Soil Structure

Most of us are not used to thinking of the tilth of the soil, but it is essential to any gardener. If soil has a healthy structure, the likelihood of erosion, compaction, run-off, flooding, and leaching are low; its drainage, aeration, and water retention are good; and its fertility is enhanced. Think of your soil as a seven-layer bean dip. There are different consistencies to each layer, and some we like better than others. The differences in the respective layers of soil are actually particles of broken-down rock, called minerals, in different levels of degradation. Over time, these minerals have settled on the earth's surface in layers and have been influenced by wind, water, vegetation, and man. Mineral particles in soil are rated by size. All soil is made of various-sized particles referred to as sand, silt, or clay, mixed with organic matter. Varying amounts of these account for differences in a garden soil's texture. While large particles of sand (0.05 to 2.0 mm) make a great beach, they're not the best soil to garden in, as anyone from SE North Carolina can attest too. Roots can grow through it easily, and nutrients, water and air move through the large spaces between particles quickly, but too quickly. This phenomenon allows leaching, which can quickly remove valuable nutrients and water from your root zone. It can also have a huge effect

The next smallest particle size is silt (.002 to .05 mm). Rain falling on dry, silty soil has trouble penetrating to the roots. It tends to run off before soaking in. But because of those smaller particles, once silt is thoroughly saturated, it holds more moisture and nutrients than sand.

Then there's clay (smaller than 0.002 mm) - too much of which is the bane of every gardener's existence. When it's dry, it shrinks and cracks. In fact, you could make bricks out of the stuff. But, if you wet it, it'll hold lots of water and nutrients. During rainy or wet periods, it often becomes waterlogged. And it doesn't warm up early in the spring, so getting into the garden to plant can be difficult.

Most soils are mixtures of sand, silt and clay. Between these inorganic particles are decaying animal and plant materials or organic matter, called humus. Living organisms --like nematodes, earthworms, and bacteria-- move through the soil, leaving miniature tunnels providing oxygen and depositing feces providing valuable materials for plant nutrition. The combination of these creatures' waste products and their remains binds with the soil particles. In clay, it forces the tightly packed particles apart improving drainage and making it easier for plant roots to penetrate the soil. In sand, it lodges in the large pore spaces and acts as a sponge, slowing drainage so the soil stays moist longer. All these factors contribute to soil structure. Good soil structure allows for the presence of oxygen in the root zone, permits water to drain through it well, and harbors nutrients for plant nutrition by preventing leaching. A soil containing roughly equal amounts of sand, silt, and clay is called loam and is considered to have good tilth and ideal for cultivation. There are coarse loams and fine loams. Fine loams have more silt and clay than sand. Coarse loams are mainly sand, which facilitates better drainage, but still contain enough silt and clay to hold moisture and nutrients and thereby support soil organisms. For this reason, coarse loams are considered some of the best soils to cultivate, with fine loams not far behind.

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Soil Amendments
A soil amendment is any material that improves the chemical or physical structure of the soil, such as water retention, fertilizer retention, permeability, water infiltration, drainage, aeration and structure; with the goal of providing a better environment for roots. There are organic and inorganic soil amendments: organic being any material that was once or is alive, ideally providing a form of nutrition; inorganic being something mined or man-made, like perlite or vermiculite.

Most people are not used to paying attention to soil nutrients past a simple NPK. Growing plants are no different than anything else, the more attention you pay to them the better results you will have. The fact is, by not paying attention to the nutrients and materials in your soil and available to your plants you are assuming your soil contains all the necessary components for plant growth. This can be a fatal assumption, especially on land that has been cleared for development, over cropped, or is subject to erosion. These types of land, including residential and commercial space, are cleared and grated to enable the passage of building inspections or have been stripped of their native soil spectrum. In so doing, the top foot or so of topsoil is cleared from the plot and all of the beneficial soil microbes and most of the residual nutrient available for plant growth is taken along with it. Keep this in mind when planting your backyard garden.

Soil nutrients exist both as complex, insoluble compounds and as simple forms usually soluble in water and readily available to plants. The complex forms must be broken down through decomposition by soil microbes and processes into simpler forms in order to benefit the plant. Herein lies a fundamental difference between soilless and soil-based cultivation and the reason why there is not a 100% organic hydroponic nutrient. In order for a plant to access a nutrient hydroponically the fertilizer must be soluble in water. If not, the plant cannot access it. By the nature of nutrient formulations, everything a plant needs to grow available in an "organic" form cannot yet be accomplished in one bottle.

Beneficial Fungi Mycchorizae can make a tremendous difference in your plant growth. Through a symbiotic relationship with the plant, mycchorizae helps the plant with nutrient uptake, amongst other things, and in return allows the plant to feed off of excess plant nutrients and carbohydrates. Wetting Agents Wetting agents are extremely beneficial soil conditioners. The chemical nature of water is such that it likes to coalesce, forming water beads similar to the beading nature of water you witness when washing your car, or the reason water bugs can skate around on a lake. This concept is also the reason that in a hydroponic system oxygen must be dissolved into your water solution. Without DO the result is stagnant water and unhappy plants. By breaking the natural surface tension of water and overcoming its tendency to form droplets a wetting agent allows fertilizers, pesticides, etc. to penetrate a variety of materials- including soil and plant tissues.

It is always a good idea to implement a wetting agent when utilizing a foliar spray in order to maximize coverage. Test it yourself. Spray first using a water solution with no wetting agent and then with a solution containing a wetting agent. You will notice a more uniform coverage with the wetting agent, actually laying down the spray ensuring that 100% of your leaf or soil is covered.

Organic Materials
There are myriad materials in multiple forms that can be utilized in soil to benefit plant growth. The decision on what to use should be made regarding what will improve the vitality of your soil, not simply the plant. For example, a synthetic fertilizer like Miracle Grow will provide needed nutrients to your plants, but will lock out nutrients already found in the ground or container and disrupt the soil processes needed to make them available. Essentially a synthetic nutrient schedule in soil is treating your soil as an inert medium as opposed to the vibrant organism that it is. This phenomenon is prevalent in the "chemlawn" services provided by most local landscaping and lawn care services. The following are several organic materials that can enhance your soil zone and, in turn, your plants. They can be utilized by working them into the soil itself or as a top dress to an existing scenario:

Alfalfa meal (~3-1-2) contains many beneficial plant materials, including amino acids, trace minerals, proteins, and sugars, and is commonly used as an animal feed. It is an excellent fertilizer material in horticulture, and is said to contain unknown growth factors, which make its mineral content more effective as plant nutrients.

Blood meal (~12-0-0) is very high in nitrogen and is very soluble in water (unlike most other dry organic fertilizers). It also contains plant growth regulators. All this together means that its effect is strong and quick, but its power will only last a short while, especially in wet weather. When applying blood meal, take care, as it will easily burn a plant's leaves.

Bone meal (~1-13-0) is an organic fertilizer applied to increase phosphorus levels in the soil (or compost). Although phosphate rock can also be used for this, bone meal will break down in the soil considerably faster and can thus be used as a quick fix; but this also means that it will not have a long-term effect on the soil.

Compost is decomposed organic material. It's N-P-K depends on the components of the compost itself. By piling kitchen scraps and garden debris in a bin or heap, gardeners create an ideal habitat for decay organisms. These microorganisms break organic material down to form humus. In addition, the heat inside the pile from all the biologic activity will kill off many disease organisms and unwanted seeds. There are multiple ways to compost, for more info go here. (link to compost page)

Cottonseed meal (~6-1-1) is a rich source of nitrogen. Unfortunately, a substantial percentage of the insecticides used in the U.S. are applied to cotton, and some of these tend to leave residues in the seeds. Most organic certification programs restrict or prohibit the use of cottonseed meal.

Cover crops will often include leguminous plants like clover and vetch, but they might also be grains like rye or oats. Cover crops are often planted as a green manure, but they also serve to prevent erosion, control weeds, and conserve water in the soil from losses due to evaporation. For more info on cover cropping go here. (link to cover cropping)

Feather meal (~12-0-0) is a common by-product of the poultry slaughter industry. Although total nitrogen levels are fairly high, the nature of feathers is such that they break down and release their nitrogen much more slowly than many products of similar price.

Fishmeal and fish emulsion: Fishmeal is high in nitrogen, and has relatively even NPK ratio of somewhere around 5-3-3. Unlike the emulsion, fishmeal is a dry organic fertilizer. The fertilizer analysis of fish emulsion varies with preparation method. Whole fish and fish parts must be digested to form a slurry, a process accomplished with the aid of either phosphoric acid or special enzymes. Acid-digested fish emulsion usually has an analysis around 4-4-1, while enzyme-digested fish emulsion is usually measured as 4-1-1. Fish emulsion may be fortified with chemical fertilizer, so organic farmers should be suspicious of any product with a nitrogen content in excess of 5%.

Green manures improve the structure and nutrient load of the soil. The most utilized green manure is mulch mowing. Removing grass in bags from your lawn eliminates a crucial nitrogen source from your lawn. Green manures may be undersown between rows of plants or sown as a cover crop. Between rows, green manures (like clover or vetch) are often mowed --their clippings left as mulch. At season's end, they are turned in to the soil like other green manures (such as rye and soybeans).

Greensand (~0-1-6) is mined from ancient sea beds; it is a dry organic fertilizer. It is useful for its ability to slowly supply to the soil as many as 22 trace minerals and micronutrients, as well as potassium and phosphorous. It has the consistency of sand, but can hold up to 15 times more moisture making it an exceptional soil conditioner.

Gypsum, which occurs naturally in sedimentary rocks, is a dry organic material that supplies two important micronutrients: calcium and sulfur. Some anecdotal data suggests that applications of gypsum on lawns may mitigate problems with turf pests such as grubs and chinch bugs.

Humus is the end result of successful composting. It is the rich, dark, and fine mixture of decomposed organic materials. Humus contains the microorganisms necessary for healthy soil, as well as a ready supply of the macro- and micronutrients necessary for healthy plants. Use humus in the garden to condition and amend soil. Mix it with the soil for general improvement or use it to side-dress hungry plants.

Kelp meal (~1-0-2) is used as a dry organic fertilizer. Dehydrated kelp contains a full compliment of minerals, trace minerals, vitamins, and amino acids It is also rich in micronutrients and plant growth hormones, as well as being an excellent source of potassium. Kelp and algae products are most utilized as a foliar spray.

Lime is produced when calcium carbonate is finely ground. Ground lime is readily
dissolved into the soil where it reduces soil acidity by releasing calcium cations. It is also a potent tool in combating grub infestations and unwanted odors in compost piles.

Manure: Nitrogen feeds the microorganisms in soil that make humus from a compost pile. Manure is rich in nitrogen (especially chicken, goat, and steer manures), and is thus a valuable component of compost. It is also rich in potassium and phosphorus. Manure should be composted (or at least aged) before use in the garden because of its high nitrogen --and ammonia-- content, which can both easily burn plants. Composting will also kill any weed seeds that may have survived the animal's stomach(s).

Mulch: Most mulches are made from organic materials, some of the best being: hay, grass clippings, fallen leaves (best when shredded), bark chips, and compost. Mulching serves to prevent moisture loss from soil, protect plants from temperature extremes, control weed growth (weed before laying mulch!), prevent water from splashing onto plant material, and as a slow-release soil amendment. For more info on mulching go here.

Peat moss is the partially decomposed remains of mosses harvested commercially from the wild. Though difficult to wet initially, peat moss can absorb up to 25 times its own weight in water and is therefore valued as a an organic soil amendment. Peat moss is acidic --with a pH of about 3 or 4.0-- and should only be used around acid-loving plants or to help lower the pH of alkaline soils. Sphagnum moss is generally recommended over standard peat moss.

Potash broadly describes any material containing potassium. More specifically, though, potash is potassium carbonate derived from wood ashes. The term potash comes from the process of extracting lye from wood ashes in iron pots.

Rock phosphate (~0-3-0) is a dry organic fertilizer used to boost phosphorous levels in the soil. Rock phosphate is slow to dissolve in water, so adding it will benefit the soil over a period of years. The phosphate found in many synthetic fertilizers is usually from rock phosphate treated with sulfuric acid to make it more soluble and thus more readily available to plants (called superphosphate).

Wood ash contains about 2% phosphate and 6% potash, but may be contaminated with heavy metals or plastic and typically has a high salt content. Wood ash is rather alkaline, and excessive use can be quite damaging to many soils. Some organic programs restrict its use.

Worm castings are the excrement deposited by earthworms as they tunnel through the soil. Castings are a rich soil amendment containing nutrients in a form usable to plants (they can be harvested and sold in bags). Over the coarse of a single day, an earthworm will produce castings equal to its own weight. For info on vermicomposting go here.

As always, feel free to contact us with any questions regarding organic amendments, or anything gardening!

Cover Cropping
Cover crops are grown to protect and improve the soil, not to harvest. Cover crops have the potential to improve soil tilth, control erosion and weeds, and maintain soil organic matter. They can reduce compaction and increase water infiltration, which decreases leaching of nutrients. Cover crops retain and recycle plant nutrients (especially nitrogen) between crops, provide habitat for beneficial microorganisms, and increase plant diversity. Cover crops may also be referred to as "green manures". Traditionally the term "green manures" has referred to plants that are turned under or incorporated into the soil while green, or soon after flowering, in order to enrich the soil. In recent years however, the term has been used more loosely, and green manure may sometimes refer to plants or plant vegetation that may be applied as mulch to the soil, both slashed and fresh or after the plant has dried out.

The concept is no different than mulch-mowing your lawn. All of the clippings you laboriously carry away from your lawn can actually be used by the growing grass as fertilizer amounting to 1 or 2 fertilizer applications per year. In fact, mulch itself is a valuable cover crop, albeit maybe not a "crop". Mulches break down over time into plant usable forms.

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