| From the pages of Kitchen Gardener Magazine Improving Clay Soils Dump on the organic matter, work it in over time, then leave well enough alone All my jeans have red stains at the knee. I go through gallons of bleach to get the red out of my socks, and my blistered fingers are tipped on Mondays with red from attempts to remove chunks of clay from the working end of my 12-pound mattock. But hey, when you live in the southern Piedmont, red clay is what you work with to "mold" a garden. It was worse in my old garden in Cotati, California. I was much taller in those days -- when it was wet, anyway -- because it seemed I always had a least two inches of sticky clay soil on the bottom of my boots. I believe I could have taken a saw and built an adobe dwelling from large blocks of clay hewn from that ground. Most of us are not blessed with a choice of soil. We're stuck with what we've got. And it seems like wherever I move, I get stuck with clay. By comparison to the clay in my old garden, the soil at my home now seems almost ideal. But it's clay nonetheless, and I've had to work diligently to upgrade the soil. Not that the soil isn't perfect (to be ecologically correct) for its intended use. My part of the county isn't called the Big Woods without reason, and the clay soil in my back yard will grow some awesome oak, maple, poplar, and hickory, without special treatment of any kind. But try to kick a spade into the ground, and you're asking for a sprained knee. If you face a similar problem, don't fret. Whether your soil has more or less clay than mine, so long as you understand what you're working with and keep at it over the years, adding organic matter and treating the soil structure right, you can get the better of clay soils and enjoy a productive kitchen garden. Clay is more promising than it's cracked up to be Before you try to manage the clay soil in your home garden, it helps to have a bit of background in soil mineralogy. The mineral fraction of a given soil consists of sand, silt, and clay particles. Clay particles are the smallest of the three, silt are intermediate in size, and sand, the largest. Clay particles, bound end to end and side to side in extensive planes, are stacked in a sandwichlike matrix and held together by electrochemical forces. This platelike stacking of horizontally arranged clay particles results in a large surface area.
Soil texture -- The textural designation of a soil is determined by its relative portions of sand, silt, and clay particles, and indicates which of the three most influence the soil's properties. Sand, silt, and clay soil properties are obviously dominated by those respective fractions. For example, clay soils (generally more than 40 percent clay) are often poorly drained. On the other hand, well-drained loam soils are mixtures of sand, silt, and clay in roughly equal proportions, and are well drained. A sandy loam, however, has much more sand and much less clay than does a clay loam. Soil structure -- Soil texture is an inherent soil property that you as a gardener cannot change (except through extreme interventions). Instead, you should direct your efforts toward improving soil structure. Soil structure is defined by the manner in which soil particles are assembled as aggregates. In clay soils, clay particles are typically arranged along a horizontal plane in a platelike structure. When these horizontal aggregations are stacked high and consolidated over time, they can be quite tight and sticky. Your aim in improving soil structure is to achieve a looser, more crumbly or granular structural aggregation. A soil with the latter structure has a friable consistency and good tilth. Tilth -- Tilth is the physical condition of the soil as it relates to ease of tillage, seedbed quality, ease of seedling emergence, and deep root penetration. A soil that drains well (yet has water-holding capacity), does not crust, takes in water rapidly, facilitates aeration, and does not make clods is said to have good tilth. And with the right management strategy, good tilth is achievable in a clay soil. Clay demands short-term and long-range strategies My initial management strategy centered on adding as much organic matter as deeply as I could, because, generally, the application of organic matter to soil improves both structure and tilth, and contributes to improvements in overall soil health. My long-range management strategy attempts to build available organic carbon and humus and to promote nutrient cycling through regular applications of compost, manure, and other organic matter, the incorporation of cover crops as green manures, rotations that include grasses and legumes, and reduced tillage. Organic matter builds soil tilth in a couple of ways. First, the organic matter coats soil particles, physically separating clay particles and aggregates from each other. Second, and more important, microorganisms that degrade organic matter produce byproducts called glomalin that bind individual clay particles together into aggregates. Particle aggregation in the topsoil reduces crusting, increases the rate of water infiltration, and reduces erosion and runoff. Though my ultimate goal continues to be to increase soil organic matter content in the garden, I was less concerned initially with the numbers than I was with achieving the benefits described above. I understood that in southeastern soils, it would be very difficult to increase the percentage of organic matter in the soil very quickly. For one thing, even large amounts of organic matter initially incorporated in the soil will rapidly break down. The organic matter fraction remaining may resist further degradation for years or even decades, but stable increases in this fraction, called the humic fraction or humus, occur very slowly. Thus, any increase in stable organic matter is necessarily a long-term goal. [ next ] |
 |
|