hoopgod32 wrote: βThu May 09, 2024 5:51 amAre you sure nitrate should be 2:1? I don't think that's accurate. I've seen a ton of cacti growers recommend
Masterblend and it contains mostly Nitrate Nitrogen (no more than 15% ammonium). GeeBee even recommends a 80/20 ratio. A good description pulled from Reddit:
From
here: "Ammonium, the positive ionic form of nitrogen, has to compete with calcium, magnesium, potassium, and most micronutrients since they are all uptaken in equivalent quantities relative to the presence in the soil. Nitrate, however, is a negative ion and only really competes with phosphorus and sulfur. It's been demonstrated across a wide variety of plants that they preferentially uptake nitrate over ammonium. When it comes to soil in the ground that has a rich and stable microbiome nitrifying bacteria are present and high enough quantities that even though pretty much all of the nitrogen going into the soil is going in as ammonium, usually in the form of organic matter, enough is converted to nitrate to not be a problem for plants. However, in containers, it's harder for nitrifying bacteria to survive and it's best to do a little bit of the work for them and just feed directly with nitrate."
From
here: "This leads to the second point, nitrogen in deserts in usually in the form of nitrate. Nitrate is very stable and the little water in deserts means it doesn't get washed away very easily. Nitrate is the form of nitrogen most cacti would have ev0lved to use and many cacti probably don't have the means to effectively use nitrogen as ammonium (with the probable exception of tropical and wet-climate cacti like Rhipsalis)."
The subreddit in your first link is specific to discussions of Trichocereus. From Durtndur (whoever that is) -- "Aim for an 80/20 ratio of nitrate nitrogen to ammoniacal nitrogen.
Trichocereus love a heavy feed compared to other cacti". If the 80/20 ratio works for Trichocereus, that's fine, but I wouldn't make any assumptions about applying it to most or all other desert genera.
Kyletsenior's post in the Reddit Cactus Corner appears to hold more weight because he was an analyst working for a fertilizer manufacturer. But as he said right up front, "I'm certainly no expert in cacti." On the other hand, we
do have an expert on the forum, MikeInOz -- professional horticulturalist with a deep knowledge of cacti. Mike uses a slow-release Cactus & Succulent fertilizer made by Osmocote, and this is the fert's chemical analysis:
- Osmocote_c&s_formulation.JPG (96.71 KiB) Viewed 492 times
(Unfortunately the Osmocote is sold only in Australia and New Zealand.) You'll note that the ammonium-nitrate ratio is roughly 1-1. What about the urea component? From "The Cal-Mag of my dreams?" thread:
MikeInOz wrote: βFri Jan 27, 2023 2:15 amUrea is converted to ammonium either in the soil by bacteria or in the plant using the enzyme urease. (they have recently discovered nickel is needed for that process but you can basically think of urea as ammonium because it is converted so quickly in the mix.)
Same thread, and this is Mike's experience with the Osmocote:
MikeInOz wrote: βMon Jan 23, 2023 6:23 amMy cacti get double the ammonium/urea N than Nitrate N. They are growing extremely well. Quite fast but still compact and with good spination. Mammillaria bertoltdii, leuthyi and hermosana have all flowered in their second year. Ariocarpus seedlings also growing fast (for arios). That's the kind of result I'm looking for! They obviously like the ammonium. I would be reluctant to change without a good reason.
There we have it -- contrary to what kyletsenior believes, desert cacti are perfectly capable of using N from ammonium.
Potting medium is an important part of the equation, and this is Mike's approach:
MikeInOz wrote: βWed Oct 11, 2023 4:38 amFor fertilizer, I use Osmocote for cacti and succulents with an K/N ratio of of about 1.3. I use gypsum of all cacti as a top dressing for Ca. For the limestone species I add washed limestone/dolomite ''sand'' trickled down into the dry mix after potting up to supply more Ca and Mg. There is also Mg and a little Ca in the osmocote and all trace elements as well. For more trace elements I use home made compost and/or 2 year old cow manure at about 10-20% depending on the species. (desert or forest/grassland habitat)
I'd consider this to be a soil-based mix -- for cacti being grown under cultivation with such a mix, a nitrate-ammonium ratio of 1-1 sounds about right. I'm growing 64 of my 68 cacti with a pure pumice and granite gravel mix (essentially a hydroponic mix), so that 1-1 ratio would lead to problems with ammonium toxicity. Based on my 13 years of sound growing experience, I found that a nitrate-ammonium ratio of 2-1 is correct for a pure mineral mix, although I think it should be fine for soil-based mixes too. There's no getting around the fact that nitrate and ammonium have 2 different functions in cactus growth:
- Nitrate pathways send N mostly to the stem.
- Ammonium pathways send N mostly to the roots.
If I had been using something like Masterblend for the last 13 years, my cacti wouldn't be doing so well. The trick is to have the right balance of nitrate and ammonium, and this is determined by the type of mix the grower is using. By the way, you'll get better advice here than you would on on social media platforms like reddit.