Climate Overrides Effects of Fertilizer and Straw Management as Controls of Nitrous Oxide Emissions After Oilseed Rape Harvest

Oilseed rape (Brassica napus L.) is an important bioenergy crop that contributes to the diversification of renewable energy supply and mitigation of fossil fuel CO2 emissions. Typical oilseed rape crop management includes the use of nitrogen (N) fertilizer and the incorporation of oilseed rape straw into soil after harvest. However, both management options risk increasing soil emissions of nitrous oxide (N2O). The aim of this 2-years field experiment was to identify the regulating factors of N cycling with emphasis on N2O emissions during the post-harvest period. As well as the N2O emission rates, soil ammonia (NH4+) and nitrate (NO3−) contents, crop residue and seed yield were also measured. Treatments included variation of fertilizer (non-fertilized, 90 and 180 kg N ha−1) and residue management (straw remaining, straw removal). Measured N2O emission data showed large intra- and inter-annual variations ranging from 0.5 (No-fert + str) to 1.0 kg N2O-N ha−1 (Fert-180 + str) in 2013 and from 4.1 (Fert-90 + str) to 7.3 kg N2O-N ha−1 (No-fert + str) in 2014. Cumulative N2O emissions showed that straw incorporation led to no difference or slightly reduced N2O emissions compared with treatments with straw removal, while N fertilization has no effect on post-harvest N2O emissions. A process-based model, CoupModel, was used to explain the large annual variation of N2O after calibration with measured environmental data. Both modeled and measured data suggest that soil water-filled pore space and temperature were the key factors controlling post-harvest N2O emissions, even though the model seemed to show a higher N2O response to the N fertilizer levels than our measured data. We conclude that straw incorporation in oilseed rape cropping is environmentally beneficial for mitigating N2O losses. The revealed importance of climate in regulating the emissions implies the value of multi-year measurements. Future studies should focus on new management practices to mitigate detrimental effects caused by global warming, for example by using cover crops.

Condensed Tannins in White Clover (Trifolium repens) Foliar Tissues Expressing the Transcription Factor TaMYB14-1 Bind to Forage Protein and Reduce Ammonia and Methane Emissions in vitro

Grazing ruminants contribute to global climate change through enteric methane and nitrous oxide emissions. However, animal consumption of the plant polyphenolics, proanthocyanidins, or condensed tannins (CTs) can decrease both methane emissions and urine nitrogen levels, leading to reduced nitrous oxide emissions, and concomitantly increase animal health and production. CTs are largely absent in the foliage of important temperate pasture legumes, such as white clover (Trifolium repens), but found in flowers and seed coats. Attempts at enhancing levels of CT expression in white clover leaves by mutagenesis and breeding have not been successful. However, the transformation of white clover with the TaMYB14-1 transcription factor from Trifolium arvense has resulted in the production of CTs in leaves up to 1.2% of dry matter (DM). In this study, two generations of breeding elevated foliar CTs to >2% of DM. The CTs consisted predominantly of prodelphinidins (PD, 75–93%) and procyanidins (PC, 17–25%) and had a mean degree of polymerization (mDP) of approximately 10 flavan-3-ol subunits. In vitro studies showed that foliar CTs were bound to bovine serum albumin and white clover proteins at pH 6.5 and were released at pH 2.-2.5. Using rumen in vitro assays, white clover leaves containing soluble CTs of 1.6–2.4% of DM significantly reduced methane production by 19% (p ≤0.01) and ammonia production by 60% (p ≤ 0.01) relative to non-transformed wild type (WT) controls after 6 h of incubation. These results provide valuable information for further studies using CT expressing white clover leaves for bloat prevention and reduced greenhouse gas emissions in vivo.

Energy and Economic Balance between Manure Stored and Used as a Substrate for Biogas Production

The aim of the study is to draw attention to the fact that reducing methane and nitrous oxide emissions as a result of traditional manure storage for several months in a pile is not only a non-ecological solution, but also unprofitable. A solution that combines both aspects—environmental and financial—is the use of manure as a substrate for a biogas plant, but immediately—directly after its removal from the dairy barn. As part of the case study, the energy and economic balance of a model farm with dairy farming for the scenario without biogas plant and with a biogas plant using manure as the main substrate in methane fermentation processes was also performed. Research data on the average emission of ammonia and nitrous oxide from 1 Mg of stored manure as well as the results of laboratory tests on the yield of biogas from dairy cows manure were obtained on the basis of samples taken from the farm being a case study. The use of a biogas installation would allow the emission of carbon dioxide equivalent to be reduced by up to 100 Mg per year. In addition, it has been shown that the estimated payback period for biogas installations is less than 5 years, and with the current trend of increasing energy prices, it may be even shorter—up to 4 years.

The potential cost of regulation of methane and nitrous oxide emissions in U.S. agriculture

Background Most studies on the environmental impacts of agriculture have attempted to measure environmental impacts but have not assessed the ability of the sector to reduce or mitigate such impacts. Only a few studies have examined greenhouse gas emissions from the sector. This paper assesses the ability of states in the U.S. to reduce agricultural emissions of methane and nitrous oxide, two major greenhouse gases (GHGs) with important global warming potential. Methods The analysis evaluates Färe’s PAC (pollution abatement cost) for each state and year, a measure of the potential opportunity costs of subjecting the sector to GHG emissions regulation. We use both hyperbolic and directional distance functions to specify agricultural technology with good and bad outputs. Results and conclusions We find that such regulations might reduce output by an average of about 2%, although the results for individual states vary quite widely.