Net scrapings as soil amendment; concern about excessive copper..

I have a potential source for net scrapings as a soil amendment.

This is the detritus from cleaning the nets from ocean-based salmon farms. Mostly of mussels, shells, seaweed, mud, fish waste... anything that can cling or clog.

Nets are protected to some degree by the application of wax with copper in it for a biocide, the same idea as copper sheathing on a boat.

The source tells me a test showed very low copper levels... and that the nets haven't been waxed in quite some time. I am waiting on the document from that previous test. Maybe his idea of low is waay too high for agricultural use...


He pays to dispose of this stuff currently. I could expect at a minimum that the company would cover trucking it to my site; we're talking 15-20 tons per load in a bin truck. Might be able to get some cash out of him beyond that, towards spreading costs.

I expect this stuff would (mostly) be really good for the soil, if handled right; he said that he had used it in his backyard with mixed results, as the amount of shell seemed to make a somewhat impervious layer in some cases. He figured grinding it would do the trick; I figure either more caution in thickness of application, and/or mixing with alder chips and composting before application, should do the trick.

I have 15 or so acres that this could be spread on, likely to increase over time. The initial area is old fields that need to be smoothed out and drainage improved, a project for next year; this would be a convenient time to add amendments..


But... that copper. Hm. And if this is a good idea, why hasn't some other farm snatched up the resource...?


What should I be reading to properly understand the ramifications of a given amount of copper in an amendment? If levels in the amendment are comparable to current & acceptable soil levels, does that necessarily mean I am fine?

Maybe no one has snatched up the resource because it's not something people would think to do.  If you'd asked me "what's a good soil amendment?" I don't think net scrapings would have ever made the list.  Good for you thinking laterally.

It is hard to visualize this but I see four potential problems:

1) copper
IMO the way to check for that is ask for a crate or two of the sludge, then do a test area and plant plants.  If a plant gets too much copper, it dies.  I'd select an area you don't care about particularly much.

2) salt
IMO the way to check for that is ask for a crate or two of the sludge, then do a test area and plant plants.  If a plant gets too much salt, it dies.  :)

3) calcium
In aquaculture, shells are a way to alter the pH and calcium carbonate (hardness) levels of the water.  It's kinda hard to alter the pH of soil, but dumping a ton of seashells on it seems like a good way. I'd do a thorough pH and hardness test on your test area, then again right after dumping the scrapings, then again a few weeks later.

4) impermeability
If you do indeed get a solid layer of algae-covered shells, I could see that leading to issues.  You could get around this by screening the sludge, but screening 25 tons seems like a chore.

Now the benefits are cost, availability, and nutrients you wouldn't easily get otherwise.  Is that worth the effort and risk? I don't know. It's a cool idea.

Rob Lineberger wrote:Maybe no one has snatched up the resource because it's not something people would think to do.  If you'd asked me "what's a good soil amendment?" I don't think net scrapings would have ever made the list.  Good for you thinking laterally.

It is hard to visualize this but I see four potential problems:

1) copper
IMO the way to check for that is ask for a crate or two of the sludge, then do a test area and plant plants.  If a plant gets too much copper, it dies.  I'd select an area you don't care about particularly much.

2) salt
IMO the way to check for that is ask for a crate or two of the sludge, then do a test area and plant plants.  If a plant gets too much salt, it dies.  :)

3) calcium
In aquaculture, shells are a way to alter the pH and calcium carbonate (hardness) levels of the water.  It's kinda hard to alter the pH of soil, but dumping a ton of seashells on it seems like a good way. I'd do a thorough pH and hardness test on your test area, then again right after dumping the scrapings, then again a few weeks later.

4) impermeability
If you do indeed get a solid layer of algae-covered shells, I could see that leading to issues.  You could get around this by screening the sludge, but screening 25 tons seems like a chore.

Now the benefits are cost, availability, and nutrients you wouldn't easily get otherwise.  Is that worth the effort and risk? I don't know. It's a cool idea.

Thanks for the feedback!


I have the copper issue pegged is the number one problem; to address the others you raise:

2) Seaweed is a common soil amendment around here, widely used, and I have never seen anyone report issues that appear linked to salt.. even people mulching with it much more frequently than I would expect to use the net-scrapings. Still something to watch, though.

3) Calcium and upwards PH amendment is probably a good thing; soils in my area are generally acidic, and liming is a common practice. I haven't done a soil test yet, but going by weed indicators I am pretty confident my soil is acidic.

4) I am pretty confident that the physical barrier issue can be address through, well, physical means. IE, don't put on too much... and/or, break it up with a roller or tiller or tracked machine... I think that spreading it thinner is the optimal solution here, but trials will tell.. Screening many tons would indeed be a chore, a noisy, smelly, diesel-draining chore that I would prefer to avoid.. but I have no idea if it is possible to do so.



A test plot is definitely a reasonable idea; I am hoping to better understand the soil chemistry before I move forward though.

This has some interesting tidbits: http://corn.agronomy.wisc.edu/Management/pdfs/a2527.pdf

'Plants grown on newly reclaimed acid organic soils occasionally exhibit copper deficiency symptoms the first few years. After the organic matter begins to decompose when the soils are drained, sufficient copper is released to support normal crop growth'
So.. in a highly organic goop, maybe the copper is mostly bound to organic matter. Does this copper show up in the test?

It sounds like an amazing resource. The more crushed the shells were the better and I'd imagine it would incorporate more easily if composted with something like horse stall cleanings first.