Wednesday, April 24, 2019

2019 garden science: homegrown nitrogen

Dogwood blooms, trees leaf out: spring!

In the last post, I discussed how the 2018 garden responded to my poorly phrased question about using wood ashes in place of some of the purchased soil amendments that I have used in past years to balance the soil, following the program in Steve Solomon’s book The Intelligent Gardener. I also used wood ashes in a few other beds in 2018. Of these, the most interesting story features the garlic and potato onion bed. For this bed I added enough wood ashes to provide all the potassium needed for 2018 (about 7 pounds of ashes for the 100 square foot bed area). Besides all of the potassium, this amount of wood ashes supplied a little less than 1/3 of the phosphorus to add, and far more calcium and magnesium than the results suggested was needed to balance the soil. Although excess magnesium (compared to calcium) is not desirable, I think there will be enough calcium added to keep the ratio in the desired range. I plan to test the soil in this bed after the onion and garlic harvest is completed in June, to learn more about the effect on the soil of adding such a large amount of wood ash – which was still within the Missouri Extension’s recommendation of 5 to 10 pounds of wood ash added per 100 square feet. And I’m eager to learn how much food I harvest! So far the plants look strong, with excellent winter survival.
 The allium bed: garlic in front, potato onions behind

While I worked on the previous post, and recalling that I hadn’t taken a soil sample in late autumn as I usually do, I decided to take a soil sample before planting most of this year’s garden and compare it to the previous several years of soil samples. Below is the spreadsheet of nutrient deficits for each year I’ve done soil sampling (the same one I put into the previous post), along with three other soil parameters that help to decipher some of the characteristics of soil. 

 Well, even if your eyes are glazing over, mine sure didn’t when I saw the spring 2019 soil results compared to those of previous years. In fact, I just about got up out of my chair and cheered! Read on to find out why. (For extra credit, take a moment to try to figure out why I was cheering before you go on. I’ll even give you a hint: it’s in the nutrient part of the spreadsheet and refers to a discussion about the soil in the previous post.)

First, before going on to the nutrients, let’s look more closely at the soil characteristics. Of these, pH and organic matter percent (OM%) are probably the ones you are most familiar with. The pH indicates soil acidity or alkalinity; a pH less than 7 is acid, 7 is neutral, and higher than 7 is alkaline. Most garden vegetables prefer soil pH to be in the range of 6.0 to 7.0, though potatoes do well at a slightly more acid pH. The pH of my soil has always been in the 6.0-7.0 range.

After I published the previous post, Chris asked me about what he interpreted as a reduction in organic matter level over the years. This gave me the chance to do something I should have done years ago: to think about the precision in measuring the OM%, rather than assuming the precision based on the number of significant figures in the reported result. Chris assumed, as I had, that by reporting the result for organic matter to hundredths of a percent, Logan Labs is implying that the precision of the test is in hundredths of a percent. (Precision is the degree of closeness of the results from multiple tests run on the same sample.) But when I re-read Erica Reinheimer’s and Steve Solomon’s 2014 revision to the worksheets presented in Solomon’s book, I learned that, in their words, “…OM% test results can vary widely, like 2X, when we send the same soil sample to the same lab.” 2X means a factor of 2: in other words, the 2019 OM% that Logan reported to me might have been as low as 1.5% or as high as 6% across different samples had I sent them multiple soil samples from the same garden!

Going back to the organic matter results across the years and keeping this low precision in mind, I notice that they are all in the 3-4% range, which Solomon suggests is about what can be expected in the US south of the Mason-Dixon line (about 39 degrees 43 minutes north). I’m about a half degree south of this line and our summers certainly quality as hot and humid. Thus I interpret the organic matter percent as remaining roughly constant over the years, to the precision of the test method. Since I’ve been adding the same volume of compost over the years, the rough equality of OM% makes sense. Unless I start making more compost so I can add more (or start making higher quality compost) and as long as I continue using Solomon’s method, the garden will likely continue to be tested at about 3-4% organic matter.

(Aside: in science, the precision of a test isn’t the same as its accuracy. Accuracy is how close the test comes to reporting the true value of what it purports to test. For the moment I’m assuming that the accuracy of the test for organic matter is good enough to fall within the precision that Reimheimer and Solomon suggest I can expect. But I don’t know if anyone knows how accurate it actually is.)

To continue, TCEC stands for total cation exchange capacity. That’s enough wonky-sounding words to make most peoples’ eyelids droop. Allow me to attempt to make some garden-level sense out of it, following the argument in Solomon’s book. Cations means positively-charged ions. In the table of nutrients, all but sulfur and phosphorus occur in the garden as positively-charged ions, and these are adsorbed onto the clay fraction of the soil. Thus TCEC correlates roughly with the amount of clay in the soil: in Solomon’s homey language, clay acts as a pantry from which more positively-charged ions can be drawn as garden plants take them up into their bodies. He suggests that a TCEC of about 10 or more correlates to a well-stocked pantry that doesn’t need any topping-up of more minerals during the growing season. My soil seems to have a TCEC of around 7 to 8, though I don’t know what the precision of the TCEC test method is. I’ve been adding humates to the soil in small quantities in an attempt to raise the TCEC, but so far to no noticeable effect. Solomon suggests adding more minerals after 8 weeks or so to gardens with low TCEC soil, but I have chosen not to do this. It would only be necessary for crops that stay in the ground significantly longer than that, which in my case is just the warm-season crops, and not all of these need it (tomatoes don’t, though it might be helpful for the others, and perhaps especially for greedy corn and disease-prone peppers).

As for sulfur and phosphorus, these occur as negatively-charged ions in soil, in association with organic matter, which acts as their pantry. Increasing the OM% would be one way to make better use of the sources of these nutrients, but as I mentioned in the previous post, without livestock to provide a source of OM beyond the limited amount I obtain from my compost piles and without a pickup truck to haul manure from close-in sources, the only other way I know to increase OM is to take beds out of production to grow green manures for a full growing season. So far I’ve not wanted to take this step, though I do allow winter-annual weeds to play the role of green manure and grow crimson clover on beds that I harvest early enough to allow it to germinate and grow enough to survive winter. Both of these are dug into the soil before growing the next crop.

Now let’s look again at the spreadsheet and pretend that we don’t see the results from the spring 2019 soil test. The soil required additions of phosphorus (the P in N-P-K) every year and sulfur every year but one. I add phosphorus as rock phosphate, which is a mined and refined mineral requiring considerable amounts of energy to prepare and transport. Solomon suggests that most of the phosphate I add isn’t immediately available to the soil, which may explain why it was deficient by about the same amount every year. Wood ashes also supply some phosphorus, but I cannot add enough to resolve the full deficiency without throwing other minerals like potassium out of balance. Sulfur, on the other hand, is available in the form of gypsum, the common name of calcium sulfate. Since the closest gypsum mine is in Kansas and it is needed in much smaller amounts than rock phosphate, I’ve been less concerned about using it. Wood ashes may provide a good substitute source of potassium, which I’ve needed to add most years, pending the results from the bed of onions and garlic and any further testing I may want to do. Calcium is of little concern: besides being included in gypsum and in wood ash, there is a large limestone quarry within 10 miles, thanks to the Missouri of long ago having been at the bottom of a sea. Thus, before the 2019 soil test, I had resigned myself to always needing to apply a source of phosphorus, with most of that needing to come from outside of the yard, while I had a possible alternate source for potassium and calcium at hand in wood ashes should the commercial sources I use become too expensive or difficult to obtain.

Now let’s take a good look at the spring 2019 results. Please direct your attention to phosphorus, and note that it is in excess. Let me repeat that: phosphorus is in excess. That means that for the first time since I began the soil testing program, I don’t need to add the mineral that I had to use the highest weight of, which cost the most to ship and is one of the two mineral sources I was most concerned about becoming dependent on due to the high demands on it. Solomon suggests, on page 142 of his book, that once the phosphorus level builds to that required for the soil and the OM% is high enough, phosphorus may remain sufficient for a decade or two. Since I’m 62 now, the current phosphorus level might be sufficient for the remainder of the time that Mike and I will live on this land as long as I can keep the OM% at its current level or perhaps increase it a bit. And potassium, the other mineral source of biggest concern, is in excess as well. In 2019 all I need to apply is some gypsum (for sulfur and some calcium), oyster-shell lime (for calcium without magnesium, which is in excess), and borax, manganese, and zinc (all of which are added in tiny amounts).

Except for the cottonseed meal that I also add. And here’s where the post is going to get, well, earthy.

To step back, the reason I’m adding cottonseed meal is to supply an organic form of nitrogen. Actually, it’s not the cottonseed meal itself that the plants use. The meal needs to be converted into a form of nitrogen, nitrate (a negatively charged ion containing nitrogen and oxygen), that plants can use. Our friends the soil microherd (everything from bacteria up through earthworms) do this by eating and excreting the meal and/or each other, gradually releasing nitrate into the soil where it can enter plant roots. The microherd becomes more active as the weather becomes hotter, which follows the plant growth cycle. And yes, to answer the question that you’re no doubt asking yourself right now, the organic matter I add does the same thing, but it’s a much less potent source of nitrogen than the cottonseed meal is. Manures are also a less potent source of nitrogen; if added at a high enough amount to equal cottonseed meal, they can bring too much salt into the soil.

But there is a homegrown source of nitrogen at hand: urine.

Human urine is one of the most potent sources of nitrogen available to the gardener. According to Carol Steinfeld’s book Liquid Gold: The Lore and Logic of UsingUrine to Grow Plants, the N-P-K value of adult urine is, on average, 11-1-2.5. That’s more nitrogen than everything but bloodmeal and monoammonium phosphate on Solomon’s revised Acid Soil Worksheet. It’s almost double the amount of nitrogen in seed meal. There’s a catch: the N-P-K value of urine is calculated for the solids in urine only, not for liquid urine, which is 95% water, meaning I have to apply a lot more urine in both volume and weight than the cottonseed meal. On the other hand, there’s no shipping charge to making use of my urine, just the schlepping charge of getting it out to my garden.

Steinfeld tells us that an average adult excretes 11 grams of nitrogen in each day’s urine. For a 180 day growing season, that amounts to 4.4 pounds of nitrogen. The cottonseed meal I add to a single 100 square foot bed provides 0.36 pounds of nitrogen to the bed during the same 180 day growing season. This suggests that if I collect and apply all the urine I produce to the garden, I can supply nitrogen to ten 100 square foot beds – which is one more than the nine beds that need it. In theory, at least, I can supply enough nitrogen through my own urine to replace all of the cottonseed meal for the entire garden.

Before going on, let’s consider arguments against applying urine. The first issue is a health issue: urine can carry pathogens which can cause serious diseases. Steinfeld writes that urine, unlike feces, transmits only a few significant diseases: leptospirosis, schistosoma, and salmonella. Of these, she says that the first two are rarely encountered outside of an aquatic tropical environment, and the last is typically inactivated shortly after excretion. I live in the temperate zone,  unfavorable for the first two. The third seems like more of a threat considering that we hear of outbreaks of salmonella from contaminated foods from time to time. But those outbreaks usually arise from high densities of livestock, which is not the case in my yard. Furthermore, I have none of these diseases, so I cannot pass them in my urine – though if I do get sick, I will refrain from using urine until I’m well again.

Joseph Jenkins, the author of The Humanure Handbook, adds yersiniosis to the list of diseases that might be caused by pathogens in urine, and he includes E. coli in the list of pathogens potentially carried by urine, another pathogen that makes for occasional news headlines and is often linked to issues with high-density livestock facilities. But, again, I have neither of these, and I’ll use my urine only when I’m well.

Urine that enters surface waters will fertilize aquatic plants. If too much urine enters the water, aquatic plants may overgrow their habitat and die. The decomposition process requires oxygen; if too many aquatic plants die too fast, decomposition can deplete the water of oxygen that other organisms need, causing die-offs. Steinfeld writes that excess nitrogen in waters, from urine or from other nitrogen sources, can lead to blue baby syndrome. For these reasons, it is imperative to apply urine only to land well above the water table and far enough from any surface waters that it cannot enter them, and only on a scale in which the urine can be absorbed and used before it reaches any underground sources of water. Also, the soil should be well aerated, so that it supports the aerobic microbes that oxidize the urine to nitrates and make it available to plants. Since my garden is near the top of a hill and on very deep and well-drained soil, and because I garden organically to support the microherd, I can fulfill these conditions. If there is any standing water in the garden, I won’t apply urine until the soil can again absorb what I apply. This is very rare, occurring only when heavy rains have saturated the soil and then more rains fall.

To use the urine, I will first collect a day’s worth of it in a 2 quart/2 liter bucket. Then I’ll dilute it with water in a sprinkling can, apply that dilution to a garden bed, and follow it with another full can of water, to ensure that all the urine is absorbed into the soil and rinsed off any part of the plant that we will eat. Moreover, I’ll arrange it so at least one day passes before I harvest anything from a bed I treat in this way.

But the scientist in me would like to do a small-scale test of the power of pee before committing to a half year of liquid gold prospecting. And just as it did in 2018, the three beds of corn, dent corn this year, offer me the opportunity for just such a test. For this test I’ll apply the 2019 re-mineralization mix including cottonseed meal, humates, and kelp meal (for micronutrients) to one of the beds of corn as a control. For another bed, I’ll replace the cottonseed meal with urine, collecting the urine once every 10 days and adding it to the bed as above, and add all the rest of the components in the 2019 re-mineralization. For the third bed, I’ll leave out the kelp meal but use cottonseed meal and all the other components of the 2019 re-mineralization mix. It’s a long way from here to the seacoast, so it would be best if I can avoid using kelp meal in the garden. I’ll observe all the plants in all three beds, noting any differences from bed to bed, and keep the harvest from each bed separate so I can calculate that bed’s yield and compare to that of the other beds and to previous years. And so Year 2 of my multi-year project to reduce the need for added minerals and to source as many of any still needed as possible locally is underway.

Monday, April 1, 2019

Corny work: A garden science experiment and what I learned from it


As part of my work to encourage readers to learn and use the scientific method in practical endeavors like gardening, I discuss and interpret a test I devised to answer a question I asked the garden in 2018. It has it all – the original question, a belated realization that the design was flawed, difficulties experienced when I attempted to perform the experiment and the necessary re-boot, and the results that I got and what little I could learn from them. Read on to find out what I did and what all of us, including me, can learn from it!

For the past several years, I have tested the re-mineralization program described by Steve Solomon in his book The Intelligent Gardener. This post from 2013 describes my garden soil at the beginning of the re-mineralization program and the materials I added to it that spring. Since then I have been taking soil samples and, using the most current worksheet (available here), determining which minerals in my soil are deficient and which are in excess. The figure below shows each year’s excesses and deficits in minerals. The units for the deficits are pounds per acre.
Each year from 2013 through 2017 I added a nitrogen source (seed meal, which soil bacteria eat and excrete as nitrates that the plants can use). The nitrogen source ensures that there is sufficient nitrate in the soil for good plant growth; the compost I add isn’t high in nitrogen and we do not keep livestock whose manure could be used for this purpose. The soil tests showed phosphorus was deficient each year, so I added soft rock phosphate to supply that macronutrient. Most years I have also added a source of sulfur (gypsum), calcium (lime, oyster shell, and/or gypsum), potassium (potassium sulfate), and boron (borax) to remedy deficiencies. When the soil test indicated a deficiency, I added mineral forms of manganese, copper, and zinc.

After the 2017 growing season, with five years of garden data to hand, I had proven to my satisfaction that the re-mineralization program produced much better results than did my attempts to follow the Ecology Action program. The garden data from 2017 shows that the majority of the best yields for each crop and variety occurred in 2013 or later, even though most of the crops were grown at wider spacing than I had grown them before 2013.

Then I looked at the data in the figure above through the fall 2017 soil sample and considered what it told me about the soil and how it had changed over the years. So far I had needed to add multiple minerals to the soil each year, in accordance with the low TCEC of my soil (meaning I could not keep a large supply of those nutrients occurring in positively-charged forms – everything from calcium down in the figure – which is due to the low clay content of my soil). I also needed to add the negatively charged minerals, sulfur and phosphorus, which are associated with the organic matter in the soil. Because we have a hot, humid summer which includes rain during the entire growing season, it is difficult to keep a high level of organic matter in the soil, and thus difficult to hold onto these minerals over time. I would add more compost to raise the organic matter level if I could make more of it, but so far I have not been able to do so.

Since I thought I would need to continue adding some minerals each year unless and until I could raise the TCEC and the organic matter level of my soil, I wondered if there were other substances I could use to re-mineralize the soil that I could source for myself, rather than having to purchase them. While cottonseed meal, soft rock phosphate, gypsum, and potassium sulfate are still readily available and cheap, all of these materials come from someplace else. The rock phosphate and potassium sulfate are both depleting. If natural gas supplies become constrained, so will the supply of the ammonia used for fertilization on commercial non-organic farms, because natural gas is used as the hydrogen source in the Haber-Bosch process that produces ammonia. In that case seed meals may become a substitute nitrogen fertilizer for commercial agriculture, which could prevent me from obtaining it or raise the price past what it makes sense for me to pay.

The first material that came to mind as something I can source was wood ash. Whenever we burn wood in our wood stove we generate wood ashes, which we store in a metal trash can to keep any live sparks that could start a fire away from combustible materials. By spring 2018 the trash can was almost full of wood ashes. In order to be able to put ashes generated in the following winter into the trash can, we needed to do something with the ashes already in it. At about that time, the Missouri Extension published an article on recycling wood ashes as a garden amendment. While their opinion was that it was best used to decrease soil acidity (Missouri soils tend to be acid due to rain during the growing season), they also mentioned that it could be used to supply potassium and phosphorus, and they provided an average analysis of P (phosphorus), K (potassium), and Ca (calcium) for wood ashes: 0.9% P, 5% K, 23% Ca, and 2% Mg (magnesium). With this information I could calculate how much of my soil’s needs could be supplied by wood ashes.

I had another material in excess which contains some nitrogen (N) and P: worm castings from the worm bin. While I use worm castings in the potting soil I make for seedlings and container plants to add N and P, the worms produce more castings than I need. With this material also needing to be made use of, I searched the web for analyses of the nutrient content of worm castings. The best I could determine from the web search, worm castings on average contain about 1% N, 0.5% P, and no K. (Whether or not my castings match this analysis I don’t know; I chose not to pay for an analysis.) Worm castings probably contain some sulfur as well, but I could not find any information on their sulfur content.

Having decided on two materials I could use for part of the re-mineralization formula, I thought about how to determine if using them instead of the purchased amendments would be effective for re-mineralization. If I wanted to do a proper experiment, I would need to include a control area where I used the usual ingredients as well as an experimental area where I tried their substitutes. The best choice was the three beds of popcorn I planned to grow in 2018. Thus, for all of the other beds except those growing beans and peas I used a mix with cottonseed meal, soft rock phosphate, dolomitic limestone (for the Mg as well as Ca), potassium sulfate, and borax for re-mineralization in 2018. For the three corn beds I could use that same mix on one bed as the control, with the other two beds available for the experimental mixes. Then I could compare the appearance of the corn plants as they grew and calculate the yields for each bed separately to determine the effect of substitution of materials.

(Why did I not use this same mix on the pea and bean beds? Because peas and beans have bacteria associated with them that supply their nitrogen needs, so I used only as much seed meal on these beds as I needed to get a good mix of the other ingredients. Those were used in the same amounts as for the other beds.)

Here I encountered the first issue in translating theory into practice. The experiment I wanted to do required four beds of popcorn: the control bed, with the same mix as the other beds; one bed with worm castings substituting for the seed meal but all other ingredients the same; one bed with wood ashes substituting for all of the limestone and potassium sulfate and some of the rock phosphate but all other ingredients the same; and one bed with both the wood ashes and the worm castings, with enough of the other ingredients to make up the remaining deficiencies. But I planned to grow only three beds of corn and did not have room to add a fourth bed. Furthermore, one of the three beds was a newly formed bed that had been planted at different times to asparagus and raspberries and, most recently, had contained weeds for a few years. I hadn’t taken a soil sample from that bed so I didn’t know how similar or different it was to the rest of the garden. After much thought, I decided to re-mineralize the reclaimed bed as if it had the same set of deficiencies and excesses as the grassy areas surrounding the beds, which I sample each year as controls along with the garden soil. In that way I could test it against the control. In the remaining bed, I used both the worm castings and the wood ashes and enough of the other ingredients to make up the remaining deficiencies, based on the fall 2017 soil analysis in the figure.

In retrospect, I realize the flaw in my design: if the yield in this bed were different from that of the control bed, I would not know which of the two substitutions was responsible for that change. Rather than trying both wood ashes and worm castings in the remaining bed, I should have chosen to try only the wood ashes. I allowed my desire to find a place for the excess worm castings to overcome my scientific judgement, when I could have added them to the compost pile instead. As my mother would say, live and learn … which you’ll notice in future garden science posts.

Beyond this theory-level flaw, I ran into difficulties I hadn’t anticipated when I attempted to prepare the mix with worm castings and wood ashes. While I usually apply compost and the re-mineralization mix separately and then cultivate the soil a few inches deep to mix them in, the castings were so wet that I thought it would be preferable to mix them with the compost and wood ashes and then spread the mix. However, the mixture proved to clump together unevenly and the mixing step took far too long to be practical.

This is where I should have taken a deep breath and dropped the worm castings out of the experimental design altogether. But, still being determined to include them, I persisted long enough to drop clumps of mixed worm castings and compost over about 1/6 of the bed area before I gave up on the castings as too heavy and wet to work as a practical nitrogen source in garden beds.

That left the wood ashes. Until I worked with them, I didn’t realize how light and fluffy they are; I couldn’t mix them evenly by hand with the rest of the ingredients. In the end, I cast the wood ashes, compost, and re-mineralization mix with seed meal onto the remainder of this bed and worked it into the top few inches of the soil as I normally do. For the part of the bed with the castings, I added the proper amount of wood ashes and remineralization mix without seed meal before cultivating it. After preparing the control and newly formed beds as I mentioned before, I added popcorn seeds to all three beds on the same day and then cared for each bed in the same way. When I harvested the ears of popcorn, I kept the ears from each bed together so that when I shelled and weighed the popcorn, I could calculate the yield, in pounds per 100 square feet, for each bed.

What were the results? First, I didn’t notice any visual differences between the plants in any of the beds until the ears of corn were ready for harvest. By that time, it looked as if there were more and larger ears in the control bed than in either of the other two beds. I didn’t see any difference in pest or disease pressure among the three beds, or any difference in plant color or height except near the end of all three beds that is partially shaded by hazelnut shrubs and is attributable to that shading.

The yields of popcorn I obtained for the three beds were as follows:

Bed 10 (control): 9.0 pounds per 100 square feet
Bed 11 (wood ashes and worm castings): 5.7 pounds per 100 square feet
Bed 12 (mix for lawn areas): 6.1 pounds per 100 square feet

I can’t do any kind of statistical analysis on the data because I didn’t set up the experiment to allow for that. But based on the results I obtained, it appears that the yield of the control bed was higher than that of either of the other two beds. The problem is, I don’t know if the yield of the experimental bed was lower because of the change in the re-mineralization ingredients, or because of the practical difficulties I encountered working with the wet worm castings and the fluffy wood ashes. And if it was the change in ingredients, I don’t know which one was responsible, or if it was an interaction between them. As for the third bed, since this is only its first year being re-mineralized and I don’t know if I used the right mix for its soil, I’m not surprised that it seems to have produced a lower yield.

There you have it: a real person doing a real experiment, experiencing real difficulties and doing her best to understand the message in the results. And it’s something any of you could have done as well as I did; it only required a good grasp of fractions and percentage, and a basic understanding of the scientific method. Tune in to the next post to find out where I’ll take my quest to use home-grown ingredients for re-mineralization in 2019!