No-till and nutrient stratification: Is it real? If so, is it a concern?

ARTICLE SUMMARY:  Dig into the science of a common assumption that nutrient stratification happens as a result of no-till practices and whether it has significant agronomic impacts.

We’ve all done it before… judged a new idea based on our preconceived notions. This is called a “heuristic,” or a shortening of the decision-making process to simplify our mental workload. Most of the time, it works well in keeping us safe from negative or even dangerous situations—as Virginia says in the TV show How I Met Your Mother, “Nothing good ever happens after 2am.”

But, there are also situations where heuristics hold us back, especially when we miss out on new, helpful information. In the case of no-till practices, I have heard farmers assume that no-till practices lead to nutrient stratification, and use this as a heuristic to stop investigating no-till practices altogether. Nutrient stratification is simply the concentration of crop nutrients in a band of soil, often at or near the surface, due to agronomic management and/or natural plant processes. By spending a bit more mental energy on research and investigation, you can find many positive reasons to adopt no-till practices and truly learn if stratification occurs and if it does, if it is actually a problem. 

The story around no-till and nutrient stratification provides an excellent example in four ways where further consideration past the heuristic proves quite helpful in making an informed decision:

1. Nature Moves Nutrients When we hear nutrient stratification, we assume farmers are the only actors. Don’t forget that plants find nutrients (isn’t that the idea of in-furrow or 2x2?) and can move nutrients through their systems and also organisms such as worms and fungi participating in the decomposition process can move nutrients throughout the soil profile. Similarly, soil biology can play a role in moving nutrients throughout the soil profile. Earthworms, in particular, can move plant residue deep into the soil profile while improving the nutrient content of the soil. So the combination of plants finding nutrients and earthworms pulling residue into the soil provides a natural process of moving nutrients into the soil profile, in addition to moisture moving many nutrients down through the soil profile. And, the healthier the soils, the healthier the soil biology—plants and animals—and the more effective at distributing nutrients. 
2. Stratification in Tilled Soils: It is mentally easy to believe stratification occurs in only no-till soils (after all, we’re not mixing the soil with tillage—another heuristic!). But how many growers have checked for stratification in tilled soils? Stratification can also occur in tilled soils, but since we don’t think it would be there, we don’t look for it.
3. Nutrient Uptake Efficiency: Don’t assume fertilizer placement is the only factor influencing plant nutrient uptake. Two other factors often influence fertilizer efficiency and use: moisture availability and soil biology. Research has found there may be a naturally higher fertility level on the soil surface when no-till is practiced, and crops in untilled soils are more efficient and effective in making use of the fertilizer through the presence of rhizobia and fungi that work with plant roots to increase the volume of soil from which plants obtain nutrients. A grower can attribute that fertilizer efficiency advantage to improved moisture management and higher soil biology from no-till.
4. Long-Term Data: Finally, we need to acknowledge some very obvious evidence: there are now thousands of long-term (20+years) no-till fields across the country, and their productivity clearly has not been significantly impacted by any nutrient stratification, and in many cases, their profitability is higher. If nutrient stratification were occurring at problematic levels, these fields would be showing signs in yield or plant populations. 

When it comes to considering a new practice to move your farm forward, keep in mind that heuristics might keep you from engaging in practices that ultimately improve your operation’s  efficiency, productivity, and profitability—especially when considering enrolling in a carbon program.