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Managed grasslands are a predominant land use in northern temperate regions. They are often on poorly drained soils and contain large stocks of soil organic carbon (SOC). It is important to understand C dynamics in grasslands to better assess their role in regional C budgets. Two adjacent grassland plots, one amended with 100 [m.sup.3][ha.sup.-1] of liquid swine manure (LSM) annually since 1978, and another unamended were killed by glyphosate in the autumn or (i) left with vegetation intact. Those killed were either (ii) left as an undisturbed chemical fallow, (iii) plowed by full-inversion tillage (FIT) in the autumn, or (iv) in the spring. Following the autumn plowing, we monitored C[O.sub.2] emissions from the fallow soil surface, C[O.sub.2] concentrations in the soil profile, soil temperature, and soil water content for 1 yr. Changes in soil aggregation, the light fraction organic matter, and microbial biomass were also monitored. Plowing decreased the total microbial biomass on average by 27 g C [m.sup.-2], the quantity of water-stable aggregates by 7 to 12% and with it the concentration of light fraction organic matter. Respiration was also reduced by 142 g C[O.sub.2]-C [m.sup.-2] by autumn-FIT and 175 g C[O.sub.2]-C [m.sup.-2] by spring-FIT on unamended soils, and 90 g C[O.sub.2]-C [m.sup.-2] by autumn-FIT and 98 g C[O.sub.2]-C [m.sup.-2] by spring-FIT on amended soils. Regression analyses suggested that reductions in C[O.sub.2] emissions were due to the placement of surface SOC at depth where soil temperature and oxygen availability were attenuated. In these soils, the cool humid conditions at depth in the soil profile may act to counter-balance the physical effects of tillage thereby preserving C deep in the soil profile. Effective calculation of C budgets and changes in SOC stocks depends on the ability to reproduce the interaction between climate, soil type, land use, and management action. A more complete understanding of the effect of management actions that modify the vertical distribution of biogeochemical (particularly organic C) and environmental parameters on soil respiration in poorly drained soils is required. doi: 10.2136/sssaj2010.0059

The effect of two dairy manure treatments, solid-liquid separation (SLS) and anaerobic digestion (AD), on methane potential and the speed of production was evaluated. Assays were performed in the lab to measure methane (CH4) production over 202 d from dairy manure samples taken before and after each treatment. Compared to raw manure, CH4 emissions on a per-L basis were reduced 81% by SLS and 59% by AD, on average. The mean (SD) ultimate CH4 emission potential (B0) per kg of volatile solids (VS) was 247 (8) L CH4 kg-1 VS for raw manure, 221 (9) L CH4 kg-1 VS for separated liquid, and 160 (4) L CH4 kg-1 VS for anaerobic digestate. Thus, SLS reduced the B0 of the liquid fraction by 11% and AD reduced B0 by up to 35% compared to raw manure. Manure treatment affected the speed of CH4 production: SLS increased the CH4 production rate and thus separated liquid manure was the fastest to produce 90% of the ultimate CH4 production. Therefore, both the speed of degradation and B0 should be considered when assessing these techniques for farm-scale manure storages, because actual emission reductions will depend on storage conditions. [ABSTRACT FROM AUTHOR]

Abstract: Managed grasslands occupy a large portion of the agricultural landbase, are rich in C and N and therefore represent a risk for emissions of N2O during landuse change. Two adjacent grassland plots, one amended with 100m3 ha−1 of liquid swine manure annually since 1978 and an unamended grassland were either (i) left with vegetation intact (Control) or killed by glyphosate in the autumn. Glyphosate-treated subplots were either (ii) left as an undisturbed chemical fallow, (iii) ploughed by full inversion tillage (FIT) in the autumn, or (iv) in the spring. Cumulative emissions of N2O over the measuring period (static chambers), soil solution NO3-N (tension lysimeters) and soil NO3-N (KCl extraction) were monitored following tillage for one fallow year. Emissions of N2O decreased in the order: amended chemical fallow (3.0gNm−2), amended spring-FIT (2.0gNm−2), amended autumn-FIT and unamended chemical fallow (1.7gNm−2, both), unamended spring-FIT (1.2gNm−2) and the unamended autumn-FIT subplots (0.9gNm−2) while grassland controls emitted 0.07 and 0.09gNm−2 for the unamended and amended plots, respectively. Emissions of N2O were positively correlated with soil solution NO3-N at 30-cm depth in the chemical fallow, but negatively with soil solution NO3-N at 45cm in FIT subplots. In chemical fallow soils, N2O was likely produced as the NO3 − mineralized at the soil surface moved down the soil profile, enriching denitrification sites at shallow depths during rainfall events. In contrast, FIT placed the C and N required for denitrification deeper in the soil profile, and complete reduction to N2 was likely favoured. On these poorly drained grassland soils, FIT reduced emissions of N2O relative to a chemical fallow by a factor of 2 to 3 for equivalent soil NO3-N. Emission factors accounting for the interaction between soil characteristics – in this case drainage conditions – and management practices may be important in providing accurate N2O emission estimates. [Copyright &y& Elsevier]