Response of irrigated crops to split-N application

Non-Peer ReviewedThe efficiency and benefits of split N applications by cereals and oilseed was evaluated at the Irrigation Fann at Outlook. In 1988, canola (Westar) received 0, 75 + 75, or 150 kg N/ha in the form of urea (U) or urea-ammonium nitrate (UAN). In 1989, durum (Kyle), soft wheat (Fielder) and canola (Westar) received 0, 100, 100+100, or 200 kg N/ha in the form of U or ammonium nitrate (AN). Plants were harvest five times during the growing season. In 1988, the second N application occurred at 54 days after planting. In 1989, the second N application for durum and soft wheat occurred at 45 days after planting (Feekes 7) and 38 days after planting for canola. In 1988, unfertilized canola showed a grain yield of 1832 kg/ha, whereas the application of 150 kg N increased grain yield to 3012 kg/ha. Split-N application, however, did not increase grain yield as compared with canola fertilized with 150 kg N/ha at time of seeding. No significant differences in grain yield between U and UAN fertilized canola were found. In 1989 canola, durum and soft wheat responded strongly to N fertilizer. Unfertilized durum showed a grain yield of 2267 kg/ha, whereas durum fertilized with 200 kg N/ha showed a grain yield of 3952 kg/ha. Grain yields for unfertilized and fertilized soft wheat were 2981 and 5358 kg/ha, respectively. N fertilization increased grain yield of canola from 1049 to 1890 kg/ha. However, no differences in grain yield were found between crops that received all fertilizer-N at time of seeding and crops that received half of its fertilizer-N 38 days after planting. It was found that most of the N required for crop growth was taken up early in the growing season. It appears that N should be available soon after seeding and that under Saskatchewan growing conditions the time frame during which the second split N application can be carried out successfully is short, or perhaps, even non-existent

Comparative responses of river biofilms at the community level to common organic solvent and herbicide exposure

International audienceResidual pesticides applied to crops migrate from agricultural lands to surface and ground waters. River biofilms are the first aquatic non-target organisms which interact with pesticides. Therefore, ecotoxicological experiments were performed at laboratory scale under controlled conditions to investigate the community-level responses of river biofilms to a chloroacetanilide herbicide (alachlor) and organic solvent (methanol) exposure through the development referenced to control. Triplicate rotating annular bioreactors, inoculated with river water, were used to cultivate river biofilms under the influence of 1 and 10 μg L−1 of alachlor and 25 mg L−1 of methanol. For this purpose, functional (thymidine incorporation and carbon utilization spectra) and structural responses of microbial communities were assessed after 5 weeks of development. Structural aspects included biomass (chlorophyll a, confocal laser scanning microscopy) and composition (fluor-conjugated lectin binding, molecular fingerprinting, and diatom species composition). The addition of alachlor resulted in a significant reduction of bacterial biomass at 1 μg L−1, whereas at 10 μg L−1, it induced a significant reduction of exopolymer lectin binding, algal, bacterial, and cyanobacterial biomass. However, there were no changes in biofilm thickness or thymidine incorporation. No significant difference between the bacterial community structures of control and alachlor-treated biofilms was revealed by terminal restriction fragment length polymorphism (T-RFLP) analyses. However, the methanol-treated bacterial communities appeared different from control and alachlor-treated communities. Moreover, methanol treatment resulted in an increase of bacterial biomass and thymidine incorporation as well. Changes in dominant lectin binding suggested changes in the exopolymeric substances and community composition. Chlorophyll a and cyanobacterial biomass were also altered by methanol. This study suggested that the concentration-dependent effect of alachlor mainly remains limited to biomass and growth inhibition without apparent changes of structural and functional characteristics measured. Our work also establishes the potential toxic effects of organic solvents on river biofilm in ecotoxicological experiments. For the ecotoxicological experiments, the alternative of dissolution in organic solvent followed by its evaporation, depositing the chemical on a glass surface prior to dissolution in river water used here, appears to allow exposure while minimizing the effect of organic solvent. © 2015, Springer-Verlag Berlin Heidelberg

Resilience and recovery: The effect of triclosan exposure timing during development, on the structure and function of river biofilm communities

Triclosan (TCS) is a ubiquitous antibacterial agent found in soaps, scrubs, and consumer products. There is limited information on hazardous effects of TCS in the environment. Here, rotating annular reactors were used to cultivate river biofilm communities exposed to 1.8μgl-1 TCS with the timing and duration of exposure and recovery during development varied. Two major treatment regimens were employed: (i) biofilm development for 2, 4 or 6 weeks prior to TCS exposure and (ii) exposure of biofilms to TCS for 2, 4 or 6 weeks followed by recovery. Biofilms not exposed to TCS were used as a reference condition. Communities cultivated without and then exposed to TCS all exhibited reductions in algal biomass and significant (p&lt;0.05) reductions in cyanobacterial biomass. No significant effects were observed on bacterial biomass. CLSM imaging of biofilms at 8 weeks revealed unique endpoints in terms of community architecture. Community composition was altered by any exposure to TCS, as indicated by significant shifts in denaturing gradient gel electrophoresis fingerprints and exopolymer composition relative to the reference. Bacterial, algal and cyanobacterial components initially exposed to TCS were significantly different from those TCS-free at time zero. Pigment analyses suggested that significant changes in composition of algal and cyanobacterial populations occurred with TCS exposure. Bacterial thymidine incorporation rates were reduced by TCS exposure and carbon utilization spectra shifted in terms substrate metabolism. Direct counts of protozoans indicated that TCS was suppressive, whereas micrometazoan populations were, in some instances, stimulated. These results indicate that even a relatively brief exposure of a river biofilm community to relatively low levels of TCS alters both the trajectory and final community structure. Although some evidence of recovery was observed, removal of TCS did not result in a return to the unexposed reference condition.</p