Challenges of accounting nitrous oxide emissions from agricultural crop residues.

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2 O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2 O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2 O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2 O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2 O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2 O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2 O emissions.

Potential for the adoption of measures to reduce N2O emissions from crop residues in Denmark.

Crop residues represent a climate change dilemma: they can promote carbon (C) sequestration, but they may also stimulate emissions of the powerful greenhouse gas nitrous oxide (N2O). Although there are crop residue management measures to reduce N2O emissions, N2O reductions achieved at national scale with these measures have been seldom studied, and how farmers' willingness to accept the measures constrains their potential remains largely unknown. Using Denmark as a case study, we combined a survey (completed by 592 farmers) and national data to assess the practical potential and obstacles for the successful implementation of management strategies to reduce N2O emissions from crop residues. Crop residue removal (particularly from vegetables and cover crops) and nitrification inhibitors were identified as effective in reducing N2O emissions from a biophysical perspective. If all aboveground crop residues from vegetables and cover crops were removed, N2O emissions could be reduced by 0.181 Gg N2ON, corresponding to 11% of the total N2O emissions from crop residues nationally. However, a low percentage of farmers would be willing to remove crop residues from the field, especially for vegetables and cover crops (25%), in connection to the possible short- to medium-term reduction in C sequestration. Similarly, use of nitrification inhibitors would reduce emissions by 0.247 Gg N2ON, corresponding to 15% of the total residue N2O emissions, and only 37% of all farmers would accept their use. Our results highlight that farmer' preferences for the adoption of measures can constrain the use of the few available effective mitigation options. Better knowledge dissemination and advisory services are crucial to address this challenge; farmers may be motivated to remove aboveground crop residues by highlighting the proportionally more important contribution of belowground residues to C sequestration, and that aboveground residues may have commercial value (biorefining, biogas, biofuel), although these options need further development.

A review and meta-analysis of mitigation measures for nitrous oxide emissions from crop residues.

Crop residues are of crucial importance to maintain or even increase soil carbon stocks and fertility, and thereby to address the global challenge of climate change mitigation. However, crop residues can also potentially stimulate emissions of the greenhouse gas nitrous oxide (N2O) from soils. A better understanding of how to mitigate N2O emissions due to crop residue management while promoting positive effects on soil carbon is needed to reconcile the opposing effects of crop residues on the greenhouse gas balance of agroecosystems. Here, we combine a literature review and a meta-analysis to identify and assess measures for mitigating N2O emissions due to crop residue application to agricultural fields. Our study shows that crop residue removal, shallow incorporation, incorporation of residues with C:N ratio > 30 and avoiding incorporation of residues from crops terminated at an immature physiological stage, are measures leading to significantly lower N2O emissions. Other practices such as incorporation timing and interactions with fertilisers are less conclusive. Several of the evaluated N2O mitigation measures implied negative side-effects on yield, soil organic carbon storage, nitrate leaching and/or ammonia volatilization. We identified additional strategies with potential to reduce crop residue N2O emissions without strong negative side-effects, which require further research. These are: a) treatment of crop residues before field application, e.g., conversion of residues into biochar or anaerobic digestate, b) co-application with nitrification inhibitors or N-immobilizing materials such as compost with a high C:N ratio, paper waste or sawdust, and c) use of residues obtained from crop mixtures. Our study provides a scientific basis to be developed over the coming years on how to increase the sustainability of agroecosystems though adequate crop residue management.

Environmentally realistic concentrations of the antibiotic Trimethoprim affect haemocyte parameters but not antioxidant enzyme activities in the clam Ruditapes philippinarum.

Several biomarkers were measured to evaluate the effects of Trimethoprim (TMP; 300, 600 and 900 ng/L) in the clam Ruditapes philippinarum after exposure for 1, 3 and 7 days. The actual TMP concentrations were also measured in the experimental tanks. The total haemocyte count significantly increased in 7 day-exposed clams, whereas alterations in haemocyte volume were observed after 1 and 3 days of exposure. Haemocyte proliferation was increased significantly in animals exposed for 1 and 7 days, whereas haemocyte lysate lysozyme activity decreased significantly after 1 and 3 days. In addition, TMP significantly increased haemolymph lactate dehydrogenase activity after 3 and 7 days. Regarding antioxidant enzymes, only a significant time-dependent effect on CAT activity was recorded. This study demonstrated that environmentally realistic concentrations of TMP affect haemocyte parameters in clams, suggesting that haemocytes are a useful cellular model for the assessment of the impact of TMP on bivalves.