Septic Biz Magazine
For Today's Onsite Pumping Professional
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There are several reasons. An easy answer is both state and federal laws require a crop to be grown but
this avoids the question. Growing a crop will reduce run off and soil erosion. We want to keep the
septage waste on the area where it was applied. If it moves to another part of the field, that part of the
field receives more septage than was planned and permitted. This may be more than the soil in that part of
the field can treat. If the septage waste moves out of the field, it may enter surface waters. This is a no-no.
The goal is to keep the wastes in the part of the field where they were applied.
The main reason for growing a crop is to remove some nitrogen and phosphorus from the “soil water” if
we may call the liquid part of the septage waste in the soil “soil water”. Soil has a limited capacity to
remove nutrients from wastes. The crop uses some of these nutrients and when the crop is harvested and
removed those nutrients are also removed and the soil in the land application field does not have to
continue holding those nutrients. The second septage is added to the soil either by surface application or
injection a large amount of septage is in contact with a small amount of soil.
This contains more nutrients than that amount of soil can treat. The “soil water” will move away from that
spot. As it moves through “new” soil, that soil will remove additional nutrients. As the “soil water”
moves through the soil, the soil the septage has moved through will have removed the maximum amount
of nutrients it can. Crop roots explore the soil for water and nutrients, and both are components of
septage. The roots will remove some of the nutrients in the soil. As the crop grows, the roots will remove
more of the nutrients that were removed by the soil from the septage. When the crop is harvested,
those nutrients are taken from the soil in the septage applicationfield to another field. The harvested crop
is not considered a waste and is not regulated. Each additional crop in that field will remove more of the
nutrients that were removed by the soil from the septage application. Harvesting and removing the crop
will lower the level of nutrients in the soil. If the crop is not harvested, the crop will take up the
nutrients but when the crop dies, the nutrients are added back to the soil. Growing crops, harvesting and
removing as much of the plant as possible will shorten the time until septage can be applied to that field
again. The amount of nutrients in the soil before septage is applied will determine the rate at which you
may apply septage. This means you must not only be a septage hauler but also a crop manager.
The crop you choose to grow, depends on what you want to do with it. You may want to raise a crop
that can be sold. What does the buyer want? If the crop is to be fed to horses, a grass crop is best. If the
crop is to be sold to a grain elevator, the crop will depend on the area of the state the field is located. In
large areas of the northern part of Michigan, corn cannot be grown for grain so you will have to choose
another crop. If the crop is to be fed to cows, you can grow corn for silage. This is actually better than
corn for grain because almost the entire crop above the ground will be removed and more nutrients will be
removed.You do not have to sell the crop. The crop may be harvested and removed and then applied to
another field as green manure. Because the crop is not regulated, the field you add the green manure to is
not required to meet the criteria for a field in which septage is applied.
There are a variety of crops that may be grown in the field where septage waste is applied. Different crops
have different capacities to remove nutrients. You make the decision of which crop to grow. If you can
use a crop, choose that crop. If you wish to use the crop to pay some of your expenses, the buyer will
help you make the choice. If you are independently wealthy (isn’t the goal of all septage haulers to be
independently wealthy?), you make the choice.
Remember, the goal of the crop is to reduce soil erosion and to remove as many nutrients from the soil as
possible.
Some additional questions to consider. Who will plant the crop? Who will spray the crop if it is required?
Who will harvest the crop? Do you have the necessary equipment? This is an opportunity to broaden
your expertise, become a crop specialist.
If you are considering a new field in which to apply septage waste, consider the amount of nutrients,
especially phosphorous, that the soil may have before you enter an agreement with a land owner to rent
or buy that field. Most farmers do not add excessive amounts of fertilizer. There are some farmers who
have spread large amount of animal manure on fields and the phosphorous levels are so high they may
not add more manure. In that case you won’t be able to add any septage waste. Before you buy or rent a
field, soil test!
Dr. Del Mokma is a Soil Scientist and professor at Michigan State University
Why do you have to grow a crop on your septage land
application site?
application site?
By Dr. Del Mokma