Anything mixed into the soil is called a soil amendment. Inorganic, synthetic soil amendments have been widely used since the mid-1940s as an inexpensive way to boost crop production, correct soil texture problems and raise or lower soil pH levels. Organic soil amendments are derived from natural sources and are part of the agricultural philosophy of sustainability and renewable energy.
Soil amendments improve the texture, friability, fertility and structure of soil. Vegetables, fruits and flowers need soil with structure to hold roots, fertility to provide nutrients, and texture to hold water. You can improve soil by adding organic materials. And you can stimulate plant growth with synthetic nutrient additives, but they do not improve soil fertility. Chemical compounds such as iron sulfate, aluminum sulphate and ammonium sulphate are used to lower the soil pH level.
Organic soil amendments are made from natural sources such as soft rock phosphate, mined potassium, alfalfa meal, cottonseed meal, feather meal, seaweed, fish meal, bat guano, blood and bone meal. Inorganic soil amendments often emphasize the nitrogen component of plant growth, which is manufactured from liquid ammonia. Other inorganic amendments include dolomite, gypsum and lime.
According to the International Fertilizer Association, scientific studies indicate that mixing inorganic and organic plant nutrients benefits crops and soil and, therefore, farmers and the environment. Some fertilizer mixes are not recommended, however, such as using agricultural lime with nitrogen-based chemical fertilizers. Organic soil amendments were shown in a 2007 study at the University of California at Davis to increase the nutrient value of tomatoes.
Organic soil amendments include all-purpose blends and single-ingredient types to improve specific soil conditions. Alfalfa meal is recommended for roses and soft rock phosphate for flowering trees and shrubs. Inorganic soil amendments often target the same soil imbalances but with chemically produced materials. Gypsum and lime are used to correct heavy clay-like soils. Both organic and inorganic amendments are available as slow-release granules, liquid concentrates and sprays.
Warning labels on inorganic soil amendments often caution the user to keep children away from the product and not use it near a water source. A high concentrate of synthetic nitrogen is harmful to health, according to the World Resources Institute report on global pollution and nitrogen overload. Organic soil additives should also be used according to the manufacturer's instructions. Homemade compost as a soil additive can be used freely.