Gardeners of all kinds will sometimes be up against the challenge of improving the soil on a patch of land. Not all soils are great for growing crops, and soil improvement is a common task for agricultural workers, whether they are engaged in a small project or a large one. In order to do soil improvements effectively, the individual will have to bring some specific skills and strategies to the table. Here are some of the commonly recommended ways to improve soil and raise the effective yield of a piece of land.
Part 1 of 3: Improving Soil Nutrients
1Check which nutrients your plants need. There are three extremely important nutrients for gardening: nitrogen (N) for leaf and stem growth, phosphorus (P) for roots, fruit, and seed, and potassium (K) for disease resistance and overall health. Young plants may need more phosphorus to focus on leaf growth, and plants typically need much less of these nutrients outside of the growing season. For best results, look up the specific plants you are growing to find out their needs. This is usually given as three "NPK" numbers, telling you the ratio or total amounts of these nutrients in that order.
- If you want a detailed report on the nutrients already in your soil, send soil samples to your local extension office or soil-testing laboratory. This is not necessary for most home gardens, unless your plants are suffering from slow growth or color changes.
2Choose fertilizers from organic sources. Plant and animal matter such as fish emulsion or fish hydrolysate provides the best type of fertilizer for long-term microbial growth, which keeps soil nutrient-rich and porous. Fertilizers synthesized in laboratories typically feed the plant without improving the soil, and in some cases may even have negative effects.
- Always protect the hands and face when working with soil additives, as these can contain some bacteria and other health threats.
3Consider using manure or other organic matter. Instead of a manufactured fertilizer, you may be able to find cheaper, unrefined options from a garden supply store or farm. Here are a few common options:
- Manure should be left to decompose for at least a month before use, to avoid damaging plants. Chicken or turkey manure is cheap, but can cause runoff issues in large fields. Cow, sheep, goat, and rabbit manure are higher quality and have a less pungent smell.
- Add bone meal for phosphorus, or blood meal for nitrogen.
4Make your own compost. New compost typically takes four to eight months to mature, unless you speed up the process with special bacterial additions. This long term project will greatly benefit both soil texture and nutrients, if you're willing to keep up the process. Set aside a large outdoor container, tightly closed to protect it from animals, but with holes for air flow. Care for it with these techniques:
- Begin with about 20% soil, manure, or mature compost; 10 to 30% raw, plant-derived food scraps; and 50 to 70% dry leaves, grass, and yard clippings. Mix these together thoroughly.
- Keep the compost warm and wet, and throw in raw, non-meat food products from kitchen scraps.
- Turn the compost with a pitchfork or shovel at least once every week or two, to introduce oxygen that encourages beneficial bacteria.
- Search for worms in moist areas underneath rocks, and add them to the compost bin.
- The compost is mature (ready to use) when it clumps together when squeezed, but can easily be broken apart. Plant fibers should still be visible, but the compost should be mostly homogenous.
5Add the fertilizing material. Whether they use solid fertilizer, rotted manure, or compost, most gardeners mix the addition thoroughly into the soil. Many crops do well with a 30% compost, 70% soil mix, but vegetables and fruits often do better with lower amounts of compost. Fertilizer amounts vary greatly depending on the concentration; follow the instructions for your particular plant.
- The "no-till" or "no-dig" gardening movement advocates adding the material to the surface, letting it decompose gradually into the soil. Practitioners consider this a more natural and less invasive way to improve soil, although full results may take years and plentiful organic matter.
- Add in autumn for best results. Many plants benefit from a "top up" every month or two during the growing season, but this varies between species and varieties.
- If you think the manure or compost may not be rotted enough, keep a circle of regular soil around plants to avoid burning them.
6Add trace elements. There are many trace elements that have a less important or less direct effect, but can cause plant health issues or poor soil if they fall below required levels. If you want to be sure to include these, mix green sand, kelp meal, or azomite into the soil before planting. For small home gardens, you may not find this necessary unless your plants develop health issues.
- The most important trace elements are iron, boron, copper, manganese, molybednum, and zinc.
- The additives described here are natural and suitable for organic farming.
7Consider crop rotation. If you plant the same type of plant in the same location year after year, it will deplete the soil nutrients more quickly. Some plants will use fewer nutrients or even add nitrogen to the soil, so a rotating schedule of plants each year will keep the nutrient levels more stable.
- For home gardening, get started with this simple guide to crop rotation. For farming, consult an experienced local farmer or agricultural extension office, as the rotation plan varies depending on the available crops.
- Farmers can also consider using overwinter "cover crops" grown to provide nutrients for the real crop. Plant a cold-hardy crop at least 30 days before the first expected frost, or 60 days if the crop is only marginally cold-hardy. Mow or cut the crop at least three or four weeks before the regular crop is planted, and leave the cover crop on the ground to decay.
8Consider adding beneficial fungi or bacteria. If your soil is kept well-aerated and supplied with nutrients, microbe populations will grow on their own, breaking down dead plant matter into nutrients your plants can reuse. For additional soil health, you may be able to purchase bacterial or fungal additions from a garden supply store, if they are suitable for your plant species. Soil that already decomposes rapidly does not need these additions, although there is no hard and fast rule for how much to use or when to stop.
- One of the most common additions is a type of fungus called mycorrhizae. This attaches to plant roots and help them absorb more nutrients and water. All plants except members of the genus Brassica (including mustard and cruciferous vegetables such as broccoli and bok choy) benefit from this, unless the soil is already in excellent shape.
- Bacteria called rhizobium are often already present in the soil, but you can purchase a rhizobium inoculant to be sure. These form a symbiotic relationship with legumes such as potatoes and beans, adding nitrogen to the soil.
Part 2 of 3: Improving Soil Texture
1Understand the soil triangle. Soil scientists divide the particles that make up soil into three categories. Sand particles are the largest, silt is somewhat smaller, and clay particles are the smallest. The ratio of these three types determines the type of soil you have, described in a chart called the "soil triangle." For most plants, you'll want to aim for a "loam," or approximately a 40-40-20 mix of sand, silt, and clay respectively.
- Succulents and cacti often prefer a "sandy loam" with 60 or 70% sand instead.
2Try a quick texture test. Pick up a small clump of soil, from beneath the top surface layer. Moisten it, then try to roll it into a ball and flatten it into a ribbon. This quick and dirty method can detect major problems, based on the following diagnosis:
- If your soil ribbon breaks before it reaches 2.5 cm (1 inch), you have loam or silt. (If it can't form a ball or ribbon at all, you have sandy soil.)
- If your ribbon measures 2.5 to 5 cm (1–2 inches) before breaking, you have clay loam. Your soil could probably benefit from more sand and silt.
- If your ribbon reaches more than 5 cm (2 inches), you have clay. Your soil will need major additives, as described at the end of this section.
3Prepare a soil sample for thorough testing. If you're still not sure about your soil, you can find out more accurate information with twenty minutes of work and a few days of waiting. To get started, discard the surface soil, then dig up a sample of your soil about 15 centimeters (6 in) deep. Spread it out on a newspaper to dry, and remove all trash, rocks, and other large debris. Break up clumps of soil, separating it as much as possible.
4Mix ingredients for a jar test. Once the soil is dry, add it to a tall, large jar until the jar is ¼ full. Add water until the jar is ¾ full, then add 5 mL (1 teaspoon) of non-foaming dishwasher detergent. Seal the jar and shake it for at least five minutes to further break it into fragments.
5Mark the jar as the soil settles. Let the jar stand for at least a couple days, marking the outside with a marker or tape at these intervals:
- After one minute, mark the jar at the top of the settled particles. These are sand, which settle first due to their larger size.
- After two hours, mark the jar again. By now, most of the silt will have settled above the sand.
- Once the water is clear, mark the jar a third time. Soil with heavy clay can take a week or two to settle, while more loamy soils may reach a clear jar after a couple days.
- Measure the distance between marks to get the amount of each particle. Divide each measurement by the total height of the particles to get the percentage of that particle type. For example, if you have 5 cm (2 in) of sand and a total 10 cm (4 in) layer of particles, your soil is 5 ÷ 10 = 0.5 = 50% sand.
6Improve your soil with compost or natural debris. If you discover you already have loam, there's no need to alter your soil. Clay soils greatly benefit from mature compost, as described in the soil nutrients section. Other natural additions such as dry leaves or grass clippings serve similar purposes.
- Old, weathered wood chips, twigs, or bark will increase water and nutrient retention, both by creating soil pores and soaking up materials for slow release. Avoid new wood, which can reduce soil nitrogen levels.
7Consider manual soil adjustment. If you have clay-heavy soil (more than 20% clay) or extremely sandy or silty soil (more than 60% sand or 60% silt), you can mix in the other types of soil to achieve a roughly even mix of sand and silt, and no more than 20% clay. This can be labor-intensive, but is faster than creating your own compost. The goal is to create a porous soil that can hold plenty of water, air, and nutrients.
- Note that you should only use sand that is salt-free and very sharp.
- Perlite, available from garden supply stores, is useful for all soil types but especially for clay soils, essentially acting as extra-large particles.
8Deal with soil compaction. Keep foot traffic and vehicle traffic to a minimum to keep the soil aerated. If the soil looks dense or crusted on top, use a pitchfork to turn over the soil and break up large clumps. For seriously compacted soil, use a machine tiller, or plug holes with a lawn aerator. Even if water retention is not an issue, densely compacted soil can kill off beneficial bacteria and fungi, and encourage harmful anaerobic bacteria.
- Mixing in organic material also helps, as described in the section on soil nutrients.
- Dandelions and other plants with long tap roots can help prevent clumping and compaction.
- Alternatively, you can follow "no-till" or "no-dig" gardening techniques to leave soil undisturbed, allowing it to form as natural soil does over a few years. Minimizing traffic is still recommended for this method.
Part 3 of 3: Adjusting Soil pH
1Take a soil sample. For accurate results, discard the topsoil until you reach soil with a consistent color and texture, typically about 5 cm (2 in) down. Dig a hole 15 cm (6 in) deep. Repeat several times across your yard or field to get a representative set of samples.
2Test the soil pH. You can send these soil samples to a local extension office or soil-testing laboratory, and pay them to test the soil's pH, or acidity. However, pH testing kits are cheaply available at garden supply stores or nurseries, and easy to conduct at home.
- Sending the samples to a professional is recommended for farmers, so you can receive an exact recommendation for how much additive to use. Home gardeners may wish to go with the cheaper, faster kit, and use trial and error with the additives.
3Check your plant's needs. Many plants prefer a slightly acidic soil, so aim for a pH of 6.5 if you don't have any other information. Ideally, find your plant's preferences online or by talking to an experienced gardener.
- If you can't find specific pH levels, assume that "acidic soils" mean a pH of 6.0 to 6.5, while "alkaline soil" means a pH of 7.5 to 8.
4Make the soil more alkaline. If your soil pH is too low for your plant, raise the soil pH with these alkaline additions. Check a garden supply store for garden lime, crushed oyster shells, or other calcium supplements, or crush egg shells to a powder at home. Mix the additive into a large amount of soil one handful at a time, testing the soil pH each time.
5Make soil more acidic. If you need to lower your soil pH level, you'll need an acidic addition instead. Mix in aluminum sulfate or sulfur from a gardening supply store, testing the pH again after each handful added.
6Test your soil every three years. Over time, your soil pH will gradually return to its usual levels, which is determined mostly by the type of minerals in your area. Unless you are having trouble adjusting the pH or your plants develop growth problems, testing your soil every three years should be fine.Ad
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- Toxic chemicals in the soil are not a common problem, but worth investigating if you live near a manufacturing area, landfill, or toxic waste site, or if you are growing edible plants by the roadside. Send soil samples to an agricultural extension for testing and advice. Dangerous chemicals may require professional containment, while others may just need diluting with additional topsoil.
- If there are cats using your garden as a toilet, discourage them by sprinkling a thin layer of straw over your garden, leaving bare circles around plants. Straw will also increase water retention and soil temperature, which can be beneficial or harmful depending on your soil characteristics and climate.
- Always protect the face, hands and other parts of the body from contamination by various soil improvement materials. Read the warning labels on products and stay educated about how to use soil improvement chemicals safely.
- When using any kind of organic matter to improve soil, try to limit the inclusion of seed pods for weed types in the soil additions. Too many of these seeds may sprout during the gardening cycle and cause problems.
- Never use cat or dog feces as manure, as these can harbor diseases dangerous to humans.
- Citrus waste is not ideal for compost, as it takes a long time to rot and reduces worm activity.
Sources and Citations
- ↑ http://organiclifestyles.tamu.edu/soil/microbeindex.html
- ↑ http://www.organicgardening.com/learn-and-grow/garden-s-homegrown-ally
- ↑ http://www.finegardening.com/improving-clay-soils
- ↑ http://www.ext.colostate.edu/mg/Gardennotes/214.html
- ↑ http://www.ext.colostate.edu/mg/Gardennotes/214.html
- ↑ http://www.finegardening.com/improving-clay-soils
- ↑ http://puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Coffee%20grounds.pdf
- ↑ http://www.gardenmyths.com/pine-needles-acidify-soil/
- ↑ http://content.ces.ncsu.edu/a-gardeners-guide-to-soil-testing.pdf