My findings that adding lots of organic matter actually helped equalize cation levels in the forest garden leads me into a discussion of the most controversial part of Steve Solomon's book.  He agrees with the organic status quo to a certain point, recommending that we add organic matter until our soil contains 4% organic matter in the south and 7% in the north, and until our CEC is at least 7, levels that are achieved through topdressing half an inch of compost per year.  However, Solomon argues that after you reach your organic matter goal, you should back off to topdressing with only a quarter inch of compost per year since adding too much organic matter unbalances your soil.

Organic matter is closely linked to nitrogen, and that was my first concern when I considered Solomon's low-compost policy.  Each 1% organic matter in your soil releases about 15 to 25 pounds of nitrogen per acre per year, and high-demand vegetables need around 200 pounds per acre.  If you run your garden hard, like I do, you might end up growing two low-demand crops and one high-demand crop each year, for a total requirement of 400 pounds of nitrogen per acre, but a more average yearly demand would be 200 to 300 pounds.

Time for some math.  The 8.95% organic matter already in my front garden (which is my best soil) would release 179 pounds of nitrogen per acre annually, but I need another 100 pounds or so.  How do I make up the nitrogen deficit if not with compost?  Solomon uses purchased additions of seed meals, feather meal, and fish meal to bring his nitrogen levels up to par.

Location	%OM	pH	Ca % sat	Mg % sat	K % sat
Powerline pasture	2.74	5.1	29.23	13.57	6.96
CP5	4.27	5.9	48.26	16.23	10.63
Mule garden	4.87	6.9	70.58	17.94	5.06
Forest aisles	5.43	6.3	52.66	17.55	12.25
CP3 and CP4	5.48	5.9	52.56	14.77	7.96
Front berries	6.53	7.1	66.25	20.12	8.7
Back garden	7.82	7.1	69.78	19.35	5.92
Blueberries	8.49	6.5	61.16	19.04	6.6
Front garden	8.95	7.3	68.47	19.92	7.08
Forest garden	9.95	7.2	59.45	24.96	10.78

While I'm not adamantly opposed to buying nitrogen amendments if it would make my garden healthier, my soil tests bring that assertion into question.  In the table above, higher organic matter levels seem to match up with sweeter soil and with a better ratio of cations.  The exception is the mule garden, which I think must have had the organic matter levels mismeasured this year.  My previous year's results showed the mule garden as having the highest organic matter levels, and my eyes back up that claim.

Granted, there is a limit to how much nitrogen vegetables can use each year, but I estimate you'd have to raise your soil up to 20% organic matter before nitrogen would start washing out into the groundwater.  I think I'll stick to my Rodale approach to nitrogen and organic matter until someone presents a stronger argument for seed meals.

This post is part of our The Intelligent Gardener lunchtime series.  Read all of the entries: The Intelligent Gardener Why soils need to be remineralized Soil cations How to fill out Solomon's soil analysis worksheets Using Solomon's worksheets to determine soil additives Do wood and straw raise soil potassium levels? Can you have too much organic matter in your soil? Clay, humus, and CEC Managing blueberry soil micronutrients Excess phosphorus in the soil

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.



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