Description: Long-term cattle grazing may degrade grassland soils, but how soil CO 2 , CH 4 and N 2 O fluxes respond to long-term cattle grazing is poorly understood. Therefore, we quantified soil CO 2 , CH 4 and N 2 O fluxes in response to four levels (none, light, heavy, very heavy) of long-term (〉65 yr) cattle grazing on a rough fescue grassland in the foothills of the Rocky Mountains, Canada over three grazing seasons. The grazed grassland soils emitted 37 to 51% more CO 2 than non-grazed soils. Grazed grassland soils were small CH 4 sinks and small N 2 O sources each season, and their cumulative emissions were both significantly affected by a cattle stocking rate × year interaction, indicating the grazing effect was a function of environmental conditions. Soil CH 4 uptake negatively correlated with soil moisture ( r =  -0.59). The 2013 grazing season had about 41% greater precipitation than average and grazing significantly decreased CH 4 uptake 31 to 38% compared with non-grazed soils. The N 2 O emissions were 122 to 179% greater with heavy and very heavy grazing than none in the wet year, unaffected by grazing in the normal precipitation year, and 72% lower with light grazing than none in the dry year. Predicting trace gas fluxes from grazed grassland soils across space and time is difficult due to interactions amongst weather conditions, edaphic properties and grazing intensity. However, long-term cattle grazing increased soil CO 2 fluxes, while the grazing effect on CH 4 uptake depended on precipitation and the soil N 2 O flux responded as a function of grazing intensity and precipitation.

Description: ABSTRACT A life cycle assessment with carbon (C) as the reference unit was used to balance the benefits of land preparation practices of establishing tall-grass prairies as a crop for reclaimed mine land with reduced environmental damage. Land preparation and management practices included disking with sub-soiling (DK-S), disking only (DK), no-tillage (NT), and no-tillage with grazing (NT-G). To evaluate the C balance and energy use of each of the land preparations, an Index of Sustainability (I s   =  C O /C I , where C O is the sum of all outputs, and C I is the sum of all inputs) was used to assess temporal changes in C. Of the four land preparation and management practices, DK had the highest I s at 8.53. This was due to having the least degradation of SOC during land use change (-730 kg ha -1  yr -1 ), and second highest aboveground biomass production (9,881 kg ha -1 ). The highest aboveground biomass production occurred with NT (11,130 kg ha -1 ), although SOC losses were similar to DK-S, which on average was 2,899 kg ha -1  yr -1 . The I s values for NT and DK-S were 2.50 and 1.44, respectively. Grazing from bison reduced the aboveground biomass to 8,971 kg ha -1 compared to NT with no grazing, although stocking density was low enough that I s was still 1.94. This study has shown that converting from cool season forage grasses to tall-grass prairie results in a significant net sink for atmospheric CO 2 three years after establishment in reclaimed mine land, due to high biomass yields compensating for SOC losses from land use change. This article is protected by copyright. All rights reserved.

Description: Grassed waterways (GWWs) transport sediment and nutrients from upland source areas to receiving waters. Watershed planners have a critical need to understand GWW sediment delivery to optimally target source area management practices. Better physically-based tools are needed to estimate sediment delivery by GWWs. This study developed several distributed sediment delivery ratio (SDR) regressions for GWWs using the process-based Water Erosion Prediction Project (WEPP) model to provide simple equations to estimate sediment delivery for planning applications. WEPP was calibrated and validated for runoff and sediment yield for large 30.2 ha and smaller 5.7 ha nested watersheds with terraces and a common GWW outlet. A crop rotation of corn, oat and alfalfa and fall tillage using chisel plow were used in the nested watersheds. A hypothetical management case without terraces using corn, oat, and alfalfa rotation with chisel plow as fall tillage was also evaluated for the 5.7 ha watershed and the GWW. The length, slope, Manning's roughness coefficient and infiltration rate for the GWW were varied and SDRs calculated for 30 representative (in terms of daily rainfall) days over a 20 year period of simulated climate. Regressions were developed for the existing (terraced) and hypothetical (non-terraced) management scenarios for early (April – July), late (August – October) and full (April – October) growing seasons. Equations developed for the non-terrace watershed had higher R 2 values compared to the terraced watershed suggesting that channel and rainfall parameters were better able to explain the variation in SDR for the non-terraced watershed. Manning's roughness coefficient was the most significant parameter for predicting SDR for both the terraced and non-terraced watersheds. The equations developed here can be used to estimate SDRs for watersheds that are drained via GWWs having similar physical characteristics: slope (1 – 5 %), Mannings's roughness coefficient (0.1 – 0.3), length (0.15 – 1 km) and infiltration rate (0.025 – 25 mm/hr). The SDRs can be used to estimate sediment yield which is an essential element for making land management decisions but is rarely measured.