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The area of most intense biological activity — ultimately the definition of soil fertility — is the rhizosphere, the zone immediately around plant roots. Plants release nutrients through their roots |
to feed their buddies in the soil — beneficial microbes and mycorrhizal fungi — that increase access to water and convert soil nutrients into forms more readily utilized by plants. |
If the intense bioactivity in the rhizosphere is the key to fertility, imagine the contribution of closely planted cover crops with vastly more root mass than more widely spaced food |
crops. Soil Texture. Mycorrhizal fungi (beneficial fungi that grow in association with plant roots) produce glomalin, a substance which glues microscopic clay and organic matter particles into aggregate clumps, stabilizing |
the soil and making it nice and crumbly. This crumbly texture is more porous to oxygen and water. Bacteria encouraged by cover crops produce polysaccharides, which also act as soil |
glues. Grass and grain cover crops with fine, dense root masses loosen soil texture as they decompose. Others, such as sweet clovers and sorghum-sudangrass hybrids, grow deep, aggressive taproots that |
break up soil compaction. Erosion Prevention. A cover crop’s tight canopy protects the soil from the drying and scouring effects of wind and the forceful impact of heavy rain. The |
loosened soil structure achieved by cover cropping allows rapid absorption of rain and prevents runoff. Soil Moisture. Organic matter added by cover crops acts like a sponge in the soil, |
absorbing rainwater and holding it for gradual release to plant roots. Thus, gardens that have been home to regular use of cover crops become more resistant to drought. Protection From |
Weeds, Diseases and Insect Damage. Garden beds frequently planted with cover crops will have fewer problems with weeds. Cover crops suppress weeds, out-competing them for water and nutrients and shading |
them under a tight canopy, sometimes releasing chemical compounds that inhibit germination of weed seeds (a phenomenon called allelopathy). Plus, the roots of cover crops release nutrients that feed beneficial |
microbes in the soil. These microbes then suppress pathogens that cause root diseases. Some cover crop plants, such as rape, rye and sorghum-sudangrass hybrids, inhibit root-knot nematodes, which can be |
disastrous to beets, carrots and other root crops in some regions. You can cut cover crops and use them as mulches to boost populations of beneficial ground-dwelling species, such as |
rove beetles and spiders. Other cover crops can provide a wonderful habitat for the pollinators that help keep your food garden thriving. Cover crops that flower, for example, provide important |
food sources for honeybees and butterflies. Cover Crop Species Depending on your climate, gardening goals and the time of year, you’ll have a variety of cover crop options. Cover crop |
species vary widely in their tolerance of cold, heat, soil moisture extremes and soil types. It’s often good practice to plant a mix of different species. The most important division |
among species is between legumes and non-legumes. Legumes, such as cowpeas, vetches and clovers, serve as hosts to rhizobia, bacterial alchemists that live in plant roots and convert nitrogen from |
the atmosphere into nitrogen compounds that help plants grow. Some of this “fixed” nitrogen remains attached to legume roots in nodules — like beads on a string — and becomes |
available to other plants after the legume dies. Non-legumes include all other cover crops: grasses such as small grains, various millets, annual and perennial rye, and sorghum-sudangrass hybrids; crucifers such |
as mustards, rape and forage radish; and buckwheat. For detailed information on the major cover crop species, see Managing Cover Crops Profitably by the Sustainable Agriculture Network. Even though this |
book is geared toward farmers, it includes great information for the home gardener. (Clicking on the link in this paragraph will take you to a page on the Sustainable Agriculture |
Research and Education program’s website where you can download a free copy of the most recent edition of this book.) Cover Cropping Strategies The most important strategy of all is: |
Do it now! When I complete a food crop harvest in fall, that same day I plant an overwinter cover crop. If I harvest a spring crop such as lettuce |
from a bed that I won’t be planting again until fall, I sow a fast-growing interim cover crop that does well in summer heat, such as buckwheat or cowpeas. The |
best time to plant a cover crop is anytime a bed is not covered by a food crop or mulch. The easiest way to incorporate more cover cropping is the |
half and half strategy: I dedicate every other garden bed to cover crops for an entire year. I may grow several fast-growing covers such as cowpeas and buckwheat in succession, |
or a cover such as sweet clover, which takes a full year to yield all its benefits. In the following year, the beds previously in cover crops now grow food |
crops, and vice versa. This strategy allows you to grow mulches in place. Using a scythe or sickle, you can cut cover crops that produce a lot of biomass — |
hairy vetch, rye, and sorghum-sudangrass hybrids — and lay them out as mulches in an adjacent bed that’s planted with food crops. Most cover crops cut when in their vegetative |
growth stage will regrow to produce even more mulch. If you can’t give half of your garden space to cover crops, how about one bed out of three? Or four? |
Or even 10? Some cold-hardy cover crops grow well through fall frosts, then die if the ground freezes solid — this is known as winterkilling, and you can use to |
your advantage. When I remove the top growth from asparagus beds in late September, I plant a mix of winter peas and oats. They create a knee-high tangle of green |
by the time the ground freezes, and they both reliably winterkill here in northern Virginia, leaving a thick, weed-suppressing mulch come spring. Plus, the leguminous peas fix nitrogen in the |
soil for the heavy-feeding asparagus. It’s possible to grow both a food crop and a cover crop in the same bed at the same time. Under tall-growing crops with a |
small footprint, such as tomatoes or pole beans, plant an undersown cover crop, such as low-growing Dutch white clover or perennial ryegrass. If such a cover has already been established, |
leave it in place as a living mulch and open up holes for large transplants such as tomatoes or broccoli, or open up rows for beans. Shade-tolerant species — annual |
ryegrass, cereal rye, hairy vetch, some clovers — can be sown as overseeded cover crops into existing crops such as corn or brassicas up to several weeks before harvest. The |
cover crops will grow slowly under the existing canopy, then come on strong when the food crop has been removed. Try frost-seeding a cover crop into overwintered grains. In late |
winter, broadcast the seeds — small round ones such as clovers work best — into the grain beds. Winter freezes and thaws will work the seeds into the soil, where |
they will germinate in spring rains. The grain could mature into a food crop for feeding your pigs or chickens while serving as a nurse crop to establish the clover, |
which will grow rapidly after you harvest the grain. Some species work as reseeding cover crops. Subclovers (cool-season legumes) will die back in winter, but the seeds they leave behind |
will remain dormant through much of the next growing season, then sprout in the fall to establish a new cover. Permanent cover crops are appropriate in orchards, vineyards and border |
areas never planted with food crops. Keeping these areas in mixed flowering species — perennials such as clovers, or annuals that reseed themselves such as crucifers — protects the soil, |
supports pollinators and encourages insect diversity. Encouraging lots of different kinds of insects is the key to preventing crop damage, as the bug-munching insects will help you control the crop-munching |
insects. In high-traffic areas, covers that can take a good deal of wear are in order, such as annual ryegrass and white clovers. Planting Cover Crops Plant cover crops with |
as much care as your food crops. Make a furrow for larger or more vigorous seeds, such as cowpeas or sorghum-sudangrass, sow thickly, and then cover with soil. For smaller |
seeds, such as clovers, crucifers and small grains, scatter, rake in, and tamp the bed with the back of a garden rake to ensure good soil contact. To speed germination, |
apply a light mulch and water occasionally. Seeds of vigorous covers, such as annual ryegrass, oats and hairy vetch, will germinate if left on the surface, especially if broadcast just |
before a soaking rain. You can plant a food crop as soon as the cover crop is killed unless there could be a temporary problem of allelopathy or nitrogen tie-up |
(keep reading for more information). In such cases, wait about three weeks or so before planting. Killing a Cover Crop It’s better to avoid deep mechanical tillage, which disrupts soil |
life and breaks down soil structure. Tall, heavy stands of cover crops, such as rye and hairy vetch, are a nightmare to till in with a power tiller in any |
case. So what’s the best way to kill a cover crop so decomposer organisms can break it down to feed your soil? Remember that a cover crop in the vegetative |
stage (i.e., not flowering) usually regrows after being cut. Most cover crops in the reproductive stage (i.e., flowering), however, will die if cut. A complete no-till strategy that works for |
most covers is to cut the cover just above soil line after it has flowered, and transplant crops such as tomatoes, peppers or broccoli through the severed tops, leaving the |
cut tops and cover crop stubs as a mulch. For small areas, use a hand sickle for the cutting. (We’ve found a used butcher knife also works well. — MOTHER) |
Or, use a heavy field hoe to chop cover crop plants just below the soil surface to kill them without disturbing the soil deeper down. Another option is to loosen |
the soil with a broadfork and pull the cover plants out by the roots, again laying them on a bed as mulch. As your soil becomes more friable, the broadfork |
may not be necessary. My favorite way to till in a cover crop is to place a hardworking flock of chickens on the bed. Allow them to roam inside a |
chicken tractor or temporary fencing. For a great example of how well this method works, check out these before-and-after photos of a garden planted with a lush mix of cover |
crops and the same garden two weeks later, after the chickens went to work on the area. Thirsty rye may deplete available soil moisture enough to inhibit the following crop |
in a dry season. A few crops — small grains such as rye and sorghum-sudangrass hybrids — may temporarily release chemicals that will inhibit the growth and germination of other |
plants. Though these allelopathic effects help with weed control, they can suppress germination and growth of food crops that follow, especially small-seeded ones, such as lettuce, spinach and onions. Just |
wait a few weeks after killing a cover crop to plant your food crop and you won’t run into problems. Cover crops susceptible to diseases, herbaceous insects or nematodes could |
serve as vectors if grown beside or followed by food crops with the same susceptibilities. If you allow cover crops to mature their seeds before being killed, they can later |
volunteer as weeds in following crops. However, the more diverse our gardening practices and the more complex our rotations, the less likely we will encounter such problems. And the more |
we learn about cover crop species, the more we discover management solutions to problems that could occur. For example, if rye has been allowed to mature, the high carbon content |
of its residues, both roots and top mass, can temporarily tie up nitrogen in the soil and inhibit growth of the following crop. But if you grow the rye in |
a mix with a compatible legume, nitrogen fixed by the legume will minimize nitrogen tie-up. Begin experimenting with cover crop species in your garden today, and you’ll soon see that |
the enormous advantages far outweigh any problems that may crop up. Ultimately, cover crops will lead to healthier soil and bigger, better harvests. For more on using cover crops in |
your garden, see Cover Crops: Options, Tips and Advantages for the Home Garden and Cover Cropping Your Garden. Harvey Ussery uses cover crops galore in his Virginia garden. His website, |
twenty-eight years ago, Arthur Firstenberg had a dental X-ray. He's been on the run ever since. That X-ray, he says, made him excruciatingly sensitive to electromagnetic fields—the low-level radiation that emanates from power lines, microwaves, and, most vexingly, cell phones. |
Now 58, Firstenberg has spent more than a decade crisscrossing the country, trying to find the last unwireless spot in America. When cell phone towers came to New York City, he moved upstate. Then he headed to Mendocino, California. These |
days, he lives out of his '87 Nissan station wagon in Santa Fe; a house is too risky. "Your neighbor could get wifi, and then you have to leave and hunt for a new home." At first, I was inclined |
to chalk Firstenberg's symptoms up to plain old paranoia. After all, the World Health Organization's website says "no study [on cell phone radiation] has shown adverse health effects at exposure levels below international guideline limits." But doctors and scientists are |
starting to scrutinize how invisible electromagnetic fields affect human health, especially when it comes to cell phones, one of the most ubiquitous sources of microwave radiation. In 2006, a Swedish study reported that 85 of 905 brain tumor patients had |
used mobile phones heavily for 10 years or more, and most of their tumors occurred on the side of their head where they usually held their phones. In March, after reviewing more than 100 studies on the link between cell |
phone use and brain cancer, a prominent Australian neurosurgeon concluded that cell phones could have a broader public health impact than smoking. The list of conditions that researchers have associated with electromagnetic radiation includes trouble focusing, fatigue, headaches, sleep disturbances, |
and Alzheimer's. (And don't forget asthma, diabetes, cataracts, and honeybee colony collapse disorder, insists Firstenberg.) So far, no one has been able to explain exactly how these seemingly benign waves could lead to cancer, much less this laundry list of |
medical woes, and for that reason, few scientists are willing to say for sure that cell phone use will make you sick—or that it won't. The heating effect of electromagnetic waves is well understood; it has been proved that they |
can burn human tissue if they're intense enough. (Think microwave oven.) Standards set by the Federal Communications Commission ensure that cell phone emissions stay well below that heating threshold. But Joachim Schüz, head of the department of biostatistics and epidemiology |
at the Danish Cancer Society, suspects that heat isn't the only way radiation causes health problems. So far, no one has been able to prove definitively that its "nonthermal" properties have any detrimental effect on living tissue. "You find one |
cell reacting, one not," he says. "So you can't really say it's due to the radio waves." Why is it easier to watch Netflix movies on a PC than a Mac? so you're about to use Netflix's "instant watching" feature |
on your MacBook, when suddenly an error message pops up: "Sorry, blame Steve Jobs." Huh? Wasn't the whole point of getting a Mac to escape Microsoft's monopolistic tentacles and have the freedom to do stuff like stream movies? The problem |
is that Apple won't license its copyright-protection software to third parties like Netflix. Predictably, Apple wouldn't emerge from behind its titanium curtain to answer our questions about why it won't let consumers use whatever video service they choose. John Sullivan |
of the Free Software Foundation suspects that Apple wants you to buy movies only from iTunes. That may keep Steve Jobs in black turtlenecks, but it ticks off dedicated Mac users, many of whom have no doubt noticed that Netflix |
movies play perfectly fine on a stodgy PC. —Leigh Ferrara Have a problem? Oh yes, you do. Go to motherjones.com/consumer-retorts to vent about annoying products and corporate policies. Selected entries will get MoJo swag. Since 1999, Schüz has been a |
principal investigator for the Interphone project, which has produced the largest body of epidemiological work on cell phones and cancer to date. The official results aren't ready yet, but 8 of the 13 countries involved have already released their initial |
data. Several of these early studies show a strong correlation between long-term cell phone use and brain tumors, both malignant and benign. Schüz cautions that the individual studies by themselves are too small to overcome some significant problems with the |
data. Finding subjects who have brain tumors and who have used their cell phones for more than 10 years is difficult, especially considering that the tumors typically take 10 to 20 years to develop. What's more, people are notoriously bad |
at remembering how much they've used their phones and which ear they hold their cell phone up to—especially if they're looking around for something to blame a brain tumor on. Ben Greenebaum, a retired physics professor and former president of |
the Bioelectromagnetics Society, an international group of radiation scientists and wireless-industry professionals, says that despite Interphone's preliminary findings, "I'm not prepared to shut anything down on the basis of what I see now." But, he admits, "I do think you |
have to be cautious and use these things when they make sense." He recommends using a headset whenever possible and warns that "if you carry it on your belt, you'll get a higher field into your stomach," even when the |
device is turned off. "So set it on the counter." Don't try to make calls where your reception is poor—phones emit more radiation when they're searching for a signal. The German and French governments have recommended that parents limit children's |
cell phone use, since less is known about the effect of radiation on developing brains. Of course, if you're really worried, you could ditch your cell phone for a quaint landline. Just don't expect the rest of the world to |
follow suit. Firstenberg has found that it's almost impossible to avoid the mobile-wielding masses. He used to ask strangers—politely—to stop talking on their phones in his presence until he got reprimanded in a grocery store for harassing a customer. "People |
get offended," he says. "They just don't know about microwave radiation." For the time being, the fcc is not considering any changes to its standards for cell phone radiation. Yet some cell phone companies have started including a pamphlet about |
potential health risks with their packaging, perhaps to guard against future litigation. And Schüz hasn't ruled out the possibility that as more data roll in, the scientific consensus could shift dramatically. "If you ask me a year from now," he |
At the heart of materials science is an understanding of the microstructure of solids. "Microstructure" is used broadly in reference to solids viewed at the subatomic (electronic) and atomic levels, and the nature of the defects at these levels. The |
microstructures of solids at various levels, especially the defects, profoundly influence the mechanical, electronic, chemical, and biological properties of solids. The phenomenological and mechanistic relationships between the microstructure and the macroscopic properties of solids are, in essence, what the materials |
science is all about. This is best represented by the "materials science triangle": synthesis-microstructure-properties. Materials engineering, on the other hand, is concerned with the design, fabrication, and testing of engineering materials. Such materials must fulfill simultaneously the dimensional properties, quali... |
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