Dissipation of Mefenoxam Residue in Watermelon and Soil Under Field Conditions
Mefenoxam is the systemic phenylamide fungicide, which is widely used in controlling phytophthora disease of tomato, cucumber, pepper and watermelon, etc. The dissipation behaviour of mefenoxam residues in watermelons and soils was studied. The whole watermelon, melon flesh and soil matrices of mefenoxam were analyzed by GC–NPD. At three different spiking levels mean recoveries and relative standard deviation from spiked samples in six replicated experiments for each matrix were in the range 89.6–98.2% and 1.5–8.1%, respectively. Under field conditions, mefenoxam dissipation rate was found to be faster in the whole watermelons than in the soils. The results showed that the half lives in whole watermelon and soil from Beijing were 3.9 and 10.0 days, respectively, and the half lives in whole watermelon and soil from Shanxi were 3.7 and 28.4 days.
Residue Analysis Methods and Degradation Regularity of Metalaxyl-M in Tobacco Leaves and Soils
Metalaxyl-M residues in tobacco leaves and soil were analyzed by high performance liquid chromatography. In this method residues were extracted with acetone and methyl alcohol, cleaned up on a column of florisil and activated carbon mixtures, and determined with an ultraviolet (UV) detector. Recoveries were 92.14%~97.12% for fresh leaves and 93.36%~96.46% for soisl respectively, and relative standard deviations (RSDs) were 3.2%~4.8% and 2.2%~2.9% respectively. The degradation rates of metalaxyl-M were faster in tobacco leaves than in soils, and the degradation half-life times were 1.2~1.5 days in tobacco leaves and 6.39~12.77 days in soils.
Compressive and flexural properties of hemp fiber reinforced concrete
The compressive and flexural properties of hemp fiber reinforced concretes (FRC) were examined in this paper. Natural hemp fiber was mixed using dry and wet mixing methods to fabricate the FRC. Mechanical properties of the FRC were investigated. The main factors affecting compressive and flexural properties of the FRC materials were evaluated with an orthogonal test design. Fiber content by weight has the largest effect. The method for casting hemp FRC has been optimised. Under the optimum conditions, compressive strength increased by 4 %, flexural strength increased by 9 %, flexural toughness increased by 144 %, and flexural toughness index increased by 214 %.