Proceedings - Soil Science Society of America最新文献

Soil carbon (C) sequestration by restoring degraded grasslands with adequate management practices offers significant opportunities for climate change mitigation while remaining highly uncertain. In this study, a combination of a biogeochemical model DayCent-CABBI and eddy covariance (EC) flux towers was applied to evaluate soil C sequestration potential (at a depth of 0–0.3 m) of management strategies in subtropical grasslands. DayCent-CABBI was calibrated for grasslands in northeast Australia using biomass and soil organic carbon (SOC) data from a long-term trial and then fine-tuned using EC flux tower data from seven sites in the region. The model was then validated with cumulative net ecosystem exchange, biomass, and SOC, resulting in root mean square errors of 1.16, 0.88, and 2.81 Mg C ha⁻¹, respectively. The model was used to project long-term changes in SOC stocks under innovative management practices (time-controlled grazing and pasture legume incorporation), estimating soil C sequestration by 0.37–0.48 and 0.15–0.26 Mg C ha⁻¹ year⁻¹ toward 2050 with the respective practices. This study confirms the validity of the Measure, Model, and Verification (MMV) approach to estimate and project soil C sequestration for evaluating SOC methodologies by grassland management within a shorter period than soil sampling—measuring the baseline SOC, modeling the C dynamics with the calibrated DayCent-CABBI, and verifying the projected soil C sequestration with EC flux tower data.

Soil apparent electrical conductivity (EC_a) measurements, although more suitable for soil salinity quantification, are often used to determine volumetric soil water content, θ_v, in site-specific crop management. Generally, the approach is to develop a field-specific calibration function between EC_a and measured θ_v, θ_v(m). Such a calibration function is possible when soil water dominates EC_a at a field. When this is not the case, θ_v(m) data taken over time may be helpful to develop a function. Data regarding θ_v(m) can be costly and time-consuming as soil samples are needed to measure bulk density and gravimetric soil water. We postulate that capacitance probes, which measure scaled frequency (SF) as an indicator of the dielectric constant to estimate θ_v, can be used to establish EC_a-θ_v calibration functions. Capacitance probes that simultaneously provide temperature readings allow for EC_a to be temperature-corrected to 25°C, enabling development of EC_a25-θ_v calibration functions. A field experiment was set up to establish whether SF readings can be used to estimate θ_v, θ_v(SF), in structured high montmorillonite clay soils accurately and determine if EC_a25-θ_v(SF) calibration functions are possible. Our results revealed that a single SF-θ_v(m) calibration function representing 12 probes, or a specific soil form, is impossible. Each capacitance probe should be calibrated separately. The parameters for EC_a25-θ_v(m) calibration functions were like EC_a25-θ_v(SF) functions. The R² for EC_a25-θ_v(m) calibration functions was higher compared to the EC_a25-θ_v(SF) functions. Further investigation of using capacitance probes to estimate θ_v for developing EC_a-θ_v functions is needed before this approach can be applied confidently.

Organic cropping systems may potentially improve soil and environmental health relative to simplified conventional systems due to the use of extended crop rotations, perennial crops, and animal manure. However, few studies have evaluated the impacts of organic row crop systems on a suite of soil health indicators relative to conventional systems across time. Thus, our objective was to assess how cropping system (conventional corn [Zea mays L.]–soybean [Glycine max L.] vs. organic corn–soybean–oat [Avena sativa L.]/alfalfa [Medicago sativa L.]–alfalfa vs. organic perennial pasture) and duration of management affect surface soil health indicators (soil biological, chemical, and physical properties) after 1–9 years of management in a Central Iowa Mollisol. Overall, the organic rotation improved six of 14 soil health indicators compared with the conventional system and the organic pasture improved eight indicators. The improved indicators included soil biological indicators, labile C and N pools, and wet-aggregate stability, but not organic C or total N concentrations. Organic systems had fewer effects on most soil chemical properties. The conventional system reduced soil C by 0.35 g kg⁻¹ year⁻¹ (r = −0.84, n = 9, p = 0.005), unlike the organic systems in which soil C levels were generally maintained. The changes in soil health indicators were attributed to use of perennials, reductions in tillage frequency (during perennial phases), manure, and differing plant residue amounts among the three systems. In conclusion, organic cropping systems can enhance soil biological and related indicators in the medium term, but have fewer effects on soil fertility indicators under the conditions of this study.

Monitoring CO₂ or O₂ concentrations within a closed, volume-defined chamber is widely used to quantify soil respiration during laboratory soil incubation experiments. The standard method of using periodic manual gas sampling is costly, labor-intensive, and frequently fails to capture the aerobic respiration process. Thus, tools that allow continuous, real-time tracking of CO₂ and O₂ concentration changes are needed for soil respiration research. This study presents a new, portable, low-cost (∼$700), open-source sensor system to measure CO₂ and O₂ concentrations in four closed chambers. We provided non-engineering end-users with step-by-step instructions on how to build the system, enabling replication and customization. System performance was tested by comparing two respiration rates using the same soil—soil with and without glucose added for 1 week. Consistent CO₂ production and O₂ consumption rates were measured at 1-min intervals, and the reliability of the system was validated by a trace gas analyzer. Two distinctive continuous apparent respiratory quotient time series between two soil treatments were observed, with higher values of CO₂ in glucose soil, demonstrating the ability of the system to capture ongoing respiration processes and sufficient sensitivity to distinguish differences among respiration substrates (i.e., glucose). The tested performance of the system highlights its capabilities for soil respiration research and the potential for further adoption in real-time gas monitoring applications.

In the coming decades, humanity will be faced with the challenge of feeding 10 billion people and managing large quantities of solid waste. These issues can be mitigated through the development of sustainable fertilizers derived from electrochemically treated waste activated sludge (EWAS) while promoting a nitrogen circular economy. This study investigates the chemistry of novel fertilizers to determine their soil chemistry dynamics. Untreated waste activated sludge (WAS) and EWAS were applied to agricultural soil and potting mix, and the resulting aqueous samples were analyzed to determine nitrogen, phosphorous, and carbon adsorption and release behaviors. Commercial inorganic and natural fertilizers were utilized for comparison. X-ray absorption near-edge structure (XANES) spectroscopy was performed to characterize phosphorus speciation in the solid phases of the novel fertilizers. Results indicated that EWAS and WAS samples released less total nitrogen into solution than other treatments due to organoclay complexation of biomolecules and differences in the solubility of the nitrogen species. Samples containing EWAS released a higher percentage of organic and total carbon into solution due to the deformation of the structure of the organic matter by the alkaline electrolysis process. The solubility of nitrogen and carbon in the sludge was increased by the electrochemical process. Solid-phase phosphorus in EWAS and WAS was characterized by XANES analysis as struvite, which is a novel finding with important implications for P management from waste-based fertilizers. These experimental findings suggest that fertilizing with EWAS could result in reduced runoff and improved soil health while facilitating domestic fertilizer production.

Jin, Q., Wang, W., Liu, X., Lin, S., Sardans, J., Fang, Y., Vancov, T., Tariq, A., Zeng, F., & Peñuelas, J. (2024). Effects of maize residue and biochar applications on soil δ13C and organic carbon sources in a subtropical paddy rice ecosystem. Soil Science Society of America Journal, 88, 2254–2265. https://doi.org/10.1002/saj2.20773

There are mismatches and omissions in the “Funding information” section.

This funding was incorrectly stated as: Hubei University of Science and Technology Doctoral Start-up Fund Project, Grant/Award Numbers: BK202312, BK202313; Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España, Grant/Award Numbers: PID2019-110521GB-I00, PID2020-115770RB-I00; National Science Foundation of China, Grant/Award Numbers: 41571287, 42077087; Departament d'Innovació, Universitats i Empresa, Generalitat de Catalunya, Grant/Award Number: SGR 2017-1005. This funding is corrected here as: National Science Foundation of China (42077086; 41571287); Youth Program of Natural Science Foundation of Hubei Province (2024AFB323); Hubei University of Science and Technology Doctoral Start-up Fund Project (BK202312; BK202313); Spanish Government grants PID2020115770RB-I, PID2022-140808NB-I00, and TED2021-132627 B–I00 funded by MCIN, AEI/10.13039/ 501100011033 European Union Next Generation EU/PRTR.

We apologize for these errors.

Biochar as a soil amendment can increase soil carbon sequestration, soil microbial diversity, overall yields, and general soil functioning. To accelerate these effects, biochar is often activated with beneficial soil microbes such as arbuscular mycorrhizal fungi or plant growth promoting bacteria via microbial inocula. However, there has been no comprehensive review of the effects of microbial inoculum additions for biochar amendments. We conducted a meta-analysis to quantify the crop and soil effects of adding biochar alone compared to adding biochar with a microbial inoculum. The meta-analysis included 56 studies and examined whether the effects depended on the source of inoculum, inoculum type, or experiment type. We found that microbial inocula increased soil N and soil organic carbon concentrations and crop productivity compared to adding biochar alone. However, these effects were limited to locally sourced and research-grade inocula, while commercial inoculum products only slightly increased soil P. Fungal inocula had stronger effects than bacterial inocula. Inoculum effects were the strongest in greenhouse studies, increasing N, plant productivity, and fungal abundance, while field studies only increased plant productivity, suggesting that biochar activation with inoculum in on-farm settings may not provide intended positive effects, and thus alternative methods for biochar activation may be needed.

There was a long-time debate about the validation of the convection-dispersion equation (CDE) and its replacement with the well-known convective lognormal transfer function model (CLT) to describe solute transport in a heterogeneous soil with uniformity at the longitudinal water flow direction and nonuniformity at the transverse direction. The objective of this study is to prove that the CDE is valid and almost identical to the CLT. Gamma probability density function (pdf) was initially assumed in this study to describe the distribution of pore-water velocity across capillary tubes in a heterogeneous soil. The capillary bundle model was used to describe solute transport without transverse solute mixing between adjacent tubes. The inverse-gamma function, a new mathematical solution of the CDE differential equation with scale-dependent dispersivity, was initially derived from the capillary bundle model and the gamma pdf. The only difference between the inverse-gamma function and the CLT is that lognormal pdf of pore-water velocity is assumed in the CLT while the two pdfs are close to each other. The inverse-gamma function and the CLT were tested with the published data from the miscible displacement experiments on the two repacked soils with different aggregate sizes. Results show that both the inverse-gamma function and the CLT fit the measured breakthrough curves in the miscible displacement experiments. The estimates of the squared coefficient of variation of the pore-water velocity in the gamma pdf were 0.314 and 0.0582 for the two soils, and they were consistent with the lognormal pdf in the CLT.

In recent decades, the determination of particle size distribution (PSD) using the laser diffraction method (LDM) has become increasingly common, supplanting traditional sedimentation techniques. Advances in everything from sample preparation to software settings have been realized globally, whether through recommendations from laser diffraction (LD) manufacturers or through user experiences. These developments seek to enhance accuracy and diminish the uncertainties associated with new methodologies. Particularly in the determination of PSD using LDM on various LD instruments and in comparison with the sieve–pipette method (SPM), discrepancies in PSD frequently arise. This article aims to mitigate these discrepancies by predefining parameters, specifically through the adjustment of LD software settings and sample preparation (employing a uniform set of dispersed samples in potassium hydroxide) on two widely used LD instruments for soil measurements: Mastersizer 3000 and Analysette 22. Additionally, these samples were analyzed using the traditional SPM (ISO 11277, 1998), with the results from LDM and SPM subsequently compared. The paper also explores the impact, range of user options, and limitations of predefined software settings on both LD instruments. Eighty soil samples were analyzed for PSD, collected from arable land in the cadastral area of Hrušky, district of Břeclav (Czech Republic), in spring 2022, from depths of 0- to 10-cm and 10- to 20-cm. Significant differences in PSD were confirmed, although the trends of the grain size distribution curves were very similar to those of LDM. Results from the Mastersizer underestimated the clay fraction by an average of 17% compared to SPM, at the expense of the sand fraction, whereas the silt fraction was underestimated by a maximum of 4%. Conversely, Analysette 22 overestimated the silt fraction by an average of 37% at the expense of the sand fraction, confirming only a slight difference in the clay fraction: 3%. Moreover, the quantity of sample entering the dispersion unit was identified as a significant issue when comparing LD instruments, despite the obscuration value being nearly identical, that is, 20%–30%. Therefore, it was not possible to achieve the same or similar weight when introducing suspension into circulation. The robustness of the obtained results underscores the importance of understanding input parameters when interpreting results between different methods.

Forest soil amendments are increasingly used in western US forests to dispose of unmerchantable woody residues, reduce wildfire risk, and improve soil properties. Our objective was to determine the effect of fertilizer and organic amendments on tree growth and organic matter decomposition after thinning. Treatments were a control, three single soil amendments (wood chips, fertilizer, and biochar), and one combined soil amendment (biochar + fertilizer), each applied after thinning a ponderosa pine (Pinus ponderosa Dougl. ex. Laws) stand. After 10 years, amendment treatments had no effect on tree diameter increment (p = 0.600), but the biochar + fertilizer and wood chip treatments significantly increased height growth (p = 0.006). To estimate belowground biological changes, we used wood stakes made from aspen (Populus tremuloides Michx.) and loblolly pine (Pinus taeda L.) as an index of microbial activity. Stakes were placed: (1) on top of the litter/amendments, (2) at the interface between the litter/amendments and mineral soil, and (3) vertically inserted into the mineral soil, and stake mass loss was measured over 5 years. Stake mass loss of each species was least on the soil surface and increased with increasing depth. Aspen stakes generally had greater mass loss at all three soil locations in the fertilizer and biochar treatments. In contrast, pine stake mass loss was lower than aspen and less affected by fertilizer. Using thinned tree biomass to create amendments can improve forest productivity by enhancing soil conditions and mitigating wildfire. However, the impact of amendments on tree growth may take decades to be detectable.