Bridging the gap: Field-based soil health assessment for nature-based soil management

Understanding soil health is pivotal for the implementation of sustainable agricultural practices. Rapid and reliable field-based methods for assessing soil respiration, labile carbon (C), and stable C are needed to complement laboratory analyses and provide on-site insights into the soil. This study explores the performance and reliability of field methods for measuring these parameters across diverse land use and soil management systems, focusing on the applicability of colorimetric and spectrophotometric techniques.

Two distinct soil sample sets were analyzed. The first set included 10 agricultural sites in Eastern Austria, with samples collected from arable fields and adjacent (semi-) natural reference strips over three time points (April, May, and June). The second set involved field trials in Pyhra and Hollabrunn, employing a randomized block design to assess soil tillage (conventional, direct seeding, minimal, and reduced tillage) and cover crops (fallow, diverse, and standard). Each treatment was replicated three times and sampled once.

Field measurements of basal soil respiration were conducted by incubating fresh soil for 12 hours in containers with an agar medium and a pH-indicator, with CO₂-induced color changes captured using RGB and Lab* data. Labile C was assessed using an adapted Weil et al. (2003) method, while stable C was extracted with 0.5 M NaOH. Laboratory validation employed gas chromatography for soil respiration and photometric methods for POxC (550 nm) and NaOH extracts (400 and 600 nm).

Field and laboratory measurements correlated well for the 10 Eastern Austrian sites (r² = 0.26 for soil respiration, r² = 0.74 for labile C, and r² = 0.52 for stable C), supporting the reliability of the field methods. Results demonstrated the ability to differentiate between arable and non-arable land use systems. However, distinguishing soil management practices (e.g., tillage and cover cropping) proved challenging, with no significant differences observed across methods.

These findings highlight the potential of field-based techniques for soil quality assessment, offering practical tools that align closely with laboratory precision. However, further refinement is needed to distinguish conventional and nature-based management systems effectively.

References:

Weil, R. R., Islam, K. R., Stine, M. A., Gruver, J. B., & Samson-Liebig, S. E. (2003). Estimating active carbon for soil quality assessment: A simplified method for laboratory and field use. American Journal of Alternative Agriculture, 18(1), 3-17.