INVESTIGATION OF HERBICIDE SORPTION IN SOILS OF RICE FIELDS IN SEBERANG PERAK AREA

Clearfield® Production Systems (CPS) had been introduced in Malaysia to effectively control weeds in paddy fields area in Malaysia, which consisted of Imidazolinone tolerant rice (IMI-TR) seeds and On Duty® herbicides (an Imidazolinone herbicide mixture of imazapic and imazapyr). However, due to their high soil persistence imazapic and imazapyr herbicides can contaminate the environment and result in damages to rotational crops and non-target aquatic plants. Soil sorption can affects the herbicidal activity and soil persistence. So, the objective of this study is to investigate the adsorption and desorption in soils of paddy field. The soil samples were taken from paddy field area in Seberang Perak area and labeled 322, 328, 327 and X–mining soil. With reference to the researches done previously, a few soil properties had been selected which are related to the adsorption and desorption process. The properties are soil pH, total organic carbon, clay content, maximum water holding capacity, field capacity and cation exchange capacity(CEC). The adsorption study was done using batch equlibration method while the desorption study was done using single-step decant-refill technique. The adsorption and desorption data obtained were fitted with the Freundlich sorption isotherm. For adsorption, the R2 value was in the range of 0.985 to 0.997 with 1/n ads value was less than 1 which indicated the isotherm was non-linear. For desorption, the R2 value was in the range of 0.906 to 1 and hysteresis coefficient,H ranging from 1.19 to 2.80. The adsorption process was much affected by soil pH, maximum water holding capacity and field capacity while the desorption process was much affected by CEC and clay content. The adsorption rate was negatively correlated to soil pH, maximum water holding capacity. In addition, the desorption rate was positively correlated with CEC and clay content. The finding of this study provides useful information to reduce the environmental contamination of On Duty® herbicides in paddy fields area.