Some wood seeds can remain dormant in soil for as long as 100 years. Cultivated land usually contains about 10 million weed seeds per acre in the top six inches of soil, according to R. B. Taylorson, USDA Science and Education Administration weed scientist. Some land may contain 100 million or more seeds.
If most of these seeds could be forced to germinate at one time, they could be killed before a crop is planted, and weed problems would be under control for many years, Taylorson says.
Using ethanol, several annual weedy grasses and a few broadleaf weeds have been forced to germinate before their time. Although ethanol has not been tested in field conditions, it has stimulated a wider range of weed seeds than most other chemicals tested, he says.
Taylorson has had 100 percent germination in forciang fall panicum, one of the principal weeds of corn and soybean acreage in the Northeast and Midwest. Witchgrass, crabgrass and barnyard grass seeds responded at better than 50 percent germination, a rate Taylorson considers the cutoff point for any seed eradication program to be cost effective.
Fall panicum and witchgrass germinated in complete darkness but crabgrass and barnyard grass needed red irradiation to induce germination. Wild oak and johnson grass have been impervious to ethanol and several other anesthetics Taylorson tested. So far, broadleaf germination has been under 50 percent.
Getting seeds to germinate in the absence of light is most important to any future weed-seed eradication program, Taylorson says. Many weed seeds require exposure to the red band of the spectrum which triggers a chemical called phytochrome to initiate the growth process.
Those that do germinate each year are exposed to sunlight through cracks in the soil or are brought to the surface during cultivation. But the vast majority of weed seeds rest in the darkness of the soil.
Greens are especially valuable nutritionally because they supply important amounts of vitamin A, ascorbic acid and iron. Pound for pound, such greens as spinach, kale and turnip greens contain many times more vitamin A than snap beans, sweet corn or green peppers, and one-half to two-thirds of the amount in carrots, a vegetable noted for its high vitamin A content. A pound of raw kale or mustard greens may contain twice the ascorbic acid found in a pound of oranges but some of this will be lost in cooking.
Because of the relative ease with which they can be grown and their high nutritional value, greens deserve an important place in the human diet, according to Dr. E. A. Borchers, Virginia Tech plant breeder.
There are actually dozens of species of plants, many growing in the wild, that reportedly have been used as greens. Such wild plants as lamb's-quarter, wild cress, pokeweed, dandelion and dock are examples. While the leaves of many plants are harmless, certain plants are known to be poisonous when eaten by humans. It is wise to say the least, to limit the kinds of wild greens eaten to those known to be safe rather than to collect them indiscriminately, according to Borchers.
Spinach is the most important of the greens grown in the U.S. While some spinach is sold to consumers fresh, a large part is either canned or frozen. There is a considerable number of spinach varieties and hybrids, many of which differ greatly from each other in such characteristics as plant size, leaf color and shape, time of seedtalk development, and disease resistance.
Greens belonging to the cabbage family including collard, kale, turnip, mustard, cabbage, cauliflower, broccoli, Brussel sprouts, Chinese cabbage, rutabaga, and kohlrabi are quite cold tolerant and are usually grown for harvest in the late fall, winter and spring in mild climates. Kale and collards grown during the summer tend to be tougher and less sweet than when grown during the cooler seasons.
Upland cress is grown for harvesting during the cool season and has a flavor resembling that of water cress and is sometimes eaten raw in salads.
The common variety of beet greens is eaten by home gardeners as greens. It is possible to use both tops and roots of young beets but the tops of large beets usually become tough and are seldom used as greens. New Zealand spinach resembles the true spinach in flavor and appearence, the tender tips of the attached branches are cooked for food, and after dipping the plant quickly resprouts. It has the advantage of thriving during hot weather.