It's a Dirty Job, But Somebody's Gotta Do It

Bulding Soils for Better Crops, Fred Magdoff’s and Harold Van Es’s homage to organic matter and its importance to soil health, references several case studies where the addition of readily available cheap or even free soil nutrient sources, such as leaves or wood chips from curbside trash pickup, must eventually be reduced once soil has reached an optimum percentage of organic material – somewhere between 3.5-5% – because further input of rotting material would lead to nutrient leaching after harvest.

At Myrtle’s place, we are used to asking ourselves “Why?”  And we are not at all pleased when we are told “You can’t do that!”

Now, we typically apply these irreverent and anti-authoritarian qualities towards those who suggest ridiculously conformist ideas, like “You can’t grow vegetables without fertilizer and pesticide.”  However, even people who know what they are talking about occasionally say something that makes us go, “What?”

Nutrient leaching is a concept that we simply refuse to accept.  It is real enough, of course; that’s not what we are saying.  Nutrient leaching is the runoff of things like nitrates or phosphorous from your topsoil, and it has serious consequences for groundwater supplies.  We are in no way suggesting that these very real issues are not a concern.

Rather, we don’t believe that high nutrient values in post-harvest soil necessarily have to result in those nutrients running off, at least not in the context of the small farm or garden plot.

Every good thing has its point of diminishing returns, of course, but to date we have seen no literature which suggests it is even possible to reach the level of organic matter in your soil which plants simply cannot take advantage of.  For anyone who has ever gone a week without turning their compost, you can relate to what we are saying.  Having to pull weeds from the compost before turning it shows just exactly how lovey-dovey the relationship is between growing things on the one hand and dead and decaying things on the other.

We are going to experiment this fall with a garden plot design whose intent is to maximize organic matter.  As we have described on numerous occasions, soil in the Brazos Valley is equivalent to the wet clay any potter would be proud to slap on a wheel.  In addition, however, it is also sadly lacking in what Magdoff and Van Es describe as “living, dead and very dead” materials.  Weeds do very well here; everything else has traditionally required a lot of external inputs.

We aim to break that mold on a large scale by doing what we have been doing all along, only in a more concerted way.  We have often talked about the deep bedding method we use with our chickens, wherein we lay down about three feet of composting leaves in the chicken coop.  The chickens then poop on the leaves, and turn the leaves over as they scratch for bugs.  This stirs the compost tea in such a way as to reduce the manure smell to negligible levels, in addition to creating the perfect external input for the garden.

We can’t really add any more chicken poop to the mixture, having maxed out how many chickens we can have in our coop, but we can do something about where the organic mixture gets off to once it’s in the garden.  Runoff from topsoil requires two key elements:  somewhere to run off from, and somewhere to run off to.  The from is still the same – the places in the garden where we apply the compost.  The to, however, is something we can control.

We are going to kill two birds with one stone; we have a lot of useless clay, compacted to the point of almost being adobe brick, which we are removing from the fish pond.  We need some way to stop topsoil from running off from the vegetable plots.

Put two and two together, and you come up with a low berm surrounding the vegetable garden, composed of solid clay.  Any soil eroding from raised mounds or rows in the vegetable garden will simply fill a furrow between the sides of the roughly rectangular berm, and will be a great place to plant the next season’s row of vegetables.  In fact, if we play our cards right, this may be a way to improve the soil tilth when we eventually move to reduce tillage – meaning we may not have to turn over the soil so often, or resort to using a roto-tiller.  Since our garden plot will eventually be comprised almost entirely of the detritus of rotted leaves and chicken poop mixed into the slimy, sludgy soil, the aeration should improve dramatically over what you get with solid Brazos Valley clay.

This would not be a good idea for a large plot, nor for a plot where the prevailing soil type is not compacted clay, like it is here in College Station, because runoff is not the only source of groundwater contamination.  Seepage is another means for high nitrogen or phosphorous content of topsoil to pollute the groundwater supply, and if you were working in a rocky or sandy topsoil, the seepage would be unacceptably high; excess nutrients would therefore be almost as bad a thing as insufficient nutrients in such soils.

In the Brazos Valley, however, if we can minimize the amount of water retention, we can minimize the amount of seepage.  This secondary source of contamination we hope to contain through aggressive planting of sunflowers on the perimeter of the garden.  This solves multiple problems, first as a trap crop keeping birds from harvesting our vegetables, and second as a means of soaking up water and nutrients from deeper in the soils.  Studies in the plains states have indicated that sunflowers do a good job of drying out soils to a surprising depth of 8-10 feet, which is more than sufficient, given how close to the surface our bedrock lay, to prevent excessive seepage from our topsoil.

Since we have a fairly small plot, we will be able to test the soil within the berm, the soil surrounding the berm, and also the mineral content of the nearest source of groundwater (the fish pond!) and get a pretty good idea of whether our theory is correct.

What we expect is that without having the open irrigation so prevalent in large scale operations, where there is simply no preventing rain water from running off the crop land and into the surrounding ecosphere, we should be able to get organic matter percentages in our soil of 10% or more and still have no appreciable impact on the surrounding water supplies.  If this turns out to be true, we suspect that our produce yields should increase geometrically, with no negative consequences to the environment. 

Magdoff and Van Es actually make numerous references to small market produce plots when discussing methods for adding organic matter and for reducing tillage; they point out that some of the unique qualities of this type of business preclude the preferred methods of improving soil, notably the use of cover crops.

This makes perfect sense; if the “growing season” is actually a year-long term, the way it is in most of Texas, then a vegetable gardener is likely to have no true “fallow” season as it is understood by large scale farmers from anywhere else in the country.  However, by essentially containerizing a roughly 1200 square foot vegetable plot, we believe we will be giving ourselves a shot at making the perfect soil.

Fingers and wingtips are crossed!  Shovels are at the ready!

Happy farming!