Adding Intercropping Maize and Faba Bean Root Residues Increases Phosphorus Bioavailability in a Calcareous Soil Due to Organic Phosphorus Mineralization

Background and aims Root residues are an important factor influencing soil phosphorus (P) availability for crop uptake, but how the residues from different species combinations in sole cropping or intercropping systems affect soil P pools remains unclear. Methods Maize and faba bean were planted as either sole crops or intercrops in a P-deficient calcareous soil with and without addition of corresponding previous crop (pre-crop) roots. This was repeated in three cultivations cycles in a greenhouse experiment. Plants sampled in each experiment were analyzed for biomass and P content, and soils sampled from all treatments in the last cultivation were analyzed for soil characteristics. Results Addition of a mixture of intercrop root residues increased biomass, total P content, microbial biomass P concentration and soil acid phosphatase activity, compared with addition of root residues of a single crop. The Hedley soil P fractions from three continuous cultivation cycles differed, depending on root residue source. The sole maize root residue with high C/P ratio caused a considerable depletion of inorganic P (NaHCO3-Pi, NaOH-Pi and 1 M HCl-Pi), and the sole faba bean root residue with lower C/P ratio caused a large depletion in Resin-P and NaHCO3-Po fractions, and the root residue of intercrops with a medium C/P ratio depleted more of the NaHCO3-Po and conc. HCl-Po fractions. However, without root residues, sole faba bean depleted more of the Resin-P, NaHCO3-Pi, NaOH-Pi and NaHCO3-Po fractions than the other two cropping systems did because of its higher P content. Conclusions Adding root residues of mixed species accelerated soil organic P mineralization (NaHCO3-Po and conc. HCl-Po) by increasing microbial biomass P concentrations and acid phosphatase activities, and thus enhanced the intercropping advantage in terms of biomass and P content in a P-deficient soil.

Variations in Soil Properties Rather than Functional Gene Abundances Dominate Soil Phosphorus Dynamics under Short-Term Nitrogen Input

Background and aims Microorganisms play a vital role in regulating soil phosphorus (P) dynamics in terrestrial ecosystems. However, how nitrogen (N) inputs trigger the functional traits of P transformation-related microorganisms to affect P fates in soil needs to be explored further. Our aims were to reveal the soil microbial functional profiles for P turnover in response to N input and to explore the relationships between soil P dynamics, soil properties and functional genes.Methods We collected soil samples from field experiments with three levels of N input over three years in an alpine meadow of the Qinghai-Tibet Plateau to determine soil P dynamics and other properties and functional genes via metagenomics.Results The soil available P and microbial biomass P were significantly affected by N inputs and significantly associated with soil properties (including soil pH, alkaline phosphatase activity, and soil total N and NO3--N contents). Meanwhile, high N input decreased the relative abundance of the pstS gene, and low N input reduced the relative abundances of ugpQ and C-P lyase genes. The pstS gene was a determinant of soil microbial biomass P and significantly correlated with soil pH. Moreover, Alphaproteobacteria with C-P lyase and Actinobacteria related to alkaline phosphatases and phosphate-specific transport were the most abundant taxa but not affected by N input.Conclusions We found relationships between the pstS gene, microbial biomass P and soil pH, and the microbial functional gene abundance was less important than soil properties in regulating soil P dynamics under short-term N inputs.

Influences of a vermicompost application on the phosphorus transformation and microbial activity in a paddy soil

A pot experiment was conducted to investigate the effects of a vermicompost (VC) application on the phosphorus (P) transformation and microbial activity in a paddy soil. Changes in the following P forms were investigated: resin-P, concentrated HCl extracted inorganic (C.HCl-P_i) and organic P (C.HCl-P_o), diluted HCl extracted inorganic P (D.HCl-P_i), NaHCO₃ extracted inorganic (NaHCO₃-P_i) and organic P (NaHCO₃-P_o), NaOH extracted inorganic (NaOH-P_i) and organic P (NaOH-P_o), and residual P. The results showed that the vermicompost application significantly (P < 0.05) affected the pH, redox potential (Eh), water soluble Fe(II), HCl-extractable Fe(II), microbial biomass carbon (MBC), microbial biomass P (MBP), MBC/MBP ratio, and acid phosphatase activity (APA) of the paddy soil. In particular, the HCl-extractable Fe(II) increased by 25–56% with the vermicompost application when compared to the control (CK). With the exception of C.HCl-P_i, the vermicompost application greatly increased the contents of the various P forms in the soil. In particular, the labile P (resin-P, NaHCO₃-P_i, and NaHCO₃-P_o) and moderately stable P (NaOH-P_i and NaOH-P_o) were significantly (P < 0.01) increased. The correlation analyses showed that NaHCO₃-P_i was significantly and positively related to the MBC, MBP, and APA, while NaHCO₃-P_o was significantly and negatively related to the MBC, MBP, and APA. Both NaOH-P_i and C.HCl-P_i were significantly and negatively related to the APA. Both NaOH-P_o and C.HCl-P_o were significantly and positively related to the MBP, while NaOH-P_i was significantly and negatively related to the MBP. These results indicated that a vermicompost application could effectively enhance the dissolution and reduction of Fe and the consequent mobilisation of NaOH-P_i. In addition, the vermicompost application significantly (P < 0.01) increased the APA and effectively mobilised the NaOH-P_o.

Influence of aerobic treated manure application on the chemical and microbiological properties of soil

Aim of study: This study evaluated the effect of the application of liquid aerobic treated manure (continuous liquid composting, CLC) on physical, chemical and biological soil properties, with the objective of monitoring changes induced by soil management with CLC as a biofertilizer.Area of study: Colonia, Uruguay (lat. 34,338164 S, long. 57,222630 W).Material and methods: Soil’s chemical properties, including nitrogen mineralization potential (NMP) and 15 microbiological properties (microbial biomass carbon, MBC; mesophylic aerobic bacteria; actinobacteria; filamentus fungi; fluorescein diacetate hydrolysis; dehydrogenase; with NMP; acid and alkaline phosphatase; cellulolose degraders; P-solubilizing bacteria; nitrifying; denitrifying and free-living N-fixing microorganisms; glomalin; and soil-pathogenicity index, SPI) were evaluated in two sites with similar cropping history, with one and three years of respective CLC application.Main results: CLC application had significant effects on soil microbial biomass (p<0.05), soil enzyme (p<0.1) and functional groups activity (p<0.05). SPI decreased in both sites with CLC application. No significant variations were detected for the chemical variables, with the exception of NMP, which was significantly high (p<0.05) in soil treated with CLC at both sites.Research highlights: The improved biological soil properties analyzed (MBC, soil enzyme activities and SPI, together with NMP) emerged as reasonable indicators to assess and monitor the effects of CLC application.

Warming and nitrogen deposition accelerate soil phosphorus cycling in a temperate meadow ecosystem

Phosphorus (P) is an essential element for living organisms and a major limiting factor in many ecosystems. In recent years, global warming and nitrogen (N) deposition have become increasingly serious, with significant effects on the P cycle in terrestrial ecosystems. A series of studies were carried out on the soil P cycle, but how climate change affects this remains unclear. Field experiments with warming and N addition were implemented since April 2007. Infrared radiators manipulated temperature, and aqueous ammonium nitrate (10 g m–2 year–1) was added to simulate N deposition. Compared with the control, N addition reduced soil total P; warming and N addition decreased soil available P; warming, N addition and warming plus N addition decreased microbial biomass P, but increased litter P; and warming and N addition increased phosphatase activity significantly. Correlation analysis showed that soil total P, available P, microbial biomass P and phosphatase activity were positively correlated with soil temperature and water content. Soil total P was positively correlated with microbial biomass P and phosphatase activity; and available P was positively correlated with microbial biomass P but negatively correlated with litter P. The results showed that warming and N deposition accelerated the soil P cycle by changing soil physical and chemical properties and soil biological activities (microbial and phosphatase activities). However, N addition reduced the capacity of microbes to fix P and reduced microbial biomass P, resulting in losses to the soil P pool, further aggravating P limitation in the Songnen Grassland ecosystem.

Fate of phosphorus fertilizer in acidic Cambisol assessed using 33P isotope labeling technique

Direct 33P labeling approach is a very powerful technique that has high sensitivity in tracing the fate of added phosphorus (P) fertilizers across various P pools. Nonetheless, only a few studies have used this approach. This study traced the fate of applied P fertilizer in acidic P-limited soil using the 33P labeling approach.The incorporation of 33P-labeled KH2PO4 in available P (PAEM), microbial biomass P (Pmic) and Fe/Al-bound P (PNaOH) pools was followed in Cambisol as influenced by C and N sources applied as glucose and ammonium sulfate, respectively.Results showed that not all of the added P fertilizer remains in available pool; instead, it was distributed to poorly-available pools. Fast, almost instantaneous P fixation by the Fe and Al oxides and immobilization by microbial uptake were recorded.Applying glucose boosts microbial growth and demand for P, resulting in increased 33P recovery. High 33P recovery in Pmic (20% of the applied 33P) and in PNaOH (45% of applied 33P) showed the dominance of P immobilization by microorganisms and adsorption by Fe and Al oxides on the fate of P in an acidic soil. Nevertheless, these can contribute to long-term P availability after the turnover of microbial biomass and desorption of fixed P.

Dimethyl carbonate and switchable anionic surfactants: two effective tools for the extraction of polyhydroxyalkanoates from microbial biomass

DMC and SAS successfully extracted PHAs from bacteria. Polymer recovery and chemical recycling were excellent, the use of toxic compounds was avoided.