Soil carbon, nitrogen and phosphorus changes from conversion of thornscrub to buffelgrass pasture in northwestern Mexico

• We evaluated soil nutrients in buffelgrass pastures and adjacent thornscrub.
• Our study found a significant reduction in extractable P in older pastures, suggesting P limitation.
• However, we did not detect any significant reduction in total C and N with pasture age.
• Long term sustainability of buffelgrass pasture in this region requires attention to nutrient dynamics.

In many regions of the world, land conversion of native plant communities to non-native pastures is usually associated with significant changes in soil nutrient contents. In Mexico, more than one million hectares of drylands have been converted to non-native pastures, with little knowledge on the biogeochemical consequences. We investigated the effects of non-native buffelgrass (Pennisetumciliare) pasture conversion on soil carbon (C), nitrogen (N) and phosphorus (P) dynamics to understand the effects of disturbance on soil nutrient in a region of the state of Sonora. Eleven sites that formed a gradient (1–44 years) of buffelgrass establishment history where buffelgrass establishment has been practiced for at least 50 years, were studied. Soil organic C, total N and P, microbial biomass C, extractable P, and mineral N contents and basal soil respiration, were measured in samples collected during the dry and rainy seasons in buffelgrass pastures and undisturbed thornscrub. Conversion to buffelgrass pastures decreased mineral N content and basal soil respiration. Extractable P decreased in older pastures (>10 years), suggesting a potential P-limitation for the permanence of long-term buffelgrass pastures in Sonora. In contrast, we did not detect a significant reduction of soil organic C, total N and P in older pastures. This study suggests that P limitation may serve as important controls on ecosystem nutrient cycling in natural vegetation and recovery of these thornscrubs after buffelgrass pasture establishment for cattle ranching.