My soil test results took just under two weeks to come back. I sent them the University of Massachusetts Soil Lab. Here's a previous post with more information.
I sent in three samples: 1-a new bed adjacent to my house, 2-my established home raised beds, and 3-my new community plot.
1-new bed adjacent to my house:
soil pH 6.4, buffer pH 6.6
nitrogen 13 ppm (add), phosphorus 22 ppm (sufficient), potassium 281 ppm (sufficient)
Micronutrient levels : all normal
Organic matter 16.6% (very high)
Lead: elevated
Recommendation: Adjust pH by adding 12 lbs lime per 100 sq ft. Add 1/4 lb nitrogen per 100 sq ft either as a complete fertilizer (e.g. 2-3 lbs 10-10-10 per 100 sq ft) or an alternate nitrogen source (e.g. 3-4 lbs dried blood 12-0-0 per 100 sq ft). For elevated lead, recommendations include grow only fruiting crops, grow ornamentals, remove a layer of soil and replenish with clean topsoil, use containers, create raised beds of at least 6 inches depth.
2-my established home raised beds:
soil pH 6.7, buffer pH 6.8
nitrogen 11 ppm (add), phosphorus 28 ppm (sufficient), potassium 116 ppm (sufficient)
Micronutrient levels : all normal
Organic matter 11.2% (very high)
Lead: low
Recommendation: Add 1/4 lb nitrogen per 100 sq ft either as a complete fertilizer (e.g. 2-3 lbs 10-10-10 per 100 sq ft) or an alternate nitrogen source (e.g. 3-4 lbs dried blood 12-0-0 per 100 sq ft).
3-my new community plot
soil pH 5.8, buffer pH 6.0
nitrogen 13 ppm (add), phosphorus 12 ppm (sufficient), potassium 157 ppm (sufficient)
Micronutrient levels : all normal
Organic matter 13% (very high)
Lead: low
Recommendation: Adjust pH by adding 20 lbs lime per 100 sq ft immediately, add an additional 13 lbs lime per 100 sq ft in small applications over successive tillings in the spring and fall. Add 1/4 lb nitrogen and 1/4 phosphorus per 100 sq ft either as a complete fertilizer (e.g. 3-4 lbs 5-10-5 per 100 sq ft) or alternate nitrogen and phosphorus sources.
topic: soil
to what do you attribute your high organic content levels?
ReplyDeleteare you concerned about the elevated lead level at the site near your house? will you adjust your plans for this spot?
The high organic content is from adding compost. I've often read that you can never add too much compost. Some gardeners even recommend growing vegetables in straight compost.
ReplyDeleteBut there are a few source I've found that say that compost/organic matter is generally very high in potassium (e.g. Steve Solomon's book "Growing Vegetables West of the Cascades"). Soils with too much potassium can cause copper, boron and manganese deficiencies in plants (source 1, source 2, source 3). My test results agree that I have a lot of potassium in all gardens. I will avoid adding additional potassium by using a nitrogen-only fertilizer.
As for the lead, I will be adjusting my gardening in the bed near the house. First off, I'm moving everything out of this bed as I had peas and leafy greens started there. I'm still considering the options. I think I'll go with a large container or two (half whisky barrels) for a couple crops (e.g. beans or lettuce) and grow ornamentals, e.g. pumpkins and gourds and flowers, in the soil around them.
Here's a very informative site on lead risks for vegetable growers.
ReplyDeleteI think it's unusual to have soil so high in organic material, most people seem to have the opposite problem. It's interesting what you say about organic material and potassium, I had never heard that before, but I can believe it. It just goes to show too much of anything can be bad!
ReplyDeleteYou are the first person I know of who got back soil test results that didn't indicate more compost was needed.
One of the problems with adding nitrogen in the form of fertilizer (organic or otherwise) is it will be soluble. There are some other names for this like 'fast acting', and so on. In short this means it will be immediately available to your plants, and in addition can be washed away by rain or watering. This means it will always be a chore to make sure you use the right amount of fertilizer.
If you don't use enough, your plants won't grow fast enough. If you use too much, you can stress or even kill your plants and cause disease problems. There will also always be fluctuations over the course of the year.
Adding compost will increase the nitrogen in your soil, and the nitrogen will be fixed instead of soluble. Of course compost will also increase the organic material. Compost is not very high in nitrogen, and since it's fixed it's not fast acting and not all available to the plants all at once, so it's also a very slow process increasing your nitrogen levels this way.
Nitrogen fixing plants on the other hand do two important things. The first is they fix nitrogen into the ground, and depending on the plant sometimes in very large quantities. The other thing nitrogen fixing plants do is consume organic material in the soil.
Once you have enough fixed nitrogen in the ground, it won't wash away and it will have a tendency to become available as your plants need it, so you just won't need to worry about it anymore.
While you might need some nitrogen fertilizer in the short run, I suggest emphasizing nitrogen fixing plants in the longer term.
That's too bad about the lead, but the advice they give you sounds reasonable.
I think I remember reading somewhere that the issue has to do with "soil health". Microbes in the soil break down the organic matter, but need nitrogen to do this. With good availability of all nutrients, the compost you add is broken down efficiently by the microbes and you can keep adding more compost. (Here's a link from Univ Mass on organic matter and soil management.)
ReplyDeleteMy soil has perpetually low nitrogen levels. Two maybe not-so-good practices I have used are making my compost predominately from fall leaves (a nitrogen-poor "brown" component) and using winter rye grass, which I have recently read actually depletes nitrogen.
I usually add one wheel barrow full of leaf compost per 30 sq ft bed each spring and I turn under a winter rye cover crop.
The soil at my new community garden has the same high organic matter readings and there leaf compost is also used in very large amounts as it is provided free from the town composing program.
I have a nice big packet of Crimson Clover seed (a nitrogen-fixing legume) that I'm looking forward to trying this year. I'll use it in place of the winter rye grass as a winter cover crop that will be turned under in the spring. I'm looking forward to the flowers. I am also considering trying this as a live summer mulch under my tomatoes.
I will also think about what I can do to improve the composition of my compost. I think I need a source for more "greens". Maybe grass clippings are a good one.
In the meantime, I think fast-acting nitrogen is the answer, keeping in mind the issues you mention. I think if I keep the levels adequate, overall soil health will gradually improve.
More advice is very welcome!