In a previous article, I touched on something that I felt could be expanded on. I made this statement:

“The initial trials with ammonium nitrate on fertile ground made the scientific and agronomic community jump for joy. Row crops became hyper productive and the food shortage was temporarily solved.”

This statement was made in passing, but I believe it takes some digging in to understand it better.

In the 1700’s cropland that was being tended by original U.S. settlers was already facing depletion. Much of the Mid-Atlantic farmland was seeing crop tonnages retreat as they attempted to cultivate more and more crops to feed the burgeoning population. Because there were plenty of acres to expand into, the tending of the soil wasn’t considered as important as it had been in Europe. Fertilizing as we know it was taking place to a point, manures, tilling, and such, but cover cropping wasn’t at the top of the list.

In a short time, the carbon that plants had been packing into the soil was evaporating into the Heavens. This type of de-mineralization of the soil took the once very healthy soil ecosystem and turned it into dehydrated and almost worthless landscape. More trees were cut, more grasses were tilled and different areas were cultivated. This cycle of human agronomic interference is nothing new. It has been done for over 10,000 years. Every civilization on earth has had their share of depleting soils and introducing man-made famine.

As time went on, the first “commercially available” fertilizer was introduced. Chilean saltpeter and fossilized bird guano was being shipped into the US with a vengeance. The product was finite though and eventually would run out. This led to the invention of the first Haber-Bosch Plant. Again, hailed as a miracle, this is the system that we rely on globally for our nitrogen nutrient inputs.

So, let’s dig into the soil science piece of this equation. Why did we see a huge flush of growth when the original synthesized material was applied? To understand this, we need to look at the soil structure and practices of the early 1900’s. After the generations had seen what happened to soil that wasn’t cared for, more detail and energy was put into caring for the topsoil. Cover crops, rotation, minimal tillage, and lots of organic matter were being used to keep our soils healthy. What we had was a relatively high functioning soil for what was being done. It was nowhere near the carbon capturing ability of pre-tilled land, but it was able to produce and reproduce year after year.

When synthesized nitrogen was applied, there was so much soil activity that the nitrogen was digested as an easy food source for bacteria. The complexity of breaking up carbon for energy in the soil world takes considerably longer than finding pre-formulated, ready to use nitrogen. So, the “shop keepers” (microbes) stopped minding the store and went on a feeding frenzy. Carbon cycling slowed to a crawl because there was no longer a need for the bacteria to use it for energy. Because of the carbon that was still plentiful and a good mix of other nutrients and minerals (because of organic decomposition) the readily available nitrogen was incredibly effective.

Seeing what was happening with the now hyper-productive yields, people thought that the effectiveness would never end. It did after a number of years and basically became less and less after the Carbon to Nitrogen ratio went out of balance. To better understand this, there is an effective equation for calculating carbon to nitrogen ratios and what is actually being appropriated to what function. This is the way that it works out for the purpose of understanding what function (plant or bacteria) is taking for its use in growth.

Example: A farmer incorporated 2560 lbs. of fresh organic matter into the soil. It contained 55% carbon with a carbon nitrogen ratio of 20:1. As this material decomposes, will there be a decrease (immobilization) or an increase (release) in soil nitrogen? And by how many pounds?

• Fresh organic matter added = 2560 lb.
• Carbon content of organic matter= 55%
• Carbon: nitrogen ratio = 20:1

Step I

• The amount of carbon present in the organic matter added to the soil.
• 2560 lb. of fresh organic matter
  x 0.55 carbon content
  ———
  =1408 lb. of carbon in organic matter
  ———

Step II

• The amount of nitrogen present in the organic matter added to the soil.
• Fresh organic matter contains 1408 lb. of carbon and its C:N ratio is 20:1
• The nitrogen content of the organic matter is
  1408 lb
  = ————– = 70 lb
  20

Step III

The amount of C and N required for the microbes to form new tissues:

• As fresh organic matter is decomposed, the microbes use 75% of the carbon for energy and, the remaining 25% of the carbon is used to form their new tissue.
• To form their new tissue, microbes use nitrogen from soil or from the added organic matter.
• Microbes require 1 lb. of N for every 8 lb. of carbon as the C:N ratio of microbes is 8:1.
• Carbon content in fresh organic matter is 1408 lb.
• Of this one fourth is used for new tissue.
• The amount of carbon used by microbes for forming new tissue
• is ———- = 352 lb.
• The amount of nitrogen required by microbes to form the new tissues:
• Microbes require 1 lb. of N for every 8 lb. of carbon to form the new tissue.
• Therefore the amount of Nitrogen required for microbes using 352 lb. of Carbon is
  352 lb.
  = ———- = 44 lb.
  8

Step IV

Finally we compare the two nitrogen values. Fresh organic matter contained 70 lb. of N, and microbes used 44 lb. of N to form new tissue. The balance nitrogen available is = 70 – 44 = 26 lb.

This may seem confusing at first, but read it thoroughly a couple of times and it will begin to make sense. This equation is highly functional when speaking of adding Carbon to the soil. It is not however, effective at seeing the actual rates that microbes are using with synthetics. But we can make some assumptions and suddenly it will become clear as to why adding active biologicals (microbes, bacteria) and heavy nitrogenous products to the soil is not an effective way to manage fertility.

Because conventional fertilizers are not carbon based, the ratios of C:N do not work. However, the energy expenditure is the same. So, if you spread 44 lbs. of N to an acre of turf, based on the above workings, bacteria will consume 27.64 lbs. just to stay alive and this will be done quickly as it is so readily available. This leaves only 16.35 lbs. (assuming 100% realization) for the plants. Now, take what is speculated about leaching, volatilization and runoff, and the numbers begin to shrink rapidly.

Now, because of the function of conventional fertilizer and its ready to use form, most bacteria find themselves out of work. They will turn to whatever carbon is available and continue to digest that matter until OM has been reduced to nothing. This is why we see soils that have been under heavy fertility for a long time become hard, less productive, and in most cases have OM less than 1.5%.

Once the balance is out of whack, more nitrogenous fertilizer is needed to correct for the carbon deficiencies in order to keep production. William Albrecht professor of soils at University of Missouri says that in the last 60 years, there has been a 38% loss of OM on farmland. This is actually very interesting.  Roughly 60 years ago, Hybrid open pollinated corn was introduced. When this happened, yields jumped like crazy and the nitrogen was poured to the crop to keep up with demand. In 1991, another breakthrough… GMO. This led to even more nitrogen because the plants were sucking the ground dry. Corn remains the highest net N input crop on the planet, but if you overlay turf on those numbers… our industry is a very close second.

All of this adds up to one thing: management of Carbon MUST BE the role of all who work to maintain or cultivate plants. Without it, we are chasing our tails to recreate the beauty we once saw. In the lawn care industry 40 years ago, companies ran 3 step fertility programs, then 4, 5, 6, 12…. We spoke about how to capitalize on that trend, but it’s from a different angle. We don’t need to apply more and more fertilizer to get the results of a less often program. Typical fertility must have more and more applied to maintain the quality that customers and operators want to see. We want to see fluctuating levels of OM as time goes on. We don’t want to see it just decrease, or just keep increasing. Once a balanced level of OM has been achieved, especially in turf grass, a near self-sustaining system will have been created. This is what we are striving for.

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