Soil metabolism of a new herbicide, [14C]Pyribenzoxim, under flooded conditions

To elucidate the fate of a new pyrimidinyloxybenzoic herbicide, pyribenzoxim, a soil metabolism study was carried out with [14C]pyribenzoxim applied to a sandy loam soil under flooded conditions. The material balance of applied radioactivity ranged from 96.4 to 104.4% and from 96.1 to 101.9% for nonsterile and sterile soils, respectively. The half-life of [14C]pyribenzoxim was calculated to be approximately 1.3 and 9.4 days for nonsterile and sterile soils, respectively. The metabolites identified during the study were 2,6-bis(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid (M1) and 2-hydroxy-6-(4,6-dimethoxypyrimidin-2-yloxy)benzoic acid (M2), resulting from the cleavage of the ester bond and subsequent hydrolysis. The nonextractable radioactivity levels increased to 37.8% for nonsterile conditions at 50 days after treatment and to 38.2% for sterile conditions at 60 days after treatment. Fractionation of the nonextractable soil residues indicated that bound radioactivity was associated mainly with humin fraction. No significant volatile products or [14C]carbon dioxide was observed during the study. On the basis of these results, pyribenzoxim is considered to undergo rapid degradation in soil by microbial and chemical reactions, mainly hydrolysis, which limits its transfer to and accumulation in lower soil layers and groundwater. Therefore, the possibility of environmental contamination from the use of pyribenzoxim is expected to be very low.     

Carbon mineralization and retention of livestock manure composts with different substrate qualities in three soils

Purpose  

Since substrate quality can influence the C mineralization pattern of compost in soils, proper selection of compost is important in increasing soil organic carbon (SOC) levels. This study investigated the effect of substrate quality of livestock manure composts on compost C mineralization and retention in soils.     

Studies of Spatial Variabilities of Airborne Metals Across Four Different Land-Use Types

The concentrations of seven metals (Fe, Pb, Mn, Ni, Cd, Cu, and Cr) associated with the total suspended particles (TSPs) were analyzed regularly from the four sampling sites of different land-use types within the boundary of Won Ju city, Korea during1991 through 1995. The mean concentration data for the four sitesselected to represent grassland, residential, commercial, and industrial areas fell in a relatively broad range of: 1440–2240 (Fe), 88–326 (Pb), 2–4 (Cd), 8–21 (Cr),194–469 (Cu), 32–95 (Mn), and 15–26 (Ni) ng m^-3. The data, when compared across the different study sites, generally exhibited systematic trends in accordance withthe site-selection scheme; most metals exhibited increase in their concentration levels across grassland through industrial site. Examinations of data also indicated the possibility that spatial factors play complicated roles on both long- and short-term distribution of metals. From all four sites studied, severalmetals (e.g., Fe, Pb, Mn, Ni, and Cd) consistently showed theirseasonal trends characteristic of high winter/spring values. In addition, the analysis of long-term distribution trendsindicated that the concentrations of many metals droppedsteadily at four sites (e.g., Fe, Pb, and Mn). When these metaldata were compared among different sites (land-use types), significant correlations were seen frequently for such metals asFe, Pb, Cd, and Cr. Investigations of inter-metal relationshipsindicated that strong correlations were more abundant from such metal pairs as Fe-Pb, Pb-Mn, and Mn-Fe. In addition, the cases for such strong correlations were seen more abundantly from grassland (and residential) than industrial (and commercial) site. Factor analysis was also conducted to distinguish sourceprocesses affecting metal distributions in the study area. Results of this analysis suggest that the metal distributions ofthe individual sites may be affected most significantly by distinctive source processes of their own.     

Purification and characterization of an antifungal protein, C-FKBP, from Chinese cabbage

An antifungal protein was isolated from Chinese cabbage (Brassica campestris L. ssp. pekinensis) by buffer-soluble extraction and two chromatographic procedures. The results of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry revealed that the isolated Chinese cabbage protein was identical to human FK506-binding protein (FKBP). A cDNA encoding FKBP was isolated from a Chinese cabbage leaf cDNA library and named C-FKBP. The open reading frame of the gene encoded a 154-amino acid polypeptide. The amino acid sequence of C-FKBP exhibits striking degrees of identity with the corresponding mouse (61%), human (60%), and yeast (56%) proteins. Genomic Southern blot analyses using the full-length C-FKBP cDNA probe revealed a multigene family in the Chinese cabbage genome. The C-FKBP mRNA was highly expressed in vegetative tissues. We also analyzed the antifungal and peptidyl-prolyl cis-trans isomerase activity of recombinant C-FKBP protein expressed in Escherichia coli. This protein inhibited pathogenic fungal strains, including Candida albicans, Botrytis cinerea, Rhizoctonia solani, and Trichoderma viride, whereas it exhibited no activity against E. coli and Staphylococcus aureus. These results suggest that recombinant C-FKBP is an excellent candidate as a lead compound for the development of antifungal agents.     

Differences in isotopic fractionation of nitrogen in water-saturated and unsaturated soils

Temporal variations in δ¹⁵N of NH₄⁺ and NO₃⁻ in water-saturated and unsaturated soils were examined in a laboratory incubation study. Ammonium sulfate (δ¹⁵N=−2.6‰) was added to 25 g samples of soil at concentrations of 160 mg N kg⁻¹. Soils were then incubated under unsaturated (50% of water holding capacity at saturation, WHC) or saturated (100% of WHC) water conditions for 7 and 36 d, respectively. During 7 d incubation of unsaturated soil, the NH₄⁺-N concentration decreased from 164.8 to 34.4 mg kg⁻¹, and the δ¹⁵N of NH₄⁺ increased from −0.4 to +57.2‰ through nitrification, as evidenced by corresponding increase in NO₃⁻-N concentration and lower δ¹⁵N of NO₃⁻ (product) than that of NH₄⁺ (substrate) at each sampling time. In saturated soil, the concentration of NH₄⁺-N decreased gradually from 162.4 to 24.2 mg kg⁻¹, and the δ¹⁵N values increased from +0.8 to +21.0‰ during 36 d incubation. However, increase in NO₃⁻ concentration was not observed due to loss of NO₃⁻ through concurrent denitrification in anaerobic sites. The apparent isotopic fractionation factors (α_s/p) associated with decrease in NH₄⁺ concentration were 1.04 and 1.01 in unsaturated and saturated soils, respectively. Since nitrification is likely to introduce greater isotope fractionation than microbial immobilization, the higher value for unsaturated soil probably reflected faster nitrification under aerobic conditions. The lower value for saturated soil suggests that immobilization and subsequent remineralization of NH₄⁺ were relatively more dominant than nitrification under the anaerobic conditions.     

Urea-nitrogen transformation and compost-nitrogen mineralization in three different soils as affected by the interaction between both nitrogen inputs

Interactive effects of a combined application of urea and compost on the fates of urea-N and net mineralization of compost-N in three soils with different contents of organic-C and inorganic-N were examined through an aerobic 6-week incubation study. Soils were each subjected to four treatments of urea and compost applied at rates of 0 and 0 mg N kg^-1 (control), 115 and 0 mg N kg^-1, 0 and 115 mg N kg^-1, and 70 and 45 mg N kg^-1, respectively. The interactive effects of a combined application of compost and urea on their N transformations varied depending on the contents of indigenous inorganic-N and organic-C in soils. Urea hydrolysis was increased by compost blending only in soils with a relatively low organic-C content. Compost blending increased N immobilization, thus decreasing nitrification of urea-derived N in soils with high organic-C and inorganic-N contents, whereas the reverse was observed in soils with low nutrient contents. Urea blending, by providing inorganic-N, consistently increased net mineralization of compost-N irrespective of soil characteristics, although the increase was much smaller in soil with high indigenous inorganic-N. From the results, it could be concluded that a combined application of chemical fertilizer would improve the compost use efficiency by increasing mineralization of compost-N particularly in soil with a low inorganic-N content. This study also suggests that compost blending would increase immobilization of urea-N in soils with high C and N contents, whereas it would increase nitrification of fertilizer-N in soils with low nutrients contents, thus resulting in increased NO₃ ^- leaching.