Alachlor degradation in soils followed first‐order reaction kinetics. Half‐lives in moist soil varied from 11.30 to 34.8 days at 25°C to 95.9 to 279.6 days at 5°C, and at 15°C varied from 15.7 to 83.1 days at 5 kPa soil water stress (field capacity) to 82.8 to 281.4 days at 1500 kPa (permanent wilting point). Degradation rates in laboratory incubations with fluctuating temperatures were predicted with reasonable accuracy from the constant‐temperature data. The degradation rate and extent of adsorption were lower in subsoils than in soils from the plough layer. Degradation rate was positively correlated with microbial biomass and microbial respiration, and adsorption was positively correlated with soil organic matter content. Persistence of alachtor in field plots was correlated well with variations in weather pattern during the period September 1990 to July 1991, with an effective half‐life varying from 20 to 60 days. Persistence in the field plots was predicted accurately by a computer model of herbicide behaviour.
A new phenolic amide, dihydro-N-caffeoyltyramine (1) was isolated from the root bark of Lycium chinense Miller, along with known compounds, trans-N-caffeoyltyramine (2), cis-N-caffeoyltyramine (3), and lyoniresinol 3alpha-O-beta-D-glucopyranoside (4). Their structures were determined by spectroscopic analysis. A NBT superoxide scavenging assay revealed that three phenolic amides showed potent antioxidative activity.
Summary
The persistence and movement of residues of alachlor, alrazine and metribuzin were measured in a mini‐lysimeter system in the field. This comprised a number of soil columns (11 cm diametert; 30 cm long), and permitted the vertical distribution of residues to be determined at. intervals alter application and the collection and analysis of leaehale water. Laboratory experiments were also performed to determine the degradation rates of the three herbicides and their strengths of adsorption by the test soil. The results showed an order of degradation rate of metribuzin> alachlor>atrazine and an order of adsorption of alacblor>atrazine>melribuzin. Movement of residues in the soil columns and concentrations in the leachate were inversely related to the strength of adsorption. Parameters derived from the laboratory data were used in conjunction with weather data for the period of the field experiment in three mathematical models of pesticide leaching: VARLEACH, LEACHP and PRZM2. In most instances, the models gave acceptable predictions of the distribution of residues in soil. This was particularly so for the less mobile compound alachlor. With the most mobile compound, metribuzin, residues were not well predicted at the later sampling dates. All three models gave accurate predictions of the volumes of drainage water, but none of them predicted the concentrations of herbicide in the leachate, presumably because they do not take account of preferential flow pathways of water and solute in the soil.
This study was conducted to redetermine the rainfall erosion factor (R factor) in USLE for the estimation of soil loss at Korea. The redetermined R factor may be applied more precisely to interpret the changes of regional/yearly/seasonal patterns, including the amount of rainfall and the kinetic energy of rainfall, in Korea. This study calculated the R factors based on 60-minute precipitation data from 60 sites covering the whole country for 30 years from 1981 to 2010. As a result, the annual mean rainfall was 4,147 MJ mm ha -1 yr -1 hr -1 in Korea. Coastal regions of Jeonnam and Gyeongnam, northwest regions of Gyeonggi, and Seoul had the greater values of R factor compared to other regions. The annual mean R factors for every decade were 3,988, 4,085, and 4,370 MJ mm ha -1 yr -1 hr -1 in 1981~1990, 1991~2000, and 2001~2010, respectively. Generally, the R factors had an increasing tendency over and over pest decades. The ratios of summer R factor to total annual mean R factor were 69.8% (1981~1990), 73.7% (1991~2000), and 74.2% (2001~2010). We found that the absolute values and the relative ratios of summer rainfall are gradually increased.
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