Welcome back to this 6th, bonus, episode of “The Story of Nitrogen”! This episode is all about nitrogen fertilizers and how we decide what rate of fertilizer to apply to our ground. This is a question I and many others have tried to tackle in our careers, and one whose answers regularly surprise and humble us. This episode is also about another question, one which anyone can relate to regardless of whether they work in agriculture or not, one which every person will have a different answer to: “How good is good enough?” Interviewees: Emerson Nafziger, Fabian Fernandez, Paul Trcka

If you want to understand how nitrogen behaves in the soil, it pays to think about two things: water and time. These two factors control when and how much nitrogen can be lost from soil. They also help explain why some landscapes accumulate the nitrate form of nitrogen while others do not. Join us as we discuss how nitrogen moves through soils, how we can control its losses, and the surprising connections between nitrate, road salt, and nuclear testing. Interviewees: Hilary Dugan, Jeff Strock, Mike Castellano, John Barry

In the Midwest, most of the nitrogen our crops use comes from organic matter in the soil rather than the fertilizers we apply. The amount of nitrogen the soil provides can change dramatically from year to year, leading to added complication for farmers. Are there ways to help us predict how our soil management, and other factors like the weather, influence the nitrogen that’s available to crops? Interviewees: Mike Castellano, Lee Frelich, Tom Pyfferroen

Why do some creatures that live in the soil benefit from more nitrogen while others are harmed? This episode tackles the question of how soil microbes are affected by nitrogen fertilizers and how this in turn changes the way we need to manage our soil. Along the way, we get some help from scientists Bruce Potter, Chelsea Carey, and Sada Egenreither, a few bad wildlife analogies, and Lucille Ball. Interviewees: Bruce Potter, Chelsea Carey, Sada Egenreither

Many of our crops need less nitrogen fertilizer when grown after legumes, such as soybeans, alfalfa, or field peas. Legumes are plants that can take- or “fix”- nitrogen out of the air, where it exists in near limitless amounts, and add it to the soil. This ability to fix nitrogen is common in nature, in environments as diverse as fields, forests, lakes, deserts, and seas, and yet the demand for nitrogen by living things is often greater than the supply produced by nitrogen fixation. Why is this the case? We look at nitrogen in our water, forests, and cropland to get to the bottom of this fundamental question. Interviewees: Chris Filstrup, Nancy Rabalais, Mary Beth Adams

How does nitrogen shape life in environments as diverse as cropland, lakes, and oceans? Why does nitrogen increase the abundance of life in some places while decreasing it in others? And why do we sometimes consider these changes “good” or “bad”? We start to tackle these questions in conversations with experts on Minnesota lakes and the Gulf of Mexico. Interviewees: Chris Filstrup, Nancy Rabalais