A method of considerably increasing vegetable production in a garden, called the "deep bed method," is described in a recently published book. It is of particular interest to gardeners who are trying to grow as much of their food as possible because of inflated prices.
"The Self-Sufficient Gardener, A Complete Guide to Growing and Preserving All Your Own Food," by John Seymour (Doubleday, 256 printed pages, illustrated, $15.95 hardcover, $7.95 paperback.)
Seymour has been growing his own vegetables and fruit for more than 40 years, lives in England, has traveled widely, and is the author of several other books.
The deep bed method should produce about four times the yield by weight of that of a conventional bed, he says. A deep bed of 100 square feet should produce 200 to 400 pounds of vegetables a year, just about enough to keep one adult in vegetables. The method is derived from age-old techniques that have been practiced in France and China, but which have never been widely adopted in the West.
The bed should be 5 feet wide and 20 feet long, Seymour says. You must never tread on it. Lay a covering of manure on top of the proposed bed. The digging is basically trenching, but you must be sure to loosen the subsoil (it is called double-digging). Dig a trench a spade wide and a spade deep at the top of the bed. Push your spade or fork into the bottom of the trench to loosen the subsoil as deep as you can. o
Dig out a second trench, next to the first one and throw the topsoil, and the manure that lies on it, into the first trench. Work the subsoil in the bottom of that too. Move on to the third trench and continue in this way until you reach the end of the bed.
Never tread on the bed nor let anybody else tread on it until you come to fork it over again the next year. The big idea is to avoid compacting the soil.
After the first year you will find the soil has been very much improved since it has not been trodden on.
The roots and earthworms will ensure that the subsoil does not get compacted again, and it is the compaction of the soil that inhibits plant growth.
In your newly dug bed either plant plats or sow seed direct in the ground just as you would a normal bed. The difference is you sow or plant four times as densely.
In almost all cases you should allow less space between the plants in all directions than you would between plants in traditional rows. The basic objective is to space the plants so that their leaves are just touching when they are mature.
Instructions are included for growing each crop by the deep bed method wherever this differs from conventional practice.
A gardener should grow as many plants as he can of the leguminosae, the pea and bean, family. They have nodules on their roots containing bacteria which fix nitrogen, Seymour says.
There is more substance to Seymour's claims than some gardeners may be prepared to accept. For example, at the summer meeting of the American Society of Agricultural Engineers, in Washngton, D.C. June 19, 1962, three USDA scientists made this report on compacted soils:
"Layers of compacted soil just below tillage depth restrict or halt plant root growth by interfering with root penetration, not by restricting air or moisture supply to the roots. Scientists had thought that poor aeration or reduced water transmission rate in compated soil might be a cause of restricted growth when roots reach these layers. However, the air and water supplies in compacted layers were adequate in experiments conducted by soil scientists.
"Roots growth was hindered only when layers of soil had so much resistance to penetration that roots could not force a passage through 2-to-8-inch compacted layers. Compacted soil layers are caused by passage of machinery across cultivated fields or by repeated tillage of the same depth."
Years ago, Dr. Fred P. Miller, University of Maryland agronomist and soil and water resource specialist, reported that if farm and garden soils in the Maryland area could be limed and fertilized to a depth of 30 inches, they could become far more productive.
The problem is, Miller said, the soil is too acid at lower depths and lacks fertility to support plant root growth. Liming and fertilizing could take care of that.
In 1978 there was a research report by Dr. Larry Fine, South Dakota State University professor of irrigation and soil management, and Paul Weeldreyer, an assistant, that plowing 30 inches deep with a large "Post" moldboard plow yielded crop increases of up to 21 percent.
Plowing sodic claypan soils 24 to 30 inches deep produced dramatic increases in small grain production in nine years of testing in North Dakota, according to Fred Sandoval, soil scientist, Northern Great Plains Research Center, Mandan, N.D. About 14 million acres of farm land in Montana, Wyoming and South Dakota are affected, his report said.