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The effects of grazing on grassland ecosystems must be understood to develop effective soil conservation measures and sustain livestock production. The objective of this research was to characterize the impact of dairy cow grazing intensity on C and N in soil and vegetation on a meadow steppe. The meadow steppe site, located near Hailaer, Inner Mongolia, China, has been grazed by dairy cattle for more than 30 years, with the last 23 years managed by the same herders. The study site never received any form of mineral fertilizer. Grazing intensity was classified as light (LG), moderate (MG) and heavy (HG) according to the vegetation utilization rate. Grazing affected biomass, total N (TN) and 15N levels, but not 13C, of above-ground plants. The above-ground biomass and δ15N decreased but TN content increased with the grazing intensity for all nine non-legume species while five legume species were not affected. Coarse root biomass also decreased with grazing intensity while TN or δ15N responses to grazing showed no consistent patterns. Soil OC and total N content decreased significantly with grazing intensity for all three sampling depths (0–10, 10–20 and 20–30 cm) while nitrate, ammonium and 13C levels were not affected by grazing intensity in all sampling depths. The decreases in soil OC suggest carbon storage in the meadow steppe declined as grazing intensity increased. Combined with the decreases in soil TN content, this also means heavy grazing could lead to decreases in soil quality and fertility. Uneven grazing intensity is an inherent feature of a season-long grazing system and there are risks to soil quality and environmental health associated with HG. We need to find the proper balance between light to heavy grazing intensity through proper grazing management and in some cases using judicious herding to distribute livestock. Some combination of HG, MG and LG could be desirable in sustainable rangeland grazing production.

Crested wheatgrass (Agropyron cristatum [L.] Gaertn.) and Russian wildrye (Elymus junceus Fisch.) are commonly used for reseeding in the more xeric Mixed Prairie of the Canadian prairies because they are perceived to be more productive than native species. However, they have been implicated in soil deterioration. The objectives of our study were to compare the aboveground net primary production and soil organic carbon (C) among monoculture communities of selected native grass species, crested wheatgrass, and Russian wildrye and to compare the native grass monocultures with their mixtures. In 1995, a 5-year study was initiated on Dark Brown Chernozemic (Typic Haploboroll) soil near Lethbridge, Alberta. Ten treatments consisting of monocultures of introduced and selected native species and mixtures of native species were established in a randomized complete block design with 4 replications. Aboveground net primary production and soil organic C were measured. Monocultures of 2 native species, green needlegrass (Stipa viridula Trin.) and blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Steud.), were more productive than crested wheatgrass or Russian wildrye under both normal moisture and drought conditions. Monocultures of these native species also tended to be more productive than their mixtures. The western wheatgrass (A. smithii Rydb.) monoculture and the western wheatgrass–blue grama mixture experienced the greatest yield reduction as a result of drought. Treatment effects on soil organic C were not detected (P . 0.05) 5 years after seeding. Soils of the June grass (Koeleria macrantha [Ledeb.] J.A. Schultes f.) community had less (P , 0.05) macro-organic C than most other treatments. Resumen

The regional scale response of soil carbon mass to long-term grazing exclusion was investigated in the Canadian Great Plains. Vegetation, litter, macro-organic matter and soil were sampled in paired grazed and ungrazed treatments from 9 independent locations along an environmental gradient in southern Alberta. Vegetation and litter carbon mass were greater on ungrazed treatments, but no consistent grazing effect was observed for macro-organic matter (roots, subsurface litter) or soil (fine particles < 2mm) carbon mass per equivalent soil mass. Soil carbon in mixed grass prairie was positively correlated with clay content, but no grazing effect could be detected when this subset (n = 7) was analyzed by ANCOVA. Comparison of multiple sites with a consistent sampling and reporting method revealed no general trend in the response of soil carbon to grazing. Current range management practices to maintain range types in good to poor condition appear to be consistent with maintaining the soil organic mat...