Other nutritional amendments that can be purchased for garden use include cottonseed meal, kelp meal, leather meal, and worm castings, as well as an array of synthetic fertilizers. The organic amendments are particularly useful where a trace element deficiency exists, while synthetic fertilizers are generally more available, less expensive, and have quicker results. However, these inert materials can be expensive and extremely large quantities are needed to do any good. If too little is added, sand can cause clay to react much like concrete. Compost, manures, and other amendments usually serve the purpose better and more economically by improving the structure or way the soil binds together.
Organic matter is a great soil improver for both clay and sandy soils.
Good sources of organic matter include manures, leaf mold, sawdust, straw, and others. These materials are decomposed in the soil by soil organisms. Various factors, such as moisture, temperature, and nitrogen availability, determine the rate of decomposition through their effects on these organisms. Adequate water must be present, and warm temperatures will increase the rate at which the microbes work. The proper balance of carbon and nitrogen in the material is needed to ensure adequate nutrient availability both to growing plants and decomposing organisms.