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