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The use of anaerobic digestates as fertilizer is proposed as a means to close agricultural nutrient cycles. However, digestates have higher inorganic nitrogen contents than raw manures, which could translate into increased emissions of potent greenhouse gases such as nitrous oxide (N 2 O) and methane (CH 4). To mitigate these emissions, the addition of biochar with high nutrient absorption capacity is suggested. To quantify the effects of anaerobic digestion and biochar amendment on N 2 O and CH 4 emissions, we conducted a study over 33 months with four different crops (silage maize, winter wheat, winter barley, and forage grass). We measured soil parameters such as mineral nitrogen, moisture, and temperature. The N 2 O emissions after application of digestates were generally similar to those observed after cattle slurry or mineral fertilizer application. The highest N 2 O emissions were observed in the first year of the experiment during maize cultivation and were strongly influenced by high soil nitrate concentrations, which were likely linked to enhanced soil organic N mineralization after ley termination. The CH 4 emissions were mostly negative. The addition of biochar to co-digested manure before application at an annual rate of 2 t ha− 1 had no effect on N 2 O emissions but led to short-lived CH 4 peaks from organic fertilizers directly after spreading. We conclude that digestates do not promote larger N 2 O emissions than mineral fertilizers or cattle slurry, and that biochar addition to digestates in small application quantities does not reduce N 2 O emissions but bears the risk of CH 4 release. • N 2 O emissions were strongly affected by crop and position in the rotation. • Highest N 2 O emissions in maize after grass-clover ley. • No consistent effect of mineral vs. liquid organic fertilizers on N 2 O emissions. • Biochar amendment to digested manure did not alter field N 2 O emissions. • Short-lived CH 4 peaks after biochar amendment to digested manure at field application. [ABSTRACT FROM AUTHOR]

Balancing the nitrogen (N) budgets of agricultural systems is essential for sustaining yields at lower environmental costs. However, it is still rare to find reports on the total N budgets of agricultural systems including all N fluxes in the literature. Here, we conducted a comprehensive study on the effects of different N fertilizers (control, synthetic fertilizer, 60% synthetic fertilizer N plus 40% pig manure N, pig manure N applied at the same rate of 280 kg N ha −1 yr −1 ) on N pools, cycling processes, fluxes and total N balances in a subtropical wheat-maize rotation system in China by monitoring in situ N fluxes combined with field 15 N-tracer and 15 N isotope-dilution techniques. The warm and wet maize season was associated with significantly larger N losses via gaseous and hydrological pathways than the cooler and drier wheat season. Nitrate leaching and NH 3 volatilization were the main N loss pathways, accounting for 78% and 93% of the annual hydrological and gaseous N losses, respectively. The field 15 N tracing experiment showed that the wheat system had a high N retention capacity (∼50% of 15 N application), although the N residence time was short. In the subsequent maize season, 90% of the residual 15 N-labeled fertilizer in the soil that had been applied to the wheat system was utilized by plants or lost to the environment. The combined application of synthetic and organic fertilizers (pig manure) or application of pig manure resulted in significantly higher soil N retention and lower NO 3 − leaching, while yields remained unaffected. However, the application of manure resulted in larger NH 3 volatilization losses compared with the application of synthetic fertilizer alone. Thus, our study suggests that a combination of synthetic and organic N fertilizers is suitable for sustaining agricultural productivity while reducing environmental N losses by fostering interactions between the soil C and N cycles. [ABSTRACT FROM AUTHOR]

Integrated nitrogen (N) management strategies could make significant contributions to improving the efficiency of N use in the northern Corn Belt, particularly for maize, which has high N requirements. Using legume cover crops has been shown to increase both the soil's capacity to supply N and nitrogen use efficiency (NUE), through the reduction in the amount of N fertilizer that must be applied to the following crops. However, the impact of non-legume crops such as winter wheat ( Triticum aestivum L.) on the diminishing return function between crop yield and N supply and its influence on N fertilizer use remains unclear. We hypothesized that maintaining wheat in short maize and soybean- based rotations is instrumental to improve cropping system performance and increase N fertilizer use efficiency while decreasing N requirements for maize. Seven maize and soybean rotations with different frequency of winter wheat with or without underseeded red clover ( Trifolium pratense L. ) were grown in two tillage systems (conventional and zone-tillage) and four long-term N regimes in Ridgetown, ON, Canada (2009–2013). Wheat in the rotation increased maize and soybean yields, negated crop yield lags due to zone-tillage, and decreased maximum economic rates of fertilizer N (MERN). The benefits of wheat in the rotation on maize yield were negated by high N rates; however, similar yields were obtained with lower N levels in rotationally grown maize, resulting in a 17% (conventional till) to 21% (zone-till) increase in partial factor productivity for N fertilizer at MERN (PFP MERN ). While N benefits to crops following wheat alone may be attributed to a higher indigenous plant available soil N, underseeding red clover further increased the agronomic efficiency (AE) of N fertilizer (AE MERN ) up to 32%. Maize yields were also less limited by N supply and less responsive to N fertilization when grown in rotation with wheat, especially in the zone-till system. These results highlight the value of wheat as a system component of dominant maize/soybean short rotations of Ontario and its potential to increase both maize and soybean productivity using less N input. [ABSTRACT FROM AUTHOR]