When European-American settlers first began ploughing in Iowa, they found the weather and local geology had combined this organic mulch with sand and silt to form a nutrient-rich type of soil ...

Beginning in the 2017 growing season, The Iowa Nutrient Research & Education ... in growers applying the nutrient only when the soil is at or below optimum levels for it – increasing from ...

(a) Soil in central Iowa with dark, organic-matter-rich topsoil. Iowa's average topsoil depth decreased from 35-45 cm to 15-20 cm during the 20th century due to farming. (b) Severe gully erosion ...