Evaluation of indirect and direct scoring methods to relate biochemical soil quality indicators to ecosystem services

Abstract

Soil health assessments use scoring curves to quantify relationships between soil quality indicators (SQIs) and ecosystem services (ESSs). We evaluated methods for scoring curve development using three labile C pools (β-glucosidase [BG], fluorescein diacetate [FDA] hydrolysis, and permanganate oxidizable carbon [POXC]).Concepts and methods for SQI interpretation used by established frameworks were assessed, with 129 studies reporting relationships to either soil organic C (SOC) (n = 367), a common surrogate for indirect estimation of ESSs, or direct measures of crop yield (n = 88), soil respiration (n = 66), and N 2 O and CH 4 emissions (n = 51). Indirect assessment of BG using SOC and site covariates resolved tillage-based differences (P < .05). Correlations between SOC and SQIs observed under different land uses suggested that use of SOC for indirect scoring would be more effective for FDA than POXC. Direct relationships were generally positive between SQIs and yield (89%), soil respiration (89%), and N 2 O and CH 4 emissions (76%), but such relationships could be nonlinear. Direct assessment revealed that both positive and negative ESS outcomes increased with labile C fraction abundance that complicates the assignment of ESS-based SQI scores. Although direct SQI scores are relatively easy to interpret, relationships between scores and SQIs can vary 10-fold for different sites and cropping systems (upland versus rice paddy), which is much greater than treatment-based differences observed within single sites. To quantify relationships between SQIs and ESS outcomes, one must measure influential site covariates (SQI-ESS covariates) along with details about management, sampling, and analysis.

Rapid improvement in soil health following the conversion of abandoned farm fields to annual or perennial agroecosystems

“…On the other hand, it was difficult to detect changes in soil health induced by the different plant systems. Only small macroaggregate OC emerged as a signal of management effects despite the documented sensitivity of other indicators, such as labile C, to management effects (Xia and Wander, 2022). The contradictory findings in this and other studies (e.g., may reflect high spatial variability levels of soil properties across the plots that masked the effects of crop systems (De et al, 2020) or it may reflect differences in establishment methods (especially since this is a one-year study).…”

“…The contradictory findings in this and other studies (e.g., may reflect high spatial variability levels of soil properties across the plots that masked the effects of crop systems (De et al, 2020) or it may reflect differences in establishment methods (especially since this is a one-year study). There is also growing evidence that soil enzyme activities related to nutrient cycling (i.e., N, P), as well as analyses of readily decomposable pools of SOM, such as permanganateoxidizable C (reactive carbon), may have potential as early and more sensitive indicators of soil ecological restoration (Martin and Sprunger, 2022;Xia and Wander, 2022). Although these factors comprise a relatively small fraction of SOM, they have turnover rates of weeks to months and may be more sensitive to soil health changes with management and land use practices.…”

Building soil to reduce climate change impacts on global crop yield

“…High-quality soils can buffer climate variability in cropping systems and sustain yield stability 16,17 . Soil organic carbon (SOC), in particular, has been suggested as an integrated and representative indicator of soil quality, which relates to soil biological and physical properties such as disease suppressiveness, heat capacity 18,19 and soil heath, with important functions such as water retention and nutrient supply 20,21 . Improving SOC can help build climate resilience to reduce risks to food insecurity 22,23 , and decrease reliance on irrigation and fertilizer application 24 .…”