Abstract: Controlled release fertilizers containing water-soluble nutrients such as potassium nitrate which are easily leached from the fertilizer by moisture in the soil have a coating which more efficiently retards the release of the nutrients and also provides citric acid soluble silicon to the soil. Nutrient particles are first coated wtih a colloid formed by the acidification of preconditioned calcium metasilicate with citric acid and then mixed with cement. The calcium metasilicate is preconditioned by heating to a temperature of at least 1300.degree. C. to sinter at least a portion of the silicate. The nutrient particles are then pelletized and cured to form a silica gel matrix containing acicular calcium metasilicate and a cement coating on the pellets.