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I've heard that nitrates increase weed germination. Is this true? If so feel free to mention what forms of nitrates encourage them to sprout most, if you happen to know (e.g. ammonium nitrate, calcium nitrate, potassium nitrate, etc.)

If it is true, my hypothesis is that bacteria use nitrates to decompose the seed coat, and maybe this encourages sprouting.

I don't know any reason why this would just be the case for weeds and not stuff you plant on purpose. Plus, it could be nice to cause all the weeds to sprout quickly, instead of several at a time (so as to have to pull them up fewer times).

Brōtsyorfuzthrāx
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It's nonsense, frankly, and I'd like to know why whoever told you that thinks it's true. If you dig an area over and add nitrogen in some form, perhaps the observation of increased weed germination means that whoever observed it thought it was the nitrogen, but it's not,its the digging. The soil is full of seeds, and digging may bring them closer to the surface, allowing germination to take place. In fact, most weeds or wild flowers prefer to grow in soil which has not received any fertilizers - most of them like poor soil, but they are opportunists; essentially, given any chance at all, they will sprout and grow, even if fertilizer has been applied.

Bamboo
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  • I don't know why the article I read said that, but it recommended other forms of nitrogen over nitrates, claiming nitrates promoted weed germination and the other nitrogen form didn't. – Brōtsyorfuzthrāx Jun 22 '18 at 23:46
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I did some searching, today, and found some kind of basis for what the article I read said.

Apparently, "… [potassium nitrate] has long been used to stimulate germination of weeds …" according to this article (with other similarly interesting statements), which is about a study testing ammonium nitrate on lambsquarter and velvetleaf, to see how it influenced seed dormancy and germination. It didn't affect the velvetleaf, but it did seem to affect the lambsquarter. I'm unclear as to whether it affected the amaranth.

Here's another article that talks about different chemicals that were experimentally used to see if they induced germination (they said they did), and one of them was potassium nitrate.

So, it seems it's more than one person who thinks its true, and that there is some kind of basis in study for it (although they still don't overtly say why they think it's true). The first also says that weed seeds have higher ammonium nitrate levels than crop seeds, which trait they suspected wad related to dormancy. I wonder if by weed seeds, they mean overwintered seeds, or any seeds that haven't been bred to germinate easily/predictably in controlled conditions, or whatever kind of seeds.

Okay, I found another article about an experiment with various substances, including a few nitrates, and this is the reason they quote why nitrates are supposed to induce germination in a certain kind of seed:

"It is found that nitrates are capable of breaking the dormancy ofAvena [sic] sterilis spp.macrocarpa Mo. seeds, which according to various authors, is due to an increase of the respiratory activity of the seeds"

I'm not sure how nitrates increase respiratory activity of seeds, though.

Brōtsyorfuzthrāx
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  • Are you only interested from a general scientific point of view? Because most of these experiments with different forms of nitrogen have been conducted for agricultural reasons, not horticultural... are you growing acres of wheat or something? – Bamboo Jun 23 '18 at 10:09
  • @Bamboo I'm a home gardener without any pertinent commercial affiliations. My garden isn't huge (just a front/back yard). I'm just trying to learn stuff that could be helpful. Like, whether or not applying nitrates in certain amounts might help seeds to sprout more often in soil that seeds have difficulty sprouting in. This question isn't about that, per se, but it helps me along the path to discovering that and other stuff. Although I have an interest in sciency things, I'm not a lot like most people who are much into science: I don't think things have to be proven to the masses to be useful. – Brōtsyorfuzthrāx Jun 23 '18 at 14:12
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    I get my sunflower seeds to sprout in 4 days by soaking them for a day in a solution of 2 g/L (20 mM) KNO3, but that's not same as dousing seeds already in the soil. Moist paper towels and dark after the soak. – Wayfaring Stranger Jun 23 '18 at 18:11
  • The original article I read wasn't a sciency sort of one, though. It was just one of those gardening, blog-type articles. – Brōtsyorfuzthrāx Jun 24 '18 at 01:34
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from the paper Brōtsyorfuzthrāx cited, Effects of Different Nitrogen Compounds and Temperatures on the Germination of Arena sterills spp. macrocarpa MO:

"The positive effect of nitrates on breaking the dormancy of A. fatua seeds is connected with their capacity to act as electron acceptors and their participation in NADH oxidation as well as their effects of increasing the NAD+/NADH ratio (ADKINS et al. 1984a).

...since they worked with ammonium nitrogen compounds, that they did not obtain such positive results, because the ammonium ions are incapable of acting as electron acceptors. This could explain the small percentages of A. sterilis spp. macrocarpa Mo. germination produced by ammonium sulphate and urea"

I am interested for agricultural reasons, though if the mechanism is real I don't see why it wouldn't also apply in horticulture. It seems possible that nitrates could increase seed germination over ammoniacal nitrogen whatever the mechanism. But I am unclear on, if that is true, why crop seeds also wouldn't then germinate more poorly. Unless whatever nitrate-linked mechanism(s) has(have) been decoupled from agricultural plants through selection.

Brandon Potter
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