The pH of finished compost has always been very near neutral, 7.0 pH, and it has nothing to do with less acid rain, alkalinized municipal water, or even what the inputs are.

kimmq is kimmsr

My city's compost is 8.3. I asked them twice if they were liming it to control the smell and they say no. Mind you, when I get some to start seedlings it always performs well.

Pinon and chamisa sounds like New Mexico, where the soils are alkaline. Would not surprise me if the water is naturally alkaline too, and the plants, and the very air itself (j/k on that last one :-). What's the pH of your soil? 7 to 8? If so your compost isn't going to make it more alkaline, so if your plants grow well, don't worry about it.

How's that for an answer - "I don't know, but don't worry about it." :-D Last time a guy said that he was telling that radar operator in Hawaii not to worry about that huge blob coming in on Pearl Harbor Day.

ha. my water used to be 9.2, now it is 9.3. and you guys complain that i worry so much about infiltration rates and capillarity and all that beyond organic stuff. alkaline compost plus alkaline soil plus caustic water -> better use rain only. In fact I discontinued the compost, not only my oak leaves.

I'm in the desert southwest, and often use a similar mix of materials to make compost. I can get all the free chipped pinon/juniper wood I want. Some goes to mulching, some to making compost for planting. Our water in the summer has more than 40 grains hardness/gallon which translates to about 2.5 grams minerals/gallon. The mineral content is a mix of calcium and magnesium. I use lots of water to keep my compost wet, so I'm adding pounds of calcium and magnesium to even a fairly small pile. In my case, the hard water, and the necessity to use a good bit of it definitely impacts the compost. My final product (just checked some outside) has a pH about 8.4. A local commercial composter produces a product with pH 8.7. Note that we get practically no rain most of the year, so rain water is not available for use.

I very much agree with tox's comment above about not worrying about your pH in the compost. Compost has a huge buffering capability, and will very slowly, if at all, change the pH of your soil. I also find that my somewhat alkaline compost works just fine for all applications. We have don't have the acid rain of the east or midwest, and our soils do tend to be naturally alkaline. I used to have to add sulphur to the soil, but usually find that most plants do fine with the natural pH of around 7.2 in the soil.

I'm curious about how much urea you add to your compost. I also use urea, ammonium nitrate, or ammonium sulfate as a nitrogen source, just a little (15 g/ cubic ft. raw materials). I use whatever nitrogen source is cheapest since we have very few green materials to add to compost.

Renais

Same here Renais. Few natural nitrogen sources. My guess is I use about 2 kilos for a little more than a cubic yard of chips I try to apply it about half dissolved in water and about half in prills to space out the N application a little. I figure it's about the equivalent of 80 pound of chicken manure altogether.

I'm not shy about giving it N, obviously, but I still try to creep up on it and not overshoot. I don't commonly smell ammonia.

My compost tests around 8+ too. I can't say I that I've seen any harm, but that's way too close to an extreme reading for me. I'm switching to ammonium sulfate.

Curious about the cause of the compost alkalinity. My tap water tests at only 100 ppm tds which isn't bad.

The carbonate/bicarbonate buffer pH is about 8.3. That's basically the pH where if you add more base, bicarbonate converts to carbonate and the pH does not change much. If you add acid, it goes the other way and the pH does not change much. Hence the term 'buffer'. I am not surprised that compost made with all that hard water is settling in around 8.

One of the great things compost does is provide ion exchange sites for minerals and nutrients which makes them more available to plants. That effect helps to counteract the hindering effect of high pH, so the soil ends up fertile despite its high pH. It should still outperform the same soil with a low organic matter content.

clearly, the SW is a place where composting will never attain the biological efficiency (soil fertility) of a mixed cover crop. If you have the chance to grow one, a simple radish/legume/grain winter mixture will cycle your nutrients, break your soil, replenish your N, and add organic matter to depth without one extra calcium ion. Plus it is much better OM than compost and supports your myc., which in the desert are fundamental. cacti are the most myc. class of plants.

The large Imperial College composting study we've discussed several times did a huge number of measurements on pH of their composts, with most falling in the range of 6-8, but some as low as 5.6, and some as high as 9.3. See http://www.imperial.ac.uk/media/imperial-college/research-centres-and-groups/environmental-and-water-resource-engineering/ecwm/phase-1/Section-6.PDF for more details.

Renais

Cover crops are laughably out of the question here. This and horse manure is all we got in large quantities.

It's a mystery, since my tap water isn't all that hard. I have a pal who is going to test some locally prepared commercial compost he ordered. Fully organic, prepared by a guy with an ag degree or two from high powered ag schools. If his is alkaline too, I'll conclude it's the plant material.