查看更多>>摘要：Catch crop (green manure) planting is considered an efficient strategy to improve soil fertility in agro-ecosystems. Methane (CH4) emissions from paddies subjected to continuous green manure amendment though is a topic that remains unexplored. To clarify the impact of continuous green manure amendment on rice yield and CH4 emissions, a long-term trial (established in 2003, Yixing, China) was designed with the field observations conducted between 2019 and 2020. Two green manure crops (milk vetch, ryegrass) were selected as the catch crop with fallow as the control, all trialed at two N application rates i) low N dosage deriving from the optimum effect between yield-N fertilizer (LN, 200 kg ha(-1)), and ii) a higher N dose as the empirical farmer's dose (HN, 270 kg ha(-1)). The results showed that continuous green manure amendment notably increased soil organic carbon (SOC) compared to that of the control, while HN significantly increased the dissolved organic nitrogen compared to LN. The rice yield among treatments remained similar, ranging from 8.6 t ha(-1) to 9.4 t ha(-1) (two years' average). CH4 emissions were notably related to green manure, and remained unaffected by N application rate. Ryegrass amendment after 18 years remarkably stimulated the CH4 emissions compared to other treatments, while the difference between milk vetch-amended and fallow treatments was found insignificant. Ryegrass increased soil mcrA gene with the abundance becoming the highest under HN. Methanogens abundance and SOC content were the main factors affecting CH4 emissions under ryegrass addition. Moreover, the CH4 emission intensity was aligned with CH4 emissions mainly due to the similar rice yield. Overall, continuous milk vetch planting is a recommended catch crop strategy that increases soil fertility and maintains rice yield without increasing CH4 emissions.
Hall, Maura J.Zhang, GeO'Neal, Matthew E.Bradbury, Steven P....
10页
查看更多>>摘要：Adding habitat within agricultural ecosystems is necessary to reverse declines in pollinator abundance and diversity. Understanding pesticide exposure to pollinator habitat near crop fields is necessary to support risk assessments. Neonicotinoids applied to maize and soybean seeds can be transported from crop fields to adjacent habitat through dust drift during planting and/or through overland runoff or subsurface flow following planting. Pollinators, especially bees (e.g. Apidae) and monarch butterflies (Danaus plexippus), could be exposed to neonicotinoids through ingestion of contaminated plant material (e.g. milkweed leaves). Neonicotinoids have been detected in pollinator-attractive habitats near crop fields; however, the magnitude and seasonal variation of the concentration of these insecticides has not been determined. We quantified concentrations of clothianidin, thiamethoxam, and imidacloprid in soil and forb leaf tissue, including milkweed (Asclepias spp.) located within reconstructed prairies (3-4 years post-establishment) within or adjacent to maize or soybean fields. Samples taken from April through August in 2017 and 2018 were analyzed with liquid chromatography-tandem mass spectrometry; 100% of soil, 80% of vegetation from blooming forbs, and 80% of milkweed leaf tissue samples had at least one neonicotinoid present above the method detection limit (0.07-0.9 ng g-1). The maximum concentrations detected in 2017 or 2018 of clothianidin, thiamethoxam, and imidacloprid in milkweed leaf tissue samples were 6.6, 12.9, and 2.8 ng g-1, respectively. These values are 10 to 130-fold lower than the chronic LC10 values for monarch larvae, indicating it is unlikely that this route of neonicotinoid exposure will cause adverse effects to monarch larvae.
NSTL
Elsevier