A field experiment with separately tile‐drained plots was used to study the ability of oilseed radish (Rhaphanus sativus L.), as a cover crop sown after harvest of a main crop of cereals or peas, to reduce nitrogen (N) and phosphorus (P) leaching losses from a clay loam in southern Sweden over 6 years. In addition to oilseed radish in pure stand, two cover crop mixtures (hairy vetch (Vicia villosa) and rye (Secale cereale) for 3 years and oilseed radish in mixture with buckwheat (Fagopyrum esculentum) for 2 years) were tested. The cover crop plots (three replicates per treatment) were compared with unplanted plots as a control. Plots cropped with oilseed radish during autumn (August–November) had significantly smaller yearly mean N concentration in drainage water over 5 of 6 years compared with unplanted controls. Mineral N content in the soil profile in autumn was significantly less in oilseed radish plots than for control plots in all years. The cover crop mixtures of hairy vetch and rye or buckwheat and oilseed radish also showed the potential to reduce soil mineral N in autumn and N concentration in drainage water, compared with unplanted controls. The cover crops had no impact on P leaching. In conclusion, oilseed radish has the ability to reduce leaching losses of N, without increasing the risk of P leaching.

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Greenhouse gas emissions from drained agricultural peatlands contribute significantly to global warming. In a laboratory study using intact cores of peat soil from eight different sites in Sweden, factors controlling the emission of the greenhouse gases nitrous oxide (N2O) and methane (CH4) were examined. Soil properties, and the abundance of the total microbial community (16S rRNA gene abundance), and genes encoding for functions controlling N2O emissions (bacterial and archaeal amoA, nirS, nirK, nosZI, and nosZII) were analyzed and compared against measured greenhouse gas emissions. Emissions were measured at different drainage levels, i.e., higher soil water suction values, since drainage is an important factor controlling greenhouse gas emissions from peat soils. The results showed that N2O and CH4 emissions were generally low, except for N2O emissions at near water-saturated conditions, for which three soils displayed high values and large variations in fluxes. Relationships between N2O emissions and soil properties were mainly linked to soil pH, with higher emissions at lower pH. However, specific assemblages of nitrogen cycling guilds that included nosZII, typically present in non-denitrifying N2O reducers, were detected in soils with low N2O emissions. Overall, these results indicate that both pH and biotic controls determine net N2O fluxes.

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