Carbon-sensitive pedotransfer functions for plant available water

Currently accepted pedotransfer functions show negligible effect of management-induced changes to soil organic carbon (SOC) on plant available water holding capacity (θAWHC), while some studies show the ability to substantially increase θAWHC through management. The Soil Health Institute\u27s North America Project to Evaluate Soil Health Measurements measured water content at field capacity using intact soil cores across 124 long-term research sites that contained increases in SOC as a result of management treatments such as reduced tillage and cover cropping. Pedotransfer functions were created for volumetric water content at field capacity (θFC) and permanent wilting point (θPWP). New pedotransfer functions had predictions of θAWHC that were similarly accurate compared with Saxton and Rawls when tested on samples from the National Soil Characterization database. Further, the new pedotransfer functions showed substantial effects of soil calcareousness and SOC on θAWHC. For an increase in SOC of 10 g kg–1 (1%) in noncalcareous soils, an average increase in θAWHC of 3.0 mm 100 mm–1 soil (0.03 m3 m–3) on average across all soil texture classes was found. This SOC related increase in θAWHC is about double previous estimates. Calcareous soils had an increase in θAWHC of 1.2 mm 100 mm–1 soil associated with a 10 g kg–1 increase in SOC, across all soil texture classes. New equations can aid in quantifying benefits of soil management practices that increase SOC and can be used to model the effect of changes in management on drought resilience

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

Labile organic nitrogen fractions: characteristics, dynamics and significance to soil nitrogen supply in agricultural soils

Short-term nitrogen (N) availability in agricultural soils is derived mostly from the labile organic N pool. A better understanding of N transformation processes that occur in key labile organic N fractions is necessary to recognize their role in N cycling and their relative contribution to N mineralization. The objectives of this thesis were to (1) examine, under field conditions, the influence of preceding legume and non-legume crops on microbial biomass N (MBN), water-extractable organic N (WEON), and particulate and light fraction organic matter N (POMN, LFOMN) across five sites and how these fractions supply N to canola (Brassica napus L.), as determined from N uptake and grain yield, and (2) investigate under controlled conditions, the incorporation and turnover of crop residue N through MBN, WEON, POMN and LFOMN. Labile organic N fractions were similar regardless of preceding crop but varied across sites due to soil and climatic conditions. The POMN was the best single predictor of soil N supply (R2 = 0.56 and R2 = 0.70 for yield and N uptake, respectively). Soil N supply was related to POMN, mineral N and sand content, which explained 68% of the variation in grain yield and 71% of the variation in N uptake. Sandy-loam and clay soils were incubated for 112 d with 15N-labelled faba bean (Vicia faba, C/N ratio = 29) and wheat (Triticum aestivum L, C/N ratio = 91) residues. After 3 d, most (17-30%) of the residue 15N was recovered in the POMN, with a greater proportion of the wheat than the faba bean residue recovered in the POMN fraction. The 15N recovered in the POMN fraction after 3 d was significantly related to mineral N released after 112 d (r = 0.78, P<0.001), with more 15N released as mineral N in sandy-loam than clay soil and from faba bean than wheat residue. Net N mineralization in whole soil (WS) + POM mixtures was better related to POM N concentration and less to soil mineral N, soil texture or pH, suggesting that the extent to which POM contributes to N mineralization depends on the crop residue chemistry from which it was derived. I conclude that the turnover of POMN is a major pathway through which mineral N is released in the short-term in agricultural soils. Current N fertilizer recommendations can be improved by considering POM and soil mineral N concentrations, soil texture and environmental conditions. This will help to minimize the negative impacts of N losses on the environment and make a significant step towards enhancing N-use efficiency in agroecosystems.La disponibilité à court terme de l'azote (N) dans les sols agricoles est essentiellement issue de la fraction labile du N organique. Une meilleure compréhension des processus de transformation de ces fractions est nécessaire pour connaitre leur rôle dans le cycle de l'azote et leur contribution relative à la minéralisation de N. Les objectifs de cette thèse étaient de (1) examiner, sous les conditions de champs, l'effet du précédent cultural (légumineuse vs non-légumineuse) sur la biomasse microbienne de l'azote (MBN), l'azote organique extrait à l'eau (WEON) et les fractions légère et particulaire de la matière organique (POMN, LFOMN) à travers cinq sites et comment ces fractions sont-elles liées à l'approvisionnement en N [canola (Brassica napus L.) prélèvement de N et rendement en grains] and (2) étudier, sous des conditions contrôlées, l'incorporation et le turnover de l'azote des résidus des cultures via MBN, WEON, POMN et LFOMN. Les fractions labiles du N organique étaient similaires quel que soit le précédent cultural mais varie avec les sites due aux sols et aux conditions climatiques. Le POMN était le meilleur indicateur de l'approvisionnement en N (R2 = 0,56 and R2 = 0,70 pour le rendement en grains et le prélèvement en N, respectivement). De plus, l'approvisionnement en N était premièrement relié à l'effet combiné de POMN, l'azote minéral et la teneur du sol en sable; ces paramètres expliquent 68% de la variation dans le rendement en grains et 71% de la variation dans le prélèvement en N .Deux sols, loam sableux et argileux, ont été incubés pendant 112 jours avec des résidus d'haricot (Vicia faba, C/N = 29) et du blé (Triticum aestivum L, C/N = 91) marqués à 15N. Après 3 jours, la majeure partie (17-30%) des résidus de 15N a été trouvée dans la fraction POMN par comparaison aux autres fractions. Une plus grande proportion de résidus de blé que de résidus d'haricot a été trouvée dans la fraction POMN. La forme minérale du 15N libérée a été plus élevée dans le sol laom-sableux que dans l'argile et avec l'incorporation de l'haricot comparée au blé. Le 15N incorporé au POMN après 3 jrs a été significativement relié à l'azote minéral libéré après 112 jrs (r = 0.78, P<0.001). La minéralisation nette dans le mélange au sol entier (WS) + POM est plus liée à la teneur en N du POM qu'à la teneur du sol en N minéral, sa texture et son pH. Ainsi, l'ampleur de la contribution de la fraction POM à la minéralisation de l'azote dépond de son origine. Dans l'ensemble, les résultats de cette étude suggèrent que le turnover de la fraction POMN est la principale voie par laquelle le N minéral est libéré dans les sols agricoles. Les recommandations actuellement utilisées en fertilisation azotée peuvent être améliorées en tenant compte des POMN, N minéral du sol, texture du sol et les conditions environnementales. Ces informations permettront de minimiser les impacts négatifs de la perte de N dans l'environnement and contribueront à l'amélioration de l'efficacité de l'utilisation de l'azote dans les agroécosystèmes

Soil Carbon Pools Before and After 21 Years of Conservation Management in Saskatchewan Soils

Non-Peer ReviewedSoils are the largest terrestrial carbon sink on Earth and increasing soil organic carbon (SOC) content is a means of sequestering atmospheric CO2. Limited work has been done to examine the effect of long-term conservation management practices on the stability of SOC in prairie soils. The objective of this study was to assess the nature and permanence of sequestered SOC in contrasting Saskatchewan soils after 21 years of conservation management practices. Ninety fields were sampled in 1996 and again at the same locations in 2018. The fields represent a diverse collection of soil types from within the five soil zones of the province. Comparisons were made between the 1996 and 2018 soils (0-10 cm) in SOC concentration, along with various labile and dynamic SOC fractions: water-extractable (WEOC), light fraction (LF-C), microbial biomass (MB-C), and respirable CO2-C during a six-week incubation. Regardless of soil zone, soils with the smallest initial SOC content accumulated more SOC (ranging from 4.7-9.8 Mg C/ha or 220-454 kg C/ha/year). There was a minor increase in WEOC content (3%), no change in LF-C content, and a substantial increase in MB-C content (41%). Except for greater CO2-C emissions from the 2018 Black soils, there was no difference in CO2-C emissions or percentage of SOC respired between the 2018 and 1996 soils, which indicates similar or greater permanence of the sequestered SOC. Our results suggest that after 21 years of conservation management practices, more of the SOC is present in an active, dynamic fraction that contributes to soil health and nutrient cyclin

Labile organic nitrogen transformations in clay and sandy-loam soils amended with 15 N-labelled faba bean and wheat residues

The results of this study suggest that mineralization of POMN is a major pathway through which mineral N is supplied in agricultural soils, with C/N ratio of crop residues and to a lesser extent soil properties, influencing the mineralization rate. Crow

An evaluation of carbon indicators of soil health in long-term agricultural experiments

Soil organic carbon (SOC) is closely tied to soil health. However, additional biological indicators may also provide insight about C dynamics and microbial activity. We used SOC and the other C indicators (potential C mineralization, permanganate oxidizable C, water extractable organic C, and β-glucosidase enzyme activity) from the North American Project to Evaluate Soil Health Measurements to examine the continental-scale drivers of these indicators, the relationships among indicators, and the effects of soil health practices on indicator values. All indicators had greater values at cooler temperatures, and most were greater with increased precipitation and clay content. The indicators were strongly correlated with each other at the site-level, with the strongest relationship between SOC and permanganate oxidizable C. The indicator values responded positively to decreased tillage, inclusion of cover crops, application of organic nutrients, and retention of crop residue, but not the number of harvested crops in a rotation. The effect of decreased tillage on the C indicators was generally greater at sites with higher precipitation. The magnitude and direction of the response to soil health practices was consistent across indicators within a site but measuring at least two indicators would provide additional confidence of the effects of management, especially for tillage. All C indicators responded to management, an essential criterion for evaluating soil health. Balancing the cost, sensitivity, interpretability, and availability at commercial labs, a 24-hr potential C mineralization assay could deliver the most benefit to measure in conjunction with SOC.Samuel Roberts Noble FoundationOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity.Foundation for Food and Agriculture ResearchOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Evaluation of aggregate stability methods for soil health

Aggregate stability is a commonly used indicator of soil health because improvements in aggregate stability are related to reduced erodibility and improved soil–water dynamics. During the past 80 to 90 years, numerous methods have been developed to assess aggregate stability. Limited comparisons among the methods have resulted in varied magnitudes of response to soil health management practices and varied influences of inherent soil properties and climate. It is not clear whether selection of a specific method creates any advantage to the investigator. This study assessed four commonly used methods of measuring aggregate stability using data collected as part of the North American Project to Evaluate Soil Health Measurements. The methods included water stable aggregates using the Cornell Rainfall Simulator (WSACASH), wet sieved water stable aggregates (WSAARS), slaking captured and adapted from SLAKES smart-phone image recognition software (STAB10), and the mean weight diameter of water stable aggregates (MWD). Influence of climate and inherent soil properties at the continental scale were analyzed in addition to method responses to rotation diversity, cash crop count, residue management, organic nutrient amendments, cover crops, and tillage. The four methods were moderately correlated with each other. All methods were sensitive to differences in climate and inherent soil properties between sites, although to different degrees. None measured significant effects from rotation diversity or crop count, but all methods detected significant increases in aggregate stability resulting from reduced tillage. Significant increases or positive trends were observed for all methods in relation to cover cropping, increased residue retention, and organic amendments, except for STAB10, which expressed a slightly negative response to organic amendments. Considering these results, no single method was clearly superior and all four are viable options for measuring aggregate stability. Therefore, secondary considerations (e.g., cost, method availability, increased sensitivity to a specific management practice, or minimal within-treatment variability) driven by the needs of the investigator, should determine the most suitable method.General Mills IncOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]