Fish fertilizer is very popular. It is reported to be a good source of nutrients and a good source of proteins, amino acids, and oils—for your plants. Can plants use fish proteins and oils? Is fish fertilizer a good source of nutrients?
Before I go any further, let me say that there is nothing wrong with using fish fertilizer. It will help make your plants grow. I have two problems with fish fertilizer: it is extremely expensive compared to other sources of fertilizer, and many of the claims for it have no basis.
Fish Emulsion vs Fish Hydrolysate
What is the difference between fish emulsion and fish hydrolysate? The difference from a plant’s point of view is minor, but if you are trying to sell product, there are big differences.
Fish emulsion and fish hydrolysate start with dead fish. In some cases this is leftover bits from the fish industry, and in other cases, this is whole fish specifically caught to make fertilizer. These are then treated with various chemicals and enzymes to break down larger organic molecules into nutrients and other small organic molecules. Further treatment can take one of two paths; it is either heated or cold processed. Fish emulsion is the end product if the heating process is used. Fish hydrolysate is the result of using cold processing.
There is great debate between the benefits of emulsion vs. hydrolysate—which is better? The reality is that plants can’t use most of the large or even small organic molecules from either process. Normally microbes in the soil degrade these to nutrients plants can use. So the argument that heat in the emulsion process is detrimental makes no sense. It is true that heat will denature proteins, but they need to be denatured for the plants to use them.
I think the arguments for or against either process are just marketing hype. I have seen no scientific evidence to support the superiority of either process.
Fish Fertilizer Benefits
Fish fertilizer is an organic product—for the most part. So it does have the benefits other organic soil additives have. It feeds plants and microbes and improves soil structure.
But proponents of fish fertilizer make claims that do not apply to other organic fertilizers. Most seem to be centered around the fact that the liquid fertilizer contains proteins and oils. We all know fish oils are very important for our health, so they must be good for plants, right? Wrong!
Plants can’t make use of large molecules such as oils and proteins; see Organic Fertilizer—What Is Its Real Value? for more details. When these molecules are added to soil, microbes digest them and turn them into small molecules like nitrate and phosphate. It is only then that plants can make use of these molecules.
Since the large molecules need to be degraded before plants can use them, there is little difference—to the plant—between proteins and oils from fish, cows (manure), or even plants. I have found no support for the claim that fish fertilizer is better than any other organic fertilizer.
The main thing plants need from fertilizer is a source of nitrogen. Garden soils usually have enough P and K and the other minor nutrients. Nitrogen is the thing that is missing in soils. Given this fact, fish fertilizer is no better or worse than other types of fertilizer.
Fish fertilizer has about 2% nitrogen, which is the same as most organic fertilizers: compost, manure, and coffee grounds.
Is Fish Fertilizer Organic?
This probably seems like a dumb question—fish are organic, so why would fish extracts not be organic? Here’s why. In the process of turning fish scraps into fertilizer, companies add a number of chemicals, including phosphoric acid and odor inhibitors. Apparently, as long as these ingredients form less than 1% of the finished product, the product can still be called organic. Who knew—organic fertilizer only needs to be 99% organic!
Cost of Nitrogen
I checked several fish fertilizers, and a common analysis is 2-4-2, and if you buy in large containers, you can get 9 lb (3.8 kg) for $25. Small quantities are even more expensive. This fertilizer has 2% nitrogen, and so the cost for the nitrogen is $33 for 100 g of nitrogen. Wow! Even fresh-caught Atlantic salmon doesn’t cost that much!!
What is the cost of 100 g of nitrogen if you buy a commercial fertilizer? Scotts sells a 30-0-9 at $17 for 6.2 kg, or $0.91 for 100 g.
Fish fertilizer is 35 times more expensive than commercial fertilizer, and plants can’t tell the difference between the two sources of nitrogen.
I can hear your objection, BUT … fish fertilizer is organic. That is true, and organic fertilizers do more than just provide nutrients. They also help build better soil by feeding microbes. Fish fertilizer is about 14% protein, which is the same as manure. A 30 lb bag of manure will cost you $4 compared to $75 for the same amount of fish protein. Manure bought in bulk is even cheaper.
I really can’t think of any good reason to buy fish fertilizer if other sources of fertilizer are available.
References:
1) Photo Source: Cheryl’s Garden Goodies
I occasionally use liquid fish fertilizer but was wondering about the mercury content. Does it get destroyed in the heating process?.
Mercury is an element as defined in chemistry, and as such can not be destroyed.
Interesting article Robert and a needed perspective. I have noticed that when I use fish emulsion fertilizer, I often see a brighter, more yellow-green flush to especially new growth than with other fertilizers. i have also noticed that my plants seem less apt to show effects of over-fertilization when I have accidentally done so. Do you know of any reason why fish fertilizer would seem to have this “buffering” effect to nutrient levels? Or am I simply suffering the effects of anecdotal evidence?
One reason you are less likely to over fertilize is that fish fertilizer contains low levels of nutrients. Using more dilute solutions makes it easier not to add too much. But then you can dilute any soluble fertilizer to get the same benefit.
If you want to know the real benefits of the various fish products, type into your browser “the benefits of fish liquids in agriculture” Nutri tech solutions and organic farming systems have some positive blurb on these and other products, kelp, molasses and humates.
Fish liquids will out perform urea when used over time
If this company is promoting the benefits of things like “kelp, molasses and humates”, then clearly their material can’t be trusted as being fact.
Re: “Fish liquids will out perform urea when used over time” – that may be true. Urea is just a nitrogen source, and fish liquids contain other nutrients as well, but it is only true if the soil is missing these other nutrients.
Do fish fertilizer, it is not advantageous in that it contains an amino acid?
Commercial fertilizers with amino acids are expensive… As for nitrogen fertilizers Robert is right…
There is little evidence that amino acids are of any extra value – other than a source of nitrogen.
Well, amino acids do have extra value, they are composed of nitrogen, carbon, and oxygen in some. Microbes use them,for the N and H mainly, critical elements to build other metabolites.
Amino acids are small enough, they can pass though cell walls. Some are excellent chelators of secondary and micronutrients. For example two glycine molecules can attach between them a calcium ion. There are commercial amino-chelated fertilizers that use this strategy. Plants can absorb these amino chelates directly through roots or foliage.
Mycorrhizal fungi have been shown to deliver amino acids directly into the roots.
Of course the amino acid glycine is used in another way for a more destructive purpose to plants, making the herbicide Glyphosate (N-(phosphonomethyl)glycine) .
I don’t think I ever said amino acids don’t have value?
Try to use blue green algae from pond water lakes and streams . Seem to me that it would be a better fertilizer than most .
I have been very interested in everything posted in this discussion and thought it would be helpful to respond to the latest post by reference to http://www.web.uvic.ca/~reimlab/reimchen_ecoforestry.pdf which discusses how salmon help the forest in British Columbia.
Thanks for the great website!
I light of all that I have read, I am still in a quandry as to what a real fertilizer is. Culture recommendation for my Violette De Bordeaux Fig call for the use of 10-10-10. What would you suggest?
A cheap water soluble fertilizer – it can be 10-10-10 or something similar.
So what would you suggest as a good alternative? In Canada, we definitely get the short end of the stick when it comes to variety of goods available as well as reasonably priced. Most of the equivalent stuff in the US is half of what it costs here, even before the poor dollar conversion currently but shipping something heavy negates all the savings. I’m only a small time gardener.
Compost or synthetic fertilizer. Mulch with wood chips in a non-veg garden and with straw in a veg garden.
It’s surprising the article makes no mention of the full spectrum of minerals present in sea food, and therefore the fertiliser. Sea water is known to have an astounding 82 elements (don’t have the link, please Google it). The only thing that prevents us from using sea water as fertiliser is the high sodium content. Fish do the wonderful job of filtering out that excess sodium and leaving you with extremely mineral rich organic matter !
BTW, if you guys are sold on fish, you really should be doing FAA … Fish amino acid … A concoction recommended by Korean natural farming. This process will break down most of the larger molecules and also multiply the microbial count before you apply all that yummy fertiliser to the soil.
Wow – 82 elements. So what. How many of these are needed by plants? I tell people plants use about 30 nutrients and that number is higher than most references.
How many of the 30 nutrients are missing from soil? Most are rarely deficient in garden soil.
Adding 82 elements to soil serves no benefit to plants or soil organisms.
Boron and Zinc deficiencies are very common in the Willamette valley where I live. Both are critical nutrients.
I agree
I have Googled it. Sea water contains “47 minerals and metals” according to Stanford University. And plants use at most 24 elements. See my new post Trace Mineral Fertilizers – How Many Nutrients Do Plants Need?
It couldn’t possibly have 82 elements in – element 82 is lead, most people consider this the heaviest non-radioactive element (or perhaps 83, bismuth). So you’d have to have everything, including the noble gases, silicon, gold etc., to even reach that number!
I suspect the choice of the number 82 isn’t a coincidence, but probably the collision point of various half-read and half-remembered ‘facts’ by someone at some point down the line.
Robert Pavlis, I just finished reading this article/thread and I found it very helpful. I appriciate how you explained some of the commonly accepted false ideas that have become so become so popular in many organic gardening circles.
I look forward to reading more of your work in the future!
Thanks,
Dan
Native Americans would start off their “3 sisters” gardens by burying fish. Then they planted nitrogen fixing legumes, along with corn and squash. They didn’t need to keep adding fish to their soil afterwards
I am not in agreement on this folklore and there is no documented proof to generalize that native Americans used fish as part of their agricultural approach to growing corn. Maize is widespread across North America and Mexico. How does this explain the tribes of the southwest: Navajo-Blue Corn, Hopi who also grew several varieties of corn & beans. I am a grower of indigenous corn myself. Corn is relayed to grass and both are heavy feeders of nitrogen. I certainly accept the permaculture approach of the three sisters method and it all makes scientific sense.
There is a lot of romantic sales pitches around based on the native Americans planting fish under there corn. In actual fact recorded litriture shows that fish were used in the U.K first and it was a tribal elder from, I forget the area now but he was kidnapped in early settlement of the US and taken to England, “educated” and he learnt from locals who used fish in gardening there. After two years he returned to his native homelands and vwollar, the fishy romance began.
Interesting – and reference for this story?