An  Imponderable

Along with robins and greening up trees, another harbinger of spring in many rural areas is the appearance of anhydrous ammonia (AA) tanks being pulled by pick-ups on the roads and by tractors in the fields. AA is a source of nitrogen necessary for plant growth, as is phosphorus and potassium - the big 3 in Von Liebig’s NPK concept of agricultural fertilization. Prior to its common use as a fertilizer beginning in the 1940’s and 50’s it was used during World War II in the construction of airport runways in war zones. AA burns the organic matter out of soils thus hardening them up enough to support landing aircraft without the need for cement runways. Today as we use it on prime agricultural soils we wonder why our soils are becoming more compacted as years go by.

We live at the bottom of an ocean of air that is composed of approximately  78% nitrogen, 21% oxygen, 0.93% argon, 0.039% carbon dioxide, water vapor at an average of 0.4% plus small amounts of other gases. At sea level the weight of all these gases over each 1 square inch of the earth’s surface is 14.7 lbs. known as Atmospheric or Barometric pressure. Doing a little math here gives us a little over a ton of air over every square foot of the earth’s surface and of that ton 78% or 1650 lbs. is nitrogen.  There are 43560 square feet per acres times 1650 equals over 70 million pounds of nitrogen over every acre. I don’t know the capacity of the AA tanks that deliver nitrogen to the fields but I do know it is infinitesimal when compared to the amount available in the air above us.

Rain and snow carry some atmospheric nitrogen to earth. High organic matter soil absorbs and preserves this water and nitrogen for future plant growth. Legumes, with suitable inoculates, grown in a good crop rotation fix atmospheric nitrogen into the soil.

Ponder this: Why do we pay big bucks for a little bit of nitrogen when that use destroys the natural fixation of free nitrogen in the soil?