We had a delivery of manure to the allotment a few weeks ago. So I did what I usually do: rearranged everything else to spend several hours with a fork and a wheelbarrow, getting as much of it as I could manage onto my plot before it all disappeared. In another year or two I hope not to have to take such drastic measures, but the heavy clay I’ve inherited doesn’t have much organic matter in it at all.
But the other thing I did was to sow some pea shoots, in two separate containers: some with just expandable coir, and some with coir plus some of the manure mixed in. This is to test for pesticide poisoning.
These were the results:
Well, that’s pretty clearly a problem.
I’ve written to the allotment society committee, and I will also be contacting Corteva about it as mentioned at https://organicgrowersalliance.co.uk/aminopyralid-the-herbicide-that-hasnt-gone-away/
Legumes and nightshades are especially sensitive to these pesticides, but I understand they can also affect sunflowers (including Jerusalem artichokes), cucurbits, lettuces and other broad-leaved plants. It can take well over a year to break down in contact with soil and sunlight, and longer in a storage pile or compost heap. It doesn’t affect grasses, but binds to the lignin in them, which is how it ends up in horse manure after the horses eat grass that has been sprayed.
A more detailed description of what these pesticides do is available at https://deepgreenpermaculture.com/2021/02/24/how-to-identify-and-treat-herbicide-contamination-of-commercial-soil-compost-and-manure/
I’m not really content with just contacting Corteva, though. So I ordered quite a bit of Pleurotus ostreatus grain spawn, stirred it into both my manure heaps, and gave it a good watering in. The centre of the heaps was still quite moist already despite the hot weather so I’m hoping the oysters will get established there. (We do get various ink cap species growing on the manure, usually, but I don’t think they can break down petrochemicals the way oysters may be able to.) I kept back a bucket of the contaminated stuff, so if the oysters do colonise the manure pile and manage to fruit, I will run another bioassay with more peas.
I’m really glad I thought to check this manure out before putting any of it on my potatoes, tomatoes or squashes.