Wednesday, July 29, 2009

Autumn Urban Gardening-Better Soil vs. More Food

Daniel here: I'm feeling a tension between two desires in the garden. The tension is at least partially the product of urban gardening (or gardening in small spaces). As Fall approaches part of me wants to plant cover crops (more on that below) and part of me wants to grow Fall food (onions, garlic, broccoli, brussels sprouts, etc.). But we can't do both, or maybe we can. So, below is the result of some of my thinking in this area especially regarding the value of not planting for food and improving soil with cover crop. I would really like to hear from others who are feeling this tension or others who have advice on soil health.

Why do I want to plant cover crops? What is a cover crop? what is it good for? Better answers found here at the National Sustainable Agriculture Information Service (click on the title to view the document). Below are my current answers to the above questions gleaned from the cover crop document and other resources I've been chewing on recently. They've helped me settle the tension described above.
**Buckwheat growing with eggplant behind. These buckwheat plants have been in the ground for a couple of weeks. They are 6-12" and I have no clue how tall they will grow. But the taller the better.

A cover crop is any crop grown to provide soil cover. Even if not tilled in later a cover crop prevents erosion by wind and water which is vital to preserving topsoil. Gardeners find many other reasons for incorporating cover crops into their gardens. The above reason applies to anyone who would like to prevent the erosion of vital topsoil. The primary motivation here is soil health. Good healthy soil is the foundation of good healthy food. So, what makes good healthy soil? Well it helps to think of the health and goodness as a product of cooperation or community. Differences in pH, nutrient concentrations, and other factors create a plethora of various habitats within the soil but we could break the major players into these groups:

1)Photosynthesizers-(plants)-use solar energy to fix CO2 and add organic matter (biomass to soil). They capture energy from the sun and air and make life possible in the soil. Cover crops are in this category. Note that harnessing solar power is very old not a new product of human industry.
2)Good bacteria and fungi-break down residue, retain nutrients in their bodies so that it is not leached out of the upper layers where it will be out of reach to garden plants, create new compounds or aggregates by releasing binding agents (excrement and mucus and making available resins) enhancing soil tilth and structure, convert nitrogen into more useful forms for garden plants, and compete with or inhibit disease causing organisms.
Good bacteria and fungi also protect plant roots from disease causing organisms, and enter into mutually beneficial relationships with plant roots by processing and delivering nutrients to roots.
3)Protozoa, nematodes and micro-arthropods graze on bacteria and fungi, release nutrients when feeding on them, control root-feeding and disease causing pests, and help control the bacterial and fungal populations.
4)Earthworms and macro-arthropods shred plant litter and build soil structure by producing fecal pellets and burrowing through the soil.

In general the bacteria, fungi, protozoa, nematodes, and arthropods make soil healthy for veggie plants but need their own sustenance to thrive and to process for veggies. Veggies depend on good soil and when we remove the fruit we remove some of the biomass and nutrients that went into their production. Cover crops then are fundamental to providing the food for the micro-organisms which provide healthy soil for the veggies.
**Buckwheat flowering.

Here is a list of major benefits of using cover crops (for large or small gardens).
1)Many fruits and vegetables need lots of nitrogen. Some cover crops actually return nitrogen to the soil by taking it from the surrounding air and delivering it through the roots making it available for next years crop. We call these nitrogen fixers.
2)Cover crops introduce biomass, immediately their roots and later their stalks, leaves, flowers, and fruits to the micro-organisms who need it to live. Veggies need the micro-organisms to break the material down to make better soil for their needs.
3)Some cover crops are actually good at capturing nutrients and specific cover crops capture specific nutrients well. These nutrients would wash further into the soil out of reach of vegetables and fruit. When they are taken in by cover crops they are drawn up and out of the soil and then returned and digested by the soil life when tilled in thereby making the same nutrients available to next years crop. We call these catch crops because unlike #1 they grab up nutrients already in the ground and hold on to them.
4)Microbial activity, and all of its benefits, increase with increase biomass provided by cover crops. Increased microbial activity (at least the good kind) is better for healthy veggies for the reasons listed above and because they fight off bad microbial activity. For instance, this season I learned about Fusarium and Verticillium fungi which inhabit poor soil and cause damage to potato, tomato, pepper, eggplant, and even okra. The GM(genetic modification) folks try and produce a kind of fruit that will be resistant to these fungi which attack the new roots and clog the vascular tissue of the plants above thereby preventing nutrients and essentially choking the plant with clogged arteries. The alternative is to improve soil health so that these fungi will be managed by a strong soil immune system (good microbes).
5)Some cover crops are excellent at breaking up compacted soil, allowing air, water, and soil life into otherwise dead zones.
6)Some cover crops mature very quickly allowing for improvement of soil in short seasons or in between Winter and Summer or Summer and Fall planting.
7) Some cover crops tolerate poorer soil and more difficult climates thereby improving otherwise ungardenable soil.
8)Cover crops suppress weeds that are of less benefit to soil health.
9)Cover crops conserve water. My dad actually reported a story told by Louis Bromfield, info here, who won the Pulitzer Prize for literature and later was a real pioneer in sustainable agriculture in Ohio. He purchased dry, useless,wasted farm land in Ohio, planted cover crops and watched as springs began to appear on land which had been dry and wasted. In other words, once the soil improved, the water was retained and built up enough to begin to form natural springs again. I found this fascinating.
**Beans being used both as a cover crop and a food producer in our Spring potato beds.

The document above will give you many good recommendations on cover crops that are useful for various purposes(it also includes a list of names which I have omitted). I have planted buckwheat this summer as other garden plants mature and die. I chose buckwheat because it tolerates poor conditions, fixes nitrogen in the soil, matures quickly, and is killed by frost (this prevents me from having to worry about it returning next year when I want to plant veggies).

Legumes are considered good cover crops because they fix large amounts of nitrogen in the soil. In these potato beds we have planted a second crop of beans (picture just above). Legumes are a cool cover crop because they are good for the soil and provide food. Peanuts and soy are two other legumes which do the same. You should check out table 4 of the document listed above. For instance Austrian Winter Beans provide 144 lbs. of nitrogen, 115 lbs. of potassium, 19 lbs. of phosphorus, and 45 lbs. of calcium per acre. Wow!

Because buckwheat matures quickly I may have time to introduce a second winter cover crop. This is not possible in some climates but Blue Lupine, called a "biologic plow" for its strong deep roots, will grow straight through the winter in our climate (it is native to the North East I believe). So, before next Spring I may be able to integrate the roots and plant matter of several generations of cover crop into the soil. This will contribute greatly to the potential of the soil to produce good nutritious food for our family.

Now back to the debate over growing food or improving soil this Fall and Winter. We are compromising. I hope to get at least one cover crop on every bed but then I will select some of the beds to practice growing food through the winter and select others for cover crop through the winter. Those that work this winter will get a cover crop in the Spring preparing them for Summer. Those that receive the cover crop this Fall/Winter will be planted in the Spring. That's the best I could come up with and I can't wait till it is much harder to accomplish than that sounds. It always is.

Some other steps we are taking to integrate biomass (the materials needed for soil life) into the soil include covering the beds with hay. Hay is cheap, provides cover for the soil in the summer helping it retain water, and then breaks down and contributes to the soil quality. We also get the free mulch from tree trimmers and right now are only integrating that inbetween beds in the paths. Here is an interesting blog post at "Garden Rant" about the value of integrating wood chips into garden beds. Go to GARDEN RANT to read new evidence that wood chips can be integrated into beds counter to standard gardening wisdom. But as I said at this point we only have it in the paths. Once it is broken down I will probably shovel onto beds and add fresh chips into the paths. Last, instead of ripping root systems out of the soil when plants die I simply cut off the stalk compost it and allow the roots to decompose in their place. This causes less disturbance to the soil community and provides food for the microbial life. When the roots decay they leave air pockets for water and oxygen to penetrate.
**Trays of Fall starts getting some sun. We have improved our seed starting soil greatly with Spaghnum Peat Moss. These kale, broccoli, and cabbage are very happy.

If your thinking that cover crops are just for the "serious gardener" or the large scale operations think again. Cover crop seeds are generally cheap and can be bought in larger bulk quantities by mail order. I am going to recommend Southern Exposure Seed Exchange for several reasons, but they have a limited variety of cover crop choices and it may be worthwhile to shop elsewhere. However, they are in the South and there are few good seed producers working in the South. They are very fast with shipping and we have had good success with their seeds.
Cover crops can be planted rather easily.
1)I removed the top layer of hay from our beds,
2)I lightly disturbed the soil with a rake, and then just cast or sprinkled the seeds lightly over the soil. This works because the seeds are cheap and most will find their way into a crevice. Most small seeds only need a 1/4" planting depth. This way you can cover a larger area quickly.
3)Then I placed the hay back on top and watered. The watering helps to cover the seeds but certainly some seeds don't get covered and don't generate. The seedlings will push right up through a light sprinkle of hay no problem.
4)If you plant in the heat, yep I did, make sure you water regularly until the seedlings are well established. In general cover crops are tougher than garden veggies, but keep an eye on them. They'll let you know if they need a drink.
**Ellen is holding my new 4 lbs. bag of buckwheat seed from Southern Exposure. She recommends you try a cover crop this Fall or next Spring to give even the smallest garden an extra boost.

My info on soil critters was taken from a useful book my dad bought me years ago at a gardening conference in Boone. It is called SOIL BIOLOGY PRIMER. It's an incredibly helpful introduction to the basic members of the soil community, their functions and roles, etc.

Last, due to my extreme fallibility there may be errors above. Don't hesitate to send a correction, ask a question for more info or clarification, or send us info you have found useful. I'll do what I can to field questions. At this point I'm having fun doing the research. No, this is not my PhD.

Until next time.

1 comment:

William Kruidenier said...

Excellent stuff -- thanks for doing the research and posting the results. Soil (like oceans) is a universe unto itself, yet is the source of physical life. Thanks for digging in the dirt and sharing what you're finding.