Getting a handle on nitrogen - the elusive nutrient

Friday, April 8, 2016

Nowadays, N is inexpensive and is used too widely and too freely. We must continue to try and get a better understanding of what N requirements are

by PAT LYNCH

Nitrogen (N) is everywhere and that is part of the problem. The air we breathe is 82 per cent N. The water we drink contains N and sometimes there is too much of it in the water. We need N to grow all crops.

At the start of the 20th century, humanity was facing global disaster. Mass starvation, long predicted, was about to happen because of lack of N for crops. Land was being cleared and all the available N was being used. Then came the discovery of guano, the excrement of seabirds and bats. Guano was found on the Chincha islands off the coast of Peru and became a major input for modern agriculture. Then, when they realized that this resource would come to an end, the soothsayers again predicted the world would starve.

Pressured to find a solution, two German scientists, Fritz Haber and Carl Bosch, discovered how to take N from the air. At first, N was used to grow crops. But N was also needed to produce munitions for the war. After the war, the plants were turned back to producing N for agriculture. Today, the basic principles of the Haber-Bosch process are still being used.

Nowadays, N is inexpensive and is used too widely and too freely. There was a time when growers never wanted to run out of N when growing a crop. So we applied more than enough to accomplish this. Those days are over. The algae blooms and problems with N runoff in rivers like the Mississippi are drawing attention to N use. Excessive levels of nitrate in drinking water are a concern.

To this end, there is increased focus on delayed applications, multiple applications and N extenders. Some believe that the aim of these practices is to give higher yields. That is only partly correct. The bigger reality is that it will lead to better yields by better use of less N.

The most accepted way of improving N efficiency is to do later applications. Using a base of 30 pounds per acre and then coming back with a later application has been a standard practice. These applications are either incorporated in or used with an "extender."

There are numerous N extenders. They work by delaying the transformation of N to a form that is easily lost to the air or ground water. Loss to ground water is more significant than loss to the air.

While there are a lot of unknowns, we do believe we know some things about N. First, in corn, side dress allows you to use less N than pre-plant while getting the same yield. Second, the use of N extenders keeps N from being available for a time. The length of this time is very dependent on weather and soil conditions. Third, higher yielding crops need more N.

There are some things that we think know. Soil type makes a difference in the quantity of N needed for top yields and higher organic matter levels help to hold residual N. That is why using a cover crop to build up organic matter is important.

There are also some things we know we do not know. Release of N from the soil is a huge variable and can account for 50 per cent or more of the N a crop uses. Think of the soil as a big chemical vat with numerous microbes, larger organisms, living and dying, and being influenced by soil reactions that change pH and availability of numerous nutrients. This great big vat is extremely influenced by soil temperature and moisture. And this is why we still have not figured out N needs. In Ontario, with such year-to-year and day-to-day variations in soil moisture and temperature, we do not have a good handle on N requirements.

But that does not mean we should give up. We must continue to try to resolve what our N requirements are. If Haber and Bosch had given up because so many people said we couldn't solve the problem of extracting N from the air, then indeed the world might have faced extreme food shortages. And we will find a way to economically extract N from water. BF

Consulting agronomist Pat Lynch, CCA (ON), formerly worked with the Ontario agriculture ministry and with Cargill.