Increased Phosphorus Availability Research Articles

Glutamic Acid-Enhanced Phosphate Fertilizer Increases Phosphorus Availability in Fluvo-Aquic Soil via Phosphamide (O = P-N) Formation, Decreasing Phosphate Fixation and Increasing Soil Microbial Diversity

Glutamic Acid-Enhanced Phosphate Fertilizer Increases Phosphorus Availability in Fluvo-Aquic Soil via Phosphamide (O = P-N) Formation, Decreasing Phosphate Fixation and Increasing Soil Microbial Diversity

Effect of phosphate fertilizer-coated Dicarboxylic Acid Polymer on rice yield and components under greenhouse conditions

A significant amount of phosphorus (P) becomes fixed by aluminium (Al) and iron (Fe) in acidic soils, leading to decreased efficiency in P utilization and subsequently lowering crop yield. Enhanced P fertilization offers a potential solution, as the dicarboxylic acid polymer (DCAP) coating on P fertilizer promotes increased plant productivity and more effective P utilization. The improvement achieved through enhanced P fertilization can contribute to higher rice yields in acidic soils, accompanied by an increase in P solubility. The study aimed to determine the impact of DCAP-mixed phosphate fertilizer on P uptake by plants, absorption efficiency, and rice yield. The results demonstrated a significant increase in available P (about 3.5 mg P/kg) when DCAP was used in a greenhouse setting, resulting in elevated yields and total P absorption (ranging from 0.03 to 0.05 grams/pot). However, the addition of 60 kg of phosphate mixed with DCAP has not yet demonstrated a significant increase in available phosphorus in the soil compared to adding just 60 kg of phosphate. The application of phosphate at a dose of 30 kg of P2O5 mixed with DCAP for growth and phosphorus absorption yield results equivalent to using 60 kg of P2O5 without DCAP. Furthermore, the use of DCAP in conjuction with 50% P fertilizer increased P availability by the same amount as that achieved with 100% P fertilizer. Consequently, DCAP reduced chemical P fertilizer in the soil by approximately 50%. However, it is essential to evaluate the effectiveness of mixed phosphate fertilizer (DCAP) under field conditions before recommending its widespread use.

Prospective bioencapsulation to improve the quality of phosphate-solubilizing biofertilizers for crop production: A review

Farmers commonly use chemical phosphorus fertilizer to increase crop yields, but long-term use may harm the environment. Biofertilizers specifically phosphate solubilizing microbes (PSMs), are used for restoring soil fertility in crop production. PSMs contribute to plant phosphorus supply by increasing phosphorus availability in the soil through organic acid and phosphatase enzyme secretion. However, the conventional biofertilizer formulation is often limited by a short shelf-life followed by a decreased microbial effectiveness. In recent years, bioencapsulation formulation have received more attention because they offer products that have a longer shelf-life, protect microbes in harsh environments, and maintain the effectiveness of biofertilizers. This literature review focuses on the latest bioencapsulation technology, the impact of bioencapsulation on phosphate-solubilizing biofertilizers, and the potential for developing bioencapsulation-based biofertilizers for sustainable agriculture. Precise formulation is crucial in bioencapsulation, influencing the quality and performance of biofertilizer inoculants. Bioencapsulated biofertilizers offer advantages such as improved nutrient management, enhanced plant stress tolerance, disease suppression, and innovative agricultural waste management. Despite longer shelf life and adaptability to various crops, further research is needed to address scalability, cost-effectiveness, and standardized encapsulation techniques. In conclusion, bioencapsulation innovations have the potential to promote sustainable and productive crop production.

Fine root presence and increased phosphorus availability stimulate wood decay in a central Amazonian rainforest

In the Amazon basin, approximately 60% of rainforest thrives on geologically old and highly weathered soils, thus decomposition represents an important mechanism for recycling nutrients from organic matter. Although dead logs and branches constitute up to 14% of the carbon stored in terrestrial ecosystems, woody debris decomposition and mainly the effect of direct nutrient cycling by plant root interaction is poorly studied and often overlooked in ecosystem carbon and nutrient budgets. Here we monitored the decomposition of five different local woody species covering a range of wood density by conducting a long‐term wood decomposition experiment over two years with factorial root presence and phosphorous (P) addition treatments in a central Amazonian rainforest. We hypothesized that woody debris decomposition is accelerated by colonizing fine roots mining for nutrients, possibly strongly affecting wood debris with lower density and higher nutrient concentration (P). We found that root colonization and P addition separately increased wood decay rates, and although fine root colonization increased when P was added, this did not result in a change in wood decay. Nutrient loss from wood was accelerated by P addition, whereas a root presence effect on nutrient mobilization was only detectable at the end of the experiment. Our results highlight the role of fine roots in priming wood decay, although direct nutrient acquisition by plants seems to only occur in more advanced stages of decomposition. On the other hand, the positive effect of P addition may indicate that microbial nutrient mobilization in woody material is driven mainly by wood stoichiometry rather than priming by root activity.

Application of Bacillus spp. Phosphate-Solubilizing Bacteria Improves Common Bean Production Compared to Conventional Fertilization.

The use of phosphate-solubilizing bacteria (PSB) can be a sustainable strategy to increase phosphorus availability and promote satisfactory crop yields. The objective of this study was to evaluate whether inoculation with PSB in common bean increases (i) growth, (ii) nutrition, (iii) yield, and (iv) grain quality, and (v) reduces the chemical phosphorus application dose to obtain maximum yields. The experiment was conducted in an Oxisol using a randomized block design in a 4 × 4 factorial scheme, with four replicates, using the cultivar IAC 2051. The first factor was four doses of P2O5 (0, 20, 40 and 60 kg ha-1), and the second factor was four doses of PSB (0, 100, 200 and 300 mL ha-1). For leaf area and leaf chlorophyll content, the association of PSB inoculation with a P2O5 dose of 40 kg ha-1 promoted the best conditions for the common bean. P2O5 application increased yield by 79 kg ha-1 for each 10 kg ha-1 added. PSB inoculation at a dose of 192 mL ha-1 promoted P export of 15.3 kg ha-1, and the PSB dose of 159 mL ha-1 increased yield by 389 kg ha-1 (12%) compared to the control. Grain quality remained within the standards required by the consumer market, being little affected by the treatments. Improvements in common bean growth and nutritional and physiological status promoted by P2O5 application and PSB were essential in increasing yield, so these are sustainable production strategies.

Eggplant growth in wheat straw-, wheat straw biochar- and compost-amended soils: a field study of CO2 emission dynamics, soil physicochemical, microbial, and nutrient effects

The growth of eggplant (Pusa Safed Baingan-1) was studied during the semi-arid (March to June) and humid sub-tropical (July to September) seasons of New Delhi, India. The individual effects of wheat straw biomass (WSBM), wheat straw biochar (WSBC) and compost versus the combined effect of WSBM plus compost and WSBC plus compost were determined under field conditions. The amendments were made at two different application rates: 1 wt% and 2 wt%. WSBC was successfully prepared in a proprietary kachcha reactor (Indian patent no. 380921), designed using locally sourced clay. Amendments were characterized using elemental analyzer, scanning electron microscopy (SEM), transmission electron (TEM) microscopy, Fourier transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). The field study was conducted in 11 (1x1-meter) plots with two replicates. Basic soil health parameters including pH, electrical conductivity (EC), water holding capacity (WHC), bulk density (BD), cation exchange capacity (CEC), soil total nitrogen (STN), soil available nitrogen (SAN), soil organic carbon (SOC), soil available phosphorus (SAP), microbial biomass carbon (MBC) and mineral contents are analyzed. Observable plant growth characteristics (germination percentage, height, number of leaves, fruits, and plant biomass) were also recorded. Biochar amendment was most beneficial for enhancing the majority of these parameters. With respect to the control, a 20% decrease in bulk density, a 30% increase in water holding capacity, a 122% increase in organic carbon, a 175% increase in total nitrogen, a 23% increase in available nitrogen, and a 473% increase in available phosphorus were recorded. Furthermore, with respect to the control, a 115% increase in CEC was recorded using the compost amendment vs 84% with WSBC. Synergism between biochar and compost was reflected by high germination percentage (44%), number of fruits (600%), plant biomass weight (243%) and soil microbial biomass carbon (286%). Biomass amendment failed to show any positive influence. In summary, biochar emerges as a superior choice compared to both biomass and compost when it comes to soil amendments.

The role of rhizosphere microbes as phosphate solubilizing bio fertilizers in shallot: a review

Crops need nutrients to grow, develop, and produce yields, both in macro and micronutrients form. One of the essential macronutrients is phosphorus (P). Phosphorus is required by plants to produce plant biomass. Andisols are often used as agricultural lands in the highlands of the tropics. This soil type has high P retention and low available P. Andisol contains clay minerals with up to 97.8% P-retention. Therefore, this condition led to low P availability, but high total P in the soils. There was a tendency to increase the dose of inorganic fertilizers, especially P fertilizer in this area. A survey reported that shallot Andisol farmers applied P fertilizer about five times of shallot recommendation rate, however, the production has not increased, yet. The high rate of chemical fertilizers causes land degradation and environmental pollution. One of the solutions to increase phosphorus availability is by improving P solubility which increases P uptake by plants. Increasing P solubility is environmentally friendly and can be done by utilizing phosphate-solubilizing microbes which are often found in the plant rhizosphere. The use of phosphate-solubilizing microbes for plants today can be found in bio-fertilizers. This method could maintain soil health and give a good impact to the plant growth and production. This review would determine the use of phosphate-solubilizing microbes to manage P deficiency in Andisol soils. Some study cases about the effect of phosphate-solubilizing microbes on plant performances would also be addressed. Currently, it is hoped that farmers will begin to implement environmentally friendly agriculture by giving phosphate-solubilizing bio fertilizers to escalate available P and production.

Application of Poultry Manure Improves the Soil Sorption Capacity and Nutrient Regime of Vineyard Soils

ABSTRACT The sorption capacity and nutrient regime under different soil management practices (C – control, T – tillage and PM – tillage + poultry manure) in productive vineyard soil (Rendzic Leptosol) in the Nitra vineyard region (Nitra-Dražovce, Slovakia, Central Europe) were studied for the years 2013–2022. With T and PM, the soil pH was significantly lower than with C. The soil sorption capacity for both studied depths (0–30 and 30–60 cm) increased in the following order: T < PM < C. For all the soil management practices and soil depths, the soil sorption complex was fully saturated with basic cations. With T, in the 0–30 cm layer, the total nitrogen (Nt) content was lower by 218 and 292 mg kg−1, respectively, than with C and PM. However, in the period 2013–2022, the Nt increased statistically significantly, by 50.9, 87.6 and 97.8 mg kg−1 year−1 with T, C and PM, respectively. The application of PM had a positive effect on the increase in available phosphorus (P) – there was an increase with C and T of 96 and 112%, respectively. The content of available P increased linearly with all soil management practices. However, in the case of T, it was statistically significant (increase of 23.2 mg kg−1 year−1) over the period of 10 years. With PM, at 0–30 cm, the content of available potassium was significantly higher, by 29 and 91%, than with treatments C and T.

An effective method of magnetic field treatment in increasing soil phosphorus availability in wheat rhizosphere

Magnetic fields are widely used as a physical energy source in industry and environmental governance. Their application in agriculture has also been reported; however, it remains unknown whether magnetic fields can be used to increase the availability of phosphorus in wheat fields and whether they have an effect on increasing phosphorus availability in the rhizosphere. In this study, we conducted an incubation experiment for soil and a field control experiment for wheat cultivation. In the wheat cultivation experiment, four magnetic field intensity treatments of 20, 40, 60, and 80 mT were set with 0 mT as a control (CK). Under the magnetic field intensity of 60 mT, the available phosphorus content increased by 7.06% at the booting stage, and acid phosphatase and alkaline phosphatase activities in rhizosphere soil increased by 19.89% and 9.26%, respectively, under 40 mT and by 12.16% and 26.70%, respectively, under 60 mT magnetic field intensities compared with CK. Moreover, compared with CK, the magnetic field mainly affected lipids and lipid-like molecules, organic oxygen compounds, phenylpropanoids, and polyketides in the rhizosphere metabolisms. The results of correlation analysis show that the abundance of rhizosphere metabolites was significantly correlated with the acid phosphatase activity, and the acid phosphatase activity was significantly correlated with the available phosphorus content. The results indicate that applying an appropriate magnetic field intensity to soil altered the abundance of wheat rhizosphere metabolites. Furthermore, the activity of phosphatase and the content of available phosphorus in the soil increased, which resulted in increased available phosphorus uptake by wheat plants. This study highlights that magnetic fields can be used as a means to increase phosphorus availability in soil.

The long-term effectiveness of biochar in increasing phosphorus availability and reducing its release risk to the environment in water-saving irrigated paddy fields

The long-term effectiveness of biochar in increasing phosphorus availability and reducing its release risk to the environment in water-saving irrigated paddy fields

Nutrient challenges with solid-phase anaerobic digestate as a peat substitute – Storage decreased ammonium toxicity but increased phosphorus availability

The solid fraction (SD) obtained after liquid – solid separation of anaerobic digestate is interesting as a potential fertilizer as well as a peat substitute in horticultural growing substrates. We investigated the effect of incubation of the SD obtained by screw-press separation of digestate produced from food waste and plant residues on potentially plant available mineral nutrients and plant growth. The NH4-N concentration was initially > 1000 mg L-1 but rapidly decreased, probably due to NH3 emission promoted by a high initial pH. No nitrate was detected during the first four weeks of incubation. The concentrations of potentially available P and Mg were closely related and strongly increased during incubation. The effect of adding 20 or 30 vol% of SD to a peat-based growing substrate on the growth of basil and lettuce was investigated before and after the incubation period. With the unincubated SD, the initial substrate NH4-N of 200–300 mg L-1 was potentially phytotoxic. Plant growth response ranged from inhibition to stimulation, probably reflecting variation in substrate ammonium status. After 96 days of incubation, ammonium concentrations had decreased with > 50% and basil growth was generally positively affected by addition of incubated SD. However, available P concentrations of 140–210 mg L-1 in the incubated substrates posed a high risk of P leakage. In conclusion, storage greatly reduced NH4-N concentrations and phytotoxicity when the SD was used as a partial substituent for peat in a horticultural growing substrate. Measures are needed, however, to limit available P concentrations in high-P solid digestate fractions.

Thermostability enhancement of Escherichia coli phytase by error-prone polymerase chain reaction (epPCR) and site-directed mutagenesis.

Phytase efficiently hydrolyzes phytate to phosphate; thus, it is widely used to increase phosphorus availability in animal feeds and reduce phosphorus pollution through excretion. Phytase is easily inactivated during feed pelleting at high temperature, and sufficient thermostability of phytase is essential for industrial applications. In this study, directed evolution was performed to enhance phytase thermostability. Variants were initially expressed in Escherichia coli BL21 for screening, then in Pichia pastoris for characterization. Over 19,000 clones were generated from an error-prone Polymerase Chain Reaction (epPCR) library; 5 mutants (G10, D7, E3, F8, and F9) were obtained with approximately 9.6%, 10.6%, 11.5%, 11.6%, and 12.2% higher residual activities than the parent after treatment at 99°C for 60min. Three of these mutants, D7, E3, and F8, exhibited 79.8%, 73.2%, and 92.6% increases in catalytic efficiency (kcat/Km), respectively. In addition, the specific activities of D7, E3, and F8 were 2.33-, 1.98-, and 2.02-fold higher than parental phytase; they were also higher than the activities of all known thermostable phytases. Sequence analysis revealed that all mutants were substituted at residue 75 and was confirmed that the substitution of cysteine at position 75 was the main contribution to the improvement of thermostability of mutants by saturation mutagenesis, indicating that this amino acid is crucial for the stability and catalytic efficiency of phytase. Docking structure analysis revealed that substitution of the C75 residue allowed the mutants to form additional hydrogen bonds in the active pocket, thereby facilitating binding to the substrate. In addition, we confirmed that the intrinsic C77-C108 disulfide bond in E. coli phytase is detrimental to its stability.

Coapplication of water treatment residual and compost for increased phosphorus availability in arable sandy soils

AbstractIntroductionSoil degradation coupled with poor access to organic nutrient resources remains a major constraint in increased crop productivity in sub‐Saharan Africa, thus hindering the continent's efforts in achieving the United Nations' Sustainable Development Goals, particularly goals 1 (end poverty), 2 (zero hunger) and 3 (improve human health). Water treatment residual (WTR), a by‐product of clean water treatment, has been identified as an alternative organic nutrient resource for crop production. However, there are some inconsistences in soil phosphorus (P) dynamics following aluminium WTR (Al‐WTR) application.Materials &amp; MethodsA laboratory experiment was conducted to evaluate the P sorption of a sandy soil amended with 10% Al‐WTR, 10% compost (C) as a quasi‐control, 10% C + 10% Al‐WTR (10% coamendment) and 5% C + 5% Al‐WTR (5% coamendment) under varying levels of pH, particle size and P concentration. We calculated crop P fertilizer requirements under different amendments.ResultsThe results demonstrated that all amendments exceeded the minimum of 0.2 mg P L−1 needed in soil solution at equilibrium to maintain plant growth. However, the maximum P sorption capacity was higher for 10% Al‐WTR single amendment, ranging from 770 to 1000 mg P Kg−1, and from 714 to 1000 mg P Kg−1 and 555 to 909 mg P Kg−1 for 10% and 5% coamendments, respectively, across a range of pH and soil particle size fractions. The coamendments showed a reduction in crop P fertilizer requirements by ranges of 30–60% and 60–70% for the 10% and 5% coamendment levels, respectively, across different pH and particle sizes, relative to 10% Al‐WTR.ConclusionResults show that the use of 5% coamendment in sandy soils increases P availability sufficiently to improve crop yields. The results provide scope for using Al‐WTR coamendments to rebuild soil health in sandy soils in urban agriculture and increase macronutrient provision in crops to support human health.

Global perspective of phosphate solubilizing microbes and phosphatase for improvement of soil, food and human health

Soil microbial flora has a pivotal role in the phyto-availability of phosphorus and other necessary minerals and nutrients. The primary class of Rhizobacteria involved in the solubilization of phosphate from non-available forms to available forms is Phosphate solubilizing bacteria (PSB). The application of Phosphate solubilizing bacteria increased phosphorus availability, which is one of the major factors responsible for the increase in the yield of crops. The phosphorus content is higher in the seeds than in the other plant parts; it helps plants in disease resistance and stress management such as winter rigors and improves the quality of fruits, vegetables, and cereal crops. Application of PSB as the biofertilizers positively affects the secretion of siderophores, nitrogen fixation, Indole acetic acid (IAA), 1-aminocylopropane-1-carboxylate (ACC) deaminase, chitinase, and protease. PSB can solubilize useful phosphate from rock phosphate and phosphate present in the combined state in lower to higher pH range (4 to 10), lower to a higher temperature (20 to 40 0C), and even in the higher salt ranges (0 to 7.5 % NaCl). Microbes help in the assimilation of phosphates and hydrocarbons by the secretions of different phosphatases such as monoesterase, diesterases, C-P lyase, and phosphatase and phytases. Using chemical P fertilizer in sustainable agricultural methods needs to be reduced. For this purpose, alternative and inexpensive technology are required so that plants can be provided with a sufficient amount of P. Phosphate solubilizing microbes can be an excellent option to replace chemical P fertilizers for improved agricultural production and soil fertility. The fertility of farm fields can be improved by using PSB as the bio-fertilizer and it will enhance the nutritional quality of plants and plant products which are directly or indirectly taken as food. Applying these microbes to soil/seeds makes good quality fruits and can help to fulfill the nutritional hunger of the world.

Effects of land use type and tank components on soil properties and sustainability of tank cascade system in the Dry Zone of north central Sri Lanka

CONTEXTVillage tank cascade system (VTCS) is a globally important agricultural heritage system in Dry Zone watersheds of Sri Lanka. Lands in these watersheds have been under changing management conditions in the recent past, hence their sustainability has been suspected. OBJECTIVEObjectives of this study were to determine current status of soil properties in different land uses and tank components of a VTCS with respect to their position in the watershed, and to assess sustainability of this agricultural system using soil organic carbon management index (CMI) as a proxy. METHODSStudy was conducted in Mahakanumulla VTCS in North Central Dry Zone of Sri Lanka. Soil samples (n = 120) were collected from lands under forest, scrub/shrub, paddy and upland crops representing all elevations in two linear transects located in higher and lower positions along the main valley. Soils from components of tanks in upper and lower positions were also collected. Soil texture and some chemical properties were measured. The CMI in different land uses was calculated using total organic carbon (TOC) and permanganate oxidizable carbon contents. RESULTS AND CONCLUSIONSEffect of land use type on soil properties did not vary with position in the watershed (p > 0.05). An increase in available phosphorus and sulphur was observed in agricultural lands. Significant decreases in TOC (33%) and total N (43%) contents were observed in paddy lands compared to those of forest lands (p < 0.01). However, CMI indicated that management practices in paddy lands and upland soils are still sustainable but scrub/shrub lands need improvements to arrest their degradation. Electrical conductivity, pH, available P, K and Zn were significantly higher in lower positions while total N was lower. Thaulla (inundation area) and Perahana (filter) tank components had regulated flow of clay particles while Kattakaduwa (interceptor) has significantly high available P and TOC contents due to high wetness. Principal component analysis revealed factors that control soil erosion, soil organic matter content, water movement, cation availability and P dynamics governed the variability of major soil properties. Accumulation of soluble salts in lands of lower positions and increase of available plant nutrients in agricultural lands suggest that management practices so far adopted have slightly degraded soil fertility in this VTCS. SIGNIFICANCEFurther degradation of soils in lower positions and scrub/shrub lands in the watershed will negatively affect the livelihood of villagers and the environment. Hence, appropriate land management policies should be introduced to this agricultural system to ensure their sustainability.

Artificial humic acid improves maize growth and soil phosphorus utilization efficiency

Phosphorus is one of the largest nutrients limiting crop productivity. Humic substances, as macromolecular polymers, are potential carbon materials responsible for soil additives to increase soil phosphorus utilization and mitigate phosphorus loss. However, the effect of artificial humic substances (A-HS) on maize agronomic traits and soil phosphorus transformation in black soil areas has not been investigated, and the mechanisms by which it affects phosphorus utilization by seedlings remain unclear. In this study, phosphate fertilizer and A-HS are jointly applied to a model soil, and maize growth and the soil phosphorus availability are determined at various A-HS concentrations in greenhouses using the root-bag technique. Herein, A-HS includes artificial humic acid and fulvic acid with commercial humic acid for comparisons. Positive effects on agronomic traits and phosphorus uptake in maize seedlings were quantified. As A-HS also influences the soil microbiome, the present study further explored the changing trend of soil acid phosphatase and phoC gene community structure by high-throughput sequencing techniques, using the Illumina MiSeq platform with Functional Annotation of Uparse annotation, to provide insights into how A-HS affects microbially mediated phosphorus transformation. The study found a declining alpha diversity of phoC microbial communities in rhizosphere and bulk soil. A-HS affects the structure of maize rhizosphere and bulk soil microbial communities and enhances soil phosphorus effectiveness and nutrient uptake by maize. As a general result, this study supports that the application of artificial humic acid in sustainable farming techniques can not only increase phosphorus availability in farmland but also stimulate the formation of a healthy soil microbiome.

'Only One Earth' – Celebrating soil science on World Environment Day 2022

'Only One Earth' – Celebrating soil science on World Environment Day 2022

Enhanced phosphorus recycling during past oceanic anoxia amplified by low rates of apatite authigenesis.

Enhanced recycling of phosphorus as ocean deoxygenation expanded under past greenhouse climates contributed to widespread organic carbon burial and drawdown of atmospheric CO2. Redox-dependent phosphorus recycling was more efficient in such ancient anoxic marine environments, compared to modern anoxic settings, for reasons that remain unclear. Here, we show that low rates of apatite authigenesis in organic-rich sediments can explain the amplified phosphorus recycling in ancient settings as reflected in highly elevated ratios of organic carbon to total phosphorus. We argue that the low rates may be partly the result of the reduced saturation state of sediment porewaters with respect to apatite linked to ocean warming and acidification and/or a decreased availability of calcium carbonate, which acts as a template for apatite formation. Future changes in temperature and ocean biogeochemistry, induced by elevated atmospheric CO2, may similarly increase phosphorus availability and accelerate ocean deoxygenation and organic carbon burial.

Response and contribution of bacterial and archaeal communities to eutrophication in urban river sediments

Excessive loading of nitrogen (N) and phosphorus (P) that leads to eutrophication mutually interacts with sediment microbial community. To unravel the microbial community structures and interaction networks in the urban river sediments with the disturbance of N and P loadings, we used high-throughput sequencing analysis and ecological co-occurrence network methods to investigate the responses of diversity and community composition of bacteria and archaea and identify the keystone species in river sediments. The alpha-diversity of archaea significantly decreased with the increased total nitrogen (TN), whereas the operational taxonomic unit (OTU) number of bacteria increased with the increase of available phosphorus (AP). The beta-diversity of archaea and bacteria was more sensitive to N content than P content. The relative abundance of predominant bacterial and archaeal taxa varied differently in terms of different N and P contents. Complexity and connectivity of bacteria and archaea interaction networks showed significant variations with eutrophication, and competition between bacteria became more significant with the increase of N content. The sensitive and the highest connective species (keystone species) were identified for different N and P loadings. Total carbon (TC), water content (WC), microbial alpha-diversity and interaction networks played pivotal roles in the N and P transformation in urban river sediments.

Increased phosphorus availability from sewage sludge ashes to maize in a crop rotation with clover

AbstractA recycling of Phosphorus (P) from the human food chain is mandatory to secure the future P supply for food production. However, many available recycled P fertilizers from sewage sludge do not have an adequate P bioavailability and, thus, are not suitable for their application in soils with pH &gt;5.5–6.0, unless being combined with efficient mobilization measures. The aim of the study was to test the P mobilization ability of red clover (Trifolium pratense L.) from two thermally recycled P fertilizers for a subsequently grown maize. Two sewage sludge ashes (SSA) were investigated in a pot experiment at soil pH 7.5 with red clover differing in its nitrogen (N) supply (added N fertilizer or biological N2 fixation (BNF)), followed by maize (Zea maize L.). Shoot dry matter of maize was almost doubled when N supply of previous grown clover was covered by BNF, instead of receiving added N fertilizer. Similarly, shoot P removal of maize following clover with BNF was significantly increased. It is suggested that the P mobilization is related to the BNF, and a proton release of N2 fixing clover roots led to the measured decrease in soil pH and thereby increased P availability of the tested fertilizers.