Dear
Jeff,
I wanted to pick your brain on a matter related to management
of heavy clay soil. We got an inch of rain the other night
but from mid-May to mid-June there was zero moisture in our
part of Ontario, Canada. Our clay soil showed signs of extreme
drought stress, while loamier ground hung in there pretty
well despite the lack of rain. I'm convinced the problem with
the heavier clay is inadequate organic matter. We've taken
good crops from this same ground when rainfall was adequate.
One year with ample spring rains, I took the heaviest hay
crop I've ever harvested in my life from this clay ground.
A mixture of red clover/brome/perennial ryegrass produced
just over 4 tons per acre from a single cut. The swath from
the back of the windrower was actually thigh-high!
My point is that the soil is not compacted, and fertility
is adequate. The only reason I can see for poor performance
under drought conditions would be inadequate organic matter
levels. I've been spreading composted sheep manure on this
ground, but it obviously needs more. This year's grain crop
(oat/barley mix) should come off early/mid-August. What are
your thoughts for a cover crop that might help build organic
matter? I'm thinking about either oilseed radish or buckwheat.
I would welcome your thoughts regarding cover crop selection,
and any other ideas for building organic matter levels.
Ian Campbell
Dear Ian,
Thanks for the email and the question on cover crop selection
and organic matter. I believe you're on the right track with
your analysis of the situation. It sounds like your fertility
is high and the only thing holding you back is the soil’s
ability to manage water. Compost is a great way to introduce
organic matter and you're already adding that. You're left
with cover crops to do the rest of the work, as you've already
identified. Oilseed radish, buckwheat, hairy vetch, small
grains (wheat, rye, oats) and any of the clovers (red, white,
sweet, etc.) will all add organic matter to the soil and loosen
it up. As the organic matter content of the soil improves
both in quantity and quality, the soil will hold water and
release it to the plants. Although you should see gradual
improvement, building soil and improving soil quality can
be a long-term process. Your clay soils may never be as rich
or productive as your loamy soils, but over time they'll improve.
Look for various places within your crop rotation to add
cover crops. Many times between the time you harvest one crop
and get ready to plant another cash crop, there is room for
a cover crop. You can get buckwheat in and out in about six
weeks for example. Then look for places to build in legumes
to fix nitrogen. And, finally, plant winter cover crops of
any type, even small grains to protect the soil, store nutrients,
and in the spring build organic matter.
Sometimes it's just helpful to know you're on the right
track…you are.
Jeff
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