Interpreting Soil Health Metrics in Semi-arid Grazinglands: An Assessment of Measurement Approaches and Relational Gradients

Abstract

The health of the soil resource has received considerable focus recently largely due to its importance to many ecological processes. Although cropland systems have been considerably studied, questions remain regarding the measurement and relationships among soil health metrics in grazinglands systems. To address some of these questions, nineteen ranch properties were sampled totaling 17,347 ha across Oklahoma and Texas in 2019 to evaluate cost effective soil carbon measurement strategies and soil health relationships across soil textures. Primary takeaways from the effort include a) more effective tools are still needed to reduce the cost of sampling and estimate accuracy of soil organic carbon concentrations in heterogeneous landscapes, b) Soil organic matter has a positive relationship with increasing soil available water holding capacity, however the magnitude is not universal, it is mediated across soil texture classes, and c) strong correlations were identified among rangelands, fine-medium textured soils, reduced bare ground, and robust soil biological biomass. Conversely croplands, and to a lesser extent pasture sites, tended to be more closely associated with coarse textured soils, increased bare ground (on croplands), and decreased biological biomass. Ultimately, total microbial biomass and its constituents along with soil organic matter provided the greatest contribution to the explaining the variation in this data set and were most closely associated with rangelands, suggesting that soil microbial biomass and soil organic matter should be considered in rangeland monitoring activities on semiarid grazinglands in the United States Southern Great Plains.