It is spring and that means it is time for farmers to get out into the fields and start planting. Farmers have to dodge rainstorms and when skies are clear they might work through the night to get seeds into the ground. Iowa has amazingly rich and robust soil for those seeds to germinate in. That rich, black topsoil does need some preparation for the ideal growth of seeds. But, have you ever wondered why farmers plow their fields before they plant?
Seeds are typically only planted an inch below the soil surface.
Farmers want to give those seeds the best chance of germinating and growing.
That means mechanically preparing seed beds by breaking the ground.
Soil can become dense and compact. Plowing also makes it easier to plant.
Plowing breaks up the blocky structure of the soil which can aid in drainage
and root growth.
Plowing fields can also turn organic matter into soil to
increase decomposition and add nutrients from the organic matter to the soil.
Many farmers spread manure from cattle and swine onto their fields. This manure
is rich in nitrogen which is essential for plant growth. Turning the soil over
not only mixes this organic matter, but it also increases oxygen in the soil
which speeds up decomposition of the organic matter and makes more oxygen available
for the plant roots.
One problem that farmers face is weeds in their field. Weeds
compete with the planted crop for water and essential nutrients. Weeds
typically grow fast and can crowd out the desired crop. One advantage of
plowing is that it can mechanically break up weed roots and disrupt weeds
from growing. By mechanically controlling weeds farmers may be able to spray
fewer herbicides to control the weeds. Harvested crops are also graded by
the amount of ‘foreign’ material in them. A bushel of wheat will be worth more
if it has fewer weed seeds in it. So, having fewer weeds can lead to increased
profit.
Planting seeds is always weather dependent. Farmers need to wait
until the soil temperature is above 50 degrees Fahrenheit so that the seeds will
germinate. Farmers want to plant as early as possible so that they can maximize
a short growing season and give their crops the best chance to be productive.
Black soil will absorb more sunlight and increase that soil temperature
more quickly than soil that has plant matter on it. Plant matter reflects
some sunlight and might delay how quickly soil temperature warms to 50 degrees
Fahrenheit.
Farming is
about decisions
There are a lot of reasons for farmers to plow or till their
fields. But, plowing does present some challenges and costs. One of the
principle problems with plowing fields is the potential wind and water erosion
that might carry soil away from the field. For this reason many farmers chose
to plant their fields using no-till technology in which last year’s organic
matter is left on the surface and seeds are drilled directly into soil without
plowing. The organic matter from previous years helps hold the soil in place.
While plowing or tilling fields can disrupt the weed lifecycle, it
can also disrupt the microorganisms in the soil and adversely affect the soil
health. Bacteria, fungi, worms and insects that all live in the soil create a
unique environment that contribute to the health of the soil. It is many of
these organisms that breakdown the organic matter in and on the soil.
Ultimately farmers need to decide if the benefits of plowing their
fields outweigh the risks of soil erosion. They can choose between conventional tillage,
reduced tillage, and conservation tillage. They need to decide
if tilling harms the microorganisms that live in the soil. Many Iowa
farmers have chosen to practice no-till farming because it does have many
positive benefits to the environment. Most farmers don’t actually ‘plow’ their
fields. They either use conservation tillage methods or do not till the soil at
all. Traditional plowing by definition turns up bare soil and buries all plant
residue leaving soil vulnerable to wind and water erosion. Plowing also creates
clods and an uneven seedbed for planting. This traditional, old fashioned form
of plowing hasn’t been practiced commonly in Iowa for 25 - 30 years. Farmers
try minimally disruptive techniques that leave much of the plant residue on the
surface of the soil helping reduce erosion. But, every field is different and
farmers need to decide what works best for them and their operation.
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