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Nitrogen (N) captured by cover crops can be recycled for use by the following crop via decomposition and net mineralization. This study assessed the magnitude of inorganic‐N released from radish (Raphanus sativus L.) and cereal rye (Secale cereale L.) residue. The experiment was designed using a five by two factorial treatment structure with five cover crop residue treatments (radish shoots, radish roots, whole radish, cereal rye shoots, and no cover crop) and two levels of residue incorporation (incorporated and surface applied). Cover crop residues were applied to a silt loam soil on an equivalent N basis, incubated for 25 weeks and sampled periodically. Generally, NH4‐N concentration increased for 7–11 days after residue application, after which, NH4‐N concentration declined and NO3‐N concentration increased due to nitrification. Mineralization during the later days (42–179 days after residue application) was negligible from radish residue, but cereal rye shoots and radish roots released significant amounts of NH4‐N, which decreased over the last 137 d. Radish roots generated significantly more NO3‐N from day 42 through 141 than any other residue, while cereal rye shoots mineralized the least amount of NO3‐N from day 42 through 86. Incorporating cereal rye residue increases the occurrence of immobilization within the first 35 days after residue application; however, incorporation increases the rate at which NO3‐N is released from residues between 42 and 179 days after residue addition, regardless of cover crop species. Incorporation of residue can increase N mineralization rate, but the effect varies across cover crop species. Core Ideas: Cover crop species influences rate of residue decomposition and mineralization of N.Immobilization of N was lower for radish residue than cereal rye regardless of incorporation.Nitrate concentrations were similar for all cover crop residues following 154 days of incubation. [ABSTRACT FROM AUTHOR]

Various soil health indicators that measure a chemically defined fraction of nitrogen (N) or a process related to N cycling have been proposed to quantify the potential to supply N to crops, a key soil function. We evaluated five N indicators (total soil N, autoclavable citrate extractable N, water‐extractable organic N, potentially mineralizable N, and N‐acetyl‐β‐D‐glucosaminidase activity) at 124 sites with long‐term experiments across North America evaluating a variety of managements. We found that 59%–81% of the variation in N indicators was among sites, with indicator values decreasing with temperature and increasing with precipitation and clay content. The N indicators increased from 6%–39% in response to decreasing tillage, cover cropping, retaining residue, and applying organic sources of nutrients. Overall, increasing the quantity of organic inputs, whether from increased residue retention, cover cropping, or rotations with higher biomass, resulted in higher values of the N indicators. Although N indicators responded to management in similar ways, the analysis cost and availability of testing laboratories is highly variable. Further, given the strong relationships of the N indicators with carbon (C) indicators, measuring soil organic C along with 24‐h potential C mineralization could be used as a proxy for N supply instead of measuring potentially mineralizable N or any other N indicator directly. Core Ideas: Nitrogen indicators of soil health vary predictably across North America with climate and soil texture.The response to soil health practices is similar across all indicators.There are strong correlations among nitrogen indicators, but also between carbon and nitrogen indicators.Soil organic carbon and 24‐h carbon mineralization potential can be used to capture nitrogen cycling. [ABSTRACT FROM AUTHOR]

Farmers, scientists, and other soil health stakeholders require interpretable indicators of soil hydraulic function. Determining which indicators to use has been difficult because of measurement disconformity, spatial and temporal variability, recently established treatments, and the effect of site characteristics on management practice differences. The North American Project to Evaluate Soil Health Measurements includes 124 sites uniformly sampled across a range of soil health management practices in North America in 2019. We compare and recommend indicators of hydraulic function that best characterize soil health. We assessed the relationship of each indicator to a suite of soil inherent properties and climate variables, the response of each indicator to soil health management practices, the effect that soil inherent properties (clay content, sand content, and pH) and climatic variables (10‐yr mean annual precipitation and temperature) had on response to management practices, and the relationship among the responses of the indicators to soil health management practices. Field capacity measured on intact cores (θFC_INTACT) was the best measure of soil hydraulic function, because it responded to management, represents a direct measure of soil hydraulic function, is proximal to stakeholder values, and its response to management was not significantly influenced by inherent and climatic variables. Other suitable indicators are bulk density, soil organic carbon (SOC), and aggregate stability, which are not direct measures of soil hydraulic function but do respond to management and may be practical in situations in which measuring θFC_INTACT is not. This study informs selection of soil health indicators to measure soil hydraulic function. Core Ideas: Across sites, management changed aggregate stability, C, and bulk density.Management also changed field capacity for intact cores, but not repacked cores.Increased residue, organic nutrient sources, less tillage, each increased field capacity by 4%.Residue retention, organic nutrients and less tillage reduced bulk density by 2–3%.Field capacity for intact cores was the most responsive and direct indicator. [ABSTRACT FROM AUTHOR]