Whole-profile soil organic matter content, composition, and stability under cropping systems that differ in belowground inputs

Abstract

Subsoils have been identified as a potential carbon sink because they typically have low soil organic carbon (SOC) concentrations and high SOC stability. One proposed strategy to increase SOC stocks is to enhance C inputs to the subsoil by increasing crop rotation diversity with deep-rooted perennial crops. Using three long-term field trials in Iowa (study durations of 60, 35, and 12 years), we examined the effects of contrasting cropping systems [maize (Zea mays L.)-soybean (Glycine max (L.) Merr) (= two-year system) vs. maize-soybean-oat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa or maize-maize-oat/ alfalfa-alfalfa (= four-year system)] on above-and below-ground C inputs, as well as the content, biochemical composition, and distribution of SOC among physical fractions differing in stability to 90 cm depth. Average annual total C inputs were similar in the two-year and four-year systems, but the proportion of C delivered belowground was 20-35 % greater in the four-year system. Despite the long duration of these studies, the effect of cropping system on SOC content to 90 cm was inconsistent across trials, ranging from −7 % to +16 % in the four-year relative to the two-year system. At the one site where SOC was significantly greater in the four-year system, the effect of cropping system on SOC content was observed in surface and subsoil layers rather than limited to the subsoil (i.e., below 30 cm).Cropping system had minimal effects on biochemical indicators of plant-derived organic matter or on the proportions of SOC in labile particulate organic matter versus stable mineral-associated organic matter. We conclude that adoption of cropping systems with enhanced belowground C inputs may increase total profile SOC, but the effect is minimal and inconsistent; furthermore, it has minor impact on the vertical distribution, biochemical composition, and stability of SOC in Mollisols of the Midwest U.S.Subsoils have been identified as a potential carbon sink because they typically have low soil organic carbon (SOC) concentrations and high SOC stability. One proposed strategy to increase SOC stocks is to enhance C inputs to the subsoil by increasing crop rotation diversity with deep-rooted perennial crops. Using three longterm field trials in Iowa (study durations of 60, 35, and 12 years), we examined the effects of contrasting cropping systems [maize (Zea mays L.)-soybean (Glycine max (L.) Merr) (= two-year system) vs. maize-soybeanoat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa or maize-maize-oat/alfalfa-alfalfa (= four-year system)] on above-and below-ground C inputs, as well as the content, biochemical composition, and distribution of SOC among physical fractions differing in stability to 90 cm depth. Average annual total C inputs were similar in the two-year and four-year systems, but the proportion of C delivered belowground was 20-35 % greater in the fouryear system. Despite the long duration of these studies, the effect of cropping system on SOC content to 90 cm was inconsistent across trials...

Stock and indices of carbon management under different soil use systems

“…This shows the impact that the areas of SC, PP, and NTS caused on the quantity and quality of C in the most superficial layers of the soil, compared with the NF area. Similar results were observed by other authors in several study areas (Rosset et al, 2019;Lavallee et al, 2020;Poffenbarger et al, 2020).…”

“…Among the many attributes analyzed to evaluate the effects of the management systems and soil quality (SQ), soil organic matter (SOM) stands out (Nanzer et al, 2019;Lavallee et al, 2020;Poffenbarger et al, 2020). Thus, one of the methods for evaluating SQ is the analysis of C compartments of the physical fractions of the SOM (Cambardella and Elliott, 1992).…”

Estimation of carbon stocks in boreal cropland soils ‐ methodological considerations

“…Persson, Bergkvist, and Kätterer (2008) found that 2‐year ley periods in a 6‐year crop rotation could at most slow the decrease in topsoil SOC stocks over a 31‐year period in Sweden. In a recent long‐term field study, Poffenbarger et al (2020) also reported minor effects of cropping systems on SOC stocks. Bolinder, Kätterer, Andrén, and Parent (2012), however, found a stronger beneficial effect of forage‐based rotation on SOC stock, most likely due to decreased tillage intensity and slight higher carbon input to the soils in comparison to the rotation with annual crops only.…”

The soil microbial carbon pump: From conceptual insights to empirical assessments

“…Global soil carbon (C) stocks are about three times greater than atmospheric C stocks (Jackson et al., 2017), so slight changes in soil organic C (SOC) stocks will impact global climate (Fargione et al., 2018; Lal, 2010; Rustad, Huntington, & Boone, 2000; Stockmann et al., 2013). Agricultural soils are a significant part of the overall reduction strategy, so investigations into the accumulation and stabilization of SOC in agricultural systems have increased considerably in recent years (Poffenbarger et al., 2020; Smith et al., 2020; Zomer, Bossio, Sommer, & Verchot, 2017). In the policy realm, the 4 per 1,000 Initiative calls for an annual increase in SOC stocks of 0.4% on agricultural lands globally to reduce the CO 2 concentration in the atmosphere (COP21, 2015; Rumpel, Lehmann, & Chabbi, 2018).…”