Monitoring the changes in soil organic carbon (SOC) pools is critical for sustainable soil and agricultural management. This case study models total and active organic carbon dynamics (2015/2016 to ...2019/2020) using digital soil mapping (DSM) techniques. Model predictors include topographic variables generated from light detection and ranging data; soil and vegetation indices derived from Landsat satellite images; and soil and crop inventory information from Agriculture and Agri-Food Canada to predict total organic carbon (TOC) and permanganate oxidizable carbon (POXc) at the 0–15 cm depth increment for a 37 km2 study area in Truro, Nova Scotia. Quantile Regression Forest and stochastic Gradient Boosting Model were utilized for prediction. Although both models performed equally well for predicting TOC and POXc, the accuracy of TOC predictions (e.g., concordance correlation coefficient (CCC) = 0.67) was better than POXc predictions (e.g., CCC = 0.53). The Landsat variables and crop inventory were dominant predictors, while topographic variables across the relatively homogeneous terrain had relatively little influence. During the study period, changes in POXc were predicted across 98% of the study area, with a mean absolute loss of 5.77 (±11.48) mg/kg/year, and in TOC on 27% of the area, with a mean absolute loss of 0.15 (±0.09) g/kg/year. While the annual crop fields observed the highest loss of TOC and POXc, the decline in pasture–grassland–forage fields was relatively low. The study reinforced the effectiveness of DSM for modeling multiple SOC pools at the farm to landscape scales.
This study investigated the influence of biosolid applications on soil carbon storage and evaluated nutrient management strategies affecting soil carbon dynamics. The research assessed alterations in ...soil pH, soil carbon stock, and soil nitrogen content within short-term and long-term biosolids-amended soils in Bible Hill, Nova Scotia, Canada, extending to a depth of 0–60 cm. The findings indicated an increase in soil pH with alkaline treatment biosolids (ATB) applications across both study sites, with a legacy effect on soil pH noted in the long-term biosolids-amended soil following a single ATB application over 13 years. Both sites demonstrated significant increases in soil total carbon (STC) and soil organic carbon (SOC) within the 0–30 cm soil depth after biosolid application, and soil inorganic carbon (SIC) accounted for approximately 5–10% of STC, specifically in the surface soil layer (0–15 cm). In the long-term study site, annual 14, 28 and 42 Mg ATB ha−1 treatments resulted in a substantial rise in soil carbon stock (59.5, 60.1 and 68.0 Mg C ha−1), marking a 25% increase compared to control soil. The SOC content in biosolids-amended soil showed a declining trend with increasing soil depth at both study sites. Notably, the carbon stock in the short-term site was observed in composted biosolids (COMP) > ATB > liquid mesophilic anaerobically digested biosolids (LMAD) from the 0–60 cm soil depth. Approximately 79–80% of the variation in SOC response at both sites was concentrated within the top 30 cm soil. Soil total nitrogen (STN) showed no significant differences at the short-term site, and STN in biosolids-amended soil decreased with increasing soil depth at the long-term site. Biosolids-induced C retention coefficients (BCR) for ATB remained consistent at both sites, ranging from −13% to 31.4% with a mean of 11.12%. BCR values for COMP ranged from 1.9% to 34.4% with a mean of 18.73%, while those for LMAD exhibited variability, spanning from −6.2% to 106.3% with a mean of 53.9%.
•Soil pH increased with alkaline treatment biosolids (ATB) applications.•Significant STC and SOC increased in top 30 cm soil depth after biosolid application.•Annual ATB treatments raised long-term soil carbon stock.•Short-term stored C followed order of composted > ATB > anaerobic digested biosolids.•Biosolids-induced C retention coefficients varied by different types of biosolids.
There has been a continued adaption and application of soil health tests across all regions of the globe; however, there are challenges related to the interpretation of the results of soil health ...tests developed in one region but applied elsewhere. To determine the factors that are the most important for interpreting soil health tests in Nova Scotia, a soil health database was constructed using soil samples from diverse cropping systems and soil orders in the region. The Comprehensive Assessment of Soil Health, developed at Cornell University in New York, was adapted and combined with other soil health measures. Principal component analysis (PCA), analysis of variance, and a correlation analysis were applied to the dataset to determine if management (i.e., cropping system) or pedogenesis (i.e., soil order) was more important as a driver of soil health test results. It was determined that cropping systems explained more variance in the dataset than soil order. Although total carbon explained the most variation in the PCA, it was highly correlated to other measures of carbon such as permanganate oxidizable carbon and respiration that may be more responsive to management changes. In addition, autoclaved-citrate extractable protein, a test for nitrogen mineralization, was more related to measures of soil carbon than other measures of soil nitrogen availability. The findings of this study provide a foundation for interpreting soil health testing results for this region and will help indicate which cropping systems and soil management practices have the greatest potential for improving soil health.
•New primers were designed to study bacterial phoC gene abundance in soil.•Higher abundances of phoC genes compared to phoD across all sites.•Higher phosphatase activity (pH 6.5) in rhizosphere ...soil.•Soil labile P was negatively correlated with phosphatase activity and phoC and phoD gene abundance.•No relationship between pre-seeding soil test P and plant P uptake or yield.
Phosphorus (P) is a limiting nutrient in many environments but plants and microbes have evolved with mechanisms for acquiring soil P, including the excretion of phosphatase enzymes. Molecular analysis of bacterial phosphatase genes can provide insight into biological P transformations and the contribution to soil P availability and plant uptake. To assess these relationships, soil and plant samples were collected from 12 organically-managed soybean fields varying in pH, labile P concentration, and potential phosphatase activity (pH 6.5) across Prince Edward Island, Canada. Real-time PCR was used to quantify bacterial phosphatase genes (phoC and phoD) in bulk and rhizosphere soil. Primers targeting class A (phoC) of the bacterial non-specific acid phosphatases (NSAPs) were designed and confirmed as effectively targeting phoC genes through sequencing, and phylogenetic comparison with acid phosphatase genes from Genbank. Across all sites, we found that labile P in bulk soil was negatively correlated with phoC and phoD gene abundance and phosphatase activity. In addition, phosphatase activity was consistently higher in rhizosphere compared to bulk soil and was significantly correlated with phoC (bulk soil only) and phoD (rhizosphere soil only) gene abundance. A positive relationship was observed between phosphatase activity, nodule weight, and plant P uptake. Quantification of bacterial genes involved in organic P transformations has been limited, with this study providing the first attempt at quantifying phoC genes in field soils.
Bacterial transformation of phosphorus (P) compounds in soil is largely dependent on soil microbial community function, and is therefore sensitive to anthropogenic disturbances such as fertilization ...or cropping systems. However, the effect of soil management on the transcription of bacterial genes that encode phosphatases, such as phoD, is largely unknown. This greenhouse study examined the effect of long-term management and P amendment on potential alkaline phosphatase (ALP) activity and phoD gene (DNA) and transcript (RNA) abundance. Soil samples (0–15 cm) were collected from the Glenlea Long-term Rotation near Winnipeg, Manitoba, to compare organic, conventional and prairie management systems. In the greenhouse, pots of soil from each management system were amended with P as either soluble mineral fertilizer or cattle manure and then planted with Italian ryegrass (Lolium multiforum). Soils from each pot were sampled for analysis immediately and after 30 and 106 days. Significant differences among the soil/P treatments were detected for inorganic P, but not the organic P in NaHCO3-extracts. At day 0, ALP activity was similar among the soil/P treatments, but was higher after 30 days for all P amendments in soil from organically managed plots. In contrast, ALP activity in soils under conventional and prairie management responded to increasing rates of manure only, with significant effects from medium and high manure application rates at 30 and 106 days. Differences in ALP activity at 30 days corresponded to the abundance of bacterial phoD genes, which were also significantly higher in soils under organic management. However, this correlation was not significant for transcript abundance. Next-generation sequencing allowed the identification of 199 unique phoD operational taxonomic units (OTUs) from the metagenome (soil DNA) and 35 unique OTUs from the metatranscriptome (soil RNA), indicating that a subset of phoD genes was being transcribed in all soils.
•Alkaline phosphatase activity was highest in organic soils regardless of P treatment.•Alkaline phosphatase responded to increasing rates of manure P, but not mineral P.•The phoD gene abundance was significantly correlated to ALP activity.•The highest number of unique phoD OTUs was in the organic soil.•Soils from the conventional system had the highest number of transcribed phoD OTUs.
Core Ideas
Soil organic C pools increased under no‐till green manure termination, and this increase persisted over 3 yr following the green manure termination method.
Total organic C and particulate ...organic matter C showed a stronger response to the green manure termination method than permanganate oxidizable C.
Tillage effects in labile soil organic C pools may be harder to detect in organic systems with high levels of C inputs.
There is continued interest in adopting no‐till practices in organic agriculture. One way to decrease tillage is to implement no‐till termination of green manures. Studies on this novel approach have focused primarily on cash crop performance and weed control. The objective of this study was to examine soil organic C distribution and dynamics as influenced by different methods of green manure termination of a spring‐planted green manure. In this green manure–wheat (Triticum aestivum L.)–fall rye (Secale cereal L.)–soybean Glycine max (L.) Merr. rotation three green manure termination methods were compared (no‐till crop roller, spring tillage, and fall tillage). A mixture of hairy vetch (Vicia villosa Roth)–oat (Avena sativa L.) was seeded in late May in two trials, the first commencing in 2013 and the second in 2014. Soil organic C was monitored for 3 yr after green manure termination. In Trial 2, total organic C was greater under no‐till green manure termination compared to fall and spring‐till termination (by 2.4 ± 1.2 Mg C ha−1 and 2.3 ± 1.3 Mg C ha−1, respectively) and the effect remained significant in all 3 yr. In Trial 1, particulate organic matter C was stratified in no‐till and concentrated at the soil surface (0–5cm) and higher overall in no‐till in Trial 2. Overall soil organic C was higher under no‐till green manure termination and the more labile pool of POXc appeared less responsive to termination treatments.
Collembola are known to feed on a wide range of soil material, predominantly rhizosphere fungi, and root-derived substances. However, diet switching from these usual food sources to living roots ...(herbivory) was previously demonstrated for one species of collembola, Protaphorura fimata, a euedaphic species. The objective of this study was to determine if diet switching can be applied to another collembola species, Folsomia candida Willem. This hemiedaphic species was given different combinations of maize plants (-13.28% δ13C, 3% δ15N) and 15N-enriched rye grass litter (-28.88% δ13C, 17 516.86% δ15N) in a C3 soil system (-27.27% δ13C, 5.27% δ15N) under controlled conditions. After 8 wk, there was clear evidence of root feeding because the δ13C signature in collembola tissue was -19.28% in the presence of maize plants alone and -18.29% with maize plants grown in soil mixed with ryegrass litter, whereas collembola in unplanted soil microcosms had a δ13C signature of -23.66%. Data analysis with a two-source isotope mixing model indicates that up to 60% of the carbon requirements of F. candida were derived from living maize roots. Whether collembola root feeding is due to grazing on roots directly or on mycorrhiza (root-fungus association) requires further investigation.
Although farmers are the key actors in managing soil health, we have little understanding of what farmers know about soil health, how they define the term, and how they manage for it on their farms. ...Interviews with 34 farmers in Maritime Canada revealed their perceptions about soil health, their methods for assessing their own soils, and their reactions to a comprehensive soil health assessment based on the Cornell Soil Health Assessment (CSHA). Farmers primarily assessed soils using aboveground indicators such as plant health and yield, as well as physical indicators such as texture or water-holding capacity. Most farmers (91%) had heard of soil health, and their definitions focused on biological and productivity aspects of the soil. Organic farmers tended to be more open to the CSHA results and were more likely to give a holistic definition of soil health than conventional farmers. Depending on what frame is invoked about soil, farmers think of soil health differently. Despite differences between farmers' perceptions and CSHA results, most farmers found CSHA results useful (71%) and planned to undertake management changes (74%) based on them. Soil health could be an 'inclusive' common ground for farmers and soil scientists to think about and manage soils.
Production of fruits and vegetables provides nutrient dense and high value crops. However, horticulture production is often very intensive and degrading to soil, with high levels of soil disturbance, ...high use of fertilizer inputs, and with prolonged periods of exposed soil. This can lead to increased soil degradation when compared to other types of cropping. We used a subset of the Atlantic Soil Health Laboratory’s database of on-farm soil samples collected between 2016 and 2018 to assess the impact of cover crop (CC) use in horticulture production in Nova Scotia on soil health. We analyzed 21 soil health parameters on soil collected from 14 fields, seven of which incorporated CCs in their crop rotation and seven of which used no CCs. The inclusion of CCs significantly increased permanganate oxidizable carbon (POX), soil respiration, autoclaved-citrate extractable (ACE) protein, residual soil nitrogen (N), and biologically available N. However, we also found that the variation in these parameters was greater when CCs were part of the rotation. This is likely attributable to the wide range of CC species used and differences in their management, such as the chosen termination method. While cover cropping is seen as a best management practice to improve soil health, simply using a CC in a horticulture rotation does not necessarily lead to improved soil health. Research trials on specific CC species and management to target soil degradation are needed to tailor recommendations to ensure the desired soil health outcomes can be achieved with CC use.
The green manure residual effect on soil health 2 years later in crop rotation is understudied. Little is known about weed biomass impact on soil microbial communities or their interactions. A ...Colchester County, NS, Canada, organic grain research trial during 2016–2017 comprised 2 or 3-year rotations with or without green manure crop prior to wheat, and then soybeans. Fall soil sampling was conducted both years. The soybean phase of the crop rotation was managed as weedy or non-weedy. Weedy soil showed significantly increased soil respiratory activity and fungal microbial biomass. Green manure treatments did not significantly influence soil health indicators.
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