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Nitrous oxide (N-N2O) emissions in the agricultural sector represent ca. 25% of total N-N2O emissions on a global scale. In Argentina, information on agricultural emissions is scarce, and thus, N-N2O emissions are estimated by IPCC equations. Most reports in Argentina have estimated N-N2O emissions at crop scale, while few studies estimated emissions at the cropping system scale. Soybean in Argentina is mainly planted as monoculture, though, the inclusion of cereals in crop rotations may modify soil properties associated with N-N2O emissions such as water-filled pore space (%WFPS), soil temperature, or nitrate content. The objectives of this work were to: i) compare N-N2O emissions in crop sequences that include soybean in different proportions; ii) evaluate the impact of these emissions in relation with N inputs (fertilizer + BNF) at the cropping sequence level, and iii) compare these observations with emissions as estimated by the IPCC equation (tier 1). During two years, N-N2O emissions, soil N-NO3-, soil WFPS, and soil temperature were measured biweekly in a long-term experiment under no-tillage in four sequences: i) full-season soybean monoculture (S-S); ii) winter cover crop/soybean (CC/S); iii) double-cropped wheat/soybean -- maize (W/S-M), and vi) double-cropped wheat/soybean -- winter cover crop/maize (W/S-CC/M). Aboveground biomass, yield (expressed in glucose equivalents), and nitrogen (N) uptake were determined for each crop at harvest. For soybean, additionally to these variables, N derived from biological N fixation (BNF) was determined, as well. N-N2O emissions were scaled to yield and to vegetative biomass. During the two years of this study, cumulated biomass (expressed in glucose equivalents) was significantly lower in S-S and CC/S (29.5 and 36.8 Mg GluEq ha−1, respectively) than in W/S-M and W/S-CC/M (48.6 and 54.6 Mg GluEq ha−1, respectively). In the same period, exported cumulated N with grains was similar among sequences averaging 277 kg N ha−1, while the largest cumulated N input (N fertilizer + BNF) was 392 kg N ha−1 in W/S-CC/M, surpassing the other sequences by 100%. N-N2O flux rates were the lowest in W/S-M (7.8 μg N-N2O m-2h−1) and the highest in CC/S (19.0 μg N-N2O m-2h−1). Therefore, at the cropping sequence level, N-N2O emissions represented on average 0.62% of cumulated N inputs. A multiple regression model indicated that N-N2O emissions were more related to soil %WFPS (0–20 cm) and soil temperature (at 10 cm). IPCC direct emission equation (tier 1) overestimated N-N2O emissions for W/S-M and W/S-CC-M. In absolute terms, sequences including cereals showed similar cumulated emissions to S-S, however, when emission were scaled to unit yield or vegetative biomass, sequences that included cereals in the rotation attenuated N-N2O losses.

Nitrogen (N) is an essential element and usually a limiting factor in corn (Zea mays, L.) production; yet N build-up in the soil might lead to nitrate (N-NO3) leaching, and release of nitrous oxide (N2O) by denitrification, thus contributing to both water and air pollution. Cover crops (CCs) have been used to scavenge surplus soil N, which might lead to a decrease in the substrate needed for N2O production from the field. The objective of this study was to determine the effect that corn-soybean rotations with different CCs, and tillage methods have on greenhouse gas (GHG) emissions and crop yields in Illinois, USA. The experimental design was a split-block arrangement of tillage (chisel vs. no-till) and CC rotations in a RCBD with 4 replications with the corn and soybean [Glycine max (L.) Merr.] phases present each year. Greenhouse gas emissions - nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) – soil available N, (NO3 and NH4) were sampled only during the actively growing cover crop period and from the corn phase of each rotation over a period of 4 years (2013–2017). Cover crop rotations included five corn-soybean rotations with different CCs and one with an unseeded control. Our results suggest that CC efficacy in a humid continental climate, like central Illinois, is associated with fall and winter temperature and precipitation. In two of the years, spring CC growth was poor due to unseasonably cold temperatures; however, in two of the other years, weather was favorable and spring CC biomass ranged from 2-3 Mg ha−1 from three of the species tested. Where spring CC biomass was measurable, a fivefold reduction in N2O emissions was associated to significant reductions in soil N-NO3. Corn yields were not improved with the utilization of CCs and a yield decrease of 12% occurred in the annual ryegrass (Lolium multiflorum Lam.) rotation. The findings from this study are the first from Illinois and one of few from the Midwest showing the potential benefits CCs have in reducing GHG emissions. Moreover, given adequate growing conditions, some CC species can significantly reduce GHG emissions, decrease residual soil N, and have no negative effects on cash crop yields.

Silver scurf, caused by the fungus Helminthosporium solani, is an important disease affecting potato tubers. Control of the disease has been hampered by the development of H. solani strains resistant to thiabendazole. Currently, there is no alternative to thiabendazole for the efficient control of the disease. In this study, 45 selected soils from the province of Quebec were tested in greenhouse assays for their effect on silver scurf development. The results showed that soil influenced significantly silver scurf development and that specific soils displayed an interesting level of suppressiveness against potato silver scurf. Investigations into the cause(s) of soil suppressiveness revealed on the one hand, significant negative correlations between silver scurf severity and soil N-NO3 and available Fe contents, and on the other hand, absence of significant correlations between silver scurf severity and the different soil microbial populations. Investigations also revealed the presence of microorganisms antagonistic to the pathogen in the most suppressive soils. The antagonist microorganisms isolated in those soils were Bacillus cereus, Cellulomonas fimi, Kocuria varians, Pseudomonas putida, Rhodococcus erythropolis and Rhodococcus globerulus. Considering that few microorganisms were previously reported to display antagonism against H. solani, these results open the way to new avenues of investigation towards achieving biocontrol of silver scurf.