Organic Matter Amendments Research Articles

Organic soil amendment effects on soil hydrology in an almond orchard evaluated using time-lapse electrical resistivity tomography

Adding organic amendments to soils in orchards has been suggested as a climate-smart agricultural practice that can increase resilience to extremes such as drought. The benefits of adding almond hulls and shells to soil include releasing potassium into the soil, improving water infiltration, reducing soil water evaporation, and enhancing water-holding capacity. In this study, soil infiltration and root water uptake (RWU) patterns of almond trees in amended and control soil treatments were investigated. An almond orchard was mulched with a mixture of almond hulls and shells used as surface-applied organic matter amendments. The combined use of time-lapse electrical resistivity tomography (ERT), stem water potential (SWP) and leaf water potential (LWP) measurements were used to evaluate RWU, soil infiltration patterns, and tree water status at different times during the study. The results of the ERT showed that the RWU patterns for the almond trees are distinct between the amended and the control treatments after the irrigation was applied. Compared to the control treatment, the amended treatment allowed the soil to store more water. Regardless of treatment, the majority of RWU patterns were observed in the top 0.5–1 m root zone depth. Almond trees began to recover from stress, as indicated by the SWP and LWP values, four hours after the start of irrigation. In addition, this was demonstrated by the ERT measurements, which revealed the RWU activity four hours after the irrigation had been applied. This research reveals that time-lapse ERT surveys combined with soil and tree water status data can infer patterns of RWU in almond trees grown with organic soil amendments and under controlled conditions. Furthermore, it was concluded that using almond hulls and shells as organic matter amendments can help almond growers improve infiltration, making almond production more resilient to climate change-related extremes such as droughts.

Comparative evaluation of 16S rRNA primer pairs in identifying nitrifying guilds in soils under long-term organic fertilization and water management.

Compared with 454 sequencing technology, short-read sequencing (e.g., Illumina) technology generates sequences of high accuracy, but limited length (<500 bp). Such a limitation can prove that studying a target gene using a large amplicon (>500 bp) is challenging. The ammonia monooxygenase subunit A (amoA) gene of ammonia-oxidizing archaea (AOA), which plays a crucial part in the nitrification process, is such a gene. By providing a full overview of the community of a functional microbial guild, 16S ribosomal ribonucleic acid (rRNA) gene sequencing could overcome this problem. However, it remains unclear how 16S rRNA primer selection influences the quantification of relative abundance and the identification of community composition of nitrifiers, especially AOA. In the present study, a comparison was made between the performance of primer pairs 338F-806R, 515F-806R, and 515F-907R to a shotgun metagenome approach. The structure of nitrifier communities subjected to different long-term organic matter amendment and water management protocols was assessed. Overall, we observed higher Chao1 richness diversity of soil total bacteria by using 515F-806R compared to 338F-806R and 515F-907R, while higher Pielou's evenness diversity was observed by using 515F-806R and 515F-907R compared to 338F-806R. The studied primer pairs revealed different performances on the relative abundance of Thaumarchaeota, AOB, and NOB. The Thaumarchaeota 16S rRNA sequence was rarely detected using 338F-806R, while the relative abundances of Thaumarchaeota detected using 515F-806R were higher than those detected by using 515F-907R. AOB showed higher proportions in the 338F-806R and 515F-907R data, than in 515F-806R data. Different primers pairs showed significant change in relative proportion of NOB. Nonetheless, we found consistent patterns of the phylotype distribution of nitrifiers in different treatments. Nitrosopumilales (NP) and Nitrososphaerales (NS) clades were the dominant members of the AOA community in soils subject to controlled irrigation, whereas Ca. Nitrosotaleales (NT) and NS clades dominated the AOA community in soils subject to flooding irrigation. Nitrospira lineage II was the dominant NOB phylotype in all samples. Overall, ideal 16S rRNA primer pairs were identified for the analysis of nitrifier communities. Moreover, NP and NT clades of AOA might have distinct environmental adaptation strategies under different irrigation treatments.

EFFECTS OF ORGANIC MATTER AMENDMENTS ON PHYSICOCHEMICAL PROPERTIES OF SOIL AND YIELD OF RAINFED RICE

Organic matter amendments play a pivotal role in improving the soil’s physiochemical properties and crop productivity. This study was conducted to examine the effects of various organic matters on soil physicochemical properties and the yield of rainfed rice in Bangladesh. The research was conducted following a randomized complete block design (RCBD) with seven treatments, viz. cow dung slurry (CDS), rice husk biochar (RHB), cow dung (CD), vermi-compost (VC) and trico-compost (TC) used @ 2 t C ha-1, and bacterial inoculant (BI) @ 4 ml plot-1. The findings indicated a reduction trend of bulk density as compared to the initial soil in all the organic matter-treated soils, where the highest reduction percent was found in the RHB (1.45%) treated plot, followed by CDS (0.74%), VC (0.74%), TC (0.74%), CD (0.73%) and BI (0.73%). Significantly higher total N was observed in inorganic matter-treated post harvested soil compared to initial soil. The highest total N was recorded in TC (0.12%) and CDS (0.12%) treated soils, followed by CD (0.11%), VC (0.11%), BI (0.11%) and RHB (0.10%). The significantly highest CEC (6.48 meq100g soil-1) was noted in RHB-added soil, while the lowest value (5.70 meq100g soil-1) was found in initial soil. The RHB exhibited the maximum quantity of P, S, and exchangeable K in post-harvest soils, with 12.75, 19.73 mg kg-1 soil, and 0.14 cmol kg-1, respectively. Plant height, tiller hill-1, panicle length, grain panicle-1, and 1000-grain weight were greatly influenced by the various treatments. In the context of grain yields, the treatments can be rated as follows: CD&gt;CDS&gt;VC&gt;RHB&gt;TC&gt;BI&gt;control. Thus, it was concluded that organic amendments improves soil fertility and the yield of rice, particularly in rainfed condition.

Microbial Proxies for Anoxic Microsites Vary with Management and Partially Explain Soil Carbon Concentration.

Anoxic microsites are potentially important but unresolved contributors to soil organic carbon (C) storage. How anoxic microsites vary with soil management and the degree to which anoxic microsites contribute to soil C stabilization remain unknown. Sampling from four long-term agricultural experiments in the central United States, we examined how anoxic microsites varied with management (e.g., cultivation, tillage, and manure amendments) and whether anoxic microsites determine soil C concentration in surface (0-15 cm) soils. We used a novel approach to track anaerobe habitat space and, hence, anoxic microsites using DNA copies of anaerobic functional genes over a confined volume of soil. No-till practices inconsistently increased anoxic microsite extent compared to conventionally tilled soils, and within one site organic matter amendments increased anaerobe abundance in no-till soils. Across all long-term tillage trials, uncultivated soils had ∼2-4 times more copies of anaerobic functional genes than their cropland counterparts. Finally, anaerobe abundance was positively correlated to soil C concentration. Even when accounting for other soil C protection mechanisms, anaerobe abundance, our proxy for anoxic microsites, explained 41% of the variance and 5% of the unique variance in soil C concentration in cropland soils, making anoxic microsites the strongest management-responsive predictor of soil C concentration. Our results suggest that careful management of anoxic microsites may be a promising strategy to increase soil C storage within agricultural soils.

Consequences of organic matter amendments for methane emissions and soil and vegetation development in a restored wetland

Consequences of organic matter amendments for methane emissions and soil and vegetation development in a restored wetland

Effect of Municipal Mulch and Poultry Litter Amendments on Soil and Tree Parameters of a Mature Peach Orchard in a Humid Subtropical Climate

Applying organic matter (OM) amendments in mature peach orchards with low organic matter content (Prunus persica (L.) Batsch.) may improve tree nutrient and water status during the growing season and enable growers to reduce synthetic fertilizer inputs. Three treatments were applied to “Juneprince” and “Scarletprince” peach trees: (1) grower standard of bare soil (GS), (2) municipal mulch (M), and (3) poultry litter with municipal mulch (PLM). Synthetic fertilizer was reduced within the M and PLM treatments each year. Soil samples were taken from under the amendments, and the nutrient and water status of the soil and trees were monitored over 3 years. Fruit yield and tree growth measurements were also recorded. Soil OM did not increase, but soil P increased in all three treatments over time. Soil Cu was reduced by adding OM amendments, while PLM increased soil Na and increased leaf K in “Scarletprince” trees. The PLM and M treatments buffered soil water compared to GS, but tree water status between treatments was largely similar. The elevated N status over time from the PLM and M treatments delayed fruit maturity and reduced cumulative yield in “Juneprince” trees. The PLM treatment increased “Scarletprince” fruit size and mass over 3 years, as well as tree size compared to GS. Covering the soil with mulch allowed for reduced synthetic fertilizer use, but further reduction of supplemental synthetic fertilizer or adjustment of amendment rates is needed to limit N and ensure desired fruit harvest windows and long-term production.

Changes in chemical fractionation of copper and zinc in soil as a function of incubation moisture content and organic matter amendments

Copper and zinc are essential micronutrients that are potentially toxic when present in excess in soils. Their bioavailability depends on their speciation in soil, but this may vary with environmental conditions. Aeration and hence redox conditions, and organic matter amendments are among the factors likely to cause variation on metal fractionation. We have monitored the chemical fractionation of both native and added copper and zinc in a clay loam top soil during a 5-month laboratory incubation. The effects of aeration (moist soil or flooded) and addition of two organic matter amendments, alfalfa straw or leaf compost, were studied. Metal spike was more labile than legacy metal, and was slowly redistributed over the incubation period. Organic matter caused short-lived flushes of metals, attributed to metal chelation with soluble organic matter. This effect was greater for straw than for more stable compost. There was no evidence that added organic matter increased the capacity of soil organic matter to immobilise metal. Flooding solubilized soil metal (hydr)oxides, releasing legacy Cu and Zn, but with less effect on the capacity to immobilise metal spike. Effects of flooding and organic matter addition were not additive. Both metals appear to be precipitated as sulphides under reducing conditions, and accounted for in the acid soluble phase. Monitoring the dynamics of metal distribution gives a more comprehensive understanding of underlying processes than would a single measurement, and is closer to in campo conditions than slurry microcosms.

Alternate wetting and drying decreases arsenic content and increases yield of rice grown in organic matter amended soil

Organic matter (OM) shows a critical role in mobilization and uptake of arsenic (As) by rice, and water management practice can mitigate this problem. However, very few research highlighted the impact of management of water on rice as influenced by OM amendment. Therefore, this study has evaluated the changes in As mobilization in paddy soil under different OM amendment and water management practices. Here, rice was grown to maturity in a two-factorial pot experiment comprising two different water management practices [continuous flooding (CF) and alternate wetting drying (AWD)] and eight combinations of As and OM amendment [comprising two As treatments (0 and 20 ppm) and four OM amendments (0, 0.25%, 0.5% and 5.0% w/w)]. Application of OM in As contaminated soil caused a significant increase in As accumulation in rice, and exhibited decreased growth and yield of rice. However, the results showed that rice growth and yield was significantly higher under AWD practice compared to CF. Arsenic concentration in rice was the lowest in As and OM control pots (44.67 µg/kg in AWD and 62.13 µg/kg in CF), and higher in As treated pots. Moreover, As concentration in rice grain increased with increasing levels of OM amendment. The As concentration in rice grain (168.44 µg/kg in AWD and 183.85 µg/kg in CF) was significantly higher in As treated pots with 0.5% OM amendment compared to other treatment combinations. Application of 5% OM in As contaminated soil did not produce any grains due to extreme toxicity. Thus, As accumulation in rice can be decreased by AWD water management technique without compromising yield. The findings suggest that applying OM in paddy soils with high soil As content should be done with caution.

Differential Gene Expression Patterns in Peach Roots under Non-Uniform Soil Conditions in Response to Organic Matter.

Organic matter (OM) amendments are often encouraged in sustainable agriculture programs but can create heterogeneous soil environments when applied to perennial crops such as peaches (Prunus persica (L.) Batsch). To better understand the responses of peach roots to non-uniform soil conditions, transcriptomic analysis was performed in a split-root study using uniform soil (the same soil type for all roots) or non-uniform soil (different soil types for each half of the root system) from either (1) autoclaved sand (S), (2) autoclaved sand with autoclaved compost (A), or (3) autoclaved sand with compost which included inherent biological soil life (B). Each uniform soil type (S, A, and B) was grouped and compared by uniform and non-uniform soil comparisons for a total of nine treatments. Comparisons revealed peach roots had differentially expressed genes (DEGs) and gene ontology terms between soil groups, with the S and B groups having a range of 106-411 DEGs and the A group having a range of 19-94 DEGs. Additionally, six modules were identified and correlated (p > 0.69) for six of the nine treatment combinations. This study broadly highlights the complexity of how OM and biological life in the rhizosphere interact with immediate and distant roots and sheds light on how non-homogenous soil conditions can influence peach root gene expression.

Elemental Sulfur and Organic Matter Amendment Drive Alkaline pH Neutralization and Mineral Weathering in Iron Ore Tailings Through Inducing Sulfur Oxidizing Bacteria.

Mineral weathering and alkaline pH neutralization are prerequisites to the ecoengineering of alkaline Fe-ore tailings into soil-like growth media (i.e., Technosols). These processes can be accelerated by the growth and physiological functions of tolerant sulfur oxidizing bacteria (SOB) in tailings. The present study characterized an indigenous SOB community enriched in the tailings, in response to the addition of elemental sulfur (S0) and organic matter (OM), as well as resultant S0oxidation, pH neutralization, and mineral weathering in a glasshouse experiment. The addition of S0 was found to have stimulated the growth of indigenous SOB, such as acidophilic Alicyclobacillaceae, Bacillaceae, and Hydrogenophilaceae in tailings. The OM amendment favored the growth of heterotrophic/mixotrophic SOB (e.g., class Alphaproteobacteria and Gammaproteobacteria). The resultant S0 oxidation neutralized the alkaline pH and enhanced the weathering of biotite-like minerals and formation of secondary minerals, such as ferrihydrite- and jarosite-like minerals. The improved physicochemical properties and secondary mineral formation facilitated organo-mineral associations that are critical to soil aggregate formation. From these findings, co-amendments of S0 and plant biomass (OM) can be applied to enhance the abundance of the indigenous SOB community in tailings and accelerate mineral weathering and geochemical changes for eco-engineered soil formation, as a sustainable option for rehabilitation of Fe ore tailings.

Accumulation of century-old biochar contributes to carbon storage and stabilization in the subsoil

Soil organic carbon (C) is a key component of the global C budget. As soil organic C turnover rates decrease with depth, agricultural practices favoring deep organic C storage will gain importance as long-term climate change mitigation strategies. In addition, amendment of pyrogenic organic matter (biochar) is considered a promising practice for sequestering C in croplands. However, so far the >30 cm depth soil organic C pool, and subsoil biochar dynamics in particular, has been understudied.To address this, we focused on leftovers from pre-industrial charcoal kilns as a proxy to study the accrual of century-old biochar in the subsoil (30–100 cm) in comparison to adjacent control soil. Using thermal and elemental analyses as well as size and density fractionations (i.e., separating particulate and mineral-associated organic matter), we determined the distribution of pyrogenic organic C within the soil profile and investigated its stabilization in depth. We measured the dissolved organic carbon (DOC) concentrations as well as absorbance and fluorescence properties of dissolved organic matter (DOM) at different depths to characterize the effects of century-old biochar accumulation on the current leaching of DOM.Our results showed that the presence of century-old biochar resulted in an increase of 53.8 ± 25.1 t C ha−1 in 0–100 cm, and 12 % of the pyrogenic organic C was stored in 30–60 cm. No difference in C stocks was observed in 60–100 cm between kiln sites and reference soils. Most of the pyrogenic organic C has been translocated as particulate organic matter, either free or occluded, to subsoils. This led to a change in the dominant fraction of organic matter in the E horizon; in reference soils 64.7 % of the total C was associated with mineral phases as opposed to only 42.3 % in soils enriched with biochar. The thermal analysis of the mineral-associated organic matter revealed that pyrogenic organic C was associated with mineral phases. With depth, DOC concentrations decreased and the relative contribution of microbial byproducts to fluorescent DOM increased. The soils enriched with century-old biochar displayed lower DOC concentrations and more aromatic DOM in the Ap horizon, which suggests biochar dissolution is still an on-going process. Our results suggest that the vertical transfers of century-old biochar mainly occurred as particle leaching in macroporosity and bioturbation but continuous dissolution has also contributed in these fine-textured cropland soils. In conclusion, the association of pyrogenic organic C with mineral phases as well as its migration in subsoil horizons promoted its physical disconnection from abiotic and biotic degrading agents, which likely contribute to the long-term stability of biochar.

The effect of organic matter amendments on soil surface stability in conventionally cultivated arable fields

AbstractIn this study, new and traditional organic wastes (green waste compost, farmyard manure (FYM), anaerobic digestate or straw) were ploughed into an arable field experiment at a range of rates (1–3 t C ha−1) and under spring and winter cropping rotations for 5 years. The stability of the soil surface structure (&lt;5 cm) was assessed in Years 3, 4 and 5 to guide the use of organic wastes in arable field management. Aggregate stability was determined by immersing each soil sample in water (fast‐wetting test, relevance to summer storms) and measuring the size distribution of the aggregates (mean weight diameter, MWD). The MWD value was compared with the different classes of aggregate stability (very stable, stable, medium, unstable or very unstable) to classify each result. All the arable field samples were classified as unstable, and there were no significant differences (p &gt; .05) in MWD after any treatment. Potentially, this approach is too imprecise to detect differences, so pore‐scale analyses using CT scanning were used. There were no significant differences in porosity or pore shape (features associated with microbial activity) between the control and organic waste treatments. The results contradicted published data from the Broadbalk experiment (established in 1843), which was the basis for this study, so its soils were studied to understand this discrepancy. Broadbalk soils were classified as unstable, including soils treated with annual FYM applications. Instead, we found a significant relationship between MWD and clay content and previous interpretations had not taken this variable (23%–39% clay content) texture into consideration. In conclusion, to achieve a stable soil surface structure, a 150% improvement in aggregate stability would be needed here and ploughing in organic wastes was not a successful management approach on these arable field experiments.

Dynamics of the Apostichopus californicus-associated flavivirus under suboxic conditions and organic matter amendment

Flaviviruses cause some of the most detrimental vertebrate diseases, yet little is known of their impacts on invertebrates. Microbial activities at the animal-water interface are hypothesized to influence viral replication and possibly contribute to pathology of echinoderm wasting diseases due to hypoxic stress. We assessed the impacts of enhanced microbial production and suboxic stress on Apostichopus californicus associated flavivirus (PcaFV) load in a mesocosm experiment. Organic matter amendment and suboxic stress resulted in lower PcaFV load, which also correlated negatively with animal mass loss and microbial activity at the animal-water interface. These data suggest that PcaFV replication and persistence was best supported in healthier specimens. Our results do not support the hypothesis that suboxic stress or microbial activity promote PcaFV replication, but rather that PcaFV appears to be a neutral or beneficial symbiont of Apostichopus californicus.

In a nutshell: almond hull and shell organic matter amendments increase soil and tree potassium status

Abstract Background Crop residues used as organic matter amendments have been shown to release potassium (K) into the soil, promoting K cycling in agronomic systems. Orchard field trials are needed to evaluate K dynamics under almond hull and shell amendments, which contain high K concentrations. Methods Three field trials in commercial almond orchards were conducted to assess the effects of surface-applied almond hull and shell amendments on K cycling within plant and soil systems. Amendment K concentrations over time, soil exchangeable K, and tree K status were measured as well as decomposition rate and crop yield. Results Hulls and shells released K rapidly under irrigation and rainfall, significantly increasing soil exchangeable K in the upper 0–10 cm soil within 2–7 weeks. Amendments increased tree leaf K status within the first 1–3 years to varying degrees depending on site. Initial amendment K concentrations decreased by at least half by dry weight within the first 25.4 cm (10 inches) of water (irrigation and precipitation) within the irrigated zone. Conclusions Almond hulls and shells can increase soil and plant K status when used as amendments on the soil surface. This practice can address byproduct utilization issues, recycle potassium (K), and reduce orchard K fertilizer demand by replacing the majority of tree K demand. Growers can tailor application rates to meet orchard-specific K management goals. Off-ground harvest preserved the hull/shell organic layer over time and maximized K cycling. Hull/shell amendments applied on the soil surface cover more soil area within the irrigated wetted zone compared to banded K fertilizer. This practice can reduce reliance on K fertilizers and reduce associated costs while providing a convenient outlet for hulls and shells.

Digging deeper: Assessing the predictive power of common greenhouse gas accounting tools for soil carbon sequestration under organic amendment

Effective project implementation and quantification of emissions reduction in climate-smart agriculture initiatives face challenges in measurement, monitoring, and verification. To address these challenges, predictive models are regularly used to estimate the emissions reduction potential of land management changes and to prioritize funding for projects. Despite their growing utility, few studies have evaluated the performance of publicly available model tools using site specific data. This study evaluated the performance and utility of four common model tools that represent the three Intergovernmental Panel on Climate Change model tiers to predict soil organic carbon storage and estimate greenhouse gas emissions on working lands under organic matter amendment. Field data from two long-term, compost application experiments in Washington State formed the basis for model simulations using DayCent, COMET-Farm, Cool Farm, and the Washington State Climate Smart Estimator (WaCSE). Soil carbon sequestration and emissions estimates varied among the evaluated models, which was expected given their differential data requirements and input capabilities. COMET-Farm, although easier to use, exhibited a higher level of bias compared to DayCent, which was expected as a mixed tier model. The DayCent model, the model engine for the COMET-Farm tool, demonstrated the ability to explain ∼50% more of the variation in the observed values compared to COMET-Farm when initiated using the same parameters. Cool Farm was unsuitable for estimating SOC sequestration benefits from compost application primarily because it did not add carbon to the soil pool following amendment. The differences in emissions estimates derived from WaCSE compared with other tools could be attributed solely to its highly constrained input parameters and basis in tier 1 emissions factors. We conclude that online tools can provide rapid estimates of greenhouse gas emissions reduction potential over larger areas or groups of farms but should be used with caution for site-specific estimates. Hence, it is crucial to clarify the intended purpose of an assessment and the designed function of model tools when evaluating their suitability for prioritizing funding for climate-smart agriculture initiatives at the individual farm level.

The effect of biogeochemical redox oscillations on arsenic release from legacy mine tailings

Exposed and un-remediated metal(loid)-bearing mine tailings are susceptible to wind and water erosion that disperses toxic elements into the surrounding environment. Compost-assisted phytostabilization has been successfully applied to legacy tailings as an inexpensive, eco-friendly, and sustainable landscape rehabilitation that provides vegetative cover and subsurface scaffolding to inhibit offsite transport of contaminant laden particles. The possibility of augmented metal(loid) mobility from subsurface redox reactions driven by irrigation and organic amendments is known and arsenic (As) is of particular concern because of its high affinity for adsorption to reducible ferric (oxyhydr)oxide surface sites. However, the biogeochemical transformation of As in mine tailings during multiple redox oscillations has not yet been addressed. In the present study, a redox-stat reactor was used to control oscillations between 7 d oxic and 7 d anoxic half-cycles over a three-month period in mine tailings with and without amendment of compost-derived organic matter (OM) solution. Aqueous and solid phase analyses during and after redox oscillations by mass spectrometry and synchrotron X-ray absorption spectroscopy revealed that soluble OM addition stimulated pyrite oxidation, which resulted in accelerated acidification and increased aqueous sulfate activity. Soluble OM in the reactor solution significantly increased mobilization of As under anoxic half-cycles primarily through reductive dissolution of ferrihydrite. Microbially-mediated As reduction was also observed in compost treatments, which increased partitioning to the aqueous phase due to the lower affinity of As(III) for complexation on ferric surface sites, e.g. ferrihydrite. Oxic half-cycles showed As repartitioned to the solid phase concurrent with precipitation of ferrihydrite and jarosite. Multiple redox oscillations increased the crystallinity of Fe minerals in the Treatment reactors with compost solution due to the reductive dissolution of ferrihydrite and precipitation of jarosite. The release of As from tailings gradually decreased after repeated redox oscillations. The high sulfate, ferrous iron, and hydronium activity promoted the precipitation of jarosite, which sequestered arsenic. Our results indicated that redox oscillations under compost-assisted phytostabilization can promote As release that diminishes over time, which should inform remediation assessment and environmental risk assessment of mine site compost-assisted phytostabilization.

Organic matter amendments on nutrient and water status within subtropical peach orchards

Organic matter amendments on nutrient and water status within subtropical peach orchards

Impacts of organic matter amendments on urban soil carbon and soil quality: A meta-analysis

Organic matter amendment application is an important avenue of beneficial waste diversion and is used to improve soil quality in agricultural and urban settings. In urban regions, amendments are used to support local food production, maintain vegetation for landscaping and recreational use, and reclaim disturbed soils. Urban regions generate large quantities of wasted organic resources for potential application aiding in creating a circular nutrient economy. There is a growing interest in understanding the effects of amendments such as compost, biosolids, and biochar on soil properties in agricultural settings. Gaps remain, however, in assessing their effects in urban land uses. We conducted a literature review to assess the effects of compost, biochar, and biosolids on soil carbon and soil quality of urban soils managed for gardening, landscaping, recreation, and reclamation. Application of organic matter amendments led to an average increase of 3.6 units of soil organic matter% (SOM%). Compost and biochar improved SOM% the most, by 3.1 and 6.5 units of SOM%, respectively. Biosolids resulted in the smallest increase in SOM% but had greater nutrient benefits than other amendments. Parameters related to chemical and physical soil quality improved with the application of amendments. Gaps in the literature remain, such as assessing urban gardens, soil to depths greater than 30 cm, and the persistence of SOM in amended soils. This meta-analysis proposes that organic matter amendments are a powerful means to improve soil quality in urban regions, provide vital cobenefits to surrounding communities, and increase soil carbon storage.

Study on Amendment of Rapeseed Meal, Soybean Meal, and NPK Fertilizer as Biostimulants in Bioremediation of Diesel-Contaminated Soil by Autochthonous Microorganisms

ABSTRACT The adverse impact of total petroleum hydrocarbons (TPH) can be mitigated through bioremediation. However, the efficiency of bioremediation is often compromised due to its slow speed. Therefore, this study aimed to evaluate the promoting effect of organic and inorganic biostimulants on the bioremediation rate of autochthonous microorganisms. The study examined the impact of rapeseed meal (biostimulation-BS1), soybean meal (BS2), and NPK fertilizer (BS3), as biostimulants on pH, bacterial and fungal count, enzymatic activities, and also TPH values of diesel-contaminated soil. The results revealed that amending the soil with rapeseed meal, soybean meal, and NPK fertilizer resulted in a significant increase in dehydrogenase and catalase activities, with 9.96, 7.7, and 6.75-fold and 2.52, 2.4, and 2.52-fold enhancement, respectively, compared to natural attenuation (NA-as control) which contains diesel-contaminated soil without any organic or inorganic amendments. Moreover, the pH value of the BS1 (6.4) and BS2 (6.77) groups was almost neutral. The growth of heterotrophic and hydrocarbon-utilizing bacteria and fungi was significantly improved with organic matter amendment (P < .05). The TPH removal efficiencies in natural attenuation, BS1, BS2, BS3, and rapeseed meal+ soybean meal+ NPK fertilizer (BS4) groups were 49.22%, 71.65%, 90.55%, 65.77%, and 55.25%, respectively. Molecular identification revealed that three hydrocarbon-utilizing bacteria belonged to various genera, including Nocardiopsis, Streptomyces, and Mammaliicoccus. Overall, this study suggests that amending organic compounds to contaminated soil is an effective, cost-effective, and eco-friendly strategy to improve the bioremediation rate of autochthonous microorganisms.

Evaluating the effects of formation and stabilization of opal/sand aggregates with organic matter amendments

Opal (SiO2·nH2O, amorphous silica), the by-product of alumina extraction from coal fly ash (CFA), has a strong adsorption capacity and is also an important component of clay minerals in soils. The combining of opal with sand to form artificial soils is an effective disposal strategy for large-scale CFA stockpiles and reduction of environmental risk. Nevertheless, its poor physical condition limits plant growth. Organic matter (OM) amendments have broad potential applications for water-holding and improving soil aggregation. Effects of OMs (vermicompost (VC), bagasse (BA), biochar (BC) and humic acid (HA)) on the formation, stability and pore characteristics of opal/sand aggregates were evaluated through 60-day laboratory incubation experiments. Results demonstrated that four OMs could reduce pH, with BC having the most significant effect, VC significantly increasing the electrical conductivity (EC) and TOC content of the aggregates. Except for HA, other OMs could improve the aggregates' water-holding capacity. The mean weight diameter (MWD) and percentage of >0.25 mm aggregates (R0.25) of BA-treated aggregates were the largest, and BA had the most noticeable contribution to macro-aggregate's formation. The best aggregate stability was obtained with HA treatment, meanwhile the percentage of aggregate destruction (PAD0.25) decreased with the addition of HA. After amendments, the proportion of organic functional groups increased, which favored aggregate's formation and stability; the surface pore characteristics were improved, with the porosity ranging from 70% to 75%, reaching the level of well-structured soil. Overall, the addition of VC and HA can effectively promote aggregates' formation and stabilization. This research may play a key role in converting CFA or opal into artificial soil. The combining of opal with sand to form artificial soil will not only solve the environmental problems caused by large-scale CFA stockpiles but will also enable the comprehensive utilization of siliceous materials in agriculture.