Just finished reading a fascinating article on soil fertility by Jon Frank (ACRES USA, Dec. 2013) that notes that gardens can “abused” by too much compost. Is there such a thing?
Frank, owner of International Ag Labs, a private soil testing firm (www.aglabs.com) gives examples of gardens “abused by too much compost” and gardens with “neglected/abandoned soil.” (See illustration)
Frank posits that if you want to have maximum nutrient density in your crops, then you should ignore humus (as it will sort itself out with proper mineral content), and should have:
— Nitrogen: manage by crop needs and conductivity;
— P and K: 200-300 pounds each, 1 to 1 ratio; increase K slightly for Potassium-loving plants;
— Calcium: 3,500-4,000 pounds per acre; calcium to magnesium ration from 7-15:1;
Conductivity: 400-600 micro Siemens/centimeter — and he gives amendments necessary to correct that (for more, see the article).
I say it’s a fascinating article because, honestly, after wracking my brain, I can think of few gardens that suffer from “too much” compost. I do remember one friend’s garden that I suspect was “too much.” The soil was so moist and rich that it probably could have served as a worm bed for all its amendments.
But even Frank notes that the solution to a garden “abused” by too much compost is simply to grow more without adding more. Maybe “abuse” is too strong a word for the issue of adding compost. Additionally, given the fact that it takes so much raw vegetative matter to create so little “black gold,” I doubt too many gardens are approaching the “abuse” stage.
Nonetheless, the figures Frank gives are instructional. Looking at the soil report I obtained for my garden from Mississippi State Cooperative Extension Service (see earlier blog), I can see that there are some interesting figures that conflict with Frank’s interpretations.
Mind you, this garden is brand new; my landlady said the backyard was used as a garden many years ago, but not in the past 10 years or so. My test and the MSU interpretation vs Frank’s interpretation:
Phosphorus — 132 lbs per acre (MSU: high) – Frank says this is low and should be 200-300 lbs. I suspect that, with adding compost, that figure will rise;
Potassium – 156 lbs per acre (MSU: low) – Frank says this is just below the 200-300 pounds that’s ideal. Again, I suspect that compost will raise that.
Magnesium – 369 lbs per acre (MSU: very high) – linked to calcium by Frank;
Zinc – 97.9 lbs per acre (MSU: very high) – Not considered most important by Frank. That could fall, if I’m growing green manures (cover crops), which I expect to do;
Calcium – 3706 lbs per acre – Falls within perfect number for Frank and within the proper ratio to Magnesium he gives.
Everyone who has a garden/farm and pays attention to soil tests probably has his/her own ideas about what the proper ratios should be and how to go about fixing them.
MSU, in my soil report, for example, suggests 34-0-0 pre plant (high nitrogen) fertilizer and 0-0-60 (high Potash) fertilizer — synthetic chemicals. In my opinion, shared by most organic growers, such a course of action would burn the soil, killing earthworms and microbes that keep the soil environment healthy.
Rather, what I intend to do is plant the seeds with a fish emulsion to provide nitrogen, then side dress (adding more natural liquid fertilizer) and foliar feeding after the plants are up. In addition, I plan to plant clover between the rows and on unused soil to build nitrogen for my fall planting.
I don’t know if this falls within Frank’s ideas or not; but I agree with his overarching conclusion that it’s the “pattern” of nutrients in the soil that’s more important than the figures alone. Visual symptoms of the plants themselves will tell you what’s going on with the soil. And: “Your role as steward of the soil is to create the right pattern in the soil.”
I would say that I disagree on his view on humus; in my opinion, developing proper humus ensures better availability of nutrients, which is what he’s aiming at. You can’t build tilth with minerals alone; you must build humus to create the environment for plants to efficiently process available nutrients. Proper humus assures adequate water retention, oxygen in the soil, and ease of root and fungal growth. This is done by rotating crops, plowing under green manure, adding compost and soil amendments, as needed.
As he notes, plants grown directly above a limestone bed can show a calcium deficiency, but biologically available calcium is as much a product of good soil structure (in my opinion) as the ratio of other minerals that can be tested in the lab.
It may be a question of which end of the microscope you are looking through; the goal — and ingredients — remain the same. But soil structure, humus, tilth, are issues that a organic gardener/farmer can readily see and control. To ignore that end of the equation may be just as much a “neglect” or “abuse” of soils as any scientific test may reveal.
For the average gardener, what does this mean? Give your soil the love it richly deserves, using natural, sustainable and organic growing methods, and it will richly reward you with healthful, nutritionally dense foods.
Jim PathFinder Ewing is a journalist, author, and former organic farmer now teaching natural, sustainable and organic agricultural practices. His latest book is Conscious Food: Sustainable Growing, Spiritual Eating (Findhorn Press). Find Jim on Facebook, follow him @EdiblePrayers or @OrganicWriter or visit blueskywaters.com.