No abstract

Chlorimuron-ethyl, ethyl-2-[[[[(4-methoxy-6-chloro-pyrimidin-2-yl)amino]carbonyl]amino] sulfonyl]benzoate, is used as a pre- and postemergence herbicide for the control of important broadleaved weeds in soybean and maize. Due to its phytotoxicity to rotation crops, concerns regarding chlorimuron contamination of soil and water have been raised. Although it is degraded in the agricultural environment primarily via pH- and temperature-dependent chemical hydrolysis, microbial transformation also has an important role. Fungi such as Fusarium and Alternaria are unable to survive in artificial media containing chlorimuron-ethyl at 25 mg L(-1) . However, Aspergillus niger survived in minimal broth containing chlorimuron at 2 mg mL(-1) . Aspergillus niger degraded the herbicide to harvest energy through two major routes of degradation. One route involves the cleavage of the sulfonylurea bridge, resulting in the formation of two major metabolites, namely ethyl-2-aminosulfonylbenzoate (I) and 4-methoxy-6-chloro-2-amino-pyrimidine (II). The other route is the cleavage of sulfonylamide linkage, which generates the metabolite N-(4-methoxy-6-chloropyrimidin-2-yl) urea (III). Two other metabolites, saccharin (IV) and N-methyl saccharin (V), formed from metabolite II, were also identified. A metabolic pathway for the degradation of chlorimuron-ethyl by A. niger has been proposed.

Chlorimuron-ethyl is relatively stable in water buffered to pH 7.0 and 9.0, but hydrolyzes readily (half-life, 14 d) in water buffered to pH 4.0. In addition, chlorimuron-ethyl photodegrades rapidly and extensively in aqueous solution. The predominant photoproducts are 4-methoxy-6-chloro-2-aminopyrimidine, ethyl 2-aminosulfonylbenzoate, N-(4-methoxy-6-chloropyrimidin-2-yl)methyl urea, and o-benzoic sulfimide (saccharin). A minor deesterified product (chlorimuron) was evident. The decrease in chlorimuron-ethyl concentration in aqueous solutions followed first-order kinetics. The rate of degradation in different types of water followed the order irrigation water > tap water > distilled water. Chlorimuron-ethyl photodegraded in pH 4, 7, and 9 buffer solutions under both UV and sunlight. A faster degradation rate in pH 4.0 buffer solution was observed. Keywords: Chlorimuron-ethyl; aqueous solution; photolysis

Soil erosion and shifting cultivation are the major constraints to agriculture in the northeastern region of India. Low acceptance of cost-intensive soil conservation technologies (e.g., terracing) calls for developing low-cost erosion control measures. Thus, a field experiment was conducted during the monsoon period of 2008 and 2009, in runoff plots on a land slope of 40% to test the hypothesis that weed cover, if properly managed, minimizes soil erosion and improves soil productivity. The treatments implemented in duplicates were: maize (Zea mays) under shifting cultivation (T 1), maize on contour lines (T 2), groundnut (Arachis hypogea) on upper and maize on lower half of treatment plot, with both on contour lines (T 3), groundnut on contour lines (T 4) and maize on contour lines with natural vegetation as buffer strips (T 5). The average sediment concentration of runoff water varied from 5.20 g L −1 (T 1) to 1.07 g L −1 (T 5) in 2008 and from 3.84 (T 1) to 0.89 g L −1 (T 5) in 2009. The soil loss ranged from 20.8 (T 1) to 4.7 Mg ha −1 (T 5), with corresponding loss of 670-147 kg ha −1 of SOC, 6.85-1.48 kg ha −1 of available N, and 2.14-0.87 kg ha −1 of available P. Weed strips and weed mulch on the upstream side of maize rows in T 5 led to formation of stable mini-terraces promoting better plant and root growth. This study indicates cover management involving selective weed retention can reduce soil erosion, favourably modify land slope and promotes soil productivity.

A number of 2-silicon substituted 1,3-dienes have been prepared by one of three routes: 1) Reactions of 1,3-dienyl Grignard reagents with silyl electrophiles or silyl Grignard reagents with 1,3-dienyl electrophiles; 2) Hydrosilylation of enynes; 3) Enyne cross metathesis. The strengths and limitations of each preparative method are discussed.