Soil Solution Samples Research Articles

Nitrogen leaching losses from pasture and winter forage crops in the West Matukituki Valley

In 2013 the Otago Regional Council (ORC) entered mediation with local farmers on changes to their Water Plan, Plan Change 6A, which sought to apply nitrogen load limits within the catchments of Lake Wanaka and Lake Hawea for all farm systems. There was little information available on nitrogen leaching losses in the high rainfall environments (c 2500 mm pa) of the South Island's high country. Agreement after mediation with the ORC and local farmers required a research project to examine differences between measured losses and outputs from OVERSEER® at a paddock and farm scale. To address this knowledge gap, a series of monitoring sites were set up in November 2014 in the West Matukituki Valley, west of Lake Wanaka. Porous soil solution samplers were installed to a depth of 50 cm in (i) a sheep- and cattle-grazed pasture, (ii) a cattle-grazed winter forage crop, and (iii) a native bush site. Results for 2015 showed that rainfall totalled 2240 mm, with calculated drainage estimated at 1330 mm. The total fluxes of dissolved N from the crop and pasture sites during the 12 months from June 2015 were 157 and 43 kg N/ha, respectively. Dissolved organic N (DON) made an unexpectedly large contribution to these fluxes, accounting for 20 and 67% of the total fluxes of dissolved N in drainage from the crop and pasture sites, respectively. Gaining a better understanding of the bioavailability of dissolved forms of organic N in leachate would help determine the risks that these forms of nutrients pose to water quality, and if they should be incorporated into models such as Overseer which do not account for DON. The project’s initial findings enabled an informed discussion on the use of modelled results from Overseer for the mitigation of N loss at a farm scale in the lakes’ catchments. It also focussed farmers’ attention on management of the nitrogen leaky parts of their farm systems, especially winter crops.

Optimal organic fertilization enhances the phytoavailability of phosphorus in the root zone of rice

AbstractOrganic fertilization is considered an effective approach in promoting agricultural green development, dramatically affecting soil phosphorus (P) availability. Nonetheless, limited information is available on the comprehensive impact of full substitution of organic fertilizer for chemical fertilizer on P speciation, phytoavailability, and apparent balance throughout different rice‐growth stages. To address this gap, a 5‐year field experiment was conducted, implementing five organic P gradients ranging from 0 (P0), 70 (P70), 140 (P140), 210 (P210) to 280 (P280) kg P2O5 ha−1 of organic fertilizer. To assess P phytoavailability in the root zone with submillimetre spatial resolutions, this study employed techniques such as the one‐ and two‐dimensional diffusive gradients in thin films (DGT) technique and the high‐resolution soil solution sampling technology (HR‐Peeper). The findings revealed that increasing P rates enhanced soil Olsen‐P and biological‐based P fractions across rice‐growth stages, primarily driven by variation in mineral‐associated P. Notably, the P140 treatment demonstrated the highest P uptake efficiency among the different rice‐growth stages, with a significant increase in soil DGT‐P, particularly in the 0–60 mm soil layer (p <0.05), providing tangible evidence for enhanced P uptake. Moreover, compared with higher P treatments (P210 and P280), the P140 treatment markedly increased P use efficiency by 31.7% and 99.0%, respectively (p <0.05). Further, with a high ratio of DGT‐P to Peeper‐P and a low apparent balance of P, organic fertilization at the rate of 140 kg P2O5 ha−1 effectively struck a balance between ensuring adequate P supply for yield stability and mitigating potential P loss risks. These results underscore the significance of optimal organic fertilization in enhancing agronomic benefits while reducing environmental risks. They offer valuable insights to support field P management strategies and government decision‐making processes.

Derivation of ecotoxicologically acceptable Cu concentrations in soil from different land uses in South Korea

This study aimed to establish ecotoxicologically acceptable Cu concentrations for soil-residing species by integrating the biotic ligand model and the species sensitivity distribution. Statistical analyses were performed on 35 soil solution samples collected from four distinct land use sites: residential, agricultural, forested, and industrial regions. The environmental parameters of these samples, including pH, dissolved organic carbon (DOC), Ca2⁺, Mg2⁺, K⁺, and Na⁺ concentrations, exhibited wide variations across the four regions. Specifically, pH and the concentrations of Mg2⁺, K⁺, and Na⁺ showed significant variability. Additionally, a strong correlation was observed between pH and Ca2⁺, as well as between the DOC concentration and Mg2⁺ and Na⁺. Using the biotic ligand model, we derived the half-maximal effective activities of Cu (EC50{Cu2+}) for 10 soil organisms based on the chemical compositions of the soil solution samples. Additionally, a species sensitivity distribution approach was employed to determine the 5% hazardous concentration (HC5) for soil biota, which was closely associated with DOC and Na⁺ concentrations, with Mg2⁺ playing a secondary role. We attributed these relationships to the formation of DOC complexes that mitigate Cu toxicity, along with competitive interactions with cations. Notably, HC5 values did not differ significantly across sampling sites (p = 0.523). Clustering based on environmental factors grouped the samples into four clusters, each containing soils from different land use types. However, the third cluster included an outlier from agricultural soil due to its unusually high pH and DOC levels. These findings suggest that it is crucial to consider site-specific soil characteristics when determining ecotoxicologically acceptable Cu concentrations, and soil solution characteristics do not always align with specific land use patterns.

Adsorption and desorption of polychlorinated biphenyls on biochar colloids with different pyrolysis temperatures: the effect of solution chemistry.

Biochar releases colloidal particles into the environment during applications and aging which can become carriers of pollutants and influence on the environmental risk of pollutants due to the excellent adsorption and migration properties of biochar colloids (BCCs). The adsorption and desorption behaviors of BCCs can be different from their bulk ones due to the colloidal size, which merits specific studies. Herein, the adsorption and desorption of 2,4,4'-trichlorobiphenyl (PCB28) as a representative on BCCs released from bulk biochars prepared from bamboo chips at 300, 500, and 700C and the effects of solution properties were specifically investigated. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. Results show that the adsorption was dominated by pore filling and π-π interaction, and thus, BCCs prepared at higher temperature with greater pore volume and aromaticity had higher adsorption of PCB28. The saturation adsorption amounts of PCB28 on BCC300, BCC500, and BCC700 were 21.9, 40.3, and 62.4mg/g, respectively. It is noteworthy that PCB28 possessed a significant desorption hysteresis from BCCs, with the hysteresis index (Ce = 80μg/L) increased from 0.380 to 0.661 as the preparation temperature of BCCs rising from 300 to 700℃. High concentration of NaCl (100mmol/L) was unfavorable for the adsorption and desorption. The presence of humic acid or fulvic acid (FA), especially the smaller FA, could inhibit the adsorption and desorption of PCB28 on BCCs due to micropore blocking. In seawater, groundwater, surface water, and soil solution samples, the PCB28 adsorption of BCCs was inhibited to varying degrees in comparison with that in deionized water, and the desorption was noticeably inhibited in the groundwater sample. These findings provide valuable information for the understanding of interactions between BCCs and organic contaminants in natural waters and for the environmental application of biochars as well.

Planting nitrogen-fixing trees in tropical Eucalyptus plantations does not increase nutrient losses through drainage

Planting nitrogen (N) fixing species can provide substantial levels of N for tree growth, but it can also result in large nutrient losses through deep drainage, threatening soil fertility. Nutrient losses through deep leaching have been little studied in tropical forest plantations and comprehensive studies are needed before planting these species on a large scale. We assessed nutrient fluxes in soil solutions collected in monocultures and mixed plantations of Acacia mangium and Eucalyptus grandis in Sao Paulo state (Brazil) on Ferralsols fertilized with potassium, phosphorus and lime. Soil solution sampling began after replanting the trees in an experiment that had already been conducted for six years in a first rotation. We collected soil solutions beneath the forest floor and at depths of 30, 100 and 300 cm, and determined nutrient concentrations monthly for 3.5 years. Drainage fluxes were calculated at the depth of the lysimeters by modeling the water fluxes with Hydrus 1D. The N concentrations in topsoil solutions were generally higher in Acacia than in Eucalyptus monocultures, confirming that the introduction of Acacia increases soil N availability. However, these differences were no more observed at 100 cm depth and total N leaching at 300 cm depth was low in all the treatments, with an average of 4.8 kg N ha−1 yr−1, probably due to the rapid root system development and high nutrient requirements of these fast-growing trees. Leaching fluxes of K+, Cl−, Ca2+ and Mg2+ peaked in the upper soil layers after fertilizer applications, but the fluxes drastically decreased in deep soil layers. The low fluxes of dissolved nutrients in deep gravitational solutions in our study suggest that the risks of nutrient leaching losses are low in fast-growing plantations established on deep Ferralsols. Our results show that planting N-fixing trees can enhance the N availability for plants without producing large leaching losses, which confirms the interest of mixed plantations with N-fixing trees.

Biotechnological potential of microorganisms isolated from the salar del hombre muerto, Argentina.

Bacterial strains were isolated from soil and aqueous solution samples from the Salar del Hombre Muerto, Argentina. A total of 141 strains were characterized and the tolerance to sodium chloride was evaluated. We performed a screening to search for molecules of biotechnological interest: carotenoids (11%), emulsifiers (95%), and exopolysaccharides (6%), and to assess the production of enzymes, including proteolytic (39%), lipolytic (26%), hemolytic (50%), and catalase activities (99%); 25 bacterial strains were selected for further studies. Some of them produced biofilms, but only Bacillus sp. HA120b showed that ability in all the conditions assayed. Although 21 strains were able to form emulsions, the emulsifying index Kocuria sp. M9 and Bacillus sp. V3a cultures were greater than 50% and, emulsions were more stable when the bacteria grew in higher salt concentrations. Only pigmented Kocuria sp. M9 showed lipolytic activity on olive oil medium and was able to produce biofilms when cultured without and with 4 M of NaCl. Yellow pigments, lipase activity, and biosurfactant production were observed for Micrococcus sp. SX120. Summarizing, we found that the selected bacteria produced highly interesting molecules with diverse industrial applications and, many of them are functional in the presence of high salt concentrations.

Mechanism of mercapto-modified palygorskite in reducing soil Cd activity

Mercapto-modified palygorskite (MP) is an efficient novel amendment with superior ability to decrease soil Cd bioavailability, but the unclear immobilization mechanism has become the bottleneck of its performance improvement and precise application. In order to clarify the Cd reducing mechanism of MP, long-term and short-term soil incubation with three types of soils (paddy soil, alluvial soil and yellow mountain soil) and sorption verification experiments were conducted to investigate the dynamic process of soil labile Cd impacted by MP and the synergetic effects on labile Fe, Mn, S and dissolved organic carbon via in-situ diffusive gradients in thin-films and soil solution sampling techniques. MP with four dosages rapidly and continuously decreased soil labile Cd contents by 14.50 % ∼ 89.16 % in long-term incubation, meanwhile low-dosage MP reduced soil labile Fe and Mn contents, but high-dosage MP increased their contents. With MP dosages increased, the effects of Fe-Mn oxides on soil labile Cd content gradually weakened. MP effectively promoted the reduction of Fe adsorbed by clay minerals and enhanced their ability to adsorb Cd. Short-term incubation showed that MP could decline soil labile Cd by 7.17 % ∼ 44.74 %, especially at the dosage 0.4 %. MP was a reduction catalyst to facilitate Fe reduction, which profited for clay minerals adsorbing Cd. The sorption experiments indicated that 0.30 % MP could adsorb 73.34 % Cd2+, promote the release of Fe2+ from the soil, and stimulate the ability of clay minerals to adsorb Cd. The results revealed that MP decreased soil labile Cd content within 2 d, and MP made soil Cd activity change out of the influence of soil Fe/Mn redox system. The mechanism will be beneficial for the large-scale application of MP in safe utilization of Cd contaminated soil.

Occupational exposure in automobile repair workshops: toxicological effects of contaminated soil in Wistar rats.

Automobile repair workshops contribute immensely to the generation of soil and water contamination. This study was conducted to compare the soil microbial load, heavy metals, and consequent toxicological effects, in three (3) automobile mechanic sites. Soil samples were randomly collected from 3 different auto mechanic workshop in Abeokuta town of Ogun-State, Nigeria. Bacterial and fungal counts were done via standard procedures. High-performance liquid chromatography was employed for the aflatoxin quantification. Also, 24 Wistar rats were divided into 4 groups (n=6), group 1-Control animals: orally administered distilled water, Group 2-administered soil sample solution from Ita Oshin mechanic site (I M), Group 3-administered soil sample solution from Ajebo mechanic site (A M), while Group 4-administered soil sample solution from Laderin mechanic site (LM), for two (2) weeks. Conventional methods were used to determine some physical and biochemical parameters in the rat's serum and tissues. Eight bacterial and fungal genera were identified from the soil samples with Bacillus subtilis and Aspergillus niger occurring most frequently. The levels of heavy metals (lead, zinc, chromium, and cadmium) analyzed were higher than the WHO permissible heavy metal limits in all samples. The activity of liver function enzymes ALP, AST, and ALT was significantly increased in the serum of animals exposed to the 3 soil solution samples when compared with the control group, with the highest recorded at Site II. High level of heavy metals and aflatoxins could predispose to several health-related hazards when humans are exposed to contaminated soil solutions around and within automobile mechanic areas.

Influence of wheat crop on carbon and nitrogen mineralization dynamics after the application of livestock manures

The growing global demand for livestock products has increased the scale of livestock farming. The management and disposal of large quantities of manures has become a serious environmental challenge. At the same time, there is a need for providing nutrients to plants in a sustainable way, in particular nitrogen (N). In this sense, a better understanding of N availability from livestock manures when applied to the soil will help to improve their use as fertilizers. It was hypothesized that the mineralization dynamics of the manures might be different depending on their composition and the presence of wheat.This work is performed to evaluate the effect of cattle manure (CM), hen manure (HM), and dairy slurry (DS), at two N rates when wheat (Triticum aestivum L.) was grown or not (bare soil) on i) protease, amidase, and urease activities and ii) dissolved organic carbon (DOC) and mineral N dynamics in soil solutions. A pot experiment was carried out in a greenhouse¸ and CM, HM, and DS were applied at 170 and 340 kg N ha−1 rates in the presence or absence of plants. Soil cores and solution samples were taken throughout the wheat growing period. Protease and amidase activities were higher for CM and DS applied at the highest N rate, respectively. Urease activity increased when wheat was grown with the lower N rate in the three manures. The DS caused higher concentrations of DOC and ammonium the day after its application than when HM and CM were used. During the first month, the nitrate concentration increased and was highest with HM, followed by DS and CM. However, the nitrate concentrations decreased in the treatments with plants after tillering. Wheat N uptake at harvest was highest with HM, followed by DS and CM. Mineralization dynamics were different in the three manures, which implies that the application times must be different.

Patterns of Nutrient Dynamics within and below the Rootzone of Collard Greens Grown under Different Organic Amendment Types and Rates

The knowledge about nutrient dynamics in the soil is pivotal for sustainable agriculture. A comprehensive research trial can retort unanswered questions. Dynamics of nutrients sourced from organic amendment types (chicken manure, dairy manure, and MilorganiteTM) applied at different rates (0, 168, 336, 672 kg total N/ha) were monitored within and below the rootzone of collard greens cultivated on a sandy loam soil in Prairie View, TX, USA. Macro- and micronutrients (e.g., TN: total nitrogen, P: phosphorous, K: potassium, Na: sodium, Ca: calcium, Mg: magnesium, B: boron, Cu: copper, Fe: iron, and Zn: zinc) were analyzed from soil solution samples collected during six sampling periods from within and below the rootzone. As hypothesized, the organic amendment types and rates significantly (p < 0.05 and/or 0.01) affected nutrient dynamics within and below the crop rootzone. Chicken manure released significantly more TN, P, K, Na, Ca, Mg, B, Cu, and Fe than the other two amendments. The application of chicken manure and MilorganiteTM resulted in higher below-the-rootzone leachate concentration of TN, Na, Mg, and Ca than in the leachates of dairy manure. Dairy manure treatments had the lowest concentrations of TN, Ca, and Mg; whereas, MilorganiteTM had the lowest concentrations of P, K, Na, B, and Cu in the collected leachates. The higher level of P (i.e., 4% in MilorganiteTM as compared to 2 and 0.5% in chicken and dairy manures, respectively, might have reduced the formation of Vesicular-Arbuscular (VA) mycorrhizae—a fungus with the ability to dissolve the soil P, resulting in slow release of P from MilorganiteTM treatment than from the other two treatments. Patterns of nutrient dynamics varied with rain and irrigation events under the effects of the soil water and time lapse of the amendment applications’ rates and types. All the macronutrients were present within the rootzone and leached below the rootzone, except Na. The dynamic of nutrients was element-specific and was influenced by the amendments’ type and application rate.

Highly selective colorimetric fluorescent probe for detecting nitrite in aqueous solution

Nitrite (NO2− ions) is a common pollutant in water and soil environment. Developing a rapid and accurate detection method for NO2− ions is always an important task. Herein, a switch-off colorimetric fluorescent probe P-NO2− was presented as the specific monitoring of NO2− ions in aqueous media. Once NO2− ions was added to the probe P-NO2− solution, the solution color changed very quickly, which was from yellow to colorless. And, the fluorescent intensity (580 nm) decreased obviously. The probe P-NO2− could test NO2− ions quantitatively (0.5–10 μM), and the detection limit was 75 nM according to 3σ/slope. Moreover, this new probe could also be used to determinate NO2− ions in the soil solution samples, river and lake water.

Relation between soil solution composition and petiole cellular extract of crops in western Mexico

Crop fertilization greatly impacts food production. However, insufficient applications can lead to poor yields. On the other hand, an excessive application leads to soil and aquifers pollution. In this paper, field studies were carried out to determine the ranges of mineral concentration and the interaction of the ions in the soil solution (SS) and the petiole cellular extract (PCE) in several cultures established in the states of Guanajuato, Colima and Jalisco, Mexico. The hypothesis states that there is a causal relationship between the mineral composition of the soil solution (SS) and the minerals and total soluble solids (TSS) in petiole cellular extract (PCE). The following cultures were studied in this research: avocado, blueberry, broccoli, cauliflower, raspberry, strawberry, lettuce, cantaloupe, papaya, and pepper. For each culture, PCE samples and SS samples using a press to break tissue and ceramic tip lysimeters were obtained. The results were processed to obtain ranges of variation within 50% of the closest values to the median. Correlations between the several ion concentrations were analyzed using analysis of variance. The results showed values (mg L-1) of NO3- (40-620), PO43- (17-66), K+ (3-377), Ca2+ (27-582), Na+ (15.3-500), Mg2+ (10-53), Fe3+ (0.6‑1.8), and Zn2+ (2.8-7.4) in soil solution, which allowed obtaining values of NO3- (27-9225), K+ (820-9375), Ca2+ (1.0-650), Na+ (25-620) and TSS (2-13 °Brix) in petiole cellular extract of petiole. Statistically significant correlations were observed between the concentrations of the SS ions regarding the concentrations in PCE in crops suggesting a relationship between the plant nutritive assimilation and cations or anions present in soil solution. The conclusion derived from this study is that ionic concentration ranges registered in the SS and in the PCE provide an approximation to the ranges of nutritional sufficiency for the horticultural crops established in the summer-winter in western Mexico.

Online Microdialysis-High-Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry (MD-HPLC-ICP-MS) as a Novel Tool for Sampling Hexavalent Chromium in Soil Solution.

Conventional soil solution sampling of species-sensitive inorganic contaminants, such as hexavalent chromium (CrVI), may induce interconversions due to disruption of system equilibrium. The temporal resolution that these sampling methods afford may also be insufficient to capture dynamic interactions or require time-consuming and expensive analysis. Microdialysis (MD) is emerging as a minimally invasive passive sampling method in environmental science, permitting the determination of solute fluxes and concentrations at previously unobtainable spatial scales and time frames. This article presents the first use of MD coupled to high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) for the continuous sampling and simultaneous detection of CrVI in soil solution. The performance criteria of the system were assessed using stirred solutions; good repeatability of measurement (RSD < 2.5%) was obtained for CrVI, with a detection limit of 0.2 μg L-1. The online MD-HPLC-ICP-MS setup was applied to the sampling of native CrVI in three soils with differing geochemical properties. The system sampled and analyzed fresh soil solution at 15 min intervals, offering improved temporal resolution and a significant reduction in analysis time over offline MD. Simple modifications to the chromatographic conditions could resolve additional analytes, offering a powerful tool for the study of solute fluxes in soil systems to inform research into nutrient availability or soil-to-plant transfer of potentially harmful elements.

Soil Solution Analysis With Untargeted GC–MS—A Case Study With Different Lysimeter Types

Surface-sourced organic compounds in infiltrating waters and percolates are transformed during their belowground passage. Biotic and abiotic processes thereby lead to continuously changing chemical environments in subsurface compartments. The investigation of such transformations of organic compounds aims for tracing subsurface fluxes as well as biotic and abiotic activity. To collect samples of soil solution, different kinds of lysimeters are available, spanning simple free-draining devices that sample water based on gravimetric flow and tension lysimeters allowing for approximating natural hydraulic conditions. Protocols for untargeted analytical profiling of organic soil solution constituents are scarce. We report here a solid phase extraction followed by GC–MS analysis, utilizing two long-term sampling devices in the Hainich Critical Zone Exploratory in Thuringia, Germany. In addition, we introduce a new lysimeter constructed exclusively from inert materials that allows for obtaining samples with little background signals in GC–MS. Polyvinylchloride (PVC)-based lysimeters introduce substantial background signals from plasticizers. We show how signals from these contaminants can be lowered during data analysis using chemometric background removal. Applying multivariate statistics for data analysis, we demonstrate the ability for monitoring of several sugars, fatty acids and phenolic acids at the topsoil-subsoil boundary and even beyond, via an untargeted analytical approach. Statistical tools facilitated the detection of differences in chemical signatures at three different land use sites. Data mining methods for metabolomics led to the identification of 3-carboxyphenylalanin as marker for a pasture site. The combined approach is suitable for the collection and extraction of topsoil and subsoil solution for untargeted metabolomics under near-natural flow conditions.

氮添加对亚热带常绿阔叶林土壤溶液化学特性的影响

土壤溶液被称作"土壤的血液"，是土壤中各种生物化学反应的中介物质，在外界环境发生变化时，土壤溶液化学成分能在其他土壤指标尚无变化之前对环境变化做出迅速响应。为了探索持续增加的大气氮（N）沉降对森林生态系统的影响，以华西雨屏区亚热带常绿阔叶林为对象，设置对照（CK，0 g m^-2 a^-1），低N（LN，5 g m^-2 a^-1），高N（HN，15 g m^-2 a^-1）三种N处理，通过人工施加硝酸铵（2017年9月起改施硝酸钠及氯化铵）的方法模拟N沉降增加情景，N处理42个月后，使用负压土壤溶液采样器定位收集A层（37-45 cm）及B层（52-60 cm）土壤溶液，并进行分析（每月1次，为期1 a）。结果表明：对照处理中A、B两层土壤溶液NO₃^-浓度达（3.94±0.77）mg/L、（4.27±1.13）mg/L，N添加显著提高两层土壤溶液NO₃^-浓度和B层NH₄⁺浓度；N添加显著降低土壤溶液pH，且显著增加Al³⁺浓度，Ca²⁺和Mg²⁺含量有增加趋势，但影响不显著；N处理使A层土壤溶液可溶性有机碳（DOC）浓度显著降低，对两层土壤溶液芳香化指数（AI）无显著影响；两层土壤溶液电导率（EC）及氧化还原电位（Eh）显著增加；此外，两层土壤溶液中许多化学成分均呈现极显著相关，特别是NO₃^-与EC相关系数达到了0.855。本研究中，对照处理极高的NO₃^-含量以及B层土壤溶液硝酸盐浓度高于A层，表明该亚热带常绿阔叶林N的有效性超过植物和微生物的总营养需求而发生淋溶，该生态系统已达到氮饱和状态，此外N添加会显著促进土壤酸化和铝离子活化，表层土壤溶液DOC的降低一定程度反映了凋落物分解受N添加的抑制作用，显著升高的氧化还原电位可能导致土壤中某些金属元素的迁移率降低。;Soil solution is called soil blood, which is the medium of various biochemical reactions in the soil. When the external environment changes, the chemical composition of the soil solution can quickly respond to the environmental changes before other soil indicators have changed. In order to explore the impact of increasing atmospheric nitrogen (N) deposition on forest ecosystems, we set up three N treatments including the control (CK, 0 g m^-2 a^-1), low N (LN, 5 g m^-2 a^-1), and high N (HN, 15 g m^-2 a^-1) in a subtropical evergreen broad-leaved forest in the raining area of west China, artificially applied ammonium nitrate to simulate the increase of N deposition (replaced with sodium nitrate and ammonium chloride since September 2017). After 42 months of N treatment, soil solution from two soil layers (layer A:37-45 cm, layer B:52-60 cm) was collected using negative pressure soil solution sampler and analyzed chemical composition once a month for a year. In CK, soil solution NO₃^- concentration reached (3.94±0.77) mg/L(layer A) and (4.27±1.13) mg/L(layer B). Nitrogen additions significantly increased soil solution NO₃^- and NH₄⁺ concentration in layer B. Nitrogen additions significantly reduced soil solution pH value and increased Al³⁺ concentration, and the concent of Ca²⁺ and Mg²⁺ increased with no significant in statistics. Nitrogen treatment significantly reduced the dissolved organic carbon (DOC) concentration in layer A, and had no significant effect on the aromatic index (AI) of soil solution in the two layers. The electrical conductivity (EC) and the redox potential (Eh) of soil solution increased significantly in two soil layers. In addition, many chemical components in the soil solution of two layers had extremely significant correlation, especially the correlation coefficient between NO₃^- and EC reached 0.855. In this study, the extremely high NO₃^- concentration in CK and higher NO₃^- concentration in layer B than in layer A indicated that the nitrogen availability of the subtropical evergreen broad-leaved forest exceeded the total nutrient requirements of plants and microorganisms, and the ecosystem had reached the state of nitrogen saturation. In addition, nitrogen addition significantly promoted soil acidification and aluminum activation. The decrease of DOC in surface soil solution to some extent reflected the inhibition of litter decomposition by nitrogen addition. The significant increase of redox potential may lead to the decrease of the mobility of some metal elements in the soil.

Speciation and Fractionation of Phosphorus Affected by Enterobacter cloacae in the Rhizosphere of Sugarcane (Saccharum officinarum L.)

The purpose of this study is to improve relative phosphorus (P) distribution in various proportions by greater solubility in the rhizosphere of plants influenced by phosphate solubilizing bacteria (PSB), P availability, and fertilizer management. For this purpose, a pot experiment was conducted with three phosphorus concentrations including 0 (P0), 20.5 (P50), and 41 (P100) mg P kg−1 and two PSB strains as well as Enterobacter cloacae R13 (R13) and E. cloacae R33 (R33) as factors which were evaluated at three harvesting times: 60, 95, and 140 days after planting (DAP) sowing. In the non-fertilized condition, treatments inoculated by R13 and R33 had higher P uptake in comparison with the non-inoculated treatment. Compared with the bulk soil, the chemical composition of the soil solution sample was affected by the dynamic properties of rhizosphere. In the inoculation-treated rhizosphere, the soluble P concentration was higher than that in the non-inoculated treatment. However, P uptake was greater in the inoculated treatments. Also, higher P free ions (H2PO4− and HPO42−) activity and lower calcium (Ca2+) and magnesium (Mg2+) activity were observed in soil solution inoculated rhizosphere as compared with the non-inoculated treatment. At all harvesting times, octacalcium and β-tricalcium phosphate minerals controlled P concentration in the rhizosphere. The pedogenic Ca-P or low soluble P (Ca8-P) was higher by up to 72.97% compared with other fractions, which can be ascribed to octacalcium and β-tricalcium phosphate minerals. In the current study, we conclude that the reduction of pH is not a major mechanism in dissolving insoluble P by E. cloacae although phosphate solubility may be attributed to the chelation process. In comparison, rhizosphere characteristics were more effective than PSB in converting the type of P-containing minerals. The results suggest that Ca8-P fraction is equivalent to octacalcium phosphate and β-tricalcium phosphate minerals in the rhizosphere of sugarcane.

Nitrate leaching losses mitigated with intercropping of deep-rooted and shallow-rooted plants

Nitrate (NO3−) leaching has been recognized as a worldwide problem, and NO3− is a major pollutant in ground and surface waters. The gradual leaching of residual NO3− into soil layers below the root zone is the main way of nitrogen (N) loss in cropping systems. The interception of NO3− by subsurface roots is crucial for crops or vegetables to utilize N. However, few studies were focused on the mechanisms of NO3− leaching under intercropping of deep-rooted and shallow-rooted plants. In a greenhouse production system, we selected deep-rooted and shallow-rooted plants for single-season intercropping planting experiments (MP, monoculture of pepper; IPA, intercropping of pepper and alfalfa; IPM, intercropping of pepper and maize). Plants were grown in core drainage lysimeters for 4 months, and leachate was collected by soil solution samplers. The results revealed N transformations between monoculture and intercropping systems by comparing NO3− leaching, N use efficiency, and microbes involved in nitrification. NO3− accumulation mainly occurred in 25–40-cm soil layer, which was affected by root morphology. Compared with monoculture, intercropping reduced NO3− leaching, in particular, pepper/maize intercropping significantly reduced NO3− leaching losses. In deep soil layers, roots of alfalfa and maize were more developed than those of the other crops, which made this corresponding intercropping system more effective in absorbing N in the subsoil. N uptakes of pepper/alfalfa intercropping and pepper/maize intercropping were 19% and 28% higher than that from the monoculture, respectively. Ammonia oxidizing bacteria (AOB) were significantly stimulated with planting especial in the topsoil, while ammonia oxidizing archaea (AOA) decreased with planting along the soil profile. These results indicated that lush plant roots immobilized N from the deep soil and thus improved N use efficiency and reduced NO3− leaching in the deep-rooted and shallow-rooted intercropping system. Intercropping of shallow-rooted pepper with deep-rooted alfalfa can enhance root nutrient absorption in deep soil layers, increasing N use efficiency and thus reducing NO3− leaching. The nitrification process in the intercropped soil was mainly regulated by AOB.

Integrated crop–livestock systems in lowlands increase the availability of nutrients to irrigated rice

AbstractIntegrated crop–livestock systems (ICLS) associated with crop rotation and soil conservation management cause numerous changes in nutrient fluxes and soil biochemical dynamics. In this sense, there is a gap in the impact of integrated production systems on nutrient dynamics and soil microbial activity in lowlands. In this context, this work had the objective of evaluating the nutrient availability and the activity of extracellular enzymes in a Gleyic Luvic Planosol under ICLS. The experiment has five paddy‐farming systems with a range of crop diversity (both in time and space) and grazing occurring mainly in the winter season. Soil solution samples were taken in cropping seasons (2014/2015, 2015/2016, and 2016/2017), from the first day after flooding (DAF) to approximately 70 DAF. The integration of rice with livestock increased urease activity (+84%), β‐glucosidase (+49%), and fluorescein diacetate (+105%), especially as the level of diversification and use intensification of pastures. In general, there was an increase in the availability of ammonium (+70%), phosphorus (+177%), potassium (+62%), and calcium (+20%) in the soil solution with the adoption of ICLS and soil conservation management, compared with the traditional rice system. Thus, the adoption of ICLS contributes to increase the process of biochemical functioning of the soil with consequent intensification of nutrient cycling and availability. Thus, the ICLS can sustainably increase nutrient availability in the soil and reduce the need to feed large amounts of fertilizer into irrigated rice production systems.

Online Nano Solid Phase Extraction Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry Workflow to Analyze Small Scale Gradients of Soil Solution Organic Matter in the Rhizosphere.

A new method combining online nano solid phase extraction coupled with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was developed to extract and analyze organic matter (OM) from microliter volumes of salt containing soil solution samples. This approach allows the reproducible analysis of only minute amounts of organic carbon (down to 10 ng C) without the need of further sample preparation. The new method was applied to unravel developing small-scale patterns of dissolved organic matter (DOM) in soil solutions of a soil column experiment in which Zea mays plants were grown for 3 weeks. Soil solution was sampled by micro suction cups from the undisturbed soil-root system once a week. Growth of the root system and, hence, position of individual roots relative to the suction cups was followed by X-ray computed tomography (X-ray CT). Our method makes it possible to resolve the chemical complexity of soil solution OM (up to 4300 molecular formulas from 2.5 μL sample). This allows to observe chemical gradients in the rhizosphere on a molecular level over time. The increasing influence of roots on soil solution OM is visible from higher molecular masses, an increasing degree of oxygenation and a higher fraction of formulas containing heteroatoms. The online nano solid phase extraction-FT-ICR-MS method provides novel insight into the processes affecting DOM in the rhizosphere, such as root exudation, microbial processes, and soil organic matter stabilization.

Approach to Petiole Sap Nutritional Diagnosis Method by Empirical Model Based on Climatic and Growth Parameters

The aim of this work is to evaluate the relationship between the nutrient concentration in petiole sap and different agronomic and climatic variables for a tomato crop grown in a greenhouse in Mediterranean conditions. In addition, the persistence of the nutrient concentration in petiole sap was investigated with the aim of determining the sampling period that implies the best trade-off nutritional information. The experiment consisted of the selection of 20 sampling points inside the greenhouse. The samples of petiole, fully expanded leaf, and soil solution samples were collected weekly from 86 to 163 days after transplanting. Chloride, NO3−-N, H2PO4−-P, Na+, K+, Ca2+, and Mg2+ concentrations were determined in petiole sap and soil solution obtained by suction cups. Nitrogen, P, K, Cl, and Na concentrations were also determined in leaf. Finally, the petiole sap nutritional diagnosis method is the highest sensitive nutritional diagnosis method which compares soil solution and nutrient leaf content related to yield, and the statistical analysis performed in this research demonstrates that crop evapotranspiration (ETc), vapor pressure deficit (DPV), and leaf area index (LAI) are considered the most significant variables that allow the development of these empirical prediction models regarding nutrient concentration in petiole sap.