Gone with the Wind (and Water)
Southeast Minnesota is a windy place. Never has this been more apparent to me than the last two weeks, when I’ve been driving through farm country, watching as the wind lifts snow off the flat, barren corn and soy fields and blows it across roads and up into the sky. The snow circling around in air currents is actually quite pretty to watch and aside from the danger that it can cause to motorists, does little harm to anything. But what happens when that snow melts and water rushes over the soil? Or when the soil dries out after the spring rains have come and gone, but the wind still blows strongly? [1] Unless there is something planted in those farm fields to hold the soil in place, the answer is no big secret: the soil washes or blows away , and in some cases, that soil can carry nutrients that were intended to help crops grow along with it. Unfortunately, those nutrients can add up to a whole lot of trouble.
Take my farm, for instance. My soil test results indicated that I bought land with excessively high levels of phosphorus and potassium. I have been unable to determine exactly how these levels came to exist, but as I wrote last time, that may be beside the point. What matters now, of course, is what these nutrients mean for the plants I intend to grow this year and for the broader ecosystem of which they are a part.
Phosphorus, nitrogen, and potassium are the three primary macronutrients that all plants need for healthy growth and maintenance. [2] Phosphorus is the primary energy carrier in plant cells and is an important component in cell membranes. Too little of it, and a plant won’t grow as vigorously. Too much of it will interfere with iron availability and decrease the uptake of copper and zinc, all micronutrients that help with photosynthesis, respiration, and other important cell functions. Weeds adore phosphorus and will proliferate wherever there is too much of it. That explains a lot; the sheer number of weeds that grew up in my lower field this past summer is enough to make any farmer shudder!
Potassium helps maintain a variety of plant metabolic activities, mostly by regulating water status, helping to transport carbohydrates throughout the plant, and producing cellulose, which is the main constituent of plant cell walls. Not enough potassium and you’ll see stem weakness, increased disease sensitivity, yellowing leaf edges, and lower quality and poorer taste of fruit. Fortunately for me, excessive levels of potassium don’t cause too much plant damage, aside from somewhat reducing the availability of calcium and magnesium. This is not ideal, but it’s also not the end of the world either.
Over time, I am told, my nutrient levels will diminish to a more reasonable level, and I should see fewer and fewer symptoms in my plants. But how they diminish is pretty important to know, too. Will it be by getting used up by the vegetables I grow, or by blowing or washing away somewhere else? (Recall that phosphorus binds to soil particles, so when my soil is on the move, so is the phosphorus.)
It would be best for everyone (except maybe for me), if my plants took it and used it up. Here’s why: my farm happens to be on the Zumbro River, which feeds into the Mississippi River, which feeds into the Gulf of Mexico. If the soil from my lower field were to blow or wash into the Zumbro right now, it would take some phosphorus with it. That phosphorus would combine with the phosphorus running off of other farm fields and lawns and golf courses [3] until it reaches concentrations that can cause some serious damage to our surface waters. [4] The plant aquatic life in waters with high levels of phosphorus is usually quite happy to see it show up; phosphorus is a plant fertilizer, after all. The problem arises when the levels of phosphorus are so elevated that they cause abnormally high production of algae and aquatic plants which, in turn, must eventually die and decompose. The process of decay requires considerable amounts of dissolved oxygen from the water, depleting the oxygen and reducing the amount of it that is available for fish and other aquatic species. These cannot survive without oxygen, and massive fish kills are observed year after year; thus, the term “dead zone.” In 2013, the dead zone in the Gulf of Mexico was the size of Connecticut, around 5,800 miles. It can be viewed from space. Not only is it a disaster for marine life, but it’s an economic problem, too, as the Gulf seafood industry was worth around $19 billion in 2011. Add problems from sediment pollution, also caused in some part from soil washing away into surface waters, and you can see why I’m a little worried about how much of my soil is finding its way down there.
So, what is a new and inexperienced farmer to do? It is REALLY windy around here. When the snow melts in the spring, waters rush through my land. There is no way that I can hold onto my soil and those nutrients without doing something, and the first thought that comes to mind is: cover up the land. Sure, keeping that excessive phosphorus here might cause me some trouble in the short term – I’m not kidding when I say I have a weed problem – but the long-term benefits of holding onto my soil more than outweigh the immediate costs. (And it is not necessarily a cheap or simple thing to plant a cover crop, as I’ll discuss in my next blog.) This is true, I think, not only on my farm, but downstream where other people are trying to feed their families and other species are trying to eke out a living. Aldo Leopold, in A Sand County Almanac (the book that started me on this sustainable food journey many years ago), wrote that what is good for the whole is also good for the individual, and it is this philosophy that I’d like to guide my work. It is clear that I will have to take the long view on things and figure out how my farm can play its own small role in healing the broader community of which it is a part.
By taking responsibility for my farm’s nutrients, I am deciding to take the hard road. The easy road would mean a bigger dead zone in the Gulf of Mexico and the only reward in choosing that path is that it’s easier. As painful and expensive as it surely will be, I guess I’d rather do something, however small that something might be. After all, no big problem has ever been solved except little by little.
[1] Of course, there are differences in how much snow and soil particles can weigh, and there is a wide range within each of these as well. Depending on how much water is in a snowflake, it can weigh more or less. Soil is composed of all sorts of different constituent parts with varying weights as well. These weight differences can impact how much and how easily snow and soil blow away. That being said, even if soil weighs more than snow in a particular instance (or even more generally), we’ve all seen the Dust Bowl footage and we know that soil is picked up and moved by the wind. Indeed, a simple internet search turns up a whole lot of academic and other fact sheets about how to minimize soil erosion by wind. For example, see this from the Minnesota Department of Agriculture.
[2] There are three other secondary macronutrients (calcium, magnesium, and sulfur) and eight recognized essential micronutrients (boron, chlorine, copper, iron, manganese, molybdenum, nickel, and zinc) as well.
[3] Although Minnesota has restricted the use of phosphorus on lawns, there remain exceptions to the rule.
[4] Nitrogen fertilizer runoff is also a big contributor, but according to the University of Minnesota, “of all cropland nutrients inputs, P (phosphorus) has been identified as the most important to prevent from reaching surface waters.”