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Carbon: the mega plant nutrient

Nitrogen, phosphorus, and carbon dioxide? CO2 is at the heart of crop production

Closeup of a plowed field, fertile, black soil.

When teaching about plant nutrition the first step was to list the various categories of nutrients starting with major nutrients and ending with the micros. For this piece I’ll reverse the order and start with micros.

The typical nutrients


Micronutrients are required in small amounts and not often added as a fertilizer. But when a micro is limiting, it can put the lid on yield just as effectively as a nitrogen deficiency. Australia has molybenum deserts where a few ounces of molybdenum per acre will produce good pasture grass on barren ground. “Micro” refers to amount, not importance.

Micronutrients include: iron, copper, manganese, zinc, boron, molybdenum, chlorine and nickel.

Specific micros often have pet crops and pet soils. Wheat is a pet crop for copper deficiency which was well documented in Kenya as long ago as the 1950s.

Secondary Nutrients:

Secondary nutrients are required in moderate amounts and must be added as fertilizer occasionally. Calcium and magnesium are in this category. Many textbooks list sulfur as a secondary nutrient but in our canola country, sulfur is major.

Major Nutrients:

Major nutrients are required in large amounts and must often be added as fertilizer to meet the needs of many crops. These are the nutrients we deal with as fertilizer on a routine basis and include: nitrogen, phosphorus, potassium and sulfur.

The big one: carbon

Carbon, hydrogen and oxygen come from air and water. Carbon is required by plants in huge quantities; that carbon comes from CO2 in the atmosphere.

On a daily basis we are hounded by folks that treat CO2 as if it were a poisonous gas. To the contrary, atmospheric CO2 is at the very heart of all our crop production efforts.

In earlier geologic times atmospheric CO2 was much higher than now. Early plant life utilized the CO2 and released oxygen which allowed current plants to evolve. The low point for atmospheric CO2 was about the mid 1980s, and CO2 has been on the increase since then. The current global level of CO2 in the atmosphere is about 410 ppm.

All we hear about from most media is the negative effects. We are painted as being headed for a collision course with high temperature, drought, low crop production and starvation.

In searching for data on CO2 enrichment and crop yields I came across data assembled and analyzed by Murray Hartman, an oilseed specialist with Alberta Agriculture and Forestry. I contacted Murray and he kindly sent more info. His term for carbon is the “mega nutrient.” Thanks Murray, for the good work and for the info.

For many decades greenhouse operators have enhanced the CO2 inside their operations to increase their crop production. On a field basis, the U.S. corn belt contests for the biggest yield on one acre of land had farmers picking a low topographic area where CO2 concentrations may be higher.

Early attempts to measure effects of higher CO2 in field situations involved some type of cage which affected temperature and confounded the experiment. Recent work labeled as FACE (Free Air Concentration Enrichment) has overcome those problems.

Some such experiments suggest that a reduction of CO2 back to the mid 1800s level would lead to an immediate 25 per cent reduction in crop yields. Further natural enhancement could lead to a further 25 per cent yield increase. There is also good evidence that crop water use efficiency is improved by higher CO2, so there could be less drought stress when rains stay away for a while.

In the past decade we have seen crop yields we would not have thought possible not long ago. I remember a colleague who, in the 1980s, calculated that the genetic potential top yield of hard red spring wheat was 60 bushels per acre. Many farmers now get 80 or better on a field basis.

We pat ourselves on the back for the good agronomy. Greatly improved varieties and seeding technology, major inputs of fertilizer and good weed control have been an important part. Many high rainfall years and soils full of water also lead to full bins.

We must now give credit to the higher CO2 in the air our plants use in their food factory. If the yield bump is as big as 25 per cent it could mean that the 70-bushel canola yields must credit 15+ bushels to the higher CO2.

Global warmers and CO2

A recent study with enhanced atmospheric CO2 in rice plots has pointed out that the higher CO2 led to reductions in protein and things like iron and zinc. The study did not mention the large yield increase — it’s all about picking bad news.

Really, folks should realize that nutrient balance is important. If we juice up the yield with more CO2 and do not add more N then of course the protein will go down. The same thing happens when we irrigate. Can anyone imagine feeding the hungry world without irrigation in dry areas?

It seems that it is the flavor of the day to treat our biggest plant nutrient as an enemy. Our food production relies on CO2.

At meetings where I continually hear about how bad the future will be I ask two questions:

  1. What thermometers do they average to come up with a global temperature?
  2. Twenty thousand years ago, what is now Saskatoon was under about a mile of ice. It all melted and not a fossil fuel to be had. What force of nature resulted in that massive global warming event?

I have yet to receive an answer to those questions.

In the grand scheme of global CO2, Canada’s emissions are a rounding error at best. We could all drop dead tomorrow and release no more CO2 to the atmosphere and the world would not know the difference. This is not to say that we should not advance solar, wind and other renewable energy sources, but for many decades to come fossil fuels will keep our economic engine ticking.

Public research

The excellent data analysis and other canola data from Murray Hartman drives home the point that there is still a place for publicly funded research. That is particularly true for research that has direct application to farmers’ bottom lines. Keep up the good work Murray and others at the Alberta Agriculture research group.

About the author


Les Henry

J.L.(Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms at Dundurn, Sask. He recently finished a second printing of “Henry’s Handbook of Soil and Water,” a book that mixes the basics and practical aspects of soil, fertilizer and farming. Les will cover the shipping and GST for “Grainews” readers. Simply send a cheque for $50 to Henry Perspectives, 143 Tucker Cres., Saskatoon, Sask., S7H 3H7, and he will dispatch a signed book.



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