Permanganate Oxidizable Carbon Research Articles

Probing the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice (Oryza sativa) - wheat (Triticum aestivum) cropping system

Biochar incorporation as a soil amendment has been shown to improve soil quality by sequestering carbon in soil for longer period of time. The two years field experiment was done at Agronomy research fields of Lovely Professional University, Phagwara, Punjab, India during 2018-19 and 2019-20 to probe the impact of biochar combined with organic and inorganic amendments on soil carbon pools of rice-wheat cropping system. The experiment was comprised with nine treatments viz., 100% Recommended Dose of Fertilizer (RDF), 50% RDF + Biochar, 50% RDF +25% FYM + Biochar, 50% RDF + 50% FYM + Biochar, 50% RDF +25% VC + Biochar, 50% RDF + 50% VC + Biochar, 50% RDF + 25% PM + Biochar, 50% RDF + 50% PM + Biochar, control (no fertilizer) and imposed in RBD design with three replications for each treatment. Pusa basmati 1121 and PBW550 varieties of rice and wheat was taken as a test crops. The results revealed that application of 50 % RDF + 50% PM + Biochar in rice and 50% RDF + 50% FYM + Biochar in wheat crop to soil significantly improved the soil carbon fractions i.e., Permanganate oxidizable carbon, Particulate organic carbon and Microbial biomass carbon at harvest of the crops during both years. This study has demonstrated that C pools in the soil can be enhanced by the biochar through stimulating soil microorganisms. Carbon storage in the soil is improved after biochar addition. By adding biochar with fertilizer and manures C sequestration can be enhanced. Based on the findings in this study, conventional fertilizer and manure application to soils could be associated with biochar through which multi-benefits (e.g., soil amendment, environment protection, and C sequestration) could be obtained simultaneously. Thus, converting rice straw to biochar for its application as soil amendment and C sequester decrease straw burning in open field in Northern India.

The impact of land conversion from boreal forest to agriculture on soil health indicators

Climate change is creating opportunities for agricultural expansion northward into the boreal forest. Converting forested land to agricultural land generally results in significant losses of organic matter (OM), which can impact soil health (SH). The objectives of this study were to assess the effects of land conversion on indicators of SH and to use the Comprehensive Assessment for Soil Health (CASH) framework to integrate measures of these indicators into a score to evaluate land conversion effects. Total carbon and nitrogen were also measured in this study. Soils (0–5 and 5–15 cm) were collected from six dairy farms near Thunder Bay, ON, that included a mature forest, a field converted from forest to agriculture <10 years ago and a field converted from forest to agriculture >50 years ago. Land conversion resulted in significant declines in permanganate oxidizable carbon, wet aggregate stability, soil respiration, and concentrations of OM, autoclave citrate extractable protein, total nitrogen, and total carbon. Lower CASH scores in the soils converted to agriculture are interpreted to represent a decline in SH but the scores, along with soil organic matter (SOM) concentrations, remain high (CASH = 80; OM = 6%). There was no effect of time since conversion, suggesting that any degradation to SH happens quickly and is closely tied to declines in SOM.

A regional assessment of permanganate oxidizable carbon for potential use as a soil health indicator in managed pine plantations

Soil health assessments require the establishment of soil indicators that are easy to measure and sensitive to changes in management practices. Despite the global demand for wood products and the intensification of silvicultural practices, very few indicators are currently used to monitor changes in soil properties and processes in managed forest plantations. Labile pools of soil organic carbon (SOC) have been widely used in agriculture to detect early alterations in carbon (C) cycling processes but are largely untested in managed forests. Here, we investigate the potential use of permanganate oxidizable carbon (POXC) to monitor impacts of silvicultural practices on soil properties in loblolly pine plantations. Soil samples were collected from 77 managed forest sites and 297 experimental plots throughout the southeastern U.S. at four soil depths: 0–10, 10–20, 20–50, and 50–100 cm. Sites encompassed plantations with ages ranging from 2 to 29 yr that were distributed over five soil orders. Silvicultural practices included herbicide, fertilization at multiple rates, and thinning. Our study showed that POXC concentration decreases with soil depth, while POXC increased proportionally to SOC with depth. POXC positively correlates with SOC, total nitrogen, and mass of soil woody detritus other than live roots, and negatively correlates with soil pH across all soil depths. Impacts of silvicultural practices on POXC concentration were variable across sites. The mean relative response of POXC to silvicultural practices was negative in general but only significant (p < 0.10) in herbicide treatments; compared to control plots herbicide plots at 50–100 cm depth had on average 20% less POXC. The decade-long rotation lengths of southern pine plantations and the carbon cycling dynamics of forest soil O horizons may impact the sensitivity of POXC as an indicator in managed plantations. In contrast to this regional analysis, monitoring POXC in local assessments may be a more practical approach to investigate short-term impacts of silvicultural practices.

Effects of land use type and tank components on soil properties and sustainability of tank cascade system in the Dry Zone of north central Sri Lanka

CONTEXTVillage tank cascade system (VTCS) is a globally important agricultural heritage system in Dry Zone watersheds of Sri Lanka. Lands in these watersheds have been under changing management conditions in the recent past, hence their sustainability has been suspected. OBJECTIVEObjectives of this study were to determine current status of soil properties in different land uses and tank components of a VTCS with respect to their position in the watershed, and to assess sustainability of this agricultural system using soil organic carbon management index (CMI) as a proxy. METHODSStudy was conducted in Mahakanumulla VTCS in North Central Dry Zone of Sri Lanka. Soil samples (n = 120) were collected from lands under forest, scrub/shrub, paddy and upland crops representing all elevations in two linear transects located in higher and lower positions along the main valley. Soils from components of tanks in upper and lower positions were also collected. Soil texture and some chemical properties were measured. The CMI in different land uses was calculated using total organic carbon (TOC) and permanganate oxidizable carbon contents. RESULTS AND CONCLUSIONSEffect of land use type on soil properties did not vary with position in the watershed (p > 0.05). An increase in available phosphorus and sulphur was observed in agricultural lands. Significant decreases in TOC (33%) and total N (43%) contents were observed in paddy lands compared to those of forest lands (p < 0.01). However, CMI indicated that management practices in paddy lands and upland soils are still sustainable but scrub/shrub lands need improvements to arrest their degradation. Electrical conductivity, pH, available P, K and Zn were significantly higher in lower positions while total N was lower. Thaulla (inundation area) and Perahana (filter) tank components had regulated flow of clay particles while Kattakaduwa (interceptor) has significantly high available P and TOC contents due to high wetness. Principal component analysis revealed factors that control soil erosion, soil organic matter content, water movement, cation availability and P dynamics governed the variability of major soil properties. Accumulation of soluble salts in lands of lower positions and increase of available plant nutrients in agricultural lands suggest that management practices so far adopted have slightly degraded soil fertility in this VTCS. SIGNIFICANCEFurther degradation of soils in lower positions and scrub/shrub lands in the watershed will negatively affect the livelihood of villagers and the environment. Hence, appropriate land management policies should be introduced to this agricultural system to ensure their sustainability.

Modeling of total and active organic carbon dynamics in agricultural soil using digital soil mapping: a case study from Central Nova Scotia

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.

Effects of organic fertilizer proportion on the distribution of soil aggregates and their associated organic carbon in a field mulched with gravel

Gravel and sand mulching is an indigenous technology that has been used for increasing soil temperature and improving crop yield and water use efficiency for at least 300 years in northwestern China. However, long-term application of inorganic fertilizer with gravel and sand mulch could decrease the soil organic carbon content, and how to improve soil fertility under gravel and sand mulching remains largely unknown. Thus, we evaluated the effects of the application of inorganic (chemical) and organic (manure) fertilizers on the distribution of soil aggregates and their associated organic carbon in a field mulched with gravel and sand. A 5-year (2014–2018) field experiment was conducted in the arid region of northwestern China. Total organic carbon (TOC), permanganate oxidizable carbon (POC), TOC reserves in soil aggregates with different particle sizes, and watermelon (Citrullus lanatus) productivity in gravel-mulched fields were analysed for the following six fertilization modes: no N fertilizer input as a control (CK), N fertilizer without organic fertilizer (CF), and organic fertilizer replacing 25%, 50%, 75%, and 100% of mineral nitrogen (recorded as OF-25%, OF-50%, OF-75% and OF-100%, respectively). The results showed that, higher manure to nitrogen fertilizer ratios were positively correlated with the percentage of soil macroaggregates (> 0.25 mm), mean weight diameter (MWD), TOC and POC concentrations, and their ratios in different particle sizes. Compared with CF, the treatments with 50% to 100% organic fertilizer significantly increased TOC storage (5.91–7.84%) in the soil profile (0–20 cm). Moreover, the CF treatment did not increase SOC concentrations or TOC storage, compared with CK. The fruit yield (2014–2018) of watermelon significantly increased by an average of 31.38% to 45.70% in the treatments with 50% to 100% organic fertilizer, respectively, compared with CF. Our results suggest that the partial replacement of chemical fertilizer with organic manure (OF-50%, OF-75% and OF-100%) could increase the proportion of macroaggregates, POC and TOC concentrations, and TOC stock in aggregates with different particle size and improve the yield of watermelon in the gravel fields of arid northwestern China mulched with gravel and sand.

Soil food web structure and function in annual row-crop systems: How can nematode communities infer soil health?

Increased agricultural management intensity is known to degrade soil food web structure and function, however, the impact of 50+ years of contrasting agricultural management practices on soil food webs is largely unknown. The relationship between soil food web structure and sensitive soil health indicators has seldom been quantified in row crop agricultural systems in the Midwest, USA. This study aims to 1) quantify soil food web structure and function in long-term systems that range in tillage intensity and perenniality over the course of a single growing season; and 2) identify the relationship between soil health indicators and soil food web structure. Nematode feeding groups and nematode indices were used to indicate soil food web structure and soil food web function, respectively. Additionally, a suite of soil health indicators including permanganate oxidizable carbon (POXC), β-glucosidase (GLU), and N-Acetyl-β-glucosaminidase (NAG) were measured in two identical long-term experimental trials with contrasting soil types (clay versus silt loam) under two tillage intensities (chisel till (CT) vs. no-till (NT)) combined with two crop rotations (corn-soy (CS) vs. corn-forage-forage (CFF)). All samples were collected in the corn phase of the rotation. Non-metric multidimensional scaling of nematode community assemblage and vector analysis demonstrated that soil food web structure was significantly related to POXC, GLU, and NAG within CFF systems. Nematode families Thornenematidae and Rhabditidae served as indicators of improved and degraded soil food web function, respectively. Our findings indicate that including perennials within a crop rotation fosters a soil food web structure that can enhance carbon and nitrogen cycling in large scale row-crop agriculture. Moreover, this study emphasizes the potential for specific nematode families to serve as indicators of soil food web function, demonstrating that nematodes should be integrated into the soil health framework.

Does the accretion of carbon fractions and their stratification vary widely with soil orders? A case‐study of an Alfisol and an Entisol of sub‐tropical eastern India

AbstractComparison of the carbon (C) stocks among different soil orders allows us to explore the role of various soil characteristics in long‐term C storage and their vulnerabilities. This study quantified and compared the accumulation rates of soil organic carbon (SOC) fractions (in 0–60 cm soil profile) in an Alfisol of Malda (25°27′33.9″N, 88°19′10.2″E) and an Entisol of Cooch Behar (26°09′62.7″N, 89°53′51.7″E) districts of West Bengal, India. We noticed a greater level of SOC (0–60 cm depth) in the Alfisol than the Entisol as the former soils were clayey in nature (fine textured) which provided the maximum stabilization of SOC compared to the Entisol (sandy textured). However, the storage of C fractions showed some peculiar results. The concentration of mineral‐associated carbon (Min‐C) was more or less similar in both the soil orders, but its stock was maximum in the Alfisol. While in the Entisol, permanganate oxidizable carbon (POX‐C) and particulate organic matter carbon (POM‐C) stocks recorded maximum among all the studied depths. A positive relation of SOC fractions and stocks with clay (r2 = &gt;0.500 in the Alfisol; r2 = &gt;0.700 in the Entisol) indicated the importance of finer fractions in profile storage of C. Min‐C contributed to SOC of about 75%–85% followed by POM‐C (3.27%–17.87%) and POX‐C (2.57%–4.22%). Higher stratification of SOC and POX‐C and POM‐C fractions was observed in Entisol; while in Alfisol, stratification of Min‐C was greater. Overall, this research demonstrated that the Alfisol has a greater potential in stabilizing Min‐C than the Entisol with POM‐C and POX‐C and the distribution of these fractions varied as per its stabilization.

Soil macrofauna and microbial communities respond in similar ways to management drivers in an irrigated maize system of Colorado (USA)

The adoption of conservation agriculture has gained considerable attention due to growing interest in managing soil biological diversity and overall soil health. However, there is limited understanding of how practices such as conservation tillage and residue retention affect soil biota across different spatial scales and are associated with alterations to other soil properties. In this study, we examined changes in soil physicochemical properties, soil macrofauna, and microbial communities at two soil depths (0–10 cm, and 10–20 cm) in a 6-year field experiment manipulating tillage and maize residue management. The following treatments were included in the experiment: no-till with residue retention; no-till with residue harvest; conventional tillage with residue retention; and conventional tillage with residue harvest. Macrofauna taxa were identified and estimated visually, while bacterial and fungal communities were identified and analyzed using high throughput sequencing and multivariate statistics including non-metric dimensional scaling and indicator species analysis. Soil physicochemical properties measured include soil carbon and nitrogen, soil moisture, permanganate oxidizable carbon, available soil phosphate, pH, electrical conductivity and aggregate stability. Residue retention increased macrofauna abundance and diversity across soil depths and tillage treatments. Fungal diversity was also highest under residue retention in the topsoil (0–10 cm), while bacterial diversity was generally higher under conventional tillage. Residue retention was the main driver of macrofauna and microbial community composition, while an interaction between tillage and residue management indicated that the effect of tillage on microbial communities was most pronounced when residues were retained. Soil carbon and nitrogen, aggregate stability, permanganate oxidizable carbon, soil moisture content, available soil phosphate and soil electrical conductivity were all enhanced under residue retention in the topsoil. Indicator species analysis suggested that macrofauna taxa belonging to Annelida, Aranaea and Chilopoda together with bacterial phyla Fibrobacteres and fungal phyla Rozellomycota were indicators for no-till combined with residue retention, while Coleoptera, Spirochaetae and Basidiomycota were indicators for conventional tillage with residue retention. Multivariate analyses suggested that total macrofauna abundance, soil carbon and pH were strongly associated with bacterial and fungal community composition in the topsoil layer. Co-inertia analysis indicated significant covariation between soil physicochemical, macrofauna, bacterial and fungal datasets, suggesting a strong association between different soil parameters and cascading effects of management on multiple soil properties. Our findings demonstrate that residue retention enhances soil biological, physical and chemical properties and that communities of soil macro- and microorganisms tend to respond in similar ways to these management interventions.

Soil biochemical properties and nutritional quality of rice cultivated in acidic inceptisols using long-term organic farming practices

ABSTRACT The enriched compost (ECM) comprising rock phosphate and biofertilizer consortia (BC) is a cheap source of organic input. A long-term field trial was initiated in kharif–2011 with the following treatment combinations used for rice sole-cropping: T1, absolute control; T2, 3.5 kg ha−1 biofertilizer consortia; T3, 5.0 t ha−1 compost (CM); T4, 5.0 t ha−1 CM + 3.5 kg ha−1 BC; T5, 2.5 t ha−1 ECM; T6, 5.0 t ha−1 ECM; and T7, 0.5 t ha−1 Azolla + 3.5 kg ha−1 BC. Owing to the usage of ECM for nine consecutive years, the organic carbon pools and biochemical properties of the soil were enhanced, and the nutritional quality of rice was enriched. Further, the potassium permanganate oxidizable carbon, total organic carbon, and microbial biomass carbon increased by 46%, 20%, and 15%, respectively, in the surface soil with T6 relative to T3. Such finding highlights the benefit of ECM application relative to CM and BC in enhancing rice nutritional quality and soil biochemical properties. Overall, the study suggests the use of 5 t ECM ha–1 to improve the soil biochemical properties and nutritional quality of rice subjected to acidic inceptisol.

Soil quality indicators in conventional and conservation tillage systems in the Brazilian Cerrado

Conventional and conservation tillage systems can alter soil aggregation and total and labile soil organic matter (SOM) contents. This study aimed to determine the degree of soil aggregation, quantify total carbon (TC), permanganate oxidizable carbon (POXC), light organic matter (LOM), and potentially mineralizable carbon (CO2-C) contents in soils aggregates, and assess soil quality indexes at sites under conventional and conservation tillage in the Cerrado region of Minas Gerais State, Brazil. Four experimental areas were analyzed: a area under conventional tillage for 20 years, a area under no-till for 6 years, a area under no-till for 18 years, and a reference area of undisturbed Cerrado vegetation. Soil aggregates retained on 8.0–4.0 mm sieves were evaluated for size class distribution and mean weight diameter. TC, POXC, LOM, daily and Total CO2-C emissions were also analyzed. These data were used to calculate the C/N ratio and sensitivity, carbon pool, and lability indexes. The results of SOM compartments were in agreement with those obtained for the soil aggregation status. 6NT and 18NT had a higher proportion of macroaggregates and higher MWD values than CT in both layers. For other classes of aggregates, CT had the highest proportions of mesoaggregates at 0–0.05 m depth and microaggregates at 0–0.10 m depth. At 0–0.05 m depth, TC and LOM contents were highest in 6NT and 18NT aggregates. In comparing the soil indexes of managed areas, we found a similar pattern to that observed for macroaggregates, MWD, TC, and LOM. CA, 6NT, and 18NT aggregates had the largest CO2-C cumulative emissions at the end of the incubation period. Environmental conditions at no-till areas promoted macroaggregate formation and preserved TC and LOM contents, resulting in a high degree of aggregate stability. Soil quality indexes were sensitive to identify changes between the reference area and managed areas. Soil aggregates from no-till areas had higher CO2-C emissions and cumulative emissions than those from the conventional tillage area.

Effect of Olive Tree – Barley/Common Vetch Agroforestry System on Soil Organic Matter Under Low-Input Conditions in a Tunisian Semi-Arid Climate

ABSTRACT The use of cover crops within olive groves, be they legume, non-legume or a mixture, has become more widespread in recent years as a practice of environmental sustainability to improve soil organic matter. Using both SC: a sole-crop and AC: an alley-cropping, Hordeum vulgare L. and Vicia sativa L. were studied with olive trees 2016 to 2019. The aim was to determine the effects of both of these systems on: TB: total biomass, POXC: Permanganate oxidizable Carbon and SOC: Soil Organic Carbon, TN: Total Nitrogen, C:N ratio; and P: available Phosphorus. These parameters were measured on 192 soil samples collected at 0–20 and 20–40 cm soil depths before planting and after crop harvesting. The results showed that within the relatively short time of three seasons, cover crops increased SOC slightly overall. Compared to the SC, AC limited crop and weed growth and produced significantly less TB, especially in 2017–18, a particularly dry season. This can be explained by the initial state of the soil which was significantly affected by the cropping system. AC enhanced SOC and stabilized the POXC during all three cropping seasons for all treatments. Mixed crop (barley and vetch) significantly increased TN in the AC over the three cropping seasons and decreased the C:N ratio. However, with barley and vetch in pure stand, the mean TN was similar to that of fallow. Also, this type of agroforestry increased the mean available phosphorus with barley, vetch and a mixture of the two compared to fallow.

Impact of long-term residue burning versus retention on soil organic carbon sequestration under a rice-wheat cropping system

Despite rice residue burning is popularized against its retention under rice-wheat system in the Indo-Gangetic Plains (IGP), limited information is available on the impacts of long-term rice residue burning versus its retention on carbon stock, soil aggregation and aggregated-associated carbon in the region. Hence, a 18 (1998–2016) years old conservation agriculture (different combinations of tillage and residue management) experiment was selected to understand the impact of CA on soil aggregation, carbon pools and soil organic carbon (SOC) stock in a rice-wheat system. Experiment was laid down in a split-plot design with three replications having three tillage management viz. zero-tillage (ZT), conventional tillage (CT) and strip tillage (ST) as main plots and three residue management options namely residue retention (R), residue burning (RB) and no-residue (NR). The total SOC content was 20% higher (p < 0.05) under ZT and residues retention over CT and residue removal, in the 0–5 cm layer. The SOC stock increased with depth (from 0 to 5 cm to 5–15 cm). ZT with added residues had 25% higher (p < 0.05) SOC stock than CT without residues because of higher aggregation with lesser disturbance in ZT promoted SOC accumulation over time. Macro-aggregate fraction was higher in ZT by 18% (p < 0.05) than CT in the 0–5 cm soil depth. Whereas, CT without residues resulted in higher silt and clay size fraction than ZT. Labile carbon (very labile + labile fractions) was 7–25% increased (p < 0.05) under ZT+R than CT-R across depth. Recalcitrant carbon (less-labile + non-labile) followed the same trend. Notably, ZT with residues retention (conservation agriculture, CA) increased 32.6–41.7% potassium permanganate oxidizable carbon than CT without residues in the 0–5 cm and 5–15 cm, respectively. No mechanical tillage in ZT with added residues over the years promoted bridging between aggregates that brought about carbon accumulation. The study highlighted the importance of CA in enhancing SOC stock, soil aggregation and managing long-term SOC content.

Distributions and Influencing Factors of Soil Organic Carbon Fractions under Different Vegetation Restoration Conditions in a Subtropical Mountainous Area, SW China

Vegetation type is known to affect soil organic carbon (SOC) storage. However, the magnitudes and distributions of SOC sequestration and driving factors for different vegetation types are still largely unknown. Thus, we studied the changes in SOC fractions along soil profiles for different vegetation restoration types and their relationships with soil properties. We selected five vegetation types and collected soil samples from depth intervals of 0–10, 10–30, 30–60, and 60–90 cm. Five soil carbon fractions and the soil properties were tested to evaluate the soil carbon fraction distributions and influencing factors. Our results demonstrated that the concentrations of total organic carbon (TOC) and five carbon fractions were strongly affected by vegetation types and soil depths. The concentrations of all five soil carbon fractions in 0–10 cm depth were higher than those in the other three soil depths and generally increased with vegetation complexity. The Pearson correlations and redundancy analysis showed that the fractions of soil glomalin-related soil protein (GRSP) and Fe oxides as well as the soil bulk densities, were the most significant related to soil TOC levels and carbon fractions, which suggests that soil biochemical and physicochemical processes are among the most important mechanisms that contribute to SOC persistence. Considering the sensitive indices of the soil carbon variables and PCA results, soil permanganate oxidizable carbon (POXC) was considered to be the most sensitive index for differentiating the effects of vegetation types. These results provide important information regarding the distributions and driving factors of the carbon fractions that result from different vegetation restoration types and will help to improve our understanding of soil carbon sequestration during vegetation restoration processes.

ResidualBradyrhizobiuminoculation effects on soybean performance and selected soil health parameters

AbstractThe persistence of inoculants from year to year in soybean [Glycine max (L.) Merr.] cultivation and the residual benefits in soybean production are pertinent to adopting such practices in sub‐Saharan Africa countries such as Ghana. A study was conducted to determine the residual effect of commercial rhizobium inoculants on soybean and selected soil health parameters after three cropping seasons. The experimental design was a split‐plot. The main plot consisted of three soybean cultivars (Jenguma, Afayak, and Songda), and the subplot comprised of three peat‐based commercial bradyrhizobium inoculants (Biofix, Legumefix, and NoduMax) and an uninoculated control. Assessments were made on nodulation, shoot dry matter (DM), grain yield, grain total N uptake, permanganate‐oxidizable carbon (POXC), soil pH, and potentially mineralizable C. Among the soybean cultivars, Afayak produced greater nodule mass on the lateral root and the whole root system compared with the other cultivars. Jenguma and Afayak yielded greater shoot DM relative to Songda. Regarding the inoculants, Biofix increased nodule mass on the lateral root and the whole root system compared with the control. Biofix and NoduMax produced superior grain yield relative to the control. Biofix also produced greater grain yield than Legumefix. A superior pod harvest index and an improved grain total N uptake were produced by Biofix compared with Legumefix and the control. Commercial inoculants enhanced POXC availability at harvest, whereas potentially mineralizable C declined with inoculation treatments. Commercial inoculants (Biofix and NoduMax) enhanced nodulation, grain yield, and selected soil health indicators 3 yr after inoculation.

Evaluation of indirect and direct scoring methods to relate biochemical soil quality indicators to ecosystem services

AbstractSoil health assessments use scoring curves to quantify relationships between soil quality indicators (SQIs) and ecosystem services (ESSs). We evaluated methods for scoring curve development using three labile C pools (β‐glucosidase [BG], fluorescein diacetate [FDA] hydrolysis, and permanganate oxidizable carbon [POXC]). Concepts and methods for SQI interpretation used by established frameworks were assessed, with 129 studies reporting relationships to either soil organic C (SOC) (n = 367), a common surrogate for indirect estimation of ESSs, or direct measures of crop yield (n = 88), soil respiration (n = 66), and N2O and CH4 emissions (n = 51). Indirect assessment of BG using SOC and site covariates resolved tillage‐based differences (P &lt; .05). Correlations between SOC and SQIs observed under different land uses suggested that use of SOC for indirect scoring would be more effective for FDA than POXC. Direct relationships were generally positive between SQIs and yield (89%), soil respiration (89%), and N2O and CH4 emissions (76%), but such relationships could be nonlinear. Direct assessment revealed that both positive and negative ESS outcomes increased with labile C fraction abundance that complicates the assignment of ESS‐based SQI scores. Although direct SQI scores are relatively easy to interpret, relationships between scores and SQIs can vary 10‐fold for different sites and cropping systems (upland versus rice paddy), which is much greater than treatment‐based differences observed within single sites. To quantify relationships between SQIs and ESS outcomes, one must measure influential site covariates (SQI–ESS covariates) along with details about management, sampling, and analysis.

Hemp biochar impacts on selected biological soil health indicators across different soil types and moisture cycles.

Application of crop residues and biochar have been demonstrated to improve soil biological and chemical properties in agroecosystems. However, the integrated effect of organic amendments and hydrological cycles on soil health indicators are not well understood. In this study, we quantified the impact of hemp residue (HR), hemp biochar (HB), and hardwood biochar (HA) on five hydrolytic enzymes, soil microbial phospholipid (PLFA) community structure, pH, permanganate oxidizable carbon (POXC) soil organic carbon (SOC), and total nitrogen (TN). We compared two soil types, Piedmont and Coastal Plain soils of North Carolina, under (i) a 30-d moisture cycle maintained at 60% water-filled pore space (WFPS) (D-W1), followed by (ii) a 7-day alternate dry-wet cycle for 42 days (D-W2), or (iii) maintained at 60% WFPS for 42 days (D-W3) during an aerobic laboratory incubation. Results showed that HR and HB significantly increased the geometric mean enzyme activity by 1-2-fold in the Piedmont soil under the three moisture cycles and about 1.5-fold under D-W in the Coastal soil. In the presence of HA, the measured soil enzyme activities were significantly lower than control under the moisture cycles in both soil types. The shift in microbial community structure was distinct in the Coastal soil but not in the Piedmont soil. Under D-W2, HR and HB significantly increased POXC (600–700 mg POXC kg-1 soil) in the Coastal soil but not in the Piedmont soil while HA increased nitrate (8 mg kg-1) retention in the Coastal soil. The differences in amendment effect on pH SOC, TN, POXC, and nitrate were less distinct in the fine-textured Piedmont soil than the coarse-textured Coastal soil. Overall, the results indicate that, unlike HA, HR and HB will have beneficial effects on soil health and productivity, therefore potentially improving soil’s resilience to changing climate.

A Bayesian approach to understand controls on total and labile soil carbon in cultivated soils of Central and Southern Malawi

Soil degradation on cultivated lands of Sub-Saharan Africa is a threat to food security. Even so, drivers of soil C total and labile pools are little understood for smallholder farms. A unique opportunity to evaluate how environment conditions management drivers was afforded by a systematically representative on-farm study of 1108 cultivated plots in marginal to mesic environments across Central and Southern Malawi. Soil sample collection and analysis and surveys of farmer practice were conducted, and linked to remote-sensed data on environmental and spectral factors. Soil properties included the following ranges (mean values per site), soil clay (6.41% to 17.36%), pH (6.09 to 6.54), soil organic carbon (SOC) (6.31 g C kg soil−1 to 16.17 g C kg soil−1), and two labile soil C assays: permanganate oxidizable carbon (POXC) (291.5 mg C kg soil−1 to 504.5 mg C kg soil−1) and 24-h mineralizable C (Cmin) (28.71 mg C kg soil−1 to 65.34 mg C kg soil−1). Incorporation of domain specialists’ expectation of uncertainty levels is key to carrying out a multiscale assessment of soil total and labile C status, thus a Bayesian linear regression approach was used for determining the influential drivers. Overall, the soil clay content is a strong predictor of SOC (0.479–0.517), POXC (0.139–0.266), and Cmin (0.125–0.223) at the 95% Bayesian credibility level from the Gibbs posterior samples. Vegetative cover, reflected by Normalized Difference Vegetation Index (NDVI), is also a dominant driver for SOC (0.234–0.329), POXC (0.163–0.285), and Cmin (0.249–0.38). Of the management practices studied, crop diversity, residue incorporation, and weed presence are all positive drivers for total soil C, whereas fertilizer N is not. At both regional and local scales, labile soil C pools (as reflected by POXC and Cmin) are not consistently responsive to management. The drivers of SOC are highly consistent, a strong indication of statistical robustness. This contributes to the understanding of patterns of carbon pools in intensively cultivated fields in Sub-Saharan Africa.

The integration of nematode communities into the soil biological health framework by factor analysis

A critique of the soil health framework is that biological indicators currently lag behind chemical and physical indicators of soil health. Incorporating nematode communities into the soil health framework could help to better reflect key aspects of soil food web structure and function and significantly contribute to ecosystem processes. However, little is understood regarding how nematode communities relate to soil biological health indicators such as permanganate oxidizable carbon (POXC), soil protein, mineralizable C, and enzyme activities in agroecosystems. Here, we use an exploratory factor analysis (EFA) to quantitatively explore which set of soil health indicators best explain a given factor (i.e. soil health trait) using data from two long term experimental trials and 44 farm fields across Ohio. Specifically, this paper aims to 1) integrate our understanding of nematode structure and function with other soil biological health indicators to describe soil health traits; and 2) determine how management practices alter soil health traits. We found that soil biological health indicators represented four underlying soil health traits: fungal organic matter processing pathway, the rate of nutrient cycling, trophic complexity, and cumulative disturbance. Results indicated that soil biological health indicators, such as enzyme activities, POXC, mineralizable C and soil protein were more integrated with nematode feeding groups than with nematode indices. Additionally, tillage intensity had a significant effect on the fungal organic matter processing pathway and the rate of nutrient cycling. This study indicates that nematode feeding groups can be readily incorporated into the soil health framework and future soil health assessments.

Exploring Overwintered Cover Crops as a Soil Management Tool in Upper-midwest High Tunnels

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.