GROWING FOOD
| Soil testing (click here for larger view) - The Good, the Bad & the Really Ugly (11:09) Michigan State University Extension Horticulturist Gary Heilig discusses the role of micronutrients - and the danger of soil contaminants.Taking soil samples (click here for larger view) - A crash course in two minutes (2:00) A VALUABLE RESOURCE : Ph.D. candidate Bianca Moebius-Clune of the Department of Crop and Soil Sciences at Cornell University invites you to visit their Web site on soil health. "The Cornell Soil Health Test we've been developing will hopefully with time become a more and more useful tool for determining whether practices are sustainable. We just finished our second season of publicly offered tests," she wrote. The site also features a manual for download. |
How to build soils today for a sustainable future
by Bonnie Bucqueroux
What soil testing can tell you - and why you need to know
Sustainable farmers understand that healthy soils translate into healthy plants (and thereby healthy people). Yes, plants will often grow under poor conditions -- many plants will even grow in gravel if you supply enough nutrients. But a sustainable system depends on treating soils as a living resource that serves as the foundation of the sustainable cycle from the land to plants to animals (including us) and back again.
It is important to recognize that the condition of your soil today depends on the geologic legacy of the soils in your area, as well as what has happened to the land since. Both natural (erosion) and manmade (cultivation) forces have an impact on soil composition and fertility.
Fertile soils contain appropriate amounts of the nutrients and minerals needed to nourish growing plants, and soil testing is an excellent, easy and affordable way to learn about the current state of your soils. This knowledge then allows you to build a plan to improve your soils over time.
Standard and optional tests
Agricultural Extension offices in counties nationwide offer inexpensive and reliable soil testing. The standard tests offer information on basic nutrients in the soil, along with individualized recommendations to improve fertility. Ag Extension can also conduct other tests for extra fees. (There are also private companies that offer testing, analysis and recommendations.)
Soil testing provides can provide you information about primary nutrients, secondary nutrients and micronutrients:
- Primary - The three primary soil nutrients are N-P-K (N stands for nitrogen/nitrates - P for phosphorus - K for potassium/potash). Soil tests typically do not test for nitrogen, because the levels are too volatile, though you can order an optional soil test for nitrate levels. (Nitrate testing is usually taken at the end of the growing season. High levels mean that you may not need to add nitrogen the following spring.)
Standard soil tests do provide information on the levels of phosphorus and potassium/potash in your soil. The report will typically include recommendations for improving soil fertility, and you can ask to have the recommendations focus on organic solutions.
Fertilizers, both conventional and organic, list the levels of the major nutrients of N-P-K in the same order on their labels. For example, a potent organic bat guano fertilizer contains N-P-K of 4-13-1, while a popular organic fertilizer like North Coast's Pro Gro is only 5-3-4. (A commercial chemical fertilizer like Miracle Go in comparision offers 15-30-15.) Remember, however, that the goal is not to see how much of a nutrient you can pour onto your soil, but to create a sustainable system that promotes soil fertility as the foundation for the cycle of having healthy soils nourish healthy plants.
- Secondary Nutrients and Micronutrients - Soil tests typically provide information on the levels of the secondary nutrients calcium and magnesium, which are related to soil pH levels (see below). Agricultural Extension also typically offers testing for micronutrients such as boron (B), copper (Cu), Manganese (Mn), zinc (Zn), and iron (Fe), for an additional fee. The role of secondary nutrients and micronutrients is less settled ground (pun intended). While there is consensus that certain plants can require specific micronutrients (for example, broccoli needs particular levels of boron to thrive), the role of other micronutrients and phytochemicals has yet to be fully explored.
As Michigan State Extension Horticulturist Gary Heilig explains in the accompany video, composting all of your vegetable and fruit residue will add a variety of exotic micronutrients and phytochemicals to your soil, and thereby to your plants. (Click here for the larger view of the video.) Testing for salts [sodium (Na), chloride (Cl) and soluble salts (SS)] is not common, but if you have concerns about salinity, especially in arid states, it may pay to test for these substances.
Soil pH
The pH value shows where your soil falls on the 0-14 scale from acid to alkaline, where 0 is acid and 14 is alkaline (and 7 is neutral). Soil tests also include a CEC rating, which measures the Cation Exchange Capacity that relates to the potassium, calcium and magnesium levels in the soil, another indicator of soil acidity. Low ratings, typical in sandy soils, constitute a low soil pH (high acidity). High ratings indicate high alkalinity.
Different crops like different levels of acidity. While blueberries want a pH between 5.0 to 5.5, a crop like asparagus will not do well if the pH falls below 6.0.
Soil pH is affected by factors such as rainfall and the kinds of fertilizers applied. Strategies to lower soil pH include agricultural liming. (There are various kinds of agricultural lime, and Clemson offers a listing of terms, as well as some information on the laws for licensing of aglime suppliers in various states.) Raising soil pH often requires adding wood ashes. (Clemson Extension also offers a guide with in-depth information on soil pH.)
Soil structure and tilth
In addition to its chemical composition, you will also want to ensure your soils exhibit healthy biological and physical properties. As we learn more about the process by which soil transfers moisture and nutrients to growing plants, the more we understand that the cycle depends on developing soils whose structure enhances this movement from soil to plant.
Soil testing often includes testing for the percentage of organic matter as an optional additional test for a fee. However, such tests are not always a reliable indicator of overall soil structure and tilty.
Penn State's Agronomy Guide on Soil Management remind us that soil health depends on a long list of factors that include soil depth, soil texture, the amount of organic matter, cation exchange capacity, permeability and even soil respiration. The guide offers a specific test for soil tilth that involves putting soil in a sieve and dunking it in water, to see how well soil aggregates hold together. A less scientific approach is to take a handful of moist soil, squeeze it and see how well it holds together (or falls apart).
Perhaps the best bet is not to rely on testing but to embark on a plan for long-term soil improvement.
Soil testing as part of a sustainable approach to soil health
Soil is complex, living system, and this brief overview can only scratch the surface of our ever-expanding knowledge about what it takes to improve soil health. A sustainable approach focuses on long-term organic strategies to build up soil fertility and soil tilth. (Our Food for Thought section includes a number of historical documents from soil experts including this PDF of the 1938 article by the late Dr. William Albrecht on building up organic matter in the soil.)
Strategies to improve soil fertility and soil tilth often include:
- Composting - Compost is a rich source of organic matter for growing food. Not only doescompsoting add soil nutrients, but it improves the structure of the soil, which enhances the process of moving moisture and nutrients from the soil into the growing plants.
- The Rodale Book of Composting: Easy Methods for Every Gardener by Grace Gershuny and Deborah L. Martin receives uniformly high marks from readers who have used their methods.
- Vermiculture/worm composting - Worm castings are a tremendously rich source of compost. Good news also is that vermiculture (raising worms) is not particularly hard to do.
- Mary Appelhof has written a charming and comprehensive book called Worms Eat My Garbage: How to Set Up and Maintain a Worm Composting System. Amazon offers the Gusanito Worm Factory Farm Bin 5 Tray Stackable system. The five trays allow you to keep the red wigglers moving up the stack, as you add kitchen scraps to each upper tray to lure them to the top, making it easier to remove the worm castings they leave behind.
- Manure/ manure tea - You can add rotted animal manure directly to the soil, but it is usually so "hot" that it can damage plants, so you need to incorporate it into the soil in the fall for spring planting. You can also add manure to your compost pile. Another alternative is to make manure "tea." My dad used to fill a pilllowcase with rotted manure. He would tie the end of the pillowcase with a rope, so that he could suspend it in a garbage can filled with water. Beginning a week later, he would begin ladling out the "tea," diluting it with water to the color of a weak tea, which he would then apply directly to the plants' roots.
- Green manure cover crops - Cornell University offers a guide to planting and turning under various cover crops such as rye, clover or buckwheat as a way to build soil health. Timing varies depending on your location, so remember to check with county extension for best practices in your area.
- No-till - USDA's Natural Resources Conservation Service offers information on Backyard and Urban Conservaition that includes a PDF from Ugly Gardener Sheila O'Riley on a recipe for no-till gardening. Another handout from Sheila explains the concept as a way to compost right in your garden.
A last word about chemical fertilizers
While "sustainable" and "organic" are not always interchangeable terms, there is good reason to question the long-term sustainability of relying on chemical fertilizers.This article from the Oregon State University's Agricultural Extension Office compares the relative benefits and drawbacks of organic and conventional fertilizers, including how the slow release of nutrients afforded by organic sources can benefit plants.
Howver, there are also concerns about the harm that chemical fertilizers can wreak on the environment, particularly their role in climate change. The International Nitrogren Initiative warns that the dangers of the dangers that result from conventional agricultural practice of injecting anhydrous ammonia into the ground to add nitrogen, which allows much of the gas to escape into the atmosphere. An article in the British publication Telegraph notes that resulting "reactive nitrogen" produced by this practice (as well as the burning of fossil fuels) contributes to "the greenhouse effect, smog, haze, acid rain, coastal 'dead zones' and ozone depletion."
In terms of economic sustainability, a soil-building program based on organic material makes good sense. An article in the Southeast Farm Press notes that the costs of nitrogen fertilizer are rising dramatically, from 12 to 31 cents per ton for anhydrous. The article also notes that " takes 32 million cubic feet of natural gas to produce one ton of ammonia," which makes future cost increases inevitable.
An inexpensive investment in soil testing can help sustainable farmers make the long-term changes that promote continued soil health without relying on the problematic quick-fix that chemical fertilizers promise.
