Understanding Your Soil
- Paul Betz, High Mowing Organic Seeds Sales Associate and owner of High Ledge Farm, VT
Until
recently, the prevailing wisdom was that one couldn’t add too much
compost to a field. When we first opened our ground, we put on a lot of
compost. I considered it to be a pro-biotic for the soil; awakening and
exciting lots of microbial life, and supplying food for that renewed
population to eat. While compost is certainly a great soil conditioner,
and it has a role on a vegetable farm, it is possible to have too much
of a good thing.
When compost is applied at a
rate sufficient to cover nitrogen demands for a crop, significant
quantities of phosphorus are spread as well. Phosphorus build-up and
run-off is a problem in many watersheds, as its presence in surface
water can lead to algal growth and then subsequent oxygen depletion in
the water. Excess nutrients can build up over time and are a problem
whether one is farming organically or conventionally. Since constant
spreading at heavy rates isn’t really a good idea, many growers are
moving to a more targeted application of nitrogen to feed the crop. The
only way to get a good indication of what and when to apply is through
soil testing.
There
are lots of qualitative ways to take the pulse of a vegetable farm; the
look and “feel” of the plants and their yield is a good way to start,
but at some point a more in depth and quantitative look at what’s
happening with your soil can be really helpful. That’s where the soil
test comes in. Soil tests aren’t expensive or complicated and they
provide a good baseline to use to ensure that you’re doing the right
thing for your farm. Even if appearances suggest that everything is
fine, a soil test can help you with targeting specifically what
amendments you need. Applying too much fertility can also be a waste of
money, as the plants can only use so much in any given season. This
will help you to be both more profitable and a better steward of your
farm.
Your basic soil test will give a few different numbers, including pH,
macro nutrient levels (N-P-K), and organic matter. The organic matter
is largely a function of your soil type. Sandier soils naturally have
lower numbers than more loamy soils. However, this number is something
to pay attention to. Growing vegetables can
be hard on a farm and all that beautiful weed-free ground creates the
perfect conditions to oxidize the organic matter in your soil. Growing
cover crops or adding compost is a way to restore that carbon.
The lab that performs the test should also give some recommendations
for amendments to meet the basic N-P-K requirements, based on crop type.
Your local extension agent can also be a source for interpretation of
your results. Another test that is helpful for full-season crops is a
Pre-Side Dress Nitrate Test. It takes a snapshot of how much Nitrogen
should be available for the rest of the season, allowing the grower to
side dress appropriately later in the season.
I prefer to take my samples in the fall. It allows me the chance to
plan for the next season and make my amendment purchases early, rather
than waiting on the results in the spring when I want to get into the
field as soon as possible. This summer, I plan to take a more advanced
measure of the health of my soil, using Cornell’s testing services.
Their comprehensive test examines the basic macronutrients and also
looks at soil “health” by doing a series of extra tests. These
additional tests look at particle size, aggregate stability, available
water capacity, active carbon, and even a root health assessment (that
is done by growing beans in the soil sample). Here’s a link to the
site: http://soilhealth.cals.cornell.edu/
As growers, we work hard to provide healthy food from our farms.
Knowing what’s going on under the surface allows not only our work to be
more productive, but insures that our farm will be better for the next
generation of farmers as well.
I hope that the 2011 season b rings everything you need for you and your farm.
Paul
