Soil Incubation Research Articles

Productivity gains in vegetables from rice husk biochar application in nutrient-poor soils in Timor-Leste

Response to fertilisation with biochar is greatest in field crops on acidic tropical soils, but limited information is available for vegetable crops. As a case-study using vegetable production in Timor-Leste, we assessed if biochar alleviates nutritional constraints to vegetables in low-nutrient soils. Field trials on vegetable crops were conducted with fertiliser combinations of rice husk biochar, phosphate and local fertiliser at three sites. A pot soil incubation trial of biochar was undertaken with soil from the acid site, where rice husk biochar had a larger effect on productivity than the other fertilisers in chili pepper, tomato and soybean with an average yield increase with biochar of 230% over control. Combining phosphate with biochar augmented the yield over biochar alone in chili pepper, tomato and soybean. At neutral and alkaline sites, fertilisation with biochar lifted mean yield over the control. Soil constraints alleviated by fertiliser were primarily from P and Zn deficiencies. Marked increases in vegetable yields, among the highest globally, were achieved with fertilisation with biochar individually and in combination with phosphate in low nutrient soil in Timor-Leste. Clearly, rice husk biochar is a promising avenue to fertilise the soil with P and Zn and increase crop productivity in Timor-Leste.

A high soil potential net nitrification was observed at 4 m depth: What are the driving factors?

AbstractStudies about nitrogen (N) mineralization and nitrification in deep soil layers are rare because N processes are considered to occur mainly in topsoil that hosts active and diverse microbial communities. This study aimed to measure the soil potential net N mineralization (PNM) and nitrification (PNN) down to 4 m depth and to discuss factors controlling their variability. Twenty‐one soil cores were collected at the Restinclières agroforestry experimental site, where 14‐year‐old hybrid walnut trees were intercropped with durum wheat. Soil cores were incubated in the dark in the laboratory at both 6 and 25°C. The soil was a deep calcic fluvisol with a fluctuating water table. It featured a black layer that was very rich in organic matter and permanently water saturated at depths between 3.0 and 4.0 m. The mean soil mineral N content was 3 mg N kg−1 soil in the upper 0.0–0.2 m layer, decreasing until a depth of 2 m and increasing to the maximum value of 25.8 mg N kg−1 soil in the black layer. While nitrate (NO3−) was the dominant form of mineral N (89%) in the upper 0.0–0.2 m layer, its proportion progressively decreased with depth until ammonium (NH4+) became almost the only form of mineral N (97%) in the saturated black layer. Laboratory soil incubation revealed that PNM and PNN occurred at all depths, although the latter remained low at 6°C. The soil nitrate content in the black layer was multiplied by 48 times after 51 days of incubation at 25°C, whereas it was almost inexistent at the sampling date. While the soil total N, the pH and the incubation temperature explained 84% of the variation in PNM, only 29% of the percent nitrification variance was explained by the incubation temperature (Tinc) and the soil C‐to‐N ratio. These results point out the necessity to consider soil potential net N mineralization and nitrification of deep soil layers to improve model predictions.

Potential solution in sustainable agriculture: improving the pH and pH buffering capacity of gray soil Acrisol from Cu Chi, Ho Chi Minh City, Vietnam using biochar combined with bentonite

<p>The acidification of agricultural soils should be avoided, and low pH soils should be corrected for better productivity. Soil improvement by applying biochar from agricultural byproducts combined with bentonite, a rich source in Vietnam, is a trend in green agriculture in the country. The current study is important in assessing the potential influences of biochar and bentonite on the pH and pH buffering capacity (pHBC) of low pH soil collected in Cu Chi, Ho Chi Minh City, Vietnam. Experimental methods, including biochar preparation (pyrolysis at 300°C, retention time: 2 h), soil incubation (time: 30 days, temperature: 27°C), and pH and pHBC determination, were performed. Research results have shown that biochar and bentonite have contributed to improving the pH and pHBC of gray soil samples. Using 1% bentonite and 1% biochar raised the pH to 6.21 and improved the pHBC of Cu Chi gray soil to 24.1 mmolH<sup>+</sup>/OH<sup>-</sup> kg<sup>-1</sup>. This dose is currently suitable for agricultural production in Vietnam. The study confirmed the applicability of biochar derived from cow manure prepared at a low pyrolysis temperature in combination with bentonite to improve soil parameters such as pH and pHBC in Cu Chi gray soil.</p>

Isolation of cadmium-resistance and siderophore-producing endophytic bacteria and their potential use for soil cadmium remediation

Endophyte-assisted phytoremediation is an emerging technique for soil heavy metals (HMs) remediation and has become a research focus in the world because of the benefits of endophytes on plant growth and uptake of HMs. In this study, multifunctional endophytic bacteria strains were isolated and screened, and the feasibility of these strains for soil cadmium (Cd) remediation was investigated by soil incubation experiments and pot experiments. All endophytic bacteria were isolated from the roots of woody plants grown on Cd-contaminated soil. Seven endophytic bacteria strains had capacities to tolerate Cd toxicity and produce siderophores, and sequence analysis of the 16S rRNA gene classified these strains as belonging to the genera Burkholderia, Pseudomonas, Pantoea, and Herbaspirillum. All strains were able to produce hydroxamate siderophores (32.40%–91.49%) and had three or more plant growth promoting properties such as phosphorus solubilization, nitrogen fixation, indole acetic acid and 1-aminocyclopropane-1-carboxylate deaminase production. They were all strongly resistant to Cd2+ toxicity, with the minimum inhibitory concentration in LB medium ranging from 1.5 mM to 9.0 mM. Except for strain Burkholderia contaminans JLS17, other strains showed decreasing removal rates within continuously elevated Cd2+ concentration of 10–100 mg L−1. Compared with the uninoculated treatment, the inoculation of strains B.contaminans JLS17, Pseudomonas lurida JLS32, and Pantoea endophytica JLS50 effectively increased the concentration of acid-soluble Cd and decreased the concentration of reducible, oxidizable, and residual Cd in the soils of different Cd contamination levels. In pot experiments, inoculation of strains JLS17 and YTG72 significantly (p < 0.05) promoted the growth of above-ground parts and root system of slash pine (Pinus elliottii) under Cd stress. This study provides a valuable biological resource for endophyte-assisted phytoremediation and a theoretical basis for the application of endophytic bacteria for remediation of Cd-contaminated soil.

Impact of bentonite on greenhouse gas emissions during pig manure composting and its subsequent application

Additives were widely investigated to retain the nutrients and mitigate the greenhouse gas emissions (GHGs) during manure composting. However, the sustained effects of additives on the GHGs emissions following incorporation of composts to soil were scarcely explored. This study evaluated the effects of bentonite added at the beginning of pig manure composting on the GHGs emissions during two successive processes, i.e., composting and soil incubation amended with composting products. Addition of bentonite did not hinder the composting process and alter the total CO2 emission. On the other hand, reduction by about 17% and 29% for CH4 and N2O emission, respectively, was achieved in the presence of bentonite during composting. Incorporation of the final composting products to soil enhanced significantly the soil C and N of various forms, and gas emissions of CO2 and N2O. However, no significant differences were observed between bentonite-manure co-compost and manure-only compost application except for the N2O emission. Compared to the manure-only compost, compost amended with bentonite reduced N2O loss by around 6.8%, but not statistically significant. This study confirmed that addition of bentonite at the composting stage can mitigate the GHGs emission considering both composting and compost application stages, with all reductions occurring at the composting stage.

Synthesis of artificial humic acid-urea complex improves nitrogen utilization

The inefficient use of conventional nitrogen (N) fertilizers leads to N enrichment in the soil, resulting in N loss via runoff, volatilization and leaching. While using artificial humic acid to prepare novel N fertilizer is a good choice to improve its efficiency, the high heterogeneity of artificial humic acid limits its structural analysis and utilization efficiency. To solve above problems, this work mainly carried out the fractionation experiments, melt penetration experiments and soil incubation experiments. The results revealed that four fractions with different aromatization degree and molecular weights were obtained by the newly proposed continuous dissolution method, particular in the extraction solution of pH = 3–4, which were extracted with the highest aromatization degree. Furthermore, artificial humic acid urea complex fertilizers prepared at pH = 3–4 significantly improved the release of NH4+-N by 38.32% on days 7 and NO3−-N by 10.30% on days 14, compared to urea application. The highly aromatic complex fertilizer with loading of urea-N was able to supply more inorganic N to the soil on days 3–14 (low molecular weight N) and to maintain a higher N content on days 70 (highly aromatized N). This can partially offset the mineralization of readily available organic N, buffering the immobilization of inorganic N from the soil when unstable organic compounds (e.g. conventional urea) were incorporated. A-HAU3-4 addition on days 70, Proteobacteria and Actinobacteriota were found to be the dominant phylum in the soil and the relative abundance of Endophytic bacteria was increased, which was conducive to the improvement of soil N utilization efficiency and soil N sequestration. Therefore, the preparation of artificial humic urea fertilizer with high aromatization degree or low molecular weight were an effective way to improve N utilization efficiency in the initial stages of soil incubation and maintain N fixation in the later stages of soil incubation. The future application of the strategy presented by this study would have an important ecological significance for alleviating agricultural N pollution.

Insight into the effect of microplastics on the adsorption and degradation behavior of thiamethoxam in agricultural soils

Thiamethoxam and microplastics are both common pollutants in farmland soil; however, few studies have focused on the interaction between thiamethoxam and microplastics in soil. Here, a batch experiment and soil incubation experiment were performed to explore the mechanism and effects of microplastics on the adsorption and degradation behaviors of thiamethoxam in soil, respectively. First, the batch experimental results indicated that the adsorption process of thiamethoxam on the microplastic/soil mixtures and soil-only systems mainly relies on chemical interactions. All sorption processes had moderate intensities of adsorption, and the sorption process occurred on the heterogeneous surface. In addition, the particle size and dose of microplastics could both affect the adsorption behavior of thiamethoxam onto microplastics/soil systems. The sorption capacity of thiamethoxam in soil decreases as the particle size of microplastics increases, but the sorption capacity increases as the dose of microplastics increases. Second, the results of the soil incubation experiment showed that the half-lives of thiamethoxam ranged from 57.7 d to 86.6 d, from 86.6 d to 173.3 d, and 115 d in the biodegradable microplastic/soil systems, nondegradable microplastic/soil systems, soil-only systems, respectively. These results indicate that biodegradable microplastics promoted the degradation of thiamethoxam, while nondegradable microplastics delayed the degradation process of thiamethoxam in soil. Overall, microplastics could change the degradation behaviors, sorption capacity and adsorption efficiency, and then affect the mobility and persistence of thiamethoxam in the soil environment. These findings contribute to understanding the influence of microplastics on the environmental fate of pesticides in the soil environment.

Reactivity of two acidity correctives in a medium texture soil

For crops to have good productivity, it is necessary to adopt agricultural practices that ensure an adequate supply of water and nutrients, and neutralize toxic elements in the soil, especially exchangeable aluminum, both in the arable layer and in the subsurface. One of these agricultural practices usually employed in both small and medium and large rural properties is the correction of soil acidity, which aims, in addition to neutralizing exchangeable aluminum, to provide calcium and magnesium for plants. Several materials have been used to correct soil acidity, with carbonates, oxides, hydroxides or silicates as neutralizing components. In the present work, the reactivity of two acidity correctives was evaluated in a soil of medium texture, with high aluminum saturation: 72.96%. The correctives used were a steel slag (calcium silicate), and a dolomitic limestone, applied in doses equivalent to one, one and a half, two, and two and a half times the analytically predicted amount, to raise the base saturation to 60%, using calcium acetate with H+ + Al3+ extractor. The study also included a control treatment, which did not receive acidity correction. The method used to evaluate the reactivity of the two correctives was soil incubation. The block design was used, with six repetitions per concealer dose. The experimental units were plastic bags with 3.0 kg of soil. After mixing the correctives with the soil, in the doses corresponding to each treatment, they were transferred to plastic bags and incubated at 70% of the maximum water retention capacity for ninety days. After the incubation period, the soil was analyzed for pH in CaCl2, pH in H2O, exchangeable aluminum (Al+3), and base saturation (V %). Steel slag and dolomitic limestone had the same efficiency to neutralize aluminum and increase base saturation. The pH in CaCl2 and pH in H2O were highly correlated, with the average pH in H2O being 0.50 units greater than the pH in CaCl2. The equation to relate pH in CaCl2 to pH in H2O was Y= 1.0273 x + 0.4716, with R2 = 0.9730. Complete neutralization of Al+3 occurred when the soil pH was raised to 5.03 (pH in CaCl2) or pH 5.50 (pH in H2O). The extraction of H+ + Al3+ with calcium acetate resulted in an underestimation of the cation exchange capacity at pH 7.0 (CTC T), and consequently of the corrective dose to be applied. On average, there was a need to double the amount of concealer predicted analytically to reach the desired base saturation. The equation to relate base saturation with corrective doses, in CaCO3 equivalents, was Y= 9.1476x + 3.8439, with R2 of 0.9449.

Phytoextraction of As by Pteris vittata L. assisted with municipal sewage sludge compost and associated mechanism

Pteris vittata L. (PV), an arsenic (As) hyperaccumulator, has a potential to extract As from As-polluted soils. Since available As in soils can be taken up by PV, As fraction variation associated rhizosphere environmental characteristics caused by municipal sewage sludge compost (MSSC) could provide possible to strengthen As phytoextraction by PV. In this study, the mechanism of phytoextraction of PV aided by MSSC was revealed from aspect of environmental characteristics of rhizosphere soils and physiological properties of PV. The effect of MSSC on available As in soils was investigated by soil incubation experiment. Furthermore, the influences of MSSC on enzymes activities, communities of soil bacteria and fungi, As concentrations, and As fraction in rhizosphere soils of PV were explored, and then the biomass and As accumulation of PV were examined by greenhouse pot experiments. After 90 days, available As in soil incubation experiment significantly increased by 32.63 %, 43.05 %, and 36.84 % under 2 %, 5 %, and 10 % treatment, respectively, compared with control treatment. Moreover, As concentrations in rhizosphere soils of PV under 2 %, 5 %, and 10 % treatment decreased by 4.62 %, 8.68 %, and 7.47 %, respectively, compared with control treatment. The available nutrients and enzyme activities in rhizosphere soils of PVs were improved under the MSSC treatment. Affected by MSSC, the dominant phylum and genus for both bacterial and fungal communities didn't change, but their relative abundance increased. Additionally, MSSC significantly increased biomass of PV with corresponding mean ranging from 2.82 to 3.42 g in shoot and 1.82 to 1.89 g in root, respectively. And the concentrations of As in shoot and root of PV treated by MSSC increased by 29.04 %–144.7 % and 26.34 %–81.78 %, respectively, in relative to control. The results of this study provided a basis for MSSC-strengthened phytoremediation for As-polluted soils.

Woodchips biochar versus bone char in a one‐year model soil incubation experiment: the importance of soil/char pH alteration on nutrient availability in soil

AbstractBACKGROUNDBiochars have become one of the most intensively and extensively investigated soil amendment materials in terms of their production, application and fate in the soil because of benefits such as increased soil quality and fertility. Biochar from woodchips and bone char from meat bone waste from a poultry slaughterhouse were prepared at 300 and 500 °C and then thoroughly mixed with two soils (cambisol and luvisol) that differed in their physicochemical parameters in ratios of 2% and 5% (w/w).RESULTSThe impact of bone and biochar amendments on nutrient availability was assessed during a one‐year model laboratory experiment. The feedstock origin and pyrolysis temperature affected the prepared materials’ physical properties and nutrient (Ca, Cu, K, Mg, Mn, P, S, Zn) availability. With increasing temperature, the structure of woodchip biochar changed from macroporous to microporous, and bone char changed from non‐porous to mesoporous. However, when mixed with soil, the biochar‐derived change in soil pH was revealed to be the most crucial parameter affecting soil nutrient mobility. Of all the tested elements, Only Cu, Fe and Zn were unaffected by biochar addition. Furthermore, temporal changes in element mobility during incubation were also elucidated.CONCLUSIONThe changes over time in element mobility indicated that soil properties were more important than bone and biochar characteristics. © 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).

Pyrolysis temperature dependent effects of biochar on shifting fluorescence spectrum characteristics of soil dissolved organic matter under warming

Biochar generally shift the content and molecular composition of soil dissolved organic matter (DOM) which represent the reactive components and have essential roles in coupling elemental cycling in soil. However, it is not clear how the effects of biochar on soil DOM composition is shifted under warming. This causes a knowledge gap to fully understand the fate of SOM affected by biochar application in a warming climate. To fill this gap, we conducted a simulated climate warming incubation of soil to study the influence of biochar with different pyrolysis temperatures and feedstock types on soil DOM components composition. Three-dimensional fluorescence spectrum analysis combining excitation emission matrix-parallel factor analysis (EEM-PARAFAC), fluorescence region integral (FRI), UV–vis spectrometry, principal component analysis (PCA), clustering analysis, Pearson correlation and multi-factor analysis of variance on fluorescence parameters (including FRI on Region I-V, FI, HIX, BIX, H/P) and soil DOC and DON content were analyzed for this purpose. Results showed that biochar shifted soil DOM composition and enhanced soil humification, which was dominantly pyrolysis-temperature dependent. Biochar shifted the soil DOM components composition probably through mediating soil microbial processing rather than direct input of their pristine DOM, and the influence of biochar on soil microbial processing was pyrolysis-temperature dependent and highly affected by warming. Medium-temperature biochar was more efficient for enhancing soil humification, by accelerating the transformation of protein-like components into humic-like components. Soil DOM composition presented a rapid response to warming, and long-term incubation may eliminate the effects of warming on shifting soil DOM composition. By revealing the heterogeneous effects of biochar with different pyrolysis temperatures on fluorescence characteristics of soil DOM components, our study provides a hint for the essential role of biochar on enhancing soil humification, and also suggests a vulnerability of biochar for soil carbon sequestration under warming.

Effects of phosphorus addition on leaf litter decomposition in two tropical tree plantations in Thailand

There is a widespread belief that organic matter decomposition in phosphorus (P)-poor tropical forests is limited by P shortage and stimulated by exogenous P addition. An incubation experiment was performed to test the effect of P addition on decomposition of litter layers taken from two tropical tree plantations. The result was compared with our earlier soil incubation experiment in the same region. Contrary to the traditional view, we found no significant effects of P addition on the litter layer decomposition, which was also in contrast with our previous soil incubation experiment that showed stimulatory effects of P addition on soil microbial respiration. The difference between our two experiments was attributed to the role of added P to release organic matter from the sorption sites on mineral soils, which made the adsorbed organic matter in soil accessible for microbes and easier to be decomposed. Overall, our incubation experiments did not support the P-limitation hypothesis: organic matter decomposition in P-poor tropical forests is limited by P shortage.

Biochar inhibited hydrogen radical-induced Cd bioavailability in a paddy soil

Herein, hydrogen (H·) radical was observed as a new pathway to produce hydroxyl (OH·) radicals that promoted cadmium sulfide (CdS) dissolution and thus Cd solubility in paddy soils. In soil incubation experiments, the bioavailable Cd concentrations in flooded paddy soils were increased by 8.44 % as the soil was aerated for 3d. For the first time, the H· radical was observed in aerated soil sludge. The association of CdS dissolution with free radicals was thereafter confirmed in an electrolysis experiment. Both H· and OH· radicals in electrolyzed water were confirmed by the electron paramagnetic resonance analysis. In the system with CdS, water electrolysis increased soluble Cd2+ concentration by 60.92 times, which was compromised by 43.2 % when the radical scavenger was introduced. This confirmed the free radicals can lead to oxidative dissolution of CdS. The H· radical was generated in systems with fulvic acid or catechol irradiated by ultraviolet lights, indicating soil organic carbon could be an important precursor for H· and OH· radicals. Biochar application decreased soil DTPA-Cd by 22–56 % invoking mechanisms besides adsorption. First, biochar quenched radicals and reduced CdS dissolution by 23.6 % in electrolyzed water in which -C-OH of biochar was oxidized to CO. Second, biochar boosted Fe/S-reducing bacteria and thus compromised CdS dissolution, as affirmed by a reversal correlation between soil available Fe2+ and DTPA-Cd concentrations. A similar phenomenon occurred in Shewanella oneidensis MR-1-inoculated soils. This study provided new insights into the bioavailability of Cd and offered feasible measures to remediate Cd-contaminated paddy soils with biochars.

Effects of source materials on desorption kinetics of carcinogenic PAHs from contaminated soils

Research investigating the desorptive behaviour of PAHs from contaminated soils often overlooked the effects of source materials, especially coal tar and coal tar pitch and materials alike. In this study, a refined experimental approach was adopted to establish a simple-to-complex continuum of systems that allow the investigation of desorption kinetics of benzo(a)pyrene (BaP) and 3 other carcinogenic PAHs (cPAHs) over an incubation period of 48 d. By comparing the modelled desorption parameters, elucidation of the effects of PAH source materials on their desorptive behaviour was achieved. Desorption of cPAHs from coal tar and pitch was enhanced when they were added to soils, with rapidly desorbing fraction (Frap) of BaP increased from 0.68% for pitch to 1.10% and 2.66% for pitch treated soils, and from 2.57% for coal tar to 6.24% for coal tar treated soil G and 8.76% for coal tar treated sand (1 d). At 1 d, desorption of target cPAHs from solvent and source material spiked soils generally followed the order of solvent > coal tar > pitch. Increases in Frap of cPAHs were observed in coal tar-treated soils after 48 d soil incubation (0.33%–1.16% for soil M, p ≥ 0.05, 6.24%–9.21% for soil G, p < 0.05) and was attributed to the continuous migration of coal tar as a non-aqueous phase liquid (NAPL) into soil pore structures. Slow desorption was dominated by source materials, whereas the extents and rates of rapid desorption (Frap and krap) were more controlled by the quantity of soil organic matter (SOM), rather than quality of SOM (as in solvent-spiked soils). The results of this study challenged the role of PAH source materials as ‘sinks’ and led to the proposed roles of coal tar and pitch and source materials alike as ‘reservoirs’ with a risk-driven perspective.

Redox Oscillations Activate Thermodynamically Stable Iron Minerals for Enhanced Reactive Oxygen Species Production.

Reactive oxygen species (ROS) play key roles in driving biogeochemical processes. Recent studies have revealed nonphotochemical electron transfer from redox-active substances (e.g., iron minerals) to oxygen as a new route for ROS production. Yet, naturally occurring iron minerals mainly exist in thermodynamically stable forms, restraining their potential for driving ROS production. Here, we report that tide-induced redox oscillations can activate thermodynamically stable iron minerals for enhanced ROS production. •OH production in intertidal soils (15.8 ± 0.5 μmol/m2) was found to be 5.9-fold more efficient than those in supratidal soils. Moreover, incubation of supratidal soils under tidal redox fluctuations dramatically enhanced •OH production by 4.3-fold. The tidal hydrology triggered redox alternation between biotic reduction and abiotic oxidation and could accelerate the production of reactive ferrous ions and amorphous ferric oxyhydroxides, making thermodynamically stable iron minerals into redox-active metastable iron phases (RAMPs) with reduced crystallinity and promoting surface electrochemical activities. Those RAMPs displayed enhanced redox activity for ROS production. Investigations of nationwide coastal soils verified that tide-induced redox oscillations could ubiquitously activate soils for enhanced ROS production. Our study demonstrates the effective formation of RAMPs from redox oscillations by hydrological perturbations, which provides new insights into natural ROS sources.

Enhancement of Soil Available Nutrients and Crop Growth in Sustainable Agriculture by a Biocontrol Bacterium Lysobacter enzymogenes LE16: Preliminary Results in Controlled Conditions

The indiscriminate use of chemical fertilizers has led to adverse environmental impacts and poor crop quality and accelerates the depletion of mineral reserves used for fertilizer production. Microbes are vital in soil nutrient cycling, and some effectively enhance soil nutrient supply and reduce chemical fertilizer usage. Biocontrol bacterium Lysobacter enzymogenes LE16 can produce various hydrolases against plant pathogens to mineralize soil organics via enzyme production. Therefore, the enzyme production, soil organic P and N mineralization, and crop agronomic performances induced by L. enzymogenes LE16 were investigated by pure culture, soil incubation, and greenhouse pot experiments. L. enzymogenes LE16 can hydrolyze lecithin and protein and convert them to inorganic P and NH4+-N. Similarly, available P and N increased as this bacterium was inoculated and grown in the tested soil. In the greenhouse pot experiment, phosphomonoesterase and protease produced by L. enzymogenes LE16 inoculant effectively mineralized soil organic P and N and enhanced soil available nutrients, thereby improving the nutrient uptake, fertilizer utilization rate, and agronomic efficiency of lettuce and pepper seedlings. Bacterial inoculation increased the lettuce yield by 6.43–11.30% and pepper fruit yield by 43.82–70.32%, even with less chemical fertilizer application. Therefore, L. enzymogenes LE16 can hydrolyze lecithin and protein in pure cultures, and mineralize organic P and N in soils, thus improving crop yield and quality and reducing chemical fertilizer application via the production of phosphomonoesterase and protease. L. enzymogenes LE16 shows potential for sustainable agriculture beyond plant protection.

Nitrogen mineralization following fall‐applied compost to subsurface drip‐irrigated processing tomatoes in California

AbstractOrganic wastes diverted from landfills can reduce greenhouse gas emissions and are used as supplemental nutrient sources for agricultural crops after they are composted. In California, compost should be applied in the fall to processing tomatoes (Solanum lycopersicum L.) to avoid delaying field preparation and transplanting in the spring. The objective of this study was to determine soil nitrogen (N) mineralization following fall application of greenwaste compost (GWC) based on the change of mineral N during a 4 month in‐field buried bag soil incubation in 2 prospective subsurface drip‐irrigated processing tomato fields (PTF1 and PTF2). GWC rates of 0, 11, 22, and 34 Mg ha−1 were evaluated in PTF1 and PTF2 in October 2019. Very dry surface soil conditions in fall 2019 and the disruptive procedure used to prepare soil for in‐field incubation using the buried bag method led us to calculate net N mineralization after adjusting for the initial mineral N concentration of the unamended (0 Mg ha−1) control. The adjusted net N mineralization was significantly less in PTF1 (8.6 mg N kg−1) than PTF2 (16.4 mg N kg−1) and the estimated net N mineralization rate of the surface 0–15 cm soil depth following GWC application to PTF1 was less than PTF2 (1.6–1.9 vs. 2.3–3.1 kg N ha−1 week−1). In‐field incubation requires soil disturbance that likely affected N mineralization and additional research should consider the feasibility of using pretreatments or pre‐incubations to account for disruption to antecedent soil conditions.

Plant Phosphorus Efficiency from Raw and Composted Agro- and Bio-Waste Anaerobic Digestates

The rising generation of organic waste (OW) can be a concern, representing at the same time a valuable opportunity for the phosphorous (P) recycling; however, yet little is known about plant-available P release from this source. In this work, two anaerobic digestates, from agro- (AWD) and bio-waste (BWD), and their respective composts (AWC and BWC), were selected to assess their P-release via sequential chemical extraction (SCE) and P species via solution 31P-NMR in NaOH+EDTA extracts. These products were also tested for the relative-P efficiency (RPEsoil) in a soil incubation (30 mg P kg−1), in comparison with a chemical-P source and a reference compost. The organic products were also compared for the ryegrass relative-P efficiency (RPEtissue) at the same P-rate (30 mg P kg−1), in a 112-day pot experiment in an Olsen-P poor soil (<3 mg kg−1), under a non-limiting N environment. The NaOH+EDTA extractions showed that inorganic P prevailed in all samples as proven by solution 31P-NMR. SCE showed very different labile-P (H2O+NaHCO3) and AW doubling BW products (84 vs. 48%); this was also confirmed by the soil incubation test in which AWD and AWC attained the best RPEsoil. Pot tests generally confirmed laboratory outcomes showing that AWD and AWC attained the best RPEtissue, from 3 to 4-folds of the BWD and BWC performance. The results showed that the feedstock mainly affects plant P availability from recycled OW and that their SCE are very informative in the description of plant-available P from this type of products to be used in rational fertilization plan.

Preparation of Novel Biodegradable Polymer Slow-Release Fertilizers to Improve Nutrient Release Performance and Soil Phosphorus Availability.

Inspired by the gradual collapse of carbon chain and the gradual release of organic elements into the external environment during the degradation of biodegradable polymers, a novel biodegradable polymer slow-release fertilizer containing nutrient nitrogen and phosphorus (PSNP) was prepared in this study. PSNP contains phosphate fragment and urea formaldehyde (UF) fragment, which are prepared by solution condensation reaction. Under the optimal process, the nitrogen (N) and P2O5 contents of PSNP were 22% and 20%, respectively. The expected molecular structure of PSNP was confirmed by SEM, FTIR, XRD, and TG. PSNP can release N and phosphorus (P) nutrients slowly under the action of microorganisms, and the cumulative release rates of N and P in 1 month were only 34.23% and 36.91%, respectively. More importantly, through soil incubation experiment and leaching experiment, it was found that UF fragments released in the degradation process of PSNP can strongly complex soil high-valence metal ions, thus inhibiting the phosphorus nutrient released by degradation to be fixed in the soil and ultimately effectively increasing the soil available P content. Compared with ammonium dihydrogen phosphate (ADP), a small molecule phosphate fertilizer that is easily soluble, the available P content of PSNP in the 20-30 cm soil layer is almost twice that of ADP. Our study provides a simple copolymerization method to prepare PSNP with excellent slow-release N and P nutrients, which can promote the development of sustainable agriculture.

Integrated application of phosphorus-accumulating bacteria and phosphorus-solubilizing bacteria to achieve sustainable phosphorus management in saline soils

The challenge of managing agricultural phosphorus (P) in saline regions entails both reducing leaching for environmental protection and maintaining soil available P levels for crop production, which could be achieved through functional microorganisms that can facilitate P transformation processes like P assimilation, inorganic P solubilization, and organic P mineralization. In this study, we proposed an integrated utilization of phosphorus-accumulating bacteria (PAB) and phosphorus-solubilizing bacteria (PSB) to reach the goal of alleviating P leaching while improving soil available P levels. The study conducted a microcosm experiment that combined a soil column test, soil incubation, and pot experiment to evaluate the effect of bacterial inoculants on soil P leaching, soil P availability, and plant P accumulation. The results showed that the application of PAB reduced 22.6 % of dissolved P leaching through the absorption of labile phosphate in the soil, and 17.3 % of particulate P leaching through the promoted soil aggregation. The integrated inoculation of PSB and PAB synergistically improved soil available P content by 18.3 % through the mineralization of soil organic P, and remarkably boosted wheat growth and its P accumulation. Microbial community analysis revealed that the integrated microbial treatment decreased the diversity of soil bacterial community and increased the abundance of native microbial species, i.g. Lysobacter and Ramlibacter, which were positively correlated with soil available P content and alkaline phosphatase level. In conclusion, the integrated microbial strategy based on halotolerant PAB and PSB has great potential for sustainable P management in saline areas and agricultural activities.