Impact of Land-use Change on Vertical Soil Bacterial Communities in Sabah.

Decline in forest productivity due to forest conversion is defining the Bornean landscape. Responses of bacterial communities due to land-use changes are vital and could define our understanding of ecosystem functions. This study reports the changes in bacterial community structure in organic soil (0-5 cm; O-Horizon) and organic-mineral soil (5-15 cm; A-Horizon) across Maliau Basin Conservation Area old growth forest (MBOG), Fragment E logged forest (FELF) located in Kalabakan Forest Reserve to Benta Wawasan oil palm plantation (BWOP) using two-step PCR amplicon analysis of bacteria DNA on Illumina Miseq next generation sequencing. A total of 30 soil samples yielded 893,752-OTU reads at ≥97% similarity from 5,446,512 good quality sequences. Soil from BWOP plantation showed highest unshared OTUs for organic (49.2%) and organic-mineral (50.9%) soil. MBOG soil showed a drop in unshared OTUs between organic (48.6%) and organic-mineral (33.9%). At phylum level, Proteobacteria dominated MBOG but shifted to Actinobacteria in logged and plantation soil. Present findings also indicated that only FELF exhibited change in bacterial communities along the soil depth, moving from the organic to the organic-mineral layer. Both layers of BWOP plantation soils deviated from other forests' soil in ß-diversity analysis. To our knowledge, this is the first report on transitions of bacterial community structures with different soil horizons in the tropical rainforest including Borneo, Sabah. Borneo tropical soils form a large reservoir for soil bacteria and future exploration is needed for fully understanding the diversity structure and their bacterial functional properties.

Establishing the extent of pesticide contamination in Irish agricultural soils.

To establish meaningful and sustainable policy directives for sustainable pesticide use in agriculture, baseline knowledge of pesticide levels in soils is required. To address this, five pesticides and one metabolite widely used in Irish agriculture and five neonicotinoid compounds pesticides were screened from soils from 25 fields. These sites represented a diversity of soil and land use types. Prothioconazole was detected in 16 of the 18 sites where it had been recently applied, with the highest maximum concentration quantified of 46 µg/kg. However, a week after application only four fields had prothioconazole concentrations above the limit of quantification (LOQ). Fluroxypyr was applied in 11 sites but was not detected above LOQ. Glyphosate and AMPA were not detected. Interestingly, neonicotinoids were detected in 96% of all sampling sites, even though they were not reported as recently applied. Excluding neonicotinoids, 60% of sites were found to contain pesticide residues of compounds that were not previously applied, with boscalid and azoxystrobin detected in 15 of the 25 sites sampled. The total number of pesticides detected in Irish soils were significantly negatively correlated with clay fraction, while average pesticide concentrations were significantly positively correlated with log Kow values. 17 fields were found to have total pesticide concentrations in excess of 0.5 µg/kg, even when recently applied pesticides were removed from calculations. Theoretical consideration of quantified pesticides determined that azoxystrobin has high leaching risk, while boscalid, which was detected but not applied, has an accumulation risk. This information provides insight into the current level of pesticide contamination in Irish agricultural soil and contributes to the European-level effort to understand potential impacts of pesticide contamination in soil.

Simultaneous determination of pesticides from soils: a comparison between QuEChERS extraction and Dutch mini-Luke extraction methods.

The expanding nature of the agricultural sector has fuelled the intensification of plant protection products usage, including pesticides. These pesticides may persist in soils, necessitating their accurate determination in a variety of soil types. However, due to their complex nature, the effective extraction of pesticide residues from soil matrices can present challenges to pesticide detection and quantification. This research compared two well-known extraction methods, QuEChERS and Dutch mini-Luke, by assessing their specificity, sensitivity, accuracy, precision and reproducibility in extracting seven distinct pesticides with a range of chemico-physical characteristics from Irish soils. The HPLC-UV conditions were optimised to separate the seven pesticides, and it was shown that both extraction methods successfully extracted neonicotinoids with recovery values ranging between 85 and 115%. Fluroxypyr and prothioconazole could not be efficiently extracted using QuEChERS, however, the recovery values of both the analytes ranged between 59 and 117% using Dutch mini-Luke. Furthermore, with the exception of prothioconazole using Dutch mini-Luke, both extraction methods resulted in reproducibility and precision values below or equal to 20%. Lastly, Dutch mini-Luke is noted to have a lower matrix effect than QuEChERS, except for prothioconazole. The comparison results showed that Dutch mini-Luke resulted in superior method sensitivity, better recovery, and lower matrix effect towards most investigated analytes and was the only extraction technique that successfully extracted all pesticides analysed in soil matrices.