Gardener's Remorse

Snow can  cover  a lot more than just kale for gardener's
experiencing remorse

Maybe it's the overcast skies of New England in winter, but I'm feeling some gardener's remorse and feel compelled to confess one of my gardening peccadilloes:  I don't always cover crop! 

I suppose there could worse failures such as not rotating crops or secretly using commercial fertilizers or insecticides, but those aren't my sins of commission.  What's worse, perhaps, is not that I don't cover crop, but how effectively I rationalize why I generally don't.  My favorite rationalizations include: 

1) it's extra work - more tilling for an aging back;

2) added expense - buying the seed;

3) Oh, I missed the planting dates;

4) I don't have enough time; and

5) cover crops will take up too much space in my small garden.

Photo: WSU

These excuses have generally worked well for me year after year allowing me to live somewhat comfortably with guilt.  The fundamental question  simply boils down to, "Are you satisfied with your garden's yield?"  Do the the plant's look healthy.  If the answer is, YES, then keep doing what you're doing; or, as in my case, what you're not doing. If the answer is, NO; then you need to start  investigating what might be the cause.  You have time now because it will be months before planting time again!

Now, speaking in further defense of myself, I will say that I regularly add compost to my planting beds at the start and end of growing seasons as well as applying mulches such as straw and grass clippings throughout season.  Combined with rotation, this seems to provide the nitrogen and other nutrients that my plants need as well as keeping many plant ailments under control.  However, I do still feel some slight pangs of guilt when I see photos, like the one to the right, of someone's planting beds brimming with cover crops. But, I guess I'll  go on living comfortably with a little guilt...

FWIW:  If you are interested in finding out a more about the advantages of cover cropping, check out our blog entry about   No-Till Gardening & Cover Cropping.


And remember...

"Guilt: The gift that keeps on giving." - Erma Bombeck

What's in Your Garden Soil:  The Carbon : Nitrogen Ratio 

Master Gardeners are always talking about using  cover crops or compost as two very important means of providing nitrogen (N) to a garden, but there is another element that influences how much N and in what form N may be present in soil. That other element is carbon (C), and we will now  review why that relationship is important as well as why  backyard gardeners should be atuned a little into the carbon/nitrogen (C:N) ratio.

Plants obtain carbon from the atmosphere by converting carbon dioxide via photosynthesis into sugars that are used to fuel their cellular processes.  Not all of this captured carbon, obviously,  is used as fuel. Plants also incorporate carbon into their cellular structures in  the forms of cellulose and lignins. A tree, remember, is one big edifice of mostly cellulose.

Where does nitrogen (N) come into play?

Nitrogen Cycle. Source: scied.ucar.edu

N is needed by living cells  to make the proteins  that are essential for growth. Plants obtain their N from soluble compounds such as nitrate  (NO3-), nitrite (NO2-), ammonia  (NH3), and ammonium (NH4+) that are available in the soil. These compounds are the result of a number of different processes involving the conversion of either atmosperic N or N from  biologic sources by the actions of various mircroorganisms. A few plants, like legumes, also can convert atmosperic N into a usable form.  Few plants, by the way, can handle ammonia directly; most plants need it to be  converted by bacteria into either nitrate(NO3-) or nitrite (NO2-

How does carbon (C) come into play?

Lots of carbon   actually can be  found in  soi and comes mainly from the   remains of decomposing plant  cellulose. This carbon  soil is not used by living plants, but it is the bread and butter for bacteria.  These bacteria, however,  also use available N sources in the soil as they  breakdown cellulose and multiply.  In the short term high amounts of   C in soil can spur rapid bacterial growth subsequently depleting  the available N for  plants.  In the long term because bacteria incorporate relatively a lot of N into their proteins, when they die and their proteins decompose, soluble N will become available again to plants albeit maybe later in the growing season when plants may be in a different growth stage and need less N.

So how much carbon (C) is too much?

As you can see, the amount of carbon versus nitrogen in soil can become a seesaw-like activity.  The ratio of C to N can vary considerably  during a season. Because soil microorganisms usually become active before plants, they can get a head start on plants for available N. If the C/N ratio is high,  e.g. greater than 33:1, bacteria may easily out compete your raddishes. This is why gardeners and farmers use cover crops and  fertilizers in the spring - to ensure that there is enough N in the soil for young plants to thrive.  

• FWIW: Gardeners  know that  using sawdust as a mulch in a garden (its C/N ratio is around 400:1)  is a "No, No" because all of the available N might be taken up by feasting bacteria.  Gardeners using straw as a mulch (its C/N ratio is about 80:1) run a similar but reduced risk, although these gardeners are probably  also adding  compost  to their gardens to maintain an overall healthy C/N ratio. 

What is a good C/N Ratio?

Depends... there is  lattitude,  and the C/N ratio naturally fluctuates due to moisture levels, temperatures, soil characteristics and plant growing cycles during the course of a growing season.   Typically a ratio between 12 - 15:1 is considered good for vegetables. In that ballpark range bacteria populations seem to be relatively stable. There is enough available N   for bacteria to break down cellulose and for  plants to grow. On the other hand, a low C/N ratio  (e.g. 9 - 10) may not be necessarily bad. Decomposition will be slowed, but will continue at a steady rate assuming you have a soil with sufficient humus content.  

What about the C/N Ratio in my compost pile?

New green organic material like clover, coffee grounds,  grass clippings & other common yard/garden waste added to a compost pile  will moderately increase the C/N ratio. The ratios of these items are in the range between 20 - 30:1.  Weeds, vegetable scraps and hay   bring higher C/N ratios  in the range of 20 - 35:1 to a compost pile. By turning over your compost for aeration and keeping it moist, you can promote the nitrification process. You can also add manures (C/N 15:1 typically) to give it quick boost of N.  When decomposition is completed, your pile will eventually wind up with ratio of around 12:1.

There are methods to determine the C/N ratio of large compost piles. These require  that you know the quantities of the materials,  e.g. tonnage,  in the pile and their basic chemical compositions.     For the backyard gardener,  however,  the        fundamental    question simply is  "Are your plants looking healthy and green?"  If yes, no problem.  If no,  you have some investigating to do because it may not be just a whacky C/N ratio...

And remember...

"If you wish to grow anything, you must understand it and to understand it in a very real way." - Russell Page

NO-TILL GARDENING & COVER CROPPING

No-till corn planted into a cover crop of cowpeas.
 Photo by Dr. Rafig Islam, OSU

Sometimes when you start thinking about something, that "something"   triggers  a  sense of confusion before you realize that the "something" that appeared simple is actually, like most things, quite complicated.

Confusion was my   first reaction when I started to think about how  no-till gardening related to cover cropping. I know that master gardeners preach about them  and farmers regularly use cover cropping to improve aspects of soil fertility and structure; but the two ideas also seemed to be somewhat contradictory top me.  

Mowed cover crop in spring. The  decomposing green  provides a mulch layer

while the roots    improve aeration as well as add  nutrients as they decay.

The idea behind no-till is that soil fertility and structure are improved by allowing the  soil's ecology to develop naturally with little or no soil disturbance.   No-till practices allow the populations of earthworms, bacteria, nematodes and, importantly, mycorrhizal fungi to increase in the soil   establishing a balanced ecology that sustains soil fertility.   Mulch and compost are typically put on top of the soil to augment any needed nutrients and to suppress the sprouting of weed seeds     arriving via the wind or bird droppings.

Traditional plowing [a deep tillage technique], as well as a gardener's   deep spading, destroys many of these healthy soil organisms; and this means, in the case of mycorrhizal fungi,  that plants will actually miss out on obtaining the water and nutrients  these critters  can also  provide to plants.  Dormant weed seeds long buried in the ground may also be moved up to the surface and  be stimulated to sprout when  exposed to daylight.    But, there are also  positive aspects of deep tilling to keep in mind.  It does introduce oxygen into the soil  quickly and that  stimulates bacteria to breakdown available organic matter releasing some nutrients in usuable form, like nitrogen, for a new crop.  It also  expedites the warming  and drying of  soil in the spring enabling earlier planting.  Over time, however, deep tilling can lead gardeners and farmers to   become more dependent on commercial fertilizers, herbicides and pesticides to compensate for   a depleted  soil ecology.

Backyard gardeners using raised beds or containers probably unconsciously incorporate a lot of no-till practices  into their garden chores, and  many of these gardeners also  use of cover crops.    The backyard gardeners, I know, mostly limit their cover crops to winter rye or buckwheat at the end of a growing season as a way to give their soil a nitrogen shot  next season because both of these cover crops  can be lightly tilled into the soil top few inches of  soil or easily mowed/rolled down without disturbing soil ecology.

FWIW:  Legume cover crops, like cowpeas, take nitrogen (N) from the air and convert it to ammonium,  and then this new N source  potentailly becomes  available to  plants in the spring. Non-legume cover crops recycle any leftover N in the soil from a prior harvest. This N  becomes available to new  plants as the roots of the cover crop decompose. But, take note, because soil microbes usually become active before new plants,  the microbes  get first dibs on available N.  If a soil's N content is low in the spring, new plants may encounter a  deficiency of N. This can happen if spring planting gets delayed by weather - the soil is too wet, too cold etc.

So, who wouldn't want to use cover crops?

Plowing  warms  and drys  soil in the spring.
Photo: Oregon SU

Cover cropping sounds like a panacea, but it gets complicated with the need for crop rotation and, of course, by the scale and variety of farming activity.  Vegetable farmers seeking to move to no-till, whether they are following conventional or organic methods, will probably find they  need to switch from row to fixed raised beds. Creating the beds is not hard; but because farming equipment  compacts the soil between the beds from repeated tracks, a grower may need  to plant different cover crops between the beds to impove the soil's ability to resist  compaction than the cover crop needed in  the raised beds. These additonal crops add  costs.

Among the factors farmers have to think about when selecting  cover crops  are:

• What's the goal? Is it  weed suppression, erosion control, nitrogen capture, adding organic matter, breaking hardpan, reducing the risk of soil diseases or pests, etc. [For some help in choosing a cover crop, Cornell offers this  Cover Crop Decision Tool.]

• Is the cover crop a good match for the character of the field's soil? - Alfalfa, e.g., needs fertile and warm temperatures to germinate as does forage raddish that promotes the break up of clay soils, but it will also attract harlequin beetels. Each field may have unique characteristics  requiring differenent cover crops. 

• What is the cash crop? Is it a field crop like many grains or legumes or is it  planted in rows? Can the cover crop be inter-planted with the cash crop, or does it need to follow the cash crop's harvest? 

• What tilling does the cover crop require? Can the cash crop sprout through last season's cover crop residue? Will the cover crop clog a seeder if its residue is left on top of the soil? 

• Will the cover crop's growth cycle be compatible with that of  the cash crop's? Will it be necessary to use a herbicide to clear the field for planting in order to harvest the cash crop in time for market or to prevent the cover crop from reseeding and becoming a weed. 

• How does crop rotation affect cover crop selection from year to year? 

Spiker aerator and tractor for reduced tillage.
A backyard gardener just needs a broad tooth fork.

Many, if not most, American farmers do    use  a mix of lite-tilling strategies, collectively called reduced tillage, usually in order to limit erosion and ideally  to minimize soil disturbance.  A small but increasing number of farmers are  also introducing  or expanding  no-till  practices into their tillage repertoire.

Farmers starting the move to no-till unfortunately frequently have to expect  yields  from these fields, especially for field crops like corn, to  decline until natural soil fertility is restored. This can be  a 7 - 9 year process   unless implementation is carefully managed -- that's a long time with a reduced income from a field until you start to see increased yields and lower costs!  Along with making such a  long term  commitment, no-till strategies need to  be tailored  for each  each field.

Cover cropping is an important component of no-till, but definitely a complicating factor.  [If you are interested in how cover crops can be employed  during  conversion to no-till to speed up the process, take a look at Ohio State University's Factsheet on Using Cover Crops to Convert to No-till.]

OSU  found that  growers can reduce the time to restore the soil's natural fertility, at least for some crops, to as little as only 2 - 3 years - a much more attractive proposition -- by employing a continuous living cover strategy, i.e.    using cover crops to eliminate/reduce the time that fields are devoid of plants. The benefits of  leaving plant material on top of the soil and roots  left undisturbed in ground over the winter months substantially promote restoration of soil health and reduce nutrient loss from erosion and runoff.  

Well, that's enough for now, I know that I have barely tilled the surface regarding  cover crops and no-till.

And remember

"There's no limit on how complicated things can get on account of one thing 

always leads to another." - E. B. White

Crop Rotation and Cover Crops

Crop Rotation in Middle Ages
Source: tenthmedeival.wordpress.com

For millennia farmers have recognized that soil fertility declines as the same fields are used for the same crops year after year.   Over generations and in different cultures, crop rotations based on two, three and four year cycles evolved as a way to keep soils  productive. [If you remember anything from middle school World History, it's probably  that during the Middle Ages the serfs let  one field lie fallow every third season.] Serfs then,  and farmers  now, also   spread animal   manures on fields as  fertilizers. 

Today, backyard  vegetable gardeners with either  just a small, single raised bed or a large fenced garden  try to avoid planting the same vegetables in the same spot year after year.  They know that it is a way to minimize the presence of some insect pests and plant pathogens. Most of these gardeners also  add compost and other fertilizers to sustain soil fertility, but   they may or may not follow  systematic crop rotation and may not use cover crops as part of their garden planning.  So let's try to make a case for  both of these activities...

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Our favorite backyard vegetables, like tomatoes and peppers, and some grains, like corn, have  relatively large appetites for nutrients. Because the root systems of many popular vegetables are relatively shallow, garden soil can become depleted of some  nutrients near the top of its upper  layer (i.e. the soil's A Horizon).  Adding compost  does return some of these nutrients to  garden soil, and the new organic matter  also promotes soil aeration and  helps to retain moisture.  Typically,  dressing a vegetable garden with about 2" of compost annually will do a lot to sustain its fertility.  Mulching also contributes organic matter and should be considered to  be part of the "compost picture." Few of us, speaking from experience, probably add either enough compost or mulch each year to our vegetable beds,  but every little bit   helps...

Source: growers learning.com

 If you don't  have a lot of your own compost, you can buy compost, but probably many gardeners simply yield to the cheaper temptation and supplement soil nutrients for another year by opening  a standard 5-10-5 bag of  synthetic fertilizer. Eventually, use of synthetic fertilizers will lead to a decline of "soil organic content" (SOC). Without new organic matter regularly being added, the diversity of garden  soil's microbial ecology simply declines (fewer types of bacteria and other  lower order critters, i.e. invertebrates  exist there).  It's these creatures that account for the breakdown of  organic matter that releases a fuller range of plant nutrients  into the soil.

Although adding compost is very important for soil fertility, unfortunately, compost alone is not quite enough.  Backyard gardeners also should systematically rotate crops and  use  cover crops in order to sustain and improve  soil fertility and texture.  [It will also get you a long way towards following really recommended  organic practices in your garden.] Together with adding compost, these two other actions will enable you to break  synthetic fertilizer addiction.

Crop Rotation

The above illustration shows a modern four year sequence of vegetable rotation in a garden plot.

NOTE: The four year cycle   evolved in 16th century Belgium  and involved rotating legumes, root   vegetables (e.g. a lot of turnips), grains,  and a fallow season of no planting. The modern  four year pattern for  backyard gardeners became popularized in the U.K. starting in the 1920's and  emphasized the importance of regularly incorporating  organic matter  into  soil to promote its  fertility.

What the modern  plan achieves is that 1) legumes replace depleted nitrogen sources, 2) root veggies  penetrate deep into the soil and move some nutrients upward,   and 3) the cycle provides  four years of usable crops with at least  a three year gap before a plot might be used again for the same crop minimizing the risk of a  crop's   exposure to  particular pathogens or insect infestations. Of course, adding compost to replace organic matter  is implicit for every year. An excellent resource about practical rotations is North Carolina State University's Center for Environmental Farming Systems publication, Crop Rotations on Organic Farms.

HINT -  Rather than pulling up bush beans, tomatoes, peppers etc. at the end of the growing season, cut them off at ground level and let their root systems decompose in the ground.  It will help keep the soil from getting compacted, leave some nutrients in the ground AND may save your back from spading...

Cover Crops

Cover crop in raised beds.
Source: paoniafarmandhome.com

For farmers, cover crops do a lot. They are used to suppress weeds, reduce erosion and compaction, add organic matter, improve soil structure and restore nutrients to name just a few benefits.  For  backyard gardeners, the benefits probably  focus mostly on adding nitrogen sources and extra organic matter.  

There are actually two seasons for planting cover crops. The first season spans early spring to early summer and  usually involves planting buckwheat, clover or a legume like a field pea. These crops grow fast allowing time for a late season crop to be planted. The second season spans late summer to early fall and frequently  involves sowing oats, field peas, or ryegrass to provide organic matter for the next season. These crops typically have deeper root systems than vegetables and bring nutrients up closer to the surface as well as adding organic matter.

I've only mentioned a few of the available cover crop options that farmers might select to improve soil.  For  backyard gardeners, using cover crops in late summer or early fall probably is the more practical option.   Either ryegrass (not winter rye) and buckwheat are  good choices  because both are annuals and can be  worked into the soil easily before they go to seed. Some gardeners  use winter rye, but it requires more effort to work it into the soil in spring after its sprouts.  For a lot more information on cover crops, consult Cornell University's Cover Crops for Vegetable Growers  website. 

Finally, for gardeners who might be interested in knowing what being an "organic  farmer" entails as well as useful information about organic farming practices, I recommend the U.S. Dept. of Agriculture's Guide to Organic Producers. This is set up as a workbook and checklist for  prospective organic farmers, but  backyard gardeners will learn a lot just be looking through it,  too...

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Source: earthwiseradio.org

About Animal Manures 

Applying animal manures to a garden can be  a  very effective way to sustain soil fertility. Organic and conventional farmers  frequently incorporate manures into their  field management strategies,  but for backyard gardeners with limited space and maybe limited access to manure sources it can be more challenging.  For a gardener with a small, e.g. 4' x 8', plot, a commercial bag of manure from a garden center etc. is attractive because the manure already has been  composted, sterilized and rendered safe from pathogens and viable weed seeds.

For a person with a larger vegetable garden, this approach is not especially economical and makes the offer of  getting fresh manure from a neighbor's pet chickens or rabbits  appealing, but it requires more thought than just saying, "Yes, I'll take all you've got."

Animal manure should be composted before being spread on the backyard garden.  If not composted, then its best to dress it either onto a fallow plot or to till it into a  bed at the end of current the   growing season so that it will decompose over the winter. In its fresh state manure can be simply too concentrated for plants to handle. For example, there may be too much nitrogen, it might be too acidic, it could contain lots of weed seeds or a pathogen (e.g. worse case: salmonella)... Or, maybe it'll be just too smelly for your backyard.  For both commercial as well as neighborly sources of  "brown gold," either check the label or ask about how "organic" the manure is.  Unless you are getting manure from an organic, or at  least, a hormone free source,  you could  be inadvertently  adding some extras like animal antibiotics to your garden's soil. 

Finally, the manure's animal source  is important to know because nutrient content varies.  Chicken manure is generally considered desirable because it contains relatively high amounts of nitrogen and potassium compared with other manures; on the other hand,  like cattle manure, the fresh variety also contains a lot of ammonia that potentially can damage plants if over applied.  Cattle manure contains a lot of organic matter and a wider range of nutrients  (as well as weed seeds), but it requires about a year to decompose. Horse manure is similar to cattle manure in content, but can take up to two years to decompose -- making it a slow release  fertilizer.  Simply do not use pet feces - the risks of exposure to parasites and harmful bacteria are too great.  If you plan to use animal manures in your garden, it's a good idea to follow the guidelines of the  National Good Agricultural Practices Program available from Cornell University's website.  It is very, very  important to know when to add manures and how to apply  them safely in your garden. 

And remember  (maybe)...

"Creating your own urban farm is as simple as planting your flowerbeds with edibles." ~Greg Peterson