I assume the units you're talking about are ppm, in which case, yes, 917 is pretty high. I believe that too much potassium interferes with the absorption of other nutrients, such as calcium (got blossom end rot?) and nitrogen (yellowing leaves?). I believe it does tend to leach out, though. I wouldn't worry too much about it.

I do have some yellowing leaves. But it wouldn't do any good to give them nitrogen would it? I guess I'll see about blossom end rot a little later.

Good article that explains all the nutrient interaction relevant to crop production. Note that K levels exceeding 20,000 ppm is not all that uncommon and that there is no "toxic" level per se. Even at your 900+ only a portion of it is in a plant-usable form and as Dan pointed out the symptoms would be insufficient N, Ca++, Mg, and Mn which are easy to remedy.

If especially concerned and if obvious problems develop then it is possible to ameliorate some of it out of the soil simply by growing an off-season cover crop. But since the source in this case is the added compost rather than the native soil the level should fall on its own as the compost decomposes.

http://www.extension.umn.edu/agriculture/nutrient-management/potassium/potassium-for-crop-production/

Dave

with that much mineral content, cover crops as Dave suggests will add organic matter without adding minerals, they are ideal for your case. plant them early, mixed, and often. You may still be on the hook for some nitrogen, watch the plants, give them moderate amounts if they look stunted. although, over time, cover crops do bring in quite a bit of N, even without legumes, you could be close to being self-sufficient.

Great advice. Thank you all. I'll plan to mingle some cover crops in and watch for signs of needed nitogen. This year I had a full garden all winter. When you get compost materials from other sources do you test it before using it? I certainly can not produce the amount of compost I need on my own, and I like to take advantage of these opportunities from the city. I am a bit worried about my tomatoes-for the first time I ordered toms from seeds of italy and started my own seedlings. I still have about 2 months before time to plant them are there any cover crops I could grow in that amount of time? Also are there any low growing cover crops I could just grow around my regular veggies-almost like a living mulch?? I have never done cover crops before...

I wouldn't get overly concerned about that K level but anything coming from a municipal compost should have a micronutrient analysis, including heavy metals- they should provide that to you upon request. The analysis would look entirely different than a soil test report. Even with a favorable report I would limit compost to 50 cu. yds. per acre- that is less than an half inch layer on the soil. Research has shown that more is not helpful. I know replies will be forthcoming to counterattack that statement.

I believe that heavy metals are a potential problem for biosolid compost, but not for yard-debris compost. I think that's because anything can get dumped in the sewer. Not easy to get a lot of Zn, Cu, Ni, Pb, Cd and Cr in yard debris.

Sure Dan, that's exaxctly why you ask for the analysis. There is a very good likelihood that a lot more than leaves and grass clippings are being composted. The key word OP used was "City". This isn't a community cull pile. I've even been involved partly in a composting project where slaughterhouse offal was included in the composted. Expect everything imaginable.

But if you are that paranoid, would you trust the analysis the city gave you. I doubt they would even have one. According to the OP, people bring by their lawn clippings and branches. Maybe they are required, I don't know.

If you fall back to the default position that compost is a soil amendment, not a nutrient source, and should be used in reasonable amounts as such then there shouldn't be any issues. It's not as if one would try to grow in straight compost or even mostly compost anyway.

Dave

That's true. The OP said that people "can" drop off yard debris. To the extent that biosolids end up in the mix, a test for heavy metals would be advisable. Now, the first thing to do is just ask the city what's in it. That could save some effort. Of course, paranoia would lead you not to believe them anyway, so ...

I'll test garden again in fall and check results. In the meantime I think I will call the ag office and see what they recommend for cover crops. I have never done cover crops because I don't really have an off-season.

if you don't have an off-season you can start early and seed something like oats and buckwheat under tall plants like tomatoes. They will grow but the toms will be taller. You can seed sorghum (which is a K consumer extraordinaire) in summer behind (north side of) your trellises. If you plant them among low growing veggies like arugula or carrots it is not going to work. In such case you will have to give the bed to the cover crop for a while. Start with those that are frost killed, oats buckwheat, or that can be killed by mowing and/or knocking down, like rye and pea. Daikon can be killed by both methods but it is hard to chop with a scythe. I like chicory as a CC even though it is an overwintering biennial because I control it by eating.

Yeah not real sure how you don't have an off-season in our zone but it isn't as if they can only be planted on date X and must be plowed in by date Y. Like glib says cover crops can really be grown at any time in any dormant space in the garden - spring crops come out, put in clover and plant the tomatoes in it. Mid-season scatter seed some rye, till it in in the fall and seed any vacant space with peas or radish or even more clover (doesn't usually get winter killed here).

It's more work and not really mandatory for the K issue but it really benefits the soil.

Dave

Thanks Dave and glib, I will do some research and try some of the cover crops you mention. I didn't realize radish was a cover crop until you mentioned it. I am able to keep some things all winter (kale, collards, carrots, spinach, etc). This year the mild winter helped, plus I use agribon when needed. I love gardening but have much to learn about soil and fertilizers. I always appreciate the great advice on this forum.