Fertile soil is one of the foundations of a healthy and productive garden. It provides structure, minerals, and a balance of living organisms and decaying organic matter to plant roots. In effect, soil is a complex, living system. It can be sick, healthy, or even dead, depending on conditions. In order to be of greatest benefit to our plants, the soil must be nutrient-rich and filled with living organisms. Many areas of the world, however, suffer from mineral depletion and loss of topsoil. With the application of compost, cover crops, and other soil management techniques, gardeners can create a fertile soil environment, which can make all the difference between a failed crop and an abundant and lasting harvest.
Worldwide Mineral Depletion
An alarming trend in the last couple of centuries has seen productive soils worldwide rapidly lose valuable minerals faster than they can be replaced. Several factors are likely causing this, including geology and weather patterns. Contemporary farming practices in particular have contributed the most to mineral loss. Widespread use of pesticides and synthetic fertilizers can imbalance the soil composition and cause rapid loss of nutrient-rich topsoil. Monoculture practices and planting crops in the same place for multiple seasons also causes mineral loss and leaves plants vulnerable to disease and pests. This leeching of nutrients can cause the soil to effectively “die,” and makes food crops more and more dependent on fertilizers.
Some areas are more vulnerable to soil loss than others, but just about any soil can be lacking in adequate minerals. The southeast US and all tropics, for example, have old soils that are low in certain nutrients. The Great Plains, meanwhile, are still recovering from the topsoil lost during the Great Dust Bowl in the 1930s. Other places, such as areas on recent lava flows in Hawaii, have never had topsoil to begin with and can take decades to develop.
Recent soil management techniques, such as the ones used on farms in Java, Indonesia have shown that providing nutrients to our crops via healthy, fertile soil is a cheaper, easier and more effective method than conventional fertilizers.
Soil And Health
Depleted soil can have a profound effect on our health and the health of our families. Crops grown in depleted soils simply don’t have enough minerals to make nutrient-rich food that keeps humans healthy. In fact, depleted soils are a major factor in the decline of fruits’ and vegetables’ nutritional value for the past 70 years. The depleted nutrition of our food begins with depleted minerals in the soil. Without fertile, mineral-rich soil, plants are unable to get what they need to grow nutritious food.
Common Missing Nutrients In Depleted Soil
The chemical processes that determine a soil’s fertility are complex, and deficiencies may be difficult to determine. Soils that are heavily fertilized may be rich in macronutrients, for example, but very poor in microorganisms and trace minerals. Following are some of the more common minerals missing in today’s depleted soils:
- Nitrogen: One of the three plant macronutrients, nitrogen leeches easily from the soil and needs to be consistently replenished. It also must be in a certain form in order for plant roots to use it. Although commercially added to the soil with ever-increasing amounts of fertilizer, nitrogen can remain available throughout all growing seasons through crop rotation, using compost, and other soil management techniques.
- Calcium: Calcium plays an important role in a plant’s structure and growth. Recent studies performed in the eastern U.S. have found that calcium levels are dropping rapidly. Usually, calcium is returned to the soil through weathered rocks and decaying matter, but modern agriculture, erosion, and acid rain has stripped this mineral away.
- Manganese: Vital for photosynthesis and other processes, this micronutrient can become depleted or unavailable to plants when soils are too wet, too high in organic matter, or too high in other elements, such as iron. Alkaline soils, such as those found in much of the southwest US, also often lack this mineral.
- Carbon: This element is critical for living microbes to survive. It is used and returned to the soil through organic matter.
As many of these minerals are lost, soils are likely to become more acidic. This in turn can exacerbate the problem, as many plants are unable to properly absorb vital nutrients in acidic soils. Checking the pH levels is an important starting point to understanding the soil’s composition.
Organic material is the vital binding agent that ensures that soil minerals are available for plants to absorb through their roots. Alive and rich in carbon and other vital nutrients, organic materials such as compost and other decaying matter adds structure to the soil, improves drainage, and helps plants fight off disease and pests.
Many amendments and techniques are available for gardeners to use to introduce healthy organic material back into depleted soil. Tilling or layering compost, and planting cover crops are all popular choices. Keep in mind, however, that rejuvenating the soil is a process that can take anywhere from weeks to years. Staying consistent and understanding the soil’s composition is important to ensuring success.
Nothing introduces living organic matter to the soil easier or more effectively than compost. In essence, compost is simply decomposed organic material. The decomposition process that creates compost is driven by a vast array of insects and microorganisms—creatures lacking in nutrient-poor soils. Compost is beneficial to soil and plants in several ways. It reintroduces living organisms ranging from centipedes to bacteria, improves soil structure, adds nutrients, and provides a healthy environment for plant roots. Households can vastly improve their soil by turning waste into black gold, virtually eliminating the need to depend on commercial fertilizers.
Many composting techniques are in use today, and many involve only a bucket and shovel. Compost can be tilled or layered on the soil, and can take anywhere from several days to several years to make, depending on the climate and technique used.
Compost tea is simply compost soaked in water for 3-7 days. Although low in macronutrients, compost tea is rich in micronutrients and beneficial microorganisms. Compost tea can be watered into the soil or used as a foliar spray for a quick plant boost. It is very effective in preventing diseases, as the microorganisms out-compete disease-causing bacteria, and is especially popular in organic gardens around the world.
Bokashi is the technique of inoculation to create compost. Nearly odorless and effective within days, bokashi is especially popular in making compost from kitchen scraps. It relies on effective microorganisms (EMs) to decompose the material. These EMs are introduced as a living culture, usually with wheat bran, and work to break down waste through fermentation. Developed in Japan, bokashi is gaining in popularity. For depleted soils, bokashi composts can speed up the process of rejuvenation.
Crop rotation is a planned order of planting throughout several growing seasons. When applied, crop rotation can prevent further soil depletion and help ensure a lasting healthy soil environment. Crop rotation is also an effective technique to dramatically increase yields and prevent crop loss due to pests or disease. The idea is to plant crops of different genera each season, and to never plant one crop in the same place two seasons in a row.
The use of cover crops is a technique that uses certain plants in between growing seasons to rejuvenate the soil. Although traditionally used on large-scale farms, these special crops can benefit any size farm or garden. Cover crops, also known as “green manure” or “green mulch,” prevent erosion and mineral leeching, fix soil nitrogen, increase living organic matter, and control pests and diseases.
Cover crops are usually planted in late fall after harvest, and then cut down and tilled into the soil before planting in spring. However, they can also be planted right next to food crops in the middle of their growing season in order to suppress weeds and attract beneficial insects. Because these crops grow rapidly to out-compete weeds, it’s important to cut down and kill them before they set seeds and spread. Once their dead leaves and stems turn brown, they can be tilled into the soil. Be sure to wait a few weeks before planting anything in these beds, so the green mulch completely decomposes.
Useful Cover Crops
- Mustard: Contains high levels of glucosinolate, compounds that are naturally toxic to pests. Very effective against soil nematodes. Mustard’s vigorous growth also introduces plenty of organic material into the soil.
- Legumes: A group that includes alfalfa, peas, and lupines. Not only do these cover crops bring nitrogen back into the soil, but they also have root nodules that house Bradyrhizobium bacteria that act as nitrogen fixers.
- Clover: Clover’s dense, low-growth habit also makes it an ideal green mulch, suppressing weeds and keeping the soil cool and moist for food crops such as corn. Many varieties can handle foot traffic and full shade. Clover also fixes nitrogen into a form available to plant roots.
With the application of compost and other techniques, farmers and gardeners can not only rejuvenate depleted soils, but keep their gardens rich and healthy for multiple seasons. Careful soil management may take some research and time, but the results—less fertilizer, fewer losses to disease and bigger yields—are more than worth it.