Les Henry: The fifth fertilizer R: nutrient balance

As the fertilizer industry focuses on 4Rs, let’s not forget that balance is important

In the fertilizer business, the 4R concept has received much attention in recent years. The idea is to ensure that fertilizer use decisions are based on selecting the right fertilizer, supplying it at the right rate, at the right time and with the right placement of fertilizer.

The first three Rs go back over 40 years. The first Grainews column I ever penned was based on nitrogen: the right source, the right rate to apply and the right time. The fourth R, right placement, came about when John Harapiak of Westco Fertilizers showed that the difference in crop yield between deep banding and broadcasting urea was enough to pay for the fertilizer.

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The concept is valid, but it does not mean that there is one recipe that fits all situations. We seem to be living in a time where appearance is the order of the day and we must all appear to be sustainable. The 4R concept has been used that way. If a seminar of a few hours is sufficient to provide a stamp to put on your place of business to certify that you are “sustainable” it creates doubt about the process.

The 4Rs are important, but the fifth R, right balance, might be even more important.

Let me acknowledge that the idea of a fifth R is not a credit to me. I first heard this idea from colleague Jeff Schoenau, professor of soil science at the University of Saskatchewan. Many Grainews readers will have heard Jeff speak — he is a very knowledgeable and popular speaker at farm events.

Canola: nitrogen and sulphur

One of the first and most dramatic nutrient balance situations I encountered was with nitrogen and sulphur for canola. Data showed that the more nitrogen poured on canola the lower the canola yield. Pour on enough nitrogen and there was no seed yield. In early days it was not known what a pig canola was for sulphur. Put on some sulphur with the nitrogen and yield shot up. Balance was the issue.

I first saw the N/S balance problem on my Dundurn farm in 1999. An application of sulphate fines with a good rain a day later saved the crop. Since that time there has not been an acre of canola planted in our area without sulphur fertilizer.

Fertilizing bromegrass

The AAFC Research Farm at Scott, Sask., (particularly researcher Harry Ukraintez) did many years of detailed fertilizer work with bromegrass both for feed and seed. Early work showed that grass was not really responsive to phosphorus, but it responded very well to N. But, when hay yields were increased to high levels by nitrogen, then the grass became very responsive to P fertilizer as well. Balance!

In reviewing data to support the above statement I also concluded that there are still many forage fields that are not really treated as a crop. That is a story for another day.

In Grainews in recent years I’ve written about “the new phosphorus story.” It has made me conclude that on many Prairie farms, including mine, the biggest limiting nutrient to higher yield goals is phosphorus. That leads me to my final story of balance.

An example of nutrient balance

The first water was spilled on the South Saskatchewan River Irrigation District in 1968 near Outlook, Sask. At first, almost all of the irrigation farmers were new to the game. They had spent their farming career realizing that rainfall was the most important variable determining how hard the trucker had to work in the fall. The thought was that pouring on the water would result in great yields.

Many were seeding stubble crops on a continuous basis for the first time. The standard fertilizer recommendation for stubble crops at that time was for 80 pounds per acre of 23-23-0 fertilizer. The water was poured on and fertilizer was applied. But the yield was very disappointing.

At that time, the University of Saskatchewan became involved. Much of my work for many years was doing the research to provide proper answers for fertilizer required to grow a decent irrigated crop.

We quickly learned that large rates of nitrogen were needed to accompany the water to be successful. By and by we had an experiment where grew a 65 bushel per acre crop of canola. Now, this was in the late 1970s when 30 bushels per acre was considered a good crop. The variety was Tower, one of the first canola varieties.

To achieve that yield we made sure that the water requirements were met and applied 100 pounds per acre of N at seeding time and an additional 100 pounds just before an irrigation on July 10. At that time, we still had the very best nitrogen fertilizer ever: 34-0-0, ammonium nitrate. It could be simply broadcast on the surface and would do a perfect job.

We also applied 20 pounds per acre of P2O5 with the seed. We did not want to go to a higher rate for fear of seedling damage. Based on that experience I concluded that canola could do quite well with a dab of phosphorus with the seed. A big mistake. Based on the evidence at hand it seemed a reasonable conclusion.

Forward to the 1990s

Some of the last field experiments I did were working with soil fertility challenges in irrigated agriculture. The irrigation allowed us to vary water and nutrients at the same time and take out much of the annual variation caused by Mother Nature. Despite having enough water and having enough nitrogen we were still not getting the yields that the genetics would provide.

One year we set a specific goal to determine what was really needed to grow 100 bushels/acre of CPS wheat. We put on the nitrogen at many different rates, at many different times and with several split applications and made sure that water stress was never a problem. Guess what? we still only grew 60 bushels per acre of CPS wheat (Biggar variety).

The next year there was an experiment to re-examine our phosphorus soil test benchmarks. We were lucky enough to find a site that was right next to the main irrigation canal but was still farmed half and half with wheat as the main crop. The phosphorus soil test was very, very low.

We set up an experiment with an irrigated block, a dryland summer follow block and the dryland stubble block. We applied 150 pounds of nitrogen per acre and enough sulphur and phosphorus to make sure that they were not limiting. The only variable was the amount of phosphorus.

Guess what? With enough phosphorus we grew 100 bu./acre of CPS wheat. (Well, call me a liar for two bushels because the actual was 98 bu./acre.) Despite that result, we were still a little slow to realize that we were really not using enough phosphorus for the crops we were seeking. Only in recent years is P back in the limelight as a major concern.

The future?

It is obvious that the question of balance must be a serious consideration in all we do with soil fertility investigations. Looking ahead, I think we need an ongoing, integrated, three-province, field-based program dealing with micronutrients. But, the details of that program are a story for another day.

About the author

Columnist

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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