Unfertilized Soil Research Articles

Адаптивно-биологизированная технология возделывания картофеля

The article presents the results of research obtained in two experiments. The objective of the research in the 2010-2012 (leached chernozem, Tambov region) and 2021-2023 (sod-podzolic medium loamy soil, Moscow region) field experiments was to study the possibilities of cultivating domestic potato varieties using adaptive biologized technologies and to compare them with the traditional mineral system. The introduction provides literature data on the degradation of arable land, including under potato plantings, and the reasons causing it. A series of experiments have proven that in order to increase the productivity of potato crop rotations, it is necessary to use green manure, calculate fertilizer doses taking into account soil fertility and the planned yield; a 50% reduction in the doses of NPK fertilizers in combination with green manure and biologically active preparations: azotovit, phosphatovit, bisolbisan, bisobifit, agrovin, etc. Under conditions of prevailing heat and drought in 2010-2012, in the experiment on leached chernozem, the effect of pre-planting treatment of tubers with bacterial preparations (azotovit, 1 l / t + phosphatovit, 1 l / t) was most pronounced in the crop rotation link [(buckwheat + vetch) - potatoes], while bacterial preparations worked well both in unfertilized soil (24.6%) and against the background of half the dose of NPK (20.2%). Also, a high effect of bacterial fertilizers was obtained when cultivating potatoes for 3 years in one place: from 10.6% against the background of a full dose of NPK to 27.0% against the background of a half dose of NPK. In a field experiment on sod-podzolic medium loamy soil (2021-2023), a relatively high potato yield (up to 29.3 t / ha) was ensured by its placement after plowing oilseed rape against the background of a half dose of N31P37K82Mg10 + biopreparations. Complex mineral nutrition against the background of plowing young weeds: [Weeds + (N33P41K79Mg7 + BisolbiFit) + 2-fold spraying of BisolbiSan and Agrovin] also made it possible to obtain a high return on investment and increase the yield to 26.5 t / ha. The increase in yield from the input of agrochemicals against the background of plowing in weed biomass was higher than the values of similar field variants with rapeseed.

Transforming Agricultural and Sulfur Waste into Fertilizer: Assessing the Short-Term Effects on Microbial Biodiversity via a Metagenomic Approach.

Fungi and soil bacteria are vital for organic matter decomposition and biogeochemical cycles, but excessive synthetic fertilizer use contributes to soil degradation and loss of biodiversity. Despite this, about 97% of soil microorganisms are unculturable, making them difficult to study. Metagenomics offers a solution, enabling the direct extraction of DNA from soil to uncover microbial diversity and functions. This study utilized metagenomics to analyze the rhizosphere of two-year-old Tonda di Giffoni hazelnut saplings treated with synthetic NPK, composted olive pomace, and an innovative fertilizer derived from sulfur-based agro-industrial waste stabilized with bentonite clay. Using 16S rDNA for bacteria and ITS2 for fungi, Illumina sequencing provided insights into microbial responses to different fertilizer treatments. The results highlighted a significant increase in the abundance of beneficial microorganisms such as Thiobacillus, Pseudoxanthomonas, and Thermomyces, especially when organic materials were included. Additionally, microbial biodiversity improved with organic inputs, as shown by increased species richness (Chao1) and diversity (Bray-Curtis) greater than 20% compared with NPK and unfertilized soils (CTR). These findings emphasize the importance of organic fertilization in enhancing soil microbial health, offering a sustainable approach to improving soil quality and hazelnut productivity.

Nitrogen Regime of the Agro-Grey Soil of a Cherry Orchard and the Yield of Trees when Applying Fertilizers

2018–2022 in order to estimate the nitrogen dozes essential for this fruit crop in the first decade after planting. The field experiment was carried out at an orchard located in the forest-steppe zone of the Central Russian upland (Orel region). Urea and potassium sulfate were applied to the soil once a year in early spring with doses arising from N30K40 to N120K160 kg/ha. The dynamics of N-NH4 in the soil of fertilized and unfertilized plots were similar, the lowest level of the indicator was in July during fruit ripening. The content of N-NO3 in unfertilized soil fluctuated slightly through the vegetation period. The fertilizer treatments led to more intensive seasonal fluctuations of N-NO3 in dependence of weather conditions. Annual fertilization led to annual increase of N-NH4 content by 2–12 and N-NO3 by 18–70 times, depending on the dose of nitrogen. But the accumulation of mineral nitrogen in root zone over the years was not revealed. The fertilizers did not affect sour cherry yield when it was lower than 15 t/ha. Still in the high-yielding season the fertilizers application in dose of N60K80 was necessary to reach the yield 20 t/ha.

The combination of crushed rock and organic matter enhances the capture of inorganic carbon in tropical soils

The use of remineralizers (REM) derived from crushed rocks has become an important option to ensure soil fertility and food and nutritional security, as well as a potential mechanism to capture CO2 efficiently, helping to mitigate climate change. The objective of this article is to present the direct and indirect effects of the use of REM in carbon capture processes through accelerated rock weathering. The tests were carried out in leaching columns where a type of rock (R), characterized as kamafugite, was used at a dosage equivalent to 40 t ha-1 incorporated into the soil (S), with or without the addition of organic compost (OC), with a dosage of 80 t ha-1, totaling four treatments with four replications: S, S + R, S + OC and S + R + OC. During a period of four months, controlled amounts of deionized water percolated the columns composed of soil, OC and R in the different treatments. The resulting leachate was collected and analyzed for 14 physicochemical parameters. After testing, the soil was sampled to evaluate fertility parameters. Significant differences (P < 0.05) were observed in the parameters Ca, Mg, K, S, Electrical Conductivity and pH in the leachates in the rock treatments compared to their respective controls, with emphasis on the effect of the rock in the presence of organic compost. In addition, increases of Mg, K, P and Mn were observed in the soil that received the rock compared to the unfertilized soil. Regarding the possibility of capturing inorganic carbon, we found statistically significant differences (P < 0.05) in the S + R + OC treatment compared to the S + OC treatment. These results confirm the potential of REM associated with organic compost (OC) to increase soil fertility and carbon capture, although in a smaller magnitude than what has been expected.

Soil zinc dynamics over time on applied organics, bacterial inoculant and zinc fertilizers in calcareous soil of southern India

Bioavailability of zinc was impacted by soil properties, externally applied sources, time, and various fractions of zinc. An experiment was conducted to investigate the bioavailable and other zinc fractions in calcareous soil and the efficiency of organic and inorganic sources on bioavailability with the presence and absence of zinc solubilizing bacteria (ZSB). The sequential extraction procedure followed at every interval of the incubation period for all forms of zinc was studied. Externally added inorganic sources significantly affected all fractions of zinc compared to untreated soils. Among them, ZnSO4 influences all forms of zinc, mainly Ws+Ex (water soluble+exchangeable) and carbonate-bound zinc, whereas Zn-EDTA maintains a high status of bioavailable zinc throughout the experimental period. On the 60th day of incubation, Zn-EDTA and ZnSO4 applied to soil maintained bioavailable zinc content of 3.71 and 2.94 times higher than that of control. Irrespective of sources, the available zinc of Zn fertilizers applied to soils was reduced with an increase in incubation days. Organic and microbial addition effects solely or combined increase the soil zinc content significantly in both fertilized and unfertilized soils. Among two different organic sources, the zinc solubility performance of farmyard manure was higher than that of vermicompost. In untreated soil, residual and carbonate-bound fractions contribute a major portion towards total zinc based on quantity. The bioavailable fraction mainly the Ws+Ex and organically bound fractions were markedly influenced in all treatments.

Enhanced carbon use efficiency and warming resistance of soil microorganisms under organic amendment

The frequency and intensity of extreme weather events, including rapid temperature fluctuations, are increasing because of climate change. Long-term fertilization practices have been observed to alter microbial physiology and community structure, thereby affecting soil carbon sequestration. However, the effects of warming on the carbon sequestration potential of soil microbes adapted to long-term fertilization remain poorly understood. In this study, we utilized 18O isotope labeling to assess microbial carbon use efficiency (CUE) and employed stable isotope probing (SIP) with 18O-H2O to identify growing taxa in response to temperature changes (5–35 °C). Organic amendment with manure or straw residue significantly increased microbial CUE by 86–181 % compared to unfertilized soils. The microorganisms inhabiting organic amended soils displayed greater resistance of microbial CUE to high temperatures (25–35 °C) compared to those inhabiting soils fertilized only with minerals. Microbial growth patterns determined by the classification of taxa into incorporators or non-incorporators based on 18O incorporation into DNA exhibited limited phylogenetic conservation in response to temperature changes. Microbial clusters were identified by grouping taxa with similar growth patterns across different temperatures. Organic amendments enriched microbial clusters associated with increased CUE, whereas clusters in unfertilized or mineral-only fertilized soils were linked to decreased CUE. Specifically, shifts in the composition of growing bacteria were correlated with enhanced microbial CUE, whereas modifications in the composition of growing fungi were associated with diminished CUE. Notably, the responses of microbial CUE to temperature fluctuations were primarily driven by changes in the bacterial composition. Overall, our findings demonstrate that organic amendments enhance soil microbial CUE and promote the enrichment of specific microbial clusters that are better equipped to cope with temperature changes. This study establishes a theoretical foundation for manipulating soil microbes to enhance carbon sequestration under global climate scenarios.

Vertical migration and leaching behavior of antibiotic resistance genes in soil during rainfall: Impact by long-term fertilization

The vertical migration and leaching behavior of antibiotic resistance genes (ARGs) during rainfall in soils subjected to long-term fertilization remain largely unclear. In this study, ARGs in vertical profiles (0−60 cm) and leachates from three soils (acidic, neutral, and calcareous) in a long-term (13 years) field fertilization experiment were monitored by high-throughput quantitative PCR after each rainfall event throughout an entire year. The results showed that, compared with unfertilized soils, long-term manure fertilization mainly promoted the vertical migration and leaching of aminoglycoside, beta-lactam, and multidrug resistance genes in the soil profiles. As a result, the annual cumulative loads of ARGs in leachates from the three soils with long-term manure fertilization were significantly increased compared to the controls and were in the order of acidic soil > neutral soil > calcareous soil. SourceTracker analyses revealed that manured soil was the predominant source of the ARGs in the soil leachate samples. Pseudomonas, Anaeromyxobacter, IMCC26256, and MND1 were identified as the dominant potential hosts responsible for the vertical migration and leaching of ARGs in the three soils. PiecewiseSEM analysis further showed that long-term manure fertilization affected the vertical migration of ARGs during rainfall mainly by altering soil properties (i.e., pH, soil organic carbon, and sand). Our results suggest that the ARGs in soils with long-term manure fertilization are a significant potential source of ARG pollution in groundwater, and the measures should be taken to mitigate the vertical migration and leaching of ARGs during rainfall.

Organic manure rather than chemical fertilization improved dark CO2 fixation by regulating associated microbial functional traits in upland red soils

Dark microbial fixation of CO2 is an indispensable process for soil carbon sequestration. However, the whole genetic information involved in dark CO2 fixation and its influence on dark CO2 fixation rates under diversified fertilization regimes were largely unclear. Here, revealed by 13C-CO2 labeling, dark CO2 fixation rates in upland red soils ranged from 0.029 mg kg−1 d−1 to 0.092 mg kg−1 d−1, and it was 75.49 % higher (P < 0.05) in organic manure (OM) soil but 44.2 % decline (P < 0.05) in chemical nitrogen fertilizer (N) soil compared to unfertilized (CK) soil. In addition, the normalized abundance and Chao1 index of dark CO2 fixation genes (KO level) were significantly different between OM and N soils, showing the highest and lowest, respectively. And they were positively (P < 0.05) correlated with dark CO2 fixation rate. Besides, among the identified CO2 fixation pathways in this study, the DC/4-HB cycle (M00374) was enriched in OM soil, yet the 3-HP cycle (M00376) was enriched in N soil, and their relative abundances were positively and negatively correlated (P < 0.05) with dark CO2 fixation rate, respectively. The PLS-SEM analysis revealed that dark CO2 fixation-related functional traits (i.e. normalized abundance, Chao1 index and gene composition) were directly and positively associated with dark CO2 fixation rate, and organic manure could exert a positive effect on soil dark CO2 fixation rate through enhancing soil properties (e.g., pH and soil organic carbon) and further altering associated microbial functional traits. These results have implications for explaining and predicting the soil CO2 fixation process from the perspective of microbial functional potential.

Sustainable crop fertilization by combining biogenic nano-hydroxyapatite and P solubilizing bacteria: Observations on barley

Nano-enabled agriculture involves researching smart nano-agrochemicals for sustainable farming. Nano-hydroxyapatite (nHAP), a phosphorus-rich compound, has the potential to be used as a fertilizer with reduced environmental impact. This study tests the effectiveness of nHAP produced from waste materials (animal bones) on barley plants (Hordeum vulgare). Two different nHAPs were prepared by thermal treatment of chicken bones at 300 °C and 700 °C (nHAP300 and nHAP700, respectively). The nanopowders were then tested in a seed toxicity trial and in a greenhouse pot experiment with barley, using Pseudomonas alloputida, a P-solubilizing bacterium (PSB). The treatments were unfertilized soil, conventional triple superphosphate (TSP), and the nHAP treatments alone. The results indicated that: (i) the nHAP materials had particle sizes of 1 micrometer (nHAP300, due to aggregation) and 50–70 nm (nHAP700), with P contents of 12.8 % and 19.6 %, respectively; (ii) no toxicity was observed on barley seeds, and nHAP300 at maximum dose stimulated root length by 45.6 % compared to the control; (iii) compared to conventional P fertilizer TSP, nHAP300 and nHAP700 stimulated root growth by 7 % and 18 %, respectively; (iv) the fraction of available P produced through nHAP300-PSB (40.6 mg kg−1) was higher than that from TSP (39.2 mg kg−1); (v) ions associated with the nHAP structure supplied supplementary nutrients, predominantly allocated in root tissues. This study provides valuable insights for future investigations to assess the implications of P nano-fertilizations in achieving sustainability in agriculture.

Home field effects on the assimilation of inorganic nitrogen fertiliser into proteinaceous amino acids

AbstractThe local adaption of soil microbial communities to native litter inputs, the so‐called home field effect (HFE), is well established, though this phenomenon has yet to be demonstrated for agriculturally relevant inorganic nutrient sources. Using compound‐specific 15N‐stable isotope probing of proteinaceous amino acids (AAs), we investigated if continuous long‐term grassland fertilisation with either ammonium or nitrate resulted in preferential assimilation by the soil microbial community of the ‘home’ N fertiliser. Relative ammonium uptake was maximal in historic ammonium treated soils and previously unfertilised soil, confirming a general microbial preference for ammonium likely due to biochemical transformation efficiencies. Assimilation of nitrate and ammonium into AAs was comparable for the historic nitrate fertilisation, indicating that microbial adaptive processes governed by historical land use can dictate the immobilisation efficiency of different fertilisers. This is the first observation of the HFE in long‐term fertilised grassland soils, with further work required to investigate abiotic or biotic mechanisms underpinning this phenomena.

Effect of soil additives on biogeochemistry of ultramafic soils—an experimental approach with Brassica napus L

Ultramafic soils are characterized by low productivity due to the deficiency of macroelements and high content of Ni, Cr, and Co. Incorporation of ultramafic soils for agricultural and food production involves the use of fertilizers. Therefore, this study aims to find the soil additive that decreases the metallic elements uptake by plant using Brassica napus as an example. In this study, we evaluate the effect of manure (0.5 g N/kg of soil), humic acids (1 g of Rosahumus/1 dm3 H2O; 44% C), KNO3 (0.13 g K/kg of soil), lime (12.5 g/kg of soil), (NH4)2SO4 (0.15 g N/kg of soil), and Ca(H2PO4)2) (0.07 g P/kg of soil) on the phytoavailability of metallic elements. The effect of soil additives on metallic elements uptake by Brassica napus was studied in a pot experiment executed in triplicates. Statistical analysis was applied to compare the effects of additives in ultramafic soil on plant chemical composition relative to control unfertilized ultramafic soil (one-way ANOVA and Kruskal–Wallis test). The study shows that in almost all treatments, metallic elements content (Ni, Cr, Co, Al, Fe, Mn) is higher in roots compared to the aboveground parts of Brassica napus except for (NH4)2SO4, in which the mechanism of Mn accumulation is opposite. The main differences between the treatments are observed for the buffer properties of soil and the accumulation of specific metals by studied plants. The soils with the addition of lime and manure have the highest buffer properties in acidic conditions (4.9-fold and 2.1-fold increase relative to control soil, respectively), whereas the soil with (NH4)2SO4 has the lowest effect (0.8-fold decrease relative to control soil). Also, the addition of manure increases the biomass of aboveground parts of B. napus (3.4-fold increase) and decreases the accumulation of Ni (0.6-fold decrease) compared to plants cultivated in the control soil. On the contrary, the addition of (NH4)2SO4 noticeably increases the accumulation of Ni, Co, Mn, and Al in aboveground parts of B. napus (3.2-fold, 18.2-fold, 11.2-fold, and 1.6-fold, respectively) compared to plant grown in control soil, whereas the humic acids increase the accumulation of Cr in roots (1.6-fold increase). Therefore, this study shows that manure is a promising fertilizer in agricultural practices in ultramafic soil, whereas (NH4)2SO4 and humic acids must not be used in ultramafic areas.

Not all soil carbon is created equal: Labile and stable pools under nitrogen input.

Anthropogenic activities have raised nitrogen (N) input worldwide with profound implications for soil carbon (C) cycling in ecosystems. The specific impacts of N input on soil organic matter (SOM) pools differing in microbial availability remain debatable. For the first time, we used a much-improved approach by effectively combining the 13C natural abundance in SOM with 21 years of C3-C4 vegetation conversion and long-term incubation. This allows to distinguish the impact of N input on SOM pools with various turnover times. We found that N input reduced the mineralization of all SOM pools, with labile pools having greater sensitivity to N than stable ones. The suppression in SOM mineralization was notably higher in the very labile pool (18%-52%) than the labile and stable (11%-47%) and the very stable pool (3%-21%) compared to that in the unfertilized control soil. The very labile C pool made a strong contribution (up to 60%) to total CO2 release and also contributed to 74%-96% of suppressed CO2 with N input. This suppression of SOM mineralization by N was initially attributed to the decreased microbial biomass and soil functions. Over the long-term, the shift in bacterial community toward Proteobacteria and reduction in functional genes for labile C degradation were the primary drivers. In conclusion, the higher the availability of the SOM pools, the stronger the suppression of their mineralization by N input. Labile SOM pools are highly sensitive to N availability and may hold a greater potential for C sequestration under N input at global scale.

Impact of Contrasting Rates of Phosphate Fertiliser Addition in Two Vertisols: Effects of Fresh Application and Residual Fertiliser on Sorption and Plant Uptake

Cropping systems in many sub-tropical and tropical regions rely on phosphorus (P) fertilisers to maintain crop yields. However, crop responses are often spatially and temporally inconsistent. This study evaluated P availability from dispersed applications of fresh phosphate fertiliser and their residual effect in two contrasting Vertisols - a major soil type for crop production. We collected soils that had received mono-ammonium phosphate (MAP) fertiliser four years prior to sampling (residual), as well as unfertilised soils to which we applied MAP at equivalent rates (‘fresh’). Soil P tests quantified the potential P availability arising from the residual and fresh P applications, and P sorption curves were generated to describe the P sorption/desorption dynamics. A 45-day pot trial evaluated wheat growth and P uptake from fresh and residual P applications in both soils. Soil tests and sorption curves reflected differences in P addition in the two soils, although the sorption characteristics did not differ appreciably in response to residual P. Crop growth and P uptake strongly increased with increasing P availability, with greater responses for the freshly applied P. Low P recovery from aged fertiliser applications demonstrated that the availability of residual P for crop uptake after dispersed applications is limited in Vertisols. P-tests and sorption measurements could collectively capture potential soil P reactions and plant P availability in two contrasting Vertisols. Residual P benefits from dispersed applications remained low. Enrichment in a defined soil volume (i.e., banding) merits further investigation in this soil type.

Influence of Agro-Industrial Waste Composts on Soil Characteristics, Growth Dynamics, and Yield of Red Cabbage and Broccoli

In this work, environmentally sound technologies for converting organic wastes into fertilizers to improve soil sustainability and crop yield have been identified and assessed. Wet wastes were combined with 50% wood sawdust and 50% wet wastes (Compost 1) or (10% Straw + 90% wet wastes) (Compost 2) to produce soil improvers with a balanced level of nutrients, and their effectiveness on soil ecosystem functioning have been tested and compared to horse manure (HM) and nitrogen–phosphorous–potassium (NPK) fertilizers. Unfertilized soil was used as a control. Soil chemical and biological properties have been detected after the harvesting of broccoli and red cabbage (90 days from the initial treatments). Three independent experiments have been conducted in an open field in a randomized complete block design with three replications (n = 9). The results showed that Compost 1 had the highest C/N ratio and cation exchange capacity (CEC), indicating a better humification of the wet material. Compost 1, even if it contained a minor amount of organic carbon, as well as less activity of fluorescein diacetate (FDA) and dehydrogenase (DHA) than Compost 2, was the most effective in improving soil quality, significantly increasing the labile fraction of organic matter, the oxidative enzyme (DHA), microbial biomass, and crop yield. Both composts increased crop productivity.

Effects of Integrated Use of &lt;em&gt;Lantana camara, Calliandra calothyrsus&lt;/em&gt; and Cow Manure with Diammonium Phosphate and Potassium Chloride on Haricot Bean Yield in the Northern Part of Burundi

Effects of Integrated Use of &lt;em&gt;Lantana camara, Calliandra calothyrsus&lt;/em&gt; and Cow Manure with Diammonium Phosphate and Potassium Chloride on Haricot Bean Yield in the Northern Part of Burundi

Nitrogen and Nod factor signaling determine Lotus japonicus root exudate composition and bacterial assembly

Symbiosis with soil-dwelling bacteria that fix atmospheric nitrogen allows legume plants to grow in nitrogen-depleted soil. Symbiosis impacts the assembly of root microbiota, but it is unknown how the interaction between the legume host and rhizobia impacts the remaining microbiota and whether it depends on nitrogen nutrition. Here, we use plant and bacterial mutants to address the role of Nod factor signaling on Lotus japonicus root microbiota assembly. We find that Nod factors are produced by symbionts to activate Nod factor signaling in the host and that this modulates the root exudate profile and the assembly of a symbiotic root microbiota. Lotus plants with different symbiotic abilities, grown in unfertilized or nitrate-supplemented soils, display three nitrogen-dependent nutritional states: starved, symbiotic, or inorganic. We find that root and rhizosphere microbiomes associated with these states differ in composition and connectivity, demonstrating that symbiosis and inorganic nitrogen impact the legume root microbiota differently. Finally, we demonstrate that selected bacterial genera characterizing state-dependent microbiomes have a high level of accurate prediction.

Costus speciosus (Koen ex. Retz.) Sm.: a suitable plant species for remediation of crude oil and mercury-contaminated soil.

The aim of this study was to evaluate the efficiency of Costus speciosus (Koen ex. Retz.) Sm. in the degradation of crude oil and reduction of mercury (Hg) from the contaminated soil in pot experiments in the net house for 180days. C. speciosus was transplanted in soil containing 19150mgkg-1 crude oil and 3.2mgkg-1 Hg. The study includes the evaluation of plant biomass, height, root length, total petroleum hydrocarbon (TPH) degradation, and Hg reduction in soil, TPH, and Hg accumulation in plants grown in fertilized and unfertilized pots, chlorophyll production, and rhizospheric most probable number (MPN) at 60-day interval. The average biomass production and heights of C. speciosus in contaminated treatments were significantly (p < 0.05) lower compared to the unvegetated control. Plants grown in contaminated soil showed relatively reduced root surface area compared to the uncontaminated treatments. TPH degradation in planted fertilized, unplanted, and planted unfertilized pot was 63%, 0.8%, and 38%, respectively. However, compared to unvegetated treatments, TPH degradation was significantly higher (p < 0.05) in vegetated treatments. A comparison of fertilized and unfertilized soils showed that TPH accumulation in plant roots and shoots was relatively higher in fertilized soils. Hg degradation in soil was significantly (p < 0.05) more in planted treatment compared to unplanted treatments. The fertilized soil showed relatively more Hg degradation in soil and its accumulation in roots and shoots of plants in comparison to unfertilized soil. MPN in treatments with plants was significantly greater (p < 0.05) than without plants. The plant's ability to produce biomass, chlorophyll, break down crude oil, reduce Hg levels in soil, and accumulate TPH and Hg in roots and shoots of the plant all point to the possibility of using this plant to remove TPH and Hg from soil.

Urea promoted soil microbial community and reduced the residual ciprofloxacin in soil and its uptake by Chinese flowering cabbage.

Antibiotics in agricultural soil can be accumulated in crops and might pose a potential risk to human health. Nevertheless, there is a lack of knowledge about the impact of nitrogen fertilizers on the dissipation and uptake of antibiotics in soils. Therefore, our aim in this study is to investigate the effects of urea fertilizer on the residues of ciprofloxacin and its uptake by Chinese flowering cabbage (Brassica parachinensis L.) as affected by the associated changes on the soil microbial community. A pot experiment has been conducted using spiked soil with 20 mg ciprofloxacin /kg soil and fertilized with urea at dosages equal to 0, 0.2, 0.4, 0.8 t/ha. Application urea especially at 0.4 t/ha decreased the residue of ciprofloxacin in the soil and its uptake by the roots and its translocation to the shoots of Chinese flowering cabbage. The translocation factors (TFs) for ciprofloxacin were significantly decreased (P < 0.05) only at the treatment of 0.4 t/ha, while no significant difference of bio-concentration factors (BCFs). The average well color development (AWCD) values, Shannon diversity, and richness index were higher in the fertilized than the un-fertilized soils, and all such indicators were greater at the treatment of 0.4 t/ha than at 0.2 and 0.8 t/ha. The carbon substrate utilization of phenolic acids at the treatments of 0.4 t/ha were greater than with other levels of urea fertilizer. In conclusion, moderate urea addition significantly increased soil microbial activity and abundance, which in turn promoted the ciprofloxacin dissipation in soil and plant tissue. The present study provides an economical and operational strategy for the remediation of ciprofloxacin contaminated soils.

Belowground exploration by trees and shrubs

Unlike trees, shrubs (i.e., multiple-stemmed woody plants) do not need evenly spaced large diameter structural roots and therefore should be more responsive to heterogeneous distributions of soil resources and spread further per unit belowground biomass. We therefore hypothesized that compared to trees, shrubs respond more to asymmetric distributions of nutrients, reach nutrient-rich patches of soil faster, and do so with less below-ground biomass. To test these three hypotheses, we planted individual seedlings of shrubs (Cornus racemosa, Rhus glabra, and Viburnum dentatum) and trees (Acer rubrum, Betula populifolia, and Fraxinus americana) in the centers of sand-filled rectangular boxes. In one direction we created a stepwise gradient of increasing nutrients with slow-release fertilizer; in the other direction, no fertilizer was added. Seedlings were harvested when their first root reached the plexiglass-covered fertilized end of their box; time taken, above-ground biomass, and below-ground biomass per nutrient segment were determined. Shrubs and trees did not consistently differ in precision of root foraging (i.e., the ratio of biomass in the fertilized and unfertilized soil) or in rates (g/day) and efficiencies (cm/day) of lateral root growth. Interspecific variation appeared more related to species’ habitats than to growth form. The fastest and most efficient roots were produced by the shrub (R. glabra) and the tree (B. populifolia), both characteristic of poor and heterogeneous soils. Root foraging by R. glabra was also facilitated by rapid rhizomatous expansion.

Do soil enzyme activities explain stimulated carbon mineralization following liming?

Losses of soil organic carbon (C) following liming have been proposed to result from stimulated C mineralization, which could occur through a variety of mechanisms including soil enzymes. Given the pH-sensitivity of enzyme activities, liming could impact catalysis of C mineralization by extracellular enzymes independently of microbial response. To this end, we evaluated the responses of C mineralization as CO2 flux, permanganate-oxidizable C (POXC), and the activities of C-hydrolytic enzymes to liming of a Haplic Ferralsol (Typic Kandiudox) in western Kenya under three differing 11-year soil fertility managements: unfertilized (UNF), mineral fertilized (MIN), and organic fertilized (ORG). Five rates of Ca(OH)2 (1.5, 3.0, 4.5, 6.0, and 7.5 t ha−1) and an unlimed control were used to establish a pH gradient of 4.6–6.4. Soil C mineralization rates assessed as CO2 production peaked within 5 d for high liming rates, and converged to a similar rate as unlimed soils after 21 d. At 28 d, activities of β-glucosidase and cellobiohydrolase decreased with increasing pH, increased for β-glucosaminidase, and were unaffected for β-galactosidase. POXC generally increased with liming rate for fertilized soils, more so in ORG and less in MIN soils, with relative increases of 18%, 5%, and 1% for ORG, MIN and UNF soils, respectively, at 7.5 relative to 0 t ha−1 liming. This study identifies potentially rapid albeit short-lived stimulation of C mineralization following addition of a highly soluble liming agent. Notably, decreases in activities of soil enzymes that catalyze the first and last step of the cellulosic C depolymerization suggests that short-term losses of soil C were not driven by enzyme activities, and may occur in spite of lowered C-hydrolytic enzyme activity. The enhanced C mineralization observed could reflect augmentation of labile C pools via non-enzymatic processes (e.g., desorption) in the short-term.