Your Reading List

Should We Be Fertilizing Deeper?

I like to think of myself as an “out of the box” thinker. Nothing pleases me more than “connecting dots” that, at first glance, appear to be unrelated.

At our 2009 Agri-Trend Farm Forum Event in Saskatoon, I attended a fascinating session on controlled traffic farming in Australia and during this presentation, I had an “Ah-ha!” moment. The following, I hope, is an explanation of the convergence of issues, ideas and technology that comprised this particular epiphany.

The idea of using controlled traffic farming was dot No. 1. Controlled traffic farming (CTF) is all about managing soil compaction by confining it to narrow strips across the land and maximizing the remaining undamaged soil area for cropping. In practice, it means matching all machinery tracks so they take up the least possible area. When utilized in the right situations, CTF increased crop yield substantially, mainly because the water use efficiency (WUE) was dramatically enhanced. This also translated into better use of plant nutrients as well. When water is used more efficiently, so are the other nutrients a crop requires.

Dot No. 2 came from the understanding that despite this year’s unusually high rainfall, much of the Prairie crop production areas suffer from a lack of water. For example, water demand by wheat on the Prairies varies with year and location, but generally ranges from 11 to 14 inches per year. By comparison, growing season precipitation averages just six to nine inches, a shortfall of about four inches, which must be compensated for by soil moisture stored from outside the growing season or irrigation.

Dot three: A significant proportion of cropped acres also suffers from compaction that is either natural, induced by man or both. Approximately 30,000,000 Prairie acres are affected.

Dot No. 4: With the increased use of low-disturbance machinery, many soils are becoming more nutrient stratified with immobile nutrients concentrated in the top few inches while depleted at depth. An example (Figure 1) is potassium (K), where in most soils, especially direct-seeded fields, the crop available K is concentrated in the top two inches and the soil profile below four inches is well below the attention level for optimal crop production. Ask yourself, where is your crop’s root system actively feeding in the middle of July, after two to three weeks of heat? Phosphorus behaves similarly, as does organic matter, soil pH and most micronutrients.

So here’s my idea. What if we connected all these dots and minimized the man-made compaction with controlled traffic farming; added common-sense soil fertility; and coupled that with intelligent zero-till ripping of soils with machines that could also inject nutrients and/or soil amendments to significant depth? We could fix a lot of yield-limiting factors in one go. I think there is huge potential here and it warrants further investigation.


Before we go there, let’s look at some background reasoning. While I sat at the CTF presentation, I remembered a data set from an old study that I puzzled on years ago during my masters studies at the University of Alberta. Figure 2 is an adaptation of that data showing the average incremental yield increase attributed to subsoiling (24 per cent) and deep placement of moderate amounts of P2O5and K2O (an additional 20 per cent). It is important to note that this subsoil was not considered compacted. Over four years, the subsoiled with subsoil PK treatment grew 112 bushels per acre more barley than the surface fertilizer-alone treatment. The deeply placed fertilizer component contributed 50 bu./ac. more barley than the subsoiled only treatment.

Let’s think about those results for a few seconds. If you were a plant breeder and you had a variety that increased yields a fraction of these amounts you would, no doubt, be given the Nobel Prize for your good works, but if you are a farmer or agronomist who accomplishes this, you will be met with skepticism.

Now, if we connect these dots with the possibility of injecting nutrients to depth while a low-disturbance machine rips apart the compaction zone, then wouldn’t we have an amazing yield-boosting system? You bet! See the green oval at depth in Figure 1? That’s where we put the immobile nutrients. Imagine you are a plant suffering from heat and your roots hit this nutrient buffet. Imagine if there was P there as well, perhaps a yield-limiting micro (such as copper, for wheat) and maybe a bit of N for the late-season yield/quality push. What else could go here to get even more synergy? Depends on the field, but I’m guessing your brain is whirling around with possibilities. How about some S to create subsoil acid? What might that do? What else can we think of? I’m guessing lots!


Now before we all run off and start building machines to rip the entire farm, we need to think this through. In order for ripping to work, we need to know where the compaction layer(s) reside. Some of us have rocks to deal with. Some areas have high-magnesium issues; others high sodium while other fields have both. Sandy and clay textures are more vulnerable to compaction, therefore more responsive to ripping. It’s generally better to rip in the fall when the soil is really dry so that subsoil shattering is optimized but this can depend on the soil type. You need to consider the crop to be grown after ripping. You need to consider what nutrients or soil amendments should be placed at depth and how deep on which field and why and how and which products and, and, and… you get the picture.

Each farm and each field needs to be evaluated individually. Some fields may need ripping more than once, which gives us an opportunity to deeply place nutrients/ amendments, a second time. If you get it right, you should be able to fix things for many, many years.

The bottom line is, people around the world are playing with various aspects of this. Pick a couple of your most challenging fields. Determine if compaction is an issue and at what depth(s). You can accomplish this by using a penetrometer, moisture probe or by digging holes. Determine whether nutrient stratification is becoming an issue by soil sampling at incremental depths. Determine what soil physical and chemical factors are playing a role. Start gearing up with precision GPS and thinking about how controlled traffic farming might work on your fields. (Editor’s note:For more on CTF see our cover story this issue.)

In order to feed, clothe and provide energy for our growing population, we are going to have to take crop production practices to the next level. The same old, same old is not going to get us there. Go ahead — connect a few dots of your own. I’d love to hear your thoughts.

ElstonSolbergisasenioragri-coachand presidentofAgri-TrendAgrology

About the author

Elston Solberg's recent articles



Stories from our other publications