The 2020 garden: further adventures with homegrown nitrogen

In 2019 I engaged in a conversation with my garden, asking it to answer a question I posed to it about the effect of using a homegrown source of nitrogen, aka urine, to replace the cottonseed meal that I had used in the past. A scientist would call my approach a simple application of the scientific method. As I related in the previous post, the conversation amounted to applying the usual re-mineralization mix, formulated to address deficiencies found in the March 2019 soil test and including cottonseed meal as usual as the nitrogen source, on one of the three beds of dent corn that I grew last year. This bed served as the control bed. For each of the other two beds of corn, I made one change in the planting conditions compared to the control bed: for one bed I replaced the cottonseed meal with urine but kept all the other components in the re-mineralization mix the same, for the other bed I used the same re-mineralization mix but planted three days later. When I harvested the corn, I kept the corncobs from each bed in separate locations and shelled each pile of corncobs separately, so that I could measure the yield of the corn that grew in each bed. I also made observations of the plants and the cobs in each bed during the growing season. This allows me to assess what the effect of that single change was on the yield and on any other observable changes among the plants in each bed.

Since I’m working with living plants in a living world, interpreting the results of such an apparently simple test really isn’t that simple. There are quite a few things that might not have been uniform between the three beds. And this doesn’t address more subtle differences, such as the fact that I knew which beds got which treatments, meaning it isn’t even a single-blind test. My hopes for what the test would reveal may have influenced the results. US society officially doesn’t accept that nonphysical causes, such as my thoughts, could have physical effects, but this has been shown to occur often enough in the medical field that only the double-blind test, where neither the patient nor the researcher knows who gets the drug or the placebo, is considered to provide reliable results. Beyond that, a host of other subtle effects are creating considerable difficulties in accepting the results of studies in the medical field. I mention this because I want you to understand why I consider the result to be more tentative than it may appear when you look at the data in the previous post.

Let’s look more closely at why I asked the garden about using urine as a home-grown nitrogen substitute last year. Cottonseed meal works well as a nitrogen source in my garden, and at the moment it’s readily available. And not even from all that far away; I’ve seen cotton fields in far southeast Missouri, and there are plenty in Arkansas just to the south.

But even though it works, and it’s readily available, it comes at a price. The price is most obvious when I pay for it, and when I have to haul the 50 pound bag of meal out of the car and into the basement. But that doesn’t account for other costs incurred in growing the cotton and getting the cottonseed meal to me.

Cotton demands a highly fertile soil. Without adding fertility, cotton-growing will render the soil it’s grown in infertile within only a few years. The fertilizer business demands a lot of diesel fuel and a lot of natural gas to produce the nitrate fertilizers the commercial growers use. (No, I don’t use organic cottonseed meal. There is so little organically grown cotton in the US that it’s prohibitively expensive to buy organic cottonseed meal.) There is more diesel fuel used to power the machinery that prepares, plants, maintains, and harvests the fields, and more used to process the cottonseeds into dry meal, and more to get that meal to me. All of that burned fuel adds to the pollutant load of the atmosphere and contributes to fossil fuel depletion. Any nitrate added to the fields over what the cotton needs to grow adds to the pollutant load of the rivers that drain cotton-growing country, most of which drain to the Mississippi River and eventually into the Gulf of Mexico, contributing to the dead zone there. If I could find a source of nitrogen that is closer to me and eliminates most if not all of the fossil fuel use and associated pollution, I would love to use it. And if in addition it is free and using it avoids a source of pollution, then what could be stopping me from using it?

As it happens, there is a free, local source of nitrogen in a form that plants can use, which requires almost no fossil fuels to collect and apply, and which avoids the more usual fate of that source, where it becomes a problem to solve. That source is urine. It’s free for the collecting and applying, which can be done in a low tech, nearly fossil fuel free manner. As long as I avoid applying more than the plants require for growth and I take precautions to keep it from running off into the local stream, it will be taken up and used and not cause pollution. As long as I only collect it when I’m well, it won’t have the potential to cause illness. Not sending that urine into the sewer system means that it won’t require energy to process before dumping it into the river, nor will any byproducts of that process pollute the river. And using it closes a loop which runs from the land to me and back to the land again. Animal urine is part of the nitrogen cycle that keeps Earth and its beings alive.

A simple calculation I did last year indicated that I generated enough nitrogen in urine to only need to collect and apply it once every 10 days to one corn bed to provide enough nitrogen for that bed for the entire growing season. Then I wanted to know if theory and the physical world are in agreement. Thus I devised and carried out the simple scientific experiment that I briefly described above. Corn is a particularly nitrogen-hungry crop, so if substituting urine for cottonseed meal works for corn, it should work in the rest of the garden as well. The data I collected suggest that urine was a successful substitute for cottonseed meal, with the caveats I mentioned above.

With this information in hand, I will expand the use of urine to the entire garden in 2020. Here I’ll discuss how I’m collecting and applying the urine, how much nitrogen an adult human produces in a day in urine, and how large a garden area that urine can supply nitrogen to.

I have already discussed health and environmental issues to be aware of when using urine. There is also a psychological issue which arises from the known health hazards of urine and from its association with feces: many if not most people consider urine dirty and dangerous and won’t want to eat anything grown with it. Urine is illegal to use on any food crops grown for sale because of the health and environmental risks associated with inappropriate use. If you were to consider using your own urine to supply nitrogen for your own garden (not that I am suggesting you should), you must first ensure that none of the food you grow with it is sold. Second, you must ensure that you yourself, and anyone who is eating the food you grow with it, knows you are using urine and favors its use. Informed consent is just as important in this case as it is in sex and medicine. Third, you must ensure you are applying the right amount, to avoid pollution of surface waters from any excess urine that cannot be used by the soil and the plants.

In my own case, my husband Mike and I favor its use, and I collect it only when I’m healthy. I use a plastic urinal such as are sold in pharmacies for collection (those of you with more exposed genitalia can collect it in any suitable container), dumping the contents into a larger lidded plastic container for storage. I pour the day’s collected urine (roughly 2 quarts) into a 2 gallon watering can and add water to fill the can. Then I sprinkle the contents of the can on whichever 100 square foot bed is to receive the previous day’s urine, following that with another 2 gallons of collected rainwater. The plastic urinal, storage container, and sprinkling can required some oil to make and to ship to me, but no more to use. Since I’m careful to apply only as much urine as the plants need, and I keep that urine out of the local sewage treatment plants, the urine turns a problem – nitrate pollution – into a solution – home-grown soil nutrition, which in turn feeds the plants I grow. The garden is surrounded by mowed grass paths and many square feet of unfertilized groundcover (a mix of lawn grasses and weeds) and trees beyond, so any nitrogen the garden or the grass paths cannot use will be absorbed and used just beyond the garden fence.

How do I know how much urine is the right amount to apply? First, I need to know how much nitrogen the plants I’m growing in the garden require. Agricultural scientists have done exhaustive experimentation to answer this question and produced tables like the one available here (page 8). A glance at the table shows that crops vary in their need for nitrogen, with potatoes and cabbages needing a lot more than, say, turnips. If I wanted to, I could calculate exactly how much urine I should apply to the area of each crop that I grow with the data in this table plus knowing how much nitrogen the average adult urinates in a day plus the square feet taken up by that crop. But in practice, I applied the same amount of cottonseed meal to each bed except for the potato bed, which received twice as much as the other beds. Since I know the weight of cottonseed meal I added to each bed and the percent of nitrogen it contains, I know how much nitrogen it added to each bed. Thus I’ll add the amount of urine that provides the same nitrogen as the cottonseed meal I used previously, except that I’ll add twice as much urine to the potato bed as I do to the other beds. In later years I will consider refining how much I apply according to the nitrogen need for each particular crop.

Here is the calculation I did in case you are curious about how you could do this in your garden (not that I am suggesting it, of course). From Steve Solomon’s book The Intelligent Gardener and the current version of the worksheets in the book, which you can find here, we note that the percent nitrogen in cottonseed meal is given as 6%. Since I know that I apply 6 pounds of cottonseed meal to each bed (12 pounds to the potato bed), the amount of nitrogen in the cottonseed meal is:

6 pounds * 0.06 = 0.36 pounds of added nitrogen to a 100 square foot bed

12 pounds * 0.06 = 0.72 pounds of added nitrogen to a 100 square foot bed of potatoes

In order to know how much urine to apply to each bed, I need to know how much nitrogen an adult human produces in that person’s urine in a day. Carol Steinfeld in Liquid Gold tells us that adult humans produce about 11 grams of nitrogen in a single day’s urine. Since there are 453 grams in a pound, if I divide 11 grams by 453 grams per pound, I will get the amount of nitrogen in a day’s urine in pounds: 

0.024 pounds of nitrogen excreted in urine each day

Now you need the length of your growing season in days; that multiplied by the amount of nitrogen in urine per day tells you how much nitrogen your urine can supply during the growing season. My growing season is about 180 to 200 days long. Using 180 days for my growing season, here is how much nitrogen I can supply to the garden if I collect it every day and apply all of it over the course of the growing season:

180 days * 0.024 pounds of nitrogen per day = 4.3 pounds of nitrogen

Above we found that each 100 square foot growing bed needs 0.36 pounds of added nitrogen, or 0.72 pounds if it is growing potatoes. If I divide 4.3 pounds of nitrogen by 0.36 pounds needed per bed, I know how many 100 square foot beds a growing season’s worth of urine will supply with enough nitrogen for good growth:

4.3 divided by 0.36 = 12 beds

I grow a total of 9 beds of vegetables and grains in the vegetable garden. Since the potato bed needs twice as much nitrogen as the other beds, then I need to supply the equivalent of 10 beds. I have 12 beds’ worth of urine, so I can supply all the nitrogen my vegetable and grain beds need over an entire growing season on just my urine. In my day planner I will keep track of which bed I add each day’s worth of urine to. In practice, each bed only needs urine applied when it has plants growing in it that haven’t been fully harvested, and I won’t apply urine any time the soil is soaked from rain, so I will add somewhat less than I have calculated above. I’ll keep track of yields as I always do and also observe each crop as it grows and make notes about any changes compared to what I’ve seen in past years. And I’ll report the results in 2021.

Besides this conversation, I’ll engage in some others. One of the questions I’m asking the garden in 2020 will be if it makes sense for me to direct-seed lettuce and some cabbage family crops in spring instead of growing and planting seedlings. Mike and I have been eating salads almost every day, but I haven’t been growing enough salad crops to supply anywhere close to what we are eating. I’d like to see if I can do better this year by direct-seeding and eating thinnings. I’ll try two separate sowings of these crops in spring, to see if I can prolong the spring salad season. I’m also trying to grow endive this year and some different varieties of crops than the usual ones I grow. And with that I’ll leave you till next month and wish you bountiful harvests in 2020!