Long-Term Soil Nitrogen and Vegetation Change on Sandhill Rangeland

Abstract

The effect of livestock grazing on organic C and N in range-Land soils is not well defmed. In this study on sandy rangehmd in western Oklahoma, we sampled 8 pastures moderately grazed by cattle and 8 adjacent exclosures ungrazed by livestock for 50 years. The sagebrush was largely controlled by herbicide in the study areas. The C and N concentrations in the surface 5 cm of soil, total herbage production, and total N uptake by vegetation were similar (P > 0.05) in grazed and nongrazed areas. CiU-bOU and N concentrations in soils sampled to a constant mass to a depth of 5 cm or less were not (P > 0.05) different from concentrations determined on soil sampled to a constant depth of 5 cm. When calculated on a content basis, grazing increased (P < 0.001) the bulk density (1.35 g cm") compared to nongrazed pastures (1.19 g cm-3 and had a significant (P < 0.01) effect on C and N in the surface 5 cm of soil. Litter and total N in litter were greater (P < 0.01) on nongrazed areas. Little bluestem (Schizachyrfum scoparium (Michx.) Nash) and sand bluestem (Andropogon haZlii Hack.) produced more herbage and had greater frequency on nongrazed areas, whereas blue grama [Bouteloua gracilis (H.B.K.)Lag. ex Griffiths], sand dropseed [Sporobolus cryptandnrs (Torr.)Gray], and western ragweed (Ambrosia pdostachya DC.) increased in frequency on grazed areas. Thus, 50 years of moderate grazing by cattle had no measurable effect on C and N concentrations in the surface 5 cm of the sandy soil or on total N uptake by plants as compared with nongrazed areas; however, significant differences occurred in species composition which may alter mechanisms of C and N balance.

Grazing exclusion alters ecosystem carbon pools in Alxa desert steppe

“…Soil N depletion with grazing is likely due to N removal with the actual livestock themselves (Reeder et al 2004), especially where herds are put into pens at night resulting in limited N return with faecal organic material to the soil system. In our study, no significant differences in soil N were found as a function of grazing removal (Table 4), possibly because any excess N was absorbed by plants to support higher plant aboveground biomass in the exclosure (Berg et al 1997). Su et al (2005) Effects of grazer exclusion on soil C pools and distribution Soil water content is fundamental to dry land ecosystem functioning because it not only drives plant productivity but also regulates biogeochemical processes in soils (Williams et al 2000;Stavi et al 2008).…”

“…Assuming SOC content was similar between the grazed and exclosure soils prior to the beginning of the treatment, over the almost 7 year restoration period, the pool of SOC decreased by 11.5% in exclosure soils (0.94 kg/m 2 ) compared with the grazed site (explained by a decrease in surface soil bulk density (Berg et al 1997) but aboveground biomass C increased by 44.8% (0.01 kg/m 2 ) and the SIC pool increased by 21.3% (3.55 kg/m 2 ). Combined, grazing exclusion led to an increase in C within the plantÁsoil system of 10.2% (2.56 kg/m 2 ).…”

Stocking rate, precipitation, and herbage production on sand sagebrush-grassland

“…On the other hand, at this same study site, standing crop of both perennial and annual forbs was lower in areas excluded from grazing for over 50 years than in adjacent areas grazed at rates of 50 to 55 AUD há' y' (Berg et al 1997). This suggests that the simple presence or absence of grazing is more important than the intensity of grazing.…”

Effects of High-Density, Short-Duration Planned Livestock Grazing on Soil Carbon Sequestration Potentials in a Coastal California Mixed Grassland

“…Soil organic C was not significantly different between the three sites. These results have been corroborated by others in SOC studies on upland and sandy rangelands (Lavado et al, 1996;Berg et al, 1997).…”