Effect of two organic amendments (liquid and solid) on simazine leaching in soil

Adsorption, degradation and leaching of simazine in a sandy soil (0.66 % or ganic C, 75 % sand, 16 % clay) and in this soil amended with two doses of a liquid organic amendment (LOA, 26 % organic matter) and a solid organic am endment (SOA, 32 % organic matter) have been investigated. Adsorption coeff icients Kf in LOA increased by a factor of 2.5 and 1.8 with high and low do se, respectively. In SOA Kf increased by a factor of 5.5 and 2.4 with high and low dose, respectively. Original and amended soils were treated with si mazine (5 kg ha(-1)) and incubated for 28 days (-33 KPa moisture content an d 20 degrees C). No changes in simazine residues with incubation time were observed for the original soil, whereas calculated half-lives were 123 d an d 69 d for the low and high dose of LOA and 158 d and 146 d for the low and high dose of SOA. Mobility was studied in handpacked soil columns. Breakth rough curves indicated greater mobility of simazine and higher recoveries i n the untreated sandy soil than in the amended soils. These results indicat e that the organic amendment reduces herbicide leaching by promoting sorpti on and degradation processes.