Minnesota Farmer

30 days: Fertilizing after the harvest

A misconception of those who are not on the farm is that we just throw fertilizer out there and hope it does some good.  Farmers do not live by the “if a little is good, more is better” creed.  Fertilizer is a costly input and must be used when and where it will give us the best crop possible.  Today is day 6 of the 30 day challenge and we are going to be talking about fertilizer.

Plants need nutrition just as all living things do.  They are able to take that nutrition from the soil.  Specifically our farm crops need Nitrogen, Phosphorus and Potassium along with smaller amounts of the elements Sulfur, Boron, Zinc, Iron, Manganese, Copper, Magnesium and Sodium.  These elements may be in combination with other elements that the plants can metabolize or break down.

Fertilizers used on the farm come in many forms.   Some are sourced from the air or mined from the soil, others are sourced from waste products of industry or agriculture.  Plants do not care what the source of the nutrition is, they need it broken down into pieces that they can use, and all forms of fertilizer will eventually break down into these forms.

Our farm uses some animal waste sourced fertilizers, manure, and some commercially sourced fertilizers.  We also make use of the left over plant materials from last years crops to help our plants grow.  The commercial fertilizers tend to break down faster and be of use in the year they are applied.  Crop and animal waste tends to break down slower and while some will be available for the next crop, some parts will take months or even years to become available to the plants.

Before any fertilizers can be applied we soil test.  A sample of our soil is taken from several parts of a field and sent in to be tested at a place like Agvise Laboratories.  They will send back a test report of what is available in our soil and a suggestion of what should be applied on our crops.  It is up to us to take that report and modify it to our conditions and expectations.

100_2499Animal waste, manure, is placed on our farm with a machine like this.  The process of turning animal waste to fertilizer was covered in yesterdays post.

100_2507Solid commercial fertilizer is placed on our farm with a spreader like this.  In either case the fertilizer needs to be mixed into the soil to preserve it for next years crop.

Nitrogen fertilizer is the largest part of a plants needs.  If the plant cannot source it directly from the air, it must come from the soil, and nitrogen is hard to keep in its place.  Nitrate (NO3) and nitrite (NO2) are naturally occurring inorganic ions that are part of the nitrogen cycle. Microbial action in soil or water decomposes wastes containing organic nitrogen into ammonia, which is then oxidized to nitrite and nitrate. Because nitrite is easily oxidized to nitrate, nitrate is the compound predominantly found in groundwater and surface waters.  Nitrate-containing compounds in the soil are generally soluble and readily migrate with groundwater.  Nitrification inhibitors can be added to nitrogen based fertilizer to slow the process of nitrite oxidation and keep the nitrogen on the soil longer.  (Urine is a good source of ammonia that becomes plant usable nitrogen.)  Because of nitrogen’s instability, we typically wait to apply most of our nitrogen after the crop is up.

Fertilizing the fields is just another part of the work that is done after the harvest.





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