Increasing Labile Soil Carbon and Nitrogen Fractions Require a Change in System, Rather Than Practice

Abstract

The influence of tillage, carbon (C) and nitrogen (N) inputs and perennialization on labile fractions of soil organic matter (SOM) has been widely investigated, but research on the temporal and depth variation of labile C and N fractions in long‐term agroecosystems representative of the US Corn Belt is lacking. In this study, labile soil fractions as influenced by different agriculture management approaches common in the north‐central United States were characterized through measurements of potentially mineralizable N (PMN), mineralizable C (C‐min), and permanganate oxidizable C (POXC), which are known indicators of the biologically active pool of SOM. Soils were sampled five times in six different cropping systems at the Wisconsin Integrated Cropping Systems Trial: three annual cropping systems (continuous corn, strip‐till corn–soybean, organic grain) and three forage cropping systems (conventional forage, organic forage, grazed pasture). Across all sampling dates (May–September) and soil depth (0–15 and 15–30 cm), forage‐based cropping systems generally had greater PMN, C‐min, and POXC, with C‐min and PMN expressing the largest differences between forage and grain‐based cropping systems. Labile soil C and N fractions across cropping systems were typically greatest in July or August and were ∼50% greater in the top 0 to 15 cm of soil than the 15 to 30 cm. These results suggest sampling timing and depth for PMN, POXC, and C‐min need to be standardized to optimize their use as soil health indicators and that shifts in the system toward perenniality will be required to increase labile C and N fractions on the highly fertile Mollisols of the US Corn Belt.

Sensitivity and variability of soil health indicators in a California cropping system

“…Our goal in this study was to assess the sensitivity and variability of a wide range of soil health indicators in the Russell Ranch Century Experiment in the Central Valley of California, a long-term experiment in which plots in a corn (Zea mays L.) and processing tomato (Solanum lycopersicum L.) rotation have been under conventional (CONV) or organic (ORG) management since 1993. Long-term research trials provide stable, controlled systems that can be used to evaluate the benefits of a management practice and to help select and interpret appropriate soil health indicators (i.e., Diederich et al, 2019;Hurisso et al, 2016;Morrow et al, 2016). The uniform conditions allow for the systematic examination of indicators' relative susceptibility to other factors like weather.…”

“…Long-term research trials provide stable, controlled systems which can be used to evaluate the benefits of a management practice and to help select and interpret appropriate soil health indicators (i.e. Diederich. Ruark, Krishnan, Arriaga, & Silva, 2019;Hurisso et al, 2016;Morrow, Huggins, Carpenter-Boggs & Reganold, 2016).…”

Permanganate oxidizable carbon for soil health: Does drying temperature matter?

“…The range of POXC values for these soil samples was intermediate (about 400–900 mg C kg −1 soil) compared with ranges reported in surveys of many soil types (0–1,500 mg C kg −1 soil, Calderón et al., 2017; Culman et al., 2012; Hurisso et al., 2016). In studies that identified POXC as a reliable indicator for detecting differences in soil health across management systems, a significant treatment difference coincided with a change in POXC of about 100 mg C kg −1 soil or greater (Culman, Snapp, Green, & Gentry, 2013; Diederich, Ruark, Krishnan, Arriaga, & Silva, 2019; Ghimire, Ghimire, Mesbah, Sainju, & Idowu, 2019; Lucas & Weil, 2012; Morrow et al., 2016; Singh et al., 2020). Because the oven drying did not cause this large of a shift in mean POXC, we do not believe that oven‐drying these soil samples would change the interpretation of the analysis or the utility of POXC as a soil health indicator.…”

Extending Cover Crop Benefits with Zone Till Management in Northern Organic Summer Squash Production

“…Therefore, we expected to observe a decrease in IR POXC after cover crop termination as cover crop residue mineralized, but this was not observed. While the sensitivity of POXC to cover cropping practices has mixed results in the literature [42][43][44], some have concluded that it better reflects practices and systems that build soil organic matter rather than nutrient turnover [45,46]. Soil inorganic N responded to cover crop termination in both soil regions and cover crop systems in 2015.…”