Type your question here!

Sunday, May 19, 2013

Lots of Nutrients are in the Soil and Water But Sometimes the Plants Can't Get to Them

Q. Are there any micronutrients in our hard Vegas water of significant quantity?   I ask because I'm wondering if say a fertilizer I use lacks a certain nutrient (say calcium), could it be made up for through regular waterings alone (assuming we remove soil from the equation and all things being equal)? Can we definitively conclude our water is calcium-rich or sulphur-rich or whatever rich?

A. Micronutrients are kind of a funny thing to try and predict. Yes, there are lots of many nutrients (micronutrients as well as major nutrients) present in our soils and water as well as calcium, magnesium and other major or macro elements but not a sizable amount of nitrogen, hopefully.

This chart shows the effect of how acid or alkaline soil water is on 12 nutrients available for plants through their roots.
Take iron in the center of the chart, for instance. The grey bar that iron resides in is wider on the left side and becomes
narrower as we follow the bar from left to right. The wide part of the band means there is plenty of iron available to the plant. As the band decreases in size, its availability to plants decreases as well. Also notice that the pH scale on the
 bottom increases from left to right. From this we can conclude that as the pH increases (becomes more alkaline) the amount of iron that the plant can get from the soil is smaller. Even though the total AMOUNT of iron is unchanged, what the plant
can get from the soil decreases as the soil (or water) becomes more alkaline. This breakeven point for the plant varies
but is basically a problem starting around a pH of 7.5. If we know the pH of a soil or water, we can get a rough idea
which nutrients, in general, will be a problem for plants or not.
Just because the micronutrients are present does not mean they will do the plant much good. They must be in a form available to the plant to use. Micronutrient (and major nutrients as well) availability to the plants depend on how alkaline or acidic the water is (pH) as well as what is called the oxidation/reduction (redox) potential of the water. As alkalinity rises (pH increases) the availability of iron, manganese and zinc become more limited. So in our soils, not just in our water, the alkalinity affects whether the plant can take up these micronutrients.

The quantity of iron in many of our soils is more than adequate for plants BUT because the soil is alkaline the plant can’t use them efficiently. By making the water or soil more acidic these micronutrients convert to a more available form and the plant can take them up. Thus we have those iron fertilizers that are mixed with sulfur to help make the soil more acidic (e.g., Ironite) and we have chelates which bind the iron in an a form available to plants and release it in this form so the plant can take it up and use it (EDDHA, EDTA, DTPA). Unlike Ironite, for instance, the chelates do not affect the acidity of the soil making the iron (or any of the other micronutrients) more available to plants.
Ironite is a product that combines sulfur and iron in a single application.
The reasoning is that the sulfur will lower the soil pH as it is "consumed"
by soil microorganisms. This lowering of the soil pH will then make
the iron residing in the soil close to it, more avaible to the plant.
Sprint 138 is an iron chelate. Chelates work on the priniciple
that this chemical "claw" protects the iron from chemical reactions
and allows the iron to be used by the plant. The chelate is EDDHA.
The chelate is then called Iron EDDHA or FeEDDHA.

Those are the two methods used to make micronutrients available to plants;
  1. increase acidity, or
  2. chelate (protect) the nutrient in a form available to plants.
So are the micronutrients in adequate supply in our water? No, but they are in high enough quantities in MOST soils in the valley to satisfy most plant requirements IF the soil were more acidic. So we end up applying a liquid calcium (usually calcium chloride) to the fruit in multiple sprays (usually five or more) as the fruit is developing to alleviate corky spot and bitter pit in a highly productive orchard. But our soil is LOADED with calcium and you would think…no… that’s impossible, it should never happen.

Just because there is a lot of something in the soil or water does not mean the plant can get to it. Sometimes, besides the pH being a problem, these nutrients may be “bound up” either as secondary minerals (calcium in the form of calcium carbonate = limestone).

Calcium carbonate does not dissolve quickly. So if crops have a high demand for calcium over a fairly short period of time (March through August) they may not be able to get enough of that mineral (calcium) from the bound form (calcium carbonate or limestone). For instance, on some cultivars of pears and apples their demand for calcium can be very high over a relatively short period of time during development and the soil cannot release enough calcium to keep up with this large and quick demand. Thus the plants become calcium deficient (from this deficiency we develop disorders like cork spot on pear and bitter pit on apple; they are the same problem, a lack of calcium, but given different names on different crops).
Bitter pit in Mutsu apple grown in the Las Vegas valley.  Even though it looks like a "cork spot" which is the name
given to this disorder in pears. The brown spot may "erupt" on the surface as a blemish like this and/or it may also
cause discoloration of the white flesh under the skin. Sometimes it does not appear until after harvest.
This is cork spot on Comice pear. Notice the green "dimples" on the outside of the skin. Also notice the brown discoloration just under the skin and reaching into the fruit. Both corky spot and bitter pit are due to a lack of available
calcium from our calcium rich desert soils of southern Nevada. Calcium sprays (in our case using calcium chloride)
sprayed on the fruit during development helps to alleviate these problems.
Golf course superintendents see this problem too in our arid West. These very expensive golf course greens and tees are built totally on sand. The grasses on these spots sometimes develop calcium deficiency even though the water contains LOTS of calcium but the sand may not. They must apply calcium to their greens and tees even though the soil surrounding the greens and tees and the water they are applying is saturated in calcium in bound up forms. Because they cannot return the clippings to these spots (interferes with play) the nutrients are carted off these areas and dumped after mowing. If they could return the clippings and let them decompose back into the grass it would lessen the problem.
If turfgrass clippings are removed from the lawn area, this does not allow the nutrients to be recycled into the lawn area.
Mulching mowers are used to cut up the clippings into tiny pieces so that they decompose rapidly and release the
nutrients back to the soil where they were in the first place.
So a long winded answer to your question. Yes, there are lots of these nutrients around but often times they are unavailable due to the chemistry of the water, the soil and interactions with the plants.


No comments:

Post a Comment