Ammonium Toxicity

[Ray]

We've had some good discussions here about nitrate/ammonium/urea sources of nitrogen, plus some debate on their applicability and what affects they have on plants, but I just read another article (by Neil Mattson a Cornell extension service professor) concerning the subject.

In the article (October 11 Growertalks) he states "When plants take up nitrogen, they may absorb more than they need to support current growth. Extra nitrogen is stored in case fertilizer levels become lower later on. Nitrate can be safely store by the plant, but when plants take up and store too much ammonium, it can cause damage to the cells."

Granted, he is concerned with fertilizers in soil, where he states that nitrifers convert the ammonium compounds into nitrates - unless the average temperature falls below 60°F, or low pH suppresses their action - which lessens the likelihood of ammonium uptake, but doesn't that imply that, to some degree, that we need to limit (not eliminate, necessarily) our application of ammonium-based fertilizers?

 

[cnycharles]

If I remember right, a consultant we had at work told us that fertilizing with ammonium based fertilizers could be a problem if the temperatures were a bit too cool. I may have written things down but it would be at work and i'm off for a few months.... it could also have been that nitrates weren't good (some sort of poisoning) if it got too cool... a number of years ago

 

[Rick]

Maybe hard to find absolutes when there are tons of variables in this complex system.

Have you gone back to your Bill Argo articles Ray?

His biggest caveatte to ammonia vs nitrate was based on alkalinity.

Regardless of the organism (even those that "eat" it for a living), ammonia is inherently more toxic than nitrate. In general by at least an order of magnitude.

Also the toxicity of ammonia increases exponentially with pH. With a constant concentration of 60 mg/L of ammonia, you can kill nitrifying bacteria at pH 8.5- 9.0, while they will be gobbling it up at pH 7.5 (you could go to hundreds of ppm at neutral pH). Nitrifying bacteria require alkalinity to process ammonia, so below pH 5.5 they get pretty inefficient again.

So I guess if the intra cellular pH of the plant cell stays acidic then it could handle/proccess a lot more than if the cellarlar pH goes up. I don't know what normal cell pH is in plants or what the range is. Seems like it might work into a discussion on CAM plants?? Anyway if CO2 becomes limiting then photosynthesizing organisms could get higher cellular pH and cause internal ammonia toxicity.

 

[Ray]

Have you gone back to your Bill Argo articles Ray?

His biggest caveatte to ammonia vs nitrate was based on alkalinity.

Yep. I spoke to him just the other day, and he remarked that "plants scrounge all nutrients really well, except for calcium and boron", and that most nutrient deficiencies are alkalinity-related.

Even though I deleted it from the quote, I agree completely about the complexity. I've read and heard about deficiencies in one metal ion that were not caused by a deficient supply of that, but by the deficiency in a totally different ion. One example was an iron deficiency brought on by the lack of phosphorus.

 

[Rick]

Yep. I spoke to him just the other day, and he remarked that "plants scrounge all nutrients really well, except for calcium and boron", and that most nutrient deficiencies are alkalinity-related.

Even though I deleted it from the quote, I agree completely about the complexity. I've read and heard about deficiencies in one metal ion that were not caused by a deficient supply of that, but by the deficiency in a totally different ion. One example was an iron deficiency brought on by the lack of phosphorus.

This interconectedness also comes out with overdosing.

One of the issues I discovered with the high K prolem is that after excess tissue K blocks Ca and Mg uptake, uptake of Phosphate is also reduced (since some phosphate uptake systems require Ca and Mg).:sob:

When you look at the generic symptom charts of individula mineral deficiencies and excesses, they are all pretty much the same! But when you see all the interconnectedness of the system, you can imagine how one thing out of wack effects everything else.

 

[Rick]

I don't know if you remember, but maybe 2- 3 years ago I was going off on how a bunch of my plants were turning purple.

So I looked at the chart that said purple = phosphate deficiency so I got on a big push for bonemeal supplementation. And in general most of these plants went back to green (i.e. must have been a phosphorus deficiency). But other growth symptoms persisted (like random erwinia infections). While Rick H in TX said he was getting Erwinia "cures" with bonemeal (or maybe getting local rebalance of K???)

But now that I looked at the deal with high K and see how even with excess amounts of PO4 hitting the plants with MSU in the first place, I could still end up with a PO4 deficiency, a Ca deficiency, an Mg deficiency.........

 

[Rick]

And while I thought I was treating a PO4 deficiency, I was simaltaneously adding Ca (which could also have been moderating the K antagonism).

 

[Rick]

Yep. I spoke to him just the other day, and he remarked that "plants scrounge all nutrients really well, except for calcium and boron", and that most nutrient deficiencies are alkalinity-related.

Unfortunately alkalinity is not 100% correlated to pH.

The hardness of the water will temper the pH of a system with relatively high alkalinity.

So unless you have the capability of conducting true alkalinity titrations, you end up fudging that info on the basis of pH and harndess knowledge.