As a farmer, it’s critical to know what pays and what doesn’t when it comes to your inputs. After decades of conducting on-farm research and soil tests, Marion has learned that surface-applied P&K fertilizer moves very little in the soil profile. Listen to learn what this means for the economics behind surface-applied P&K.
“For many many years, I was just buying fertilizer and I was a no-tiller so I just spread it on top of the ground. Every time I’d come to yield check the following fall I’d maybe spend $50 for fertilizer and I might get $25 worth of grain or I’d spend $100 for fertilizer and get $50 for the grain.
That doesn’t make a lot of sense, so I was questioning whether or not I really needed the fertilizer.
Then, going to conferences and hearing people talking about stratification. We’ve been no-tilling for 20, 30 years, 40 years and you get to thinking about it well phosphorus doesn’t move very far in the soil and neither does potassium, so the majority of what I was sprinkling on top was just staying on top!
The fact of the matter is corn roots were sucking it out of the soil profile faster than I could get it to move and replenish. So, we took soil probes and probed eight inches deep, and then we tested every two inches to discover what stratification might be occurring.
About 47% of the phosphorus 44% of the potassium is right in the top two inches and that’s the aha moment because during the summer when the corn plant needs phosphorus and potassium or during its entire life. As the soil dries, the top two inches of the soil profile dries out first. The conflict begins because that is where the nutrients are and moisture moves them to the roots. So almost half of my fertilizer is residing in dry soil and corn roots grow down not up and so I’m missing the boat. And, the corn plant suffers because of it.
As you move on down, we see less than 20 percent of it in the next two inches, the next two inches, the next two inches, etc. I was using fertilizer at the right rates, but I just wasn’t putting it in the right place. So, what I learned is that it is more important where you put the fertilizer than how much you apply. You can go to our website and you can get the actual numbers on stratification.
Our new philosophy now is we’re working on ways of being able to root-zone band the nutrients. As you can see in this little hole that we dug here that is eight-inches deep. Whatever method you choose, it’s most important to apply the nutrients down into the soil profile closer to the roots. So, the next growing season the nutrients will be below the corn plant, not above the corn plant.
So, to summarize, what I’ve learned is if i’m looking for an economic advantage from P&K, I’m going to struggle to get a return on investment when I’m surface applying, so I must incorporate it at the root zone in order to get a good return on investment.”
Academic Studies on Stratification
Nutrient Stratification in No-till Soils
by John H. Grove, Raymond C. Ward, and Ray R. Weil
Nutrient ‘stratification’ commonly refers to a distribution of nutrients that is non-uniform with soil depth, and especially to situations with higher concentrations of nutrients (such as phosphorus or potassium) near the soil surface. Nutrient stratification certainly does occur in agricultural soils, but is generally not a problem for plant nutrition, and is at times beneficial. Nutrient stratification has existed since soils began weathering and coming under the influence of terrestrial plants with roots. Nutrient stratification apparently was not an issue for the functioning or robustness of prairie or forest ecosystems, which endured and frequently prospered for thousands or even millions of years without any mechanism for redistributing nutrients other than biological processes and water percolation. However, in the minds of many agriculturalists the common assumption or implication is that soil nutrient stratification is inherently a negative attribute for crop production, and one which must be alleviated by deep fertilizer placement and/or tillage. This article will explore the evidence for or against this proposition, as well as reviewing the plant and soil processes involved in both the creation and mitigation of nutrient stratification.
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