1 hr 6 min

The Fallacy of Mainstream Potassium and Nitrogen Fertilization with Richard Mulvaney Regenerative Agriculture Podcast

    • Earth Sciences

In this episode of the Regenerative Agriculture Podcast, John interviews Professor Richard Mulvaney from the University of Illinois. Dr. Mulvaney is a prolific soil fertility scientist and researcher with many published papers relating to nitrogen and potassium uptake in crops. His work with Dr. Saeed Khan led to the development of the Illinois Soil Nitrogen Test (ISNT). John and Dr. Mulvaney discuss nitrogen uptake in crops, how soil should provide most of the needed nitrogen, and the fallacy that applying nitrogen builds soil organic matter. He also describes the “potassium paradox”, how significant amounts of potassium are available from the soil, and the damaging cycle that is created when applying potash. 
Nitrogen Fertilization (00:00:53)
Dr. Mulvaney began working in soil fertility in the 1980s with a focus on minimizing nitrogen fertilizer loss to increase crop uptake, specifically in regard to the isotope N-15. In collaboration with Dr. Saeed Khan in the 1990s, he found evidence that in some cases, fertilizer nitrogen on corn has no statistically significant response. At the time, most soil scientists were operating with the assumption that the optimal amount of fertilizer nitrogen is found by multiplying 1.2 times an expected yield goal, then deducting nitrogen credits such as a previous legume. In a project in Illinois studying on-farm plots, around 33 of 75 studied sites showed no significant response to fertilizer nitrogen, a finding inconsistent with the 1.2 method. The unfertilized yields, or check yields, were very high and not significantly increased with an application of nitrogen. Thus, Dr. Mulvaney hypothesized that the 1.2 calculation might not be as reliable as previously thought. Dr. Khan and Dr. Mulvaney conducted research to determine the difference between plots used in that study that were responsive and those that were unresponsive to fertilizer nitrogen applications. His wife noted that while soil scientists understand how carbon in plants is heterogeneous and decomposes at different rates, they assume that nitrogen is all the same. Examining the differences within nitrogen forms made clear that the plants at the non-responsive sites had sufficient levels of nitrogen available from the soil and so did not need nitrogen fertilizer applications. Using diffusion on the soil samples from the same study, they found that non-responsive soils were consistently testing higher in amino sugar nitrogen. 
The prevailing thought at the time was that fertilizer is the primary source of nitrogen for crop uptake, especially for corn. However, Mulvaney’s and Khan’s data shows that at least two thirds of the nitrogen in the crop at harvest is supplied from the soils, rather than from applied fertilizer nitrogen. In soils with higher amounts of amino sugar nitrogen, applications of fertilizer nitrogen are a waste of money because most or all of the nitrogen is supplied by the soil. It follows that measured soil nitrogen is only correlated with crop response to applied nitrogen when soil tests measure amino sugar nitrogen. 
The 1.2 method was developed from research trials on static plots. These corn plots received the same fertilizer treatments each year. On the unfertilized plots, corn used the nutrients from the soil with no nitrogen fertilizer added. Microbes will also use nitrogen from the soil to break down crop residues, depleting the following crop of nitrogen and depressing yields. The depletion of nitrogen resulting in depressed yields on the unfertilized plots makes the fertilizer effect appear more dramatic in comparison. Because the 1.2 method is based on static plots, it and its related assumptions are invalid when applied to farmer fields. Similarly, the assumption that one-third of the nitrogen will come from the soil is incorrect. In reality, two-thirds of the nitrogen is supplied from soils and only one third or less comes from fertilizer. These misconceptions have misled growers on

In this episode of the Regenerative Agriculture Podcast, John interviews Professor Richard Mulvaney from the University of Illinois. Dr. Mulvaney is a prolific soil fertility scientist and researcher with many published papers relating to nitrogen and potassium uptake in crops. His work with Dr. Saeed Khan led to the development of the Illinois Soil Nitrogen Test (ISNT). John and Dr. Mulvaney discuss nitrogen uptake in crops, how soil should provide most of the needed nitrogen, and the fallacy that applying nitrogen builds soil organic matter. He also describes the “potassium paradox”, how significant amounts of potassium are available from the soil, and the damaging cycle that is created when applying potash. 
Nitrogen Fertilization (00:00:53)
Dr. Mulvaney began working in soil fertility in the 1980s with a focus on minimizing nitrogen fertilizer loss to increase crop uptake, specifically in regard to the isotope N-15. In collaboration with Dr. Saeed Khan in the 1990s, he found evidence that in some cases, fertilizer nitrogen on corn has no statistically significant response. At the time, most soil scientists were operating with the assumption that the optimal amount of fertilizer nitrogen is found by multiplying 1.2 times an expected yield goal, then deducting nitrogen credits such as a previous legume. In a project in Illinois studying on-farm plots, around 33 of 75 studied sites showed no significant response to fertilizer nitrogen, a finding inconsistent with the 1.2 method. The unfertilized yields, or check yields, were very high and not significantly increased with an application of nitrogen. Thus, Dr. Mulvaney hypothesized that the 1.2 calculation might not be as reliable as previously thought. Dr. Khan and Dr. Mulvaney conducted research to determine the difference between plots used in that study that were responsive and those that were unresponsive to fertilizer nitrogen applications. His wife noted that while soil scientists understand how carbon in plants is heterogeneous and decomposes at different rates, they assume that nitrogen is all the same. Examining the differences within nitrogen forms made clear that the plants at the non-responsive sites had sufficient levels of nitrogen available from the soil and so did not need nitrogen fertilizer applications. Using diffusion on the soil samples from the same study, they found that non-responsive soils were consistently testing higher in amino sugar nitrogen. 
The prevailing thought at the time was that fertilizer is the primary source of nitrogen for crop uptake, especially for corn. However, Mulvaney’s and Khan’s data shows that at least two thirds of the nitrogen in the crop at harvest is supplied from the soils, rather than from applied fertilizer nitrogen. In soils with higher amounts of amino sugar nitrogen, applications of fertilizer nitrogen are a waste of money because most or all of the nitrogen is supplied by the soil. It follows that measured soil nitrogen is only correlated with crop response to applied nitrogen when soil tests measure amino sugar nitrogen. 
The 1.2 method was developed from research trials on static plots. These corn plots received the same fertilizer treatments each year. On the unfertilized plots, corn used the nutrients from the soil with no nitrogen fertilizer added. Microbes will also use nitrogen from the soil to break down crop residues, depleting the following crop of nitrogen and depressing yields. The depletion of nitrogen resulting in depressed yields on the unfertilized plots makes the fertilizer effect appear more dramatic in comparison. Because the 1.2 method is based on static plots, it and its related assumptions are invalid when applied to farmer fields. Similarly, the assumption that one-third of the nitrogen will come from the soil is incorrect. In reality, two-thirds of the nitrogen is supplied from soils and only one third or less comes from fertilizer. These misconceptions have misled growers on

1 hr 6 min