Pesticide retention by inorganic soil amendments

Pesticide retention by eight inorganic soil amendments, the majority of whi ch are used in turf was evaluated using a laboratory-based technique with r adiolabeled pesticides. Amendments evaluated were derived from various natu rally-occurring deposits of zeolites, diatomaceous earths, and fired clays and are intended to provide long-lived, stable, and uniformly sized particl es that can contribute favorable water- and nutrient-retention properties t o the root zone. Sand, sedge pear, and a Marvyn loamy sand soil (Ap horizon ) were included for comparative purposes. Pesticides evaluated included the herbicides imazaquin and oxadiazon and the fungicide/herbicide fenarimol. Pesticide retention was evaluated with a soil solution technique. Amendment s evaluated had considerable variation in cation exchange capacity (CEC), e ffective CEC (ECEC), surface area (SA), and field capacity with lesser vari ation in particle size distribution and particle density. Scanning electron microscopy revealed that surface texture was variable but frequently rough and porous. Pesticide retention was also variable but generally more than chat of sand and frequently equivalent. to sedge pear. Only with fenarimol and amendments that had been Ca+2-saturated could retention be correlated w ith any of the individual Physical or chemical parameters that are generall y assumed to govern pesticide adsorption, which in this case were CEC and S A. Imazaquin retention by unaltered amendments was correlated only with the products of SA and CEC, and SA and ECEC. Retention of both oxadiazon and f enarimol by unaltered amendments could not be correlated with any individua l physical and chemical parameters or products thereof. Pesticide retention by these amendments is probably the cumulative sum of both true adsorption and physical entrapment.