Phytotoxic activity of pethoxamid in soil under different moisture conditions

Abstract

The phytotoxic activity of soil-applied pethoxamid [2-chloro-N -(2-ethoxyethyl)-N -(2methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.

Residual phytotoxic activity of pethoxamid in soil and its concentration in soil water under different soil moisture conditions

“…1991). In our previous study (Dhareesank et al . 2005), the phytotoxic activity of pethoxamid was highest under the highest soil moisture conditions and it decreased with decreasing soil moisture content.…”

“…Air‐dried, sieved Tennoudai soil (9% soil moisture, 5.18% total carbon, 3.90% total organic carbon, cation exchange capacity = 24.6 m eq 100 g −1 , pH (H 2 O) = 5.7, 36.0% sand, 38.8% silt, 25.2% clay, field capacity = 70%; Dhareesank et al . 2005) was used in this study.…”

“…Rice ( Oryza sativa cv. Kiyohatamochi) was used as a test plant (Dhareesank et al . 2005) and the just‐germinated seeds were planted immediately below the soil surface and covered with the applied soil in the pot at 0, 1, 3, 5, 10, 15, and 20 days after mixing.…”

“…Determination of the amount of pethoxamid in soil water and in the soil solid phase was conducted according to the method in the previous study (Dhareesank et al . 2005).…”

“…Pethoxamid in the centrifuged soil was extracted with 80% (v/v) acetonitrile and the extracted solution was prepared for HPLC analysis. The amount of pethoxamid was determined by a liquid chromatograph (SCL‐10A; Shimadzu, Kyoto, Japan) equipped with an auto‐injector system (SIL‐10A; Shimadzu, Kyoto, Japan), an inertsil column (4.6 × 250 mm, particle size = 5 µm; ODS‐2; GL Sciences, Tokyo, Japan), a UV spectrophotometer detector (SPD‐10A; Shimadzu, Kyoto, Japan) operating at 245 nm, and a chromatocorder (Dhareesank et al . 2005).…”