What are the key functions of biological soil crusts in rangeland soils, and which management practices protect them?

• A. Biocrusts stabilize soil, fix nitrogen, and reduce erosion; protect by minimizing off-road traffic, disturbance, and excessive grazing on crusted surfaces.
• B. Biocrusts destabilize soil and increase erosion; protection involves increasing off-road traffic.
• C. Biocrusts only affect nitrogen fixation; protection is through irrigation.
• D. Biocrusts are cosmetic; no management needed.

Answer: (A)

Biological soil crusts on rangeland soils perform essential surface-level functions: they bind soil particles together with microbial filaments and mucopolysaccharides, creating a stable crust that protects the soil from wind and water erosion. This stabilization is crucial in exposed arid and semi-arid environments where bare soil can erode quickly. In addition, many crust organisms, especially cyanobacteria, fix atmospheric nitrogen, adding biologically available nitrogen to the surface soil and supporting early plant growth and nutrient cycling. By shaping the surface microhabitat, crusts also influence water infiltration and seedbed conditions, which affect germination and establishment of vegetation.

Protecting these crusts hinges on keeping the surface intact and undisturbed. Minimizing off-road vehicle use and other disturbances on crusted surfaces helps prevent physical breakage of the crust that would expose vulnerable soil to erosion. Limiting trampling and excessive grazing on crusted patches preserves their structure and function, allowing them to continue stabilizing soil and contributing to soil fertility. Proper grazing management, such as appropriate stocking rates and targeted rotational grazing, reduces the likelihood of crust loss and the associated erosion risks, supporting the long-term health of the rangeland.