After my last post a gardening mentor contacted me with some suggestions on how I could improve my gardening practices (many thanks to my mentor!). As a result I’ve revisited the discussion on soil re-mineralization in Steve Solomon’s book The Intelligent Gardener (TIG), comparing it to the gardening method espoused by Ecology Action in the eighth edition of John Jeavons’ book How to Grow More Vegetables (HTGMV). In this post I’ll discuss what I’ve learned and how I will respond.
As part of my overall goal to grow a complete diet in a small area I have dedicated the last two years to developing a better understanding of my garden soil and its contribution to the goal. To do that I take soil samples at the end of the gardening season and have them analyzed for a range of major and minor nutrients and certain other parameters that affect crop growth. With the results from the analysis and using the information on soil mineral balancing in TIG I develop a plan to add organic fertilizers to the soil to address any deficiencies found by the soil test. By keeping track of how each crop that I grow fares over the course of the season and comparing that to how that crop fared before I began to re-mineralize the soil in 2013, I can determine what, if any, positive changes occurred as a result. I take the soil samples at the end of the growing season instead of shortly before it begins because my soil often does not thaw before early March, yet I should be planting spring crops as the month ends. Taking the samples in early March leaves insufficient time to prepare and mail them, have them run and receive the results, analyze the results to determine the soil prescription, and purchase and receive any needed fertilizers in time to add them to the earliest plantings.
The soil sample taken at the end of the 2014 gardening season shows calcium and magnesium at their target levels, compared to the deficiency of calcium and excess of magnesium found in early 2013 before two years of re-mineralization. In TIG Solomon notes that soil with a proper ratio of these two minerals has better structure. I felt that for myself when digging beds for the summer crops in 2014. Soil that had been quite sticky before is now easy to dig using an ordinary shovel and my middle-aged muscles. I can dig a 100 square foot bed in 1 1/2 hours versus around 4 hours before re-mineralization.
When my mentor contacted me I had worked out a fertilizer mix to re-mineralize in 2015. After sharing that information and the soil test results with him, he made some suggestions for my consideration. One of them was to add manganese sulfate to parts of the garden but not to others, to see if a deficiency in manganese relative to iron might be affecting certain crops.
The more important information he shared regarded nitrogen. As organic matter is eaten by the soil microorganisms, they release nitrogen in a form that plants can use. My mentor felt that many plants would grow better if they received more nitrogen than was present in the organic matter already in the soil and the compost and fertilizer mix that I had applied in 2014. Because I live in an area with hot summer days and nights, which leads to high microorganism feeding activity and rapid depletion of their food sources, the amount of cottonseed meal I included in the 2014 mix did not provide enough nitrogen for the needs of many crops. In 2013 I had added three quarts of cottonseed meal to each 100 square foot bed per the discussion in TIG. That at least doubled the amount of nitrogen available in each bed compared to using only compost, and yields increased in many cases. But I had been concerned about creating a dependence on imported nitrogen. In 2014, accordingly, I reduced the amount of cottonseed meal I added by 1/3, to two quarts per 100 square foot bed, while keeping the amount of home-generated compost constant. I noted that yields went down for many crops compared to 2013. My mentor suggested using four quarts of oilseed meal in the 2015 fertilizer mix as well as the 1/4 inch thick layer of compost that I normally add to keep nitrogen levels high enough for strong growth.
He also pointed out that because I have light soil (TCEC less than 10), meaning not much clay or humus present in the soil to hold onto the minerals that I apply to it, I might try side-dressing long season crops such as fall cabbage, tomatoes, sweet potatoes, and corn with another dose of the fertilizer mix every 6 weeks or so. TIG uses the analogy of clay and humus as the soil’s pantry. My light soil has a small pantry, insufficient to provide mineral meals to crops that remain at the dinner table for a long time. Occasional replenishing of the pantry will keep them growing strongly the whole season. Accordingly my mentor adjusted the quantities of soft rock phosphate and potassium sulfate for the 2015 fertilizer mix about 1/3 lower compared to what I had calculated. Lower-demand, short-season crops should still receive enough minerals to yield well. The long-season, higher-demand crops will get what they need with the extra dose of minerals and nitrogen from side-dressing. Assuming all else is equal, therefore, I hypothesize that by using the modified complete fertilizer mix on all beds and adding another dose to the long-season crops about 6 weeks or so into their season, yields of most crops, especially the long-season, higher-demand crops, should increase in 2015 versus 2013 and 2014.
HTGMV’s gardening method, which I had attempted to follow for over a decade, emphasizes growing grain crops in about 60% of the garden space. The grain crops provide two yields important to the method: the straw, which provides the carbon needed to produce enough compost to spread a layer 1/4 inch deep on the entire garden, and concentrated calories for the gardener, in the form of the seed grain. The grain crops, as well as special root crops that yield well and have a high amount of calories for their weight, form the backbone of a garden grown according to this method. HTGMV emphasizes this calorie gardening and its focus on increasing the weight per unit area obtained from these crops because of its concern with increasing human population and decreasing area of farmlands. Growing a higher yield on a smaller area addresses both of these concerns.
When I read the material on potassium in TIG, however, I began to wonder if HTGMV’s method might have a flaw that they do not acknowledge. TIG points out that the least expensive way to increase agricultural yields is to increase the amount of potassium in the soil relative to the other minerals that plants use. A potassium-rich soil can grow plants with high amounts of the carbohydrates, sugars, and fats that provide calories. However, other minerals are required to make the proteins, enzymes, and vitamins that we need for optimum health. In Solomon’s opinion, if potassium is just a little bit scarce relative to the other major and minor plant nutrients, the yield (weight per unit area) of the food grown will be somewhat reduced, but the plants will make the highest concentration of nutrients in proportion to the calories they contain. Hence he targets for less potassium relative to the other nutrients in order to grow nutrient-dense food. Nutrient-dense food, he feels, makes for healthier people, so he is willing to trade off some yield in order to grow the most nutrient-dense food that he can.
A goal common to both gardening methods is to build and maintain what each considers to be the proper levels of and balances among soil minerals. To do that you need to know what the levels of the various minerals are and, if they are not in balance, how to safely move them in that direction. Accomplishing this goal begins with collecting soil samples and sending them to a soil testing service. Gardeners often submit soil samples to their state extension service, but extension services typically provide only a restricted amount of information on the minerals in highest quantity. Thus both HTGMV and TIG recommend dedicated soil testing services for soil mineral analysis. Timberleaf Soil Testing, the soil testing service recommended in HTGMV, requires the purchase of two different test suites on each sample, the Basic Soil Test and Trace Mineral Soil Test, to obtain levels of all the minerals tested for by Logan Labs, the testing service recommended in TIG, at more than twice the cost of testing done by Logan Labs. The Basic Soil Test that you must buy from Timberleaf includes several other kinds of tests that are not mentioned in TIG or done by Logan Labs, one factor in the increased cost. Another part of the increased cost is accounted for by Timberleaf’s also providing some individualized information on what kinds and how much fertilizer to use to bring the soil into balance as well as individualized information related to the parameters they test for that Logan Labs does not. Logan Labs does not provide any soil information beyond the levels of the minerals, the soil pH, the organic matter level, and the TCEC, nor does it provide information on how to remedy the deficiencies in the cost of its basic test. However, someone who wants to follow the re-mineralization program in TIG but does not feel confident enough to convert Logan Labs’ soil test results into amounts of fertilizer to use to remedy deficiencies can subscribe to OrganiCalc at $9.50 per year to obtain that information. Put the cost of Logan Labs’ soil test and a one-year subscription to OrganiCalc together and you have still spent less money than the equivalent tests and information from Timberleaf.
HTGMV and TIG differ in the depth of their discussions of soil fertility and the range of potential materials with which to remedy patterns of deficiency and excess. The discussion of soil fertility in HTGMV is brief and sketchy, compared to the extensive and detailed discussion in TIG. HTGMV does not discuss what the target levels of each nutrient should be and that information is not provided on Timberleaf’s website, while TIG discusses two different sets of mineral targets and why a gardener might choose one over the other. Further, compared to the wide range of potential nutrient sources given in TIG because of differing soil types and resultant patterns of mineral deficiencies and excess, HTGMV offers a very restricted range of nutrient sources to remedy deficiencies. Many organic fertilizers that were recommended in earlier editions of HTGMV are no longer recommended “because of potential problems with disease, pesticide residue, or heavy metal toxicity” (page 74). Unfortunately, that leaves out inexpensive and readily available sources of organic nitrogen such as oilseed meals and a wide range of fertilizers approved for organic farms to address differing soils and their needs. TIG acknowledges that oilseed meals from conventional farms may contain traces of pesticides and may be produced from genetically engineered seeds. All of us need to examine the various factors pertinent to each fertilizer material that might be appropriate for our soil and make the best choices we can from the limited information we have available. TIG prefers to offer a broader range of potential fertilizers, allowing us to weigh the choices involved and then make our own decision on what to use.
Suppose we find that we need to import a range of organic fertilizers and oilseed meal to up nutrient levels enough to grow nutrient-dense crops as described in TIG, or the more restricted range of fertilizers and nitrogen sources that HTGMV recommends to fulfill whatever its soil mineral target levels are. Both methods have as a goal importing the fewest resources from outside the garden and say that following their method will move garden soil in that direction over a period of years. Both methods have as a goal growing good yields of high-quality produce. Is there a basis for making a choice between them? I cannot give a definitive answer to that question although the discussion above highlights some of the factors that I think are relevant to that choice. As I’ve noted before, I only had one soil test done on my potential garden space in the decade I’d been gardening it before beginning re-mineralization. While I’d been following various aspects of HTGMV’s method, I had not done it as rigorously as they suggest; I never followed all the steps in the same year. I haven’t used Timberleaf’s soil testing services so I don’t know how its target levels and results might differ from Logan Labs’ and TIG’s. What I do know is that after over a decade of imperfectly following HTGMV’s method, yields were declining in many cases and none were increasing. Insect pressure and disease problems were increasing for some crops. After two years of following TIG’s method imperfectly (not giving long season crops sufficient nitrogen), insect and disease pressure has declined and yields have stayed the same or increased.
Ecological sustainability, a concept at the heart of HTGMV, needs to be understood in the broadest possible way. Focusing too intently on growing the most food in the smallest possible space as the answer to the problem of increasing human population and decreasing farmland area may not allow us to consider how everything interacts to produce that food and the impact that food has on our health. For instance, if we are producing less nutrient-dense food as a result of focusing excessively on increasing yield (weight per unit area), we may need to eat more of that food in an attempt to obtain the nutrients we need. If that’s the case, even if someone following TIG does not obtain as high a yield as someone following HTGMV, the latter may find she needs to increase the size of her garden in order to eat the same amount of nutrients as is produced by someone following TIG’s method on the same soil.
Considering the discussion above, I plan to optimize yield and nutrition by following TIG’s method as well as I can over the next several years. TIG suggests that as the soil minerals approach closer to the target levels, it might be possible to greatly reduce outside inputs while maintaining mineral levels and balance. After just two years I have been able to reduce additions of calcium and sulfur. As I learn how much it will be possible to reduce inputs to my own soil I will also gain enough information on yields obtained from this method to begin to sketch out minimum-area garden plans that will work for our soil and climate. And, of course, I’ll post what I learn here.
Discussions of garden methods have their place — and so do concrete plans. In the next post I’ll discuss the concrete details of new tools, new procedures, and new crops for the 2015 garden.