Organic Farmer February / March 2020

Mixing the compost.
Continued from Page 27
resistance. Potassium also improves a plant’s
hardiness to cold and increases vegetable
size.
Plants lacking in potassium are weak and
grow slowly. The fruit is small, sometimes
shriveled. Leaves show discoloration at the
margins and tips. Like with phosphorus,
only about one percent of the soil potassium
is available to plants.
In Western Oregon’s Willamette Valley, “a
lot of farms really don’t need more phosphorus
or potassium,” Nick said.
Aggregate Formation
Organic matter also helps with aggregate
formation, which is the process of sand, silt
and clay coming together to form larger-sized
granules. Larger granules create
nice, crumbly soil. Good soil structure
allows water to easily penetrate the surface.
Crumbly soil also creates better aeration,
better water infiltration, and a better ability
to retain water.
Hummus
Although low in nitrogen, hummus is
the most mature soil component. In most
soils, hummus makes up 70-80 percent
of the organic matter. Increasing soil
hummus improves both soil and crop
growth. Adding hummus to the soil has
long lasting effects. Not only does it feed
the soil for the season, or even for the following
season—it breaks down slowly and
will continue to feed the soil for decades.
Sometimes hummus can last for hundreds
of years. Straw and cornstalks are high in
carbon and low in nitrogen. Both decompose
slowly and are efficient suppliers
of hummus.
Cover Crops
Cover crops—or green manure—build
nutrient-rich organic matter in the soil.
The plants collect the sun’s rays, which
powers photosynthesis. The plants take in
carbon dioxide from the air to produce
food for the plant, and food for the microorganisms
living in the root zone. Clean
oxygen is released into the atmosphere
during this same process.
place. So, in fields with high fertility levels,
a cover crop could save farmers money
in fertilizer costs. If farmers have a lot of
phosphorous in their fields, cover crops are
a good way to go—by adding nitrogen, Nick
said, without adding more phosphorous.
Nick suggests sending a cover crop sample
into a testing lab before incorporating it into
the soil. The lab can analyze for dry matter
and nitrogen content. Such a test can predict
how much nitrogen will be released in that
growing season.
OSU offers a free online organic fertilizer
and cover crop fertilizer calculator, with a
mineralization model. “It’s not the be all and
end all, but it’s useable and grower friendly,”
Nick said. This calculator is intended for
growing conditions in Western Oregon and
Western Washington.
Nick points out that farmers in different
regions with different soil types and precipitation
levels will need to check with
their local extension agents, or land-grant
university.
Well-aggregated soil improves root growth.
It also provides a healthy habitat for soil
organisms. In turn, the organisms create a
favorable environment for plant growth.
Cover crops such as young legumes and
cereals are high in nitrogen. They decompose
quickly and produce less hummus
than chopped straw or cornstalks.
A cover crop works to keep nutrients in
Annual soil tests are the best way to determine
crop needs and monitor soil pH levels.
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Organic Farmer February/March 2020