Effects of climate, intrinsic soil properties, and management on soil health indicators of carbon dynamics

Abstract:

Soil organic carbon has been integral to the concept of soil health for decades. Both the storage of carbon and the cycling of carbon are included as key functions related to soil health. A variety of indicators have been proposed to quantify various aspects of carbon dynamics, and many of these indicators have been included in soil health indices like the Cornell Assessment of Soil Health, the Haney test, and the Soil Management Assessment Framework. The North American Project to Assess Soil Health Measurements sampled 124 long-term agricultural research sites across North America to evaluate indicators of soil health including eight related to carbon: soil organic carbon, active carbon (permanganate oxidizable carbon), 24 and 96 hour respiration, microbial biomass from Phospholipid Fatty Acid (PLFA) Analysis, beta glucosidase enzyme activity, water extractable organic carbon, and autoclaved citrate extractable protein. The wide geographic scope of the project permits an evaluation of climate and intrinsic soil properties on these indicators at the site level. Each site also had at least two treatments related to at least one of the following types of management: decreased tillage, cover cropping, increasing crop diversity, or adding organic amendments. We compared the indicators to each other and evaluated how predictable they were based on the site-level climate and soil factors factors and management within a site. With the exception of PLFA biomass, all the indicators were moderately correlated with each other. Active carbon was the best single predictor for the majority of indicators, but adding additional indicators did not improve the prediction. Climate and soil texture could predict between 0-20% of the variance in the indicators with soil organic carbon having the strongest relationships. With the exception of PLFA biomass, the indicators were sensitive to the management with a 5-25% increase in the indicators associated with adding soil health management practices. In general, the 24 hour respiration was most sensitive to management. Other factors such as cost, ease of analysis, and the possibility for field analysis will affect the decision of which indicator to choose, but seven of the indictors appear to provide shared information about carbon dynamics.