Relationship between imidacloprid residues and control effect on cotton aphids in arid region.

In this case, the dissipation and residues of imidacloprid as well as its control efficacy against aphids (Aphis gossypii Glover) in cotton cropping system were reported. After the final spray at the rates of 10.5-42.5 g a.i. ha-1, the initial deposits were 0.59-2.25 mg kg-1 with half-lives of 2.12-2.84 days on leaves and 0.06-0.21 mg kg-1 with half-lives of 1.51-4.20 days in soil, respectively. The initial residues were significantly higher with longer persistence in the upper position of the leaf than in middle and lower positions. The different application dosages could induce a significant difference in the initial deposits, but not show consistent correlation with the dissipation rate. The repeated applications of imidacloprid could alter its residue levels and dissipation rates. The long-term residue concentrations of imidacloprid (60 days after the final application) reached to the nondetectable level in soil. Combined with the control efficacy results, it was considered that the recommended dose of imidacloprid on cotton could be used effectively and safe in this arid area from the view of crop protection and environmental contamination.

Carbonyl sulfide (COS) and carbon disulfide (CS2) exchange fluxes between cotton fields and the atmosphere in the arid area in Xinjiang, China.

Due to the important roles of carbonyl sulfide (COS) and carbon disulfide (CS2) in atmospheric chemistry, this study was designed to determine different proportions of COS and CS2 fluxes contributed from different sources, i.e., vegetation, soil and roots, at monthly and hourly timescales in the arid area in Xinjiang, China. Results indicated that the seasonal net uptake of COS by vegetation was predominant in the growing season. The CS2 fluxes from vegetation and soils had no significant seasonal variations compared with COS. The exchange rates of COS and CS2 have been found to be stimulated by the addition of nutrients in the form of urea fertilizer. Compared with the results of plots that were treated only with nitrogen, the treatments with both nitrogen and sulfur displayed no significant difference in the exchange fluxes. The results of compartment experiments indicated that the aboveground plants had the highest uptake of COS and had a vital role in the uptake of COS during the main growth period. The shares of COS emissions from the soil and roots increased to 6-17% and 55-58%, respectively, in the total COS fluxes when conditions, such as drought and senescence, were unfavorable for the developmental of vegetation. Observations of the preliminary diurnal fluxes indicated that the fluxes that occurred at night, with contributions from soils and plants, accounted for 27% of the total daily uptake of COS uptake. These quantitative results may be reasonably accounted for the use of COS as a promising tracer to obtain independent constraints on terrestrial carbon exchange at regional to global scales for their response to special environmental conditions in semiarid area.