Soil texture refers to the percentage of sand, silt, and clay particles that make up soil. Sand particles are large with big pores while clay particles are small with tiny pores. Clay and humus particles give soil cation exchange capacity and improve fertility. Ideal soil structure forms stable aggregates. Primary cultivation aerates soil and incorporates organic matter while secondary cultivation firms soil into a crumb structure that supports root growth. A crumb soil structure is best for horticulture.