Minerals make up the solid part of soil. Nutrients are created from minerals and other elements. The mineral content of soil determines the mineral content of the food grown on it. Mineral analysis of soil has become important in organic gardening and sustainable agriculture because health of the soil is an indicator of nutritional value of food.
“In most soils, minerals represent about 45 percent of the total volume, water and air about 25 percent each, and organic matter from 2 to 5 percent,” according to the National Sustainable Agricultural Information Service. Soil minerals come in three general particle sizes, and these determine the soil texture. These particle sizes are sand, silt and clay. Silt has the smallest mineral particle size, sand the largest, and clay is between the two.
Soil texture depends on mineral size. Soil texture determines soil’s ability to hold plant life and decayed animal residue. Large mineral particles in sandy soil cannot hold water or plant root structures well. Silt consists mainly of quartz mineral. Clay has plate-like mineral particles that create a large surface area.
Healthy soil created from minerals contains six nutrients needed in the largest amounts: nitrogen, phosphorus, potassium, calcium, magnesium and sulphur. Seven other mineral nutrients are needed in lesser amounts: iron, manganese, copper, zinc, boron, chlorine and molybdenum. Synthetic fertilizers that add high levels of nitrogen unbalance soil’s normal growth processes.
The nutrient content of agricultural soil determines the nutritional value of food grown on it. The nutrient content of soil can be depleted from over-use of synthetic fertilizers and agricultural practices that reduce organic matter in the soil. “Our soils are a lot like we are,” says Dennis Hinkamp in a Utah State University Extension report on soil health. “If we use and abuse them too much, they become sick and weak.”
Soil mineral content analysis tests are available from county agricultural extension offices and independent laboratories. (See Resources) Adding mature compost to soil is recommended as a way to increase mineral content and therefore the nutritional value of food grown on the soil. Soil needs the full range of micro and macro nutrients for healthy plant growth.