30 to 40% of our land area world-wide is used as rangeland. Knowing how nutrient budgets in these ecosystems respond to grazing in the long-term allows us to better understand global nutrient cycles. Grazing exclosures have been in place at the Northern Great Basin Experimental Range since 1936. These are in pastures that have otherwise been managed with a moderate rotational cattle grazing regime. In 2019, after 83 years of treatment, we compared nutrient cycling in nine of these exclosures and their paired grazed pastures using Plant Root Symulator Probes (20 probes per pasture per grazing treatment for the full growing season). To better understand nutrient budgets we installed probes directly among plant roots and in root exclusion cylinders. The difference between the two values allows us to estimate plant nutrient uptake in micrograms.
Results/Conclusions
Across all pastures plants absorbed Ca, Mg, and NO3-. We found that plants in grazed pastures absorbed significantly more NO3-, Cu and S than plants in ungrazed pastures (p-value < 0.05), this is likely from an increased need for vegetative regrowth post defoliation. The pattern was similar for NH4+, but variation was much higher so a true difference is uncertain. Interestingly, there was actually a buildup of K and P in the presence of plant roots, more so in ungrazed pastures than grazed pastures (p-values < 0.05), indicating that this process is not simply an artifact of fecal and urine deposition. Plants did not uptake Mg, Ca, Al, B, Fe, Mn, or Zn differently between grazed and ungrazed pastures.