydroxide, a salt is formed which is less dangerous to users, but as with any chemical can be misused.
The salt formed from Phosphorous acid is called calcium phosphite or calcium phosphonate depending on what naming system is used to describe it. Whereas when these bases are reacted with phosphoric acid, the result is calcium or potassium phosphate. These salts are relatively benign in contact with skin. Labels on containers often call phosphorous acid, “soil applied” whereas the phosphite forms are called “leaf applied”. The “soil applied” when applied to a leaf can cause damage, whereas, the leaf applied is much less likely to cause damage to both plant and applicator. It can be applied to the soil, as well. It's much safer to use the leaf applied in either application technique.
The phosphites are often registered as fertilizers, but they have little nutrient effect. Most of their effect is to boost the plant's immunity to Phytophthoras and pythiums. This is called fungistasis and the material is called a fungistat. They don't act as a fungicide when normally applied to kill these organisms.
So you can see there is a lot of confusion in the phosphorous world. Knowing the proper spelling, pronunciation and use is note only good grammar, it makes good farming.
To read more, see:
http://plantscience.psu.edu/research/centers/turf/extension/factsheets/phosphonate-products
https://edis.ifas.ufl.edu/hs254
http://grammarist.com/spelling/phosphorous-phosphorus/
There are few documented cases of phosphorus (P) deficiency in tree crops in California.
p deficiency in citrus
Farm Call: Alternative Fumigant Use and Nutritional Deficiency?
I have an ongoing study with an alternative fumigant (not chloropicrin) compared to an unfumigated control up against the methyl bromide/chloropicrin standard. There's some other stuff in here too, that will be discussed at a later date.
The collaborating grower observed a few weeks ago that plants in the unfumigated control and alternative fumigant were going yellow, in particular the older leaves. That this was not occurring to any sizable degree in the methyl bromide standard was notable.
As many of you my readers know, I really frown upon the identification of leaf yellowing as being caused by this or that deficiency in the absence of any sort of laboratory analysis, so I took two leaf samples from each of the three treatments and submitted them to Perry Labs here in town.
Table 1: Average of two leaf blade samples from unfumigated check, alternative fumigant and methyl bromide standard
Unfumigated check | Alternative Fumigant | Methyl bromide standard | |
%N | 2.9 | 2.7 | 3.0 |
%P | 0.35 | 0.33 | 0.52 |
%K | 1.2 | 1.15 | 1.34 |
%Ca | 1.84 | 2.03 | 1.70 |
%Mg | 0.53 | 0.60 | 0.52 |
%Na | 0.3 | 0.3 | 0.3 |
ppm Fe | 134 | 72 | 95 |
ppm B | 49 | 52 | 54 |
ppm Zn | 11 | 11 | 11 |
ppm Cu | 4.4 | 4.1 | 3.6 |
ppm Mn | 282 | 296 | 304 |
Remembering that two samples per treatment aren't going to give us a what can be called a truly scientific conclusion, these results do at least give us a look at what is going on. First of all, the yellowing probably isn't from nitrogen, which is showing up very much at sufficiency in all treatments. Ditto Ca, Mg and the micros (note that original sample Fe numbers are all over the place); Na is low.
Circling back, we do see that P is lower in both unfumigated and the alternative than the methyl bromide standard, plus the symptoms show up in the older leaves, which checks out for a very mobile element like P. K is just under that recommended from the revised nutrient guidelines from the work I did with Tim Hartz at UC Davis. Additionally, P and K, which come into contact with roots via diffusion in the soil solution (meaning the roots need to grow to the minerals since they are both pretty immobile in the soil) as opposed to mass flow as is the case with nitrate (meaning the nutrient moves to the root since it is mobile), could have their uptake rates reduced by a lessened abundance of roots and root hairs.
The question is then if what we are seeing here is that the lower root growth stemming from less than accustomed fumigation efficacy is also a cause of an apparent deficiency in phosphorous and maybe potassium.
Yellowing of leaves in the alternative fumigant.
Same thing, yellowing of leaves in the unfumigated control.
Plants in the methyl bromide/chloropicrin standard; green, lush, productive.
Announcing a Meeting on January 30 on Strawberry Mineral Nutrition
This post is to announce a meeting on strawberry mineral nutrition to take place this coming January 30. I think it might be good to spend a little bit of time on the current salt situation as well, seeing as it is related to nutrition and water.
First presentation will be in Spanish, and the second in English, with translation provided for both.
Growers and PCA's - bring a copy soil and/or tissue sample analysis for review of sufficiencies/deficiencies/toxicities in our final exercise.
Look forward to seeing you there!
MG156
The Deal with Phosphite Fertilizers
Here is another interesting aspect of plant nutrition drawn from the October 23 Soil Fertility Short Course at UC Davis.
Phosphorous (P), an essential element for plants, does not occur alone in nature and rather it combines with oxygen and hydrogen. Bonded with four oxygen atoms P makes phosphate, and when bonded with three atoms of oxygen and one atom of hydrogen, P forms phosphite.
The fully oxidized phosphate (the one with four oxygen atoms) is the most stable form of P in the environment, and is preferentially taken up by microbes and plant roots. Then again, phosphate is adsorbed to soil particles more than phosphite, meaning it is less available. However, it does not necessarily follow that this enhanced availability of P via phosphite results in more uptake by plants, but even so, fertilizer formulations of phosphite plus calcium, magnesium or potassium have been formulated with the intent of taking advantage of this greater solubility in the soil.
Several studies examining a greater availability of P through phosphite have found that when phosphite is applied at an equivalent rate of P to phosphate fertilizer, it consistently underperformed when measured in terms of crop productivity, especially in the first year of cropping. In the way of explanation, the slower oxidation process of phosphite to the plant-root preferred phosphate, may be part of the equation of why the phosphite is not as effective as phosphate, in spite of having greater mobility.
In lay terms we can say, yes, phosphite might more available to plants in the soil, but they don’t want it as much as they want phosphate.
On the other hand, foliar applications of phosphite have shown that, while it can be converted to phosphate on the leaves by microbes living there, it is more readily absorbed into the foliage of some crop plants like citrus and avocados. Phosphite application (usually once at pre-bloom and perhaps a second time later in the season) to the foliage of avocados or oranges has resulted in more flowers, greater fruit yield and size, total soluble solids and anthocyanin concentrations.
For further reading, see the paper below, which among other things implies that the positive results experienced in oranges and avocados could be replicated in berries…
http://www.spectrumanalytic.com/support/library/pdf/Phosphite_Fertilizers_What%20are%20they.pdf
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