Long-Term Mineral Fertilization Improved the Grain Yield and Phosphorus Use Efficiency by Changing Soil P Fractions in Ferralic Cambisol

Long-Term Organic Fertilization Strengthens the Soil Phosphorus Cycle and Phosphorus Availability by Regulating the pqqC- and phoD-Harboring Bacterial Communities

The pqqC and phoD genes encode pyrroloquinoline quinone synthase and alkaline phosphomonoesterase (ALP), respectively. These genes play a crucial role in regulating the solubilization of inorganic phosphorus (Pi) and the mineralization of organic phosphorus (Po), making them valuable markers for P-mobilizing bacterial. However, there is limited understanding of how the interplay between soil P-mobilizing bacterial communities and abiotic factors influences P transformation and availability in the context of long-term fertilization scenarios. We used real-time polymerase chain reaction and high-throughput sequencing to explore the characteristics of soil P-mobilizing bacterial communities and their relationships with key physicochemical properties and P fractions under long-term fertilization scenarios. In a 38-year fertilization experiment, six fertilization treatments were selected. These treatments were sorted into three groups: the non-P-amended group, including no fertilization and mineral NK fertilizer; the sole mineral-P-amended group, including mineral NP and NPK fertilizer; and the organically amended group, including sole organic fertilizer and organic fertilizer plus mineral NPK fertilizer. The organically amended group significantly increased soil labile P (Ca2-P and enzyme-P) and Olsen-P content and proportion but decreased non-labile P (Ca10-P) proportion compared with the sole mineral-P-amended group, indicating enhanced P availability in the soil. Meanwhile, the organically amended group significantly increased soil ALP activity and pqqC and phoD gene abundances, indicating that organic fertilization promotes the activity and abundance of microorganisms involved in P mobilization processes. Interestingly, the organically amended group dramatically reshaped the community structure of P-mobilizing bacteria and increased the relative abundance of Acidiphilium, Panacagrimonas, Hansschlegelia, and Beijerinckia. These changes had a greater positive impact on ALP activity, labile P, and Olsen-P content compared to the abundance of P-mobilizing genes alone, indicating their importance in driving P mobilization processes. Structural equation modeling indicated that soil organic carbon and Po modulated the relationship between P-mobilizing bacterial communities and labile P and Olsen-P, highlighting the influence of SOC and Po on the functioning of P-mobilizing bacteria and their impact on P availability. Overall, our study demonstrates that organic fertilization has the potential to reshape the structure of P-mobilizing bacterial communities, leading to increased P mobilization and availability in the soil. These findings contribute to our understanding of the mechanisms underlying P cycling in agricultural systems and provide valuable insights for enhancing microbial P mobilization through organic fertilization.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Variability in Soil Parent Materials at Different Development Stages Controlled Phosphorus Fractions and Its Uptake by Maize Crop

An adequate phosphorus (P) supply in the rhizosphere is essential for proper P uptake through plant roots. Distributions of P varies depending on the soil structure, formation, and the parent material from which it originates. More research is needed to determine whether soil depth and parent materials have an impact on P distribution. It was hypothesized that the type of soil formed by different parent materials is related to P uptake and soil P fractions. Soil samples were taken from different profiles at various stages of development in loess, alluvium, shale, and sandstone parent materials. The samples were analyzed for P fractions using the Jiang and Gu fractionation scheme. In the present study, the P fractions were controlled according to the quantity and the components, such as organic matter, clay minerals, carbonates, iron, and aluminum oxides. Studying the phosphatase enzyme activity related to P fractions, the soil parent material, and their development was highly beneficial in defining which P pools are more accessible to plants, as well as the effect of phosphatase in limiting P availability. Among all the tested parent materials, the total P in soils derived from the loess parent material was higher (792 mg kg−1) than in soils derived from alluvium, shale, and sandstone, respectively. The amount of apatite P in alluvium parent material was higher, accounting for 51–56% of total P. Other P forms varied significantly in parent materials in the following order loess > alluvium > shale >> sandstone. Phosphatase enzyme was found to be an indicator of P availability by limiting its uptake by plants.

The Variation of Soil Phosphorus Fractions and Microbial Community Composition under Consecutive Cucumber Cropping in a Greenhouse

The distribution of phosphorus (P) fractions in soil plays a decisive role in soil P bioavailability; however, the characteristics of soil P fractions under consecutive cropping in a solar greenhouse remain unclear. To evaluate the effects of the long-term successive vegetable cropping on soil P fractions and the microbial community composition in greenhouse soil, a continuous long-term cropping experiment was conducted using cucumber (Cucumis sativus L.) in a solar greenhouse starting from 2006 to 2018. Soil P fractions and the microbial community composition were determined using the Hedley continuous extraction method and the phospholipid fatty acid (PLFA) method, respectively, in the 1st, 9th, 13th, and 21st rounds of cultivation. The soil total phosphorus (TP) content increased from 0.90 g·kg−1 in the 1st round to 3.07 g·kg−1 in the 21st round of cucumber cultivation. With an increase in continuous cropping rounds, soil available phosphorus (AP) increased and the phosphorus activation coefficient (PAC) decreased, with no significant difference between the 13th and 21st rounds. After 21 rounds of continuous cropping, the soil organic matter (SOM) content was 16.34 g·kg−1, 1.42 times that of the 1st round. The abundance of soil bacteria, actinomycetes, Gram-negative bacteria (G−), Gram-positive bacteria (G+), and total PLFAs initially increased with continuous cropping rounds, but then decreased significantly, and the ratios of fungi:bacteria (F/B) and G+/G− bacteria also increased significantly with continuous cropping rounds. The contents of soil labile P, moderately labile P, and non-labile P increased significantly over 21 continuous cropping rounds. Together, these results demonstrate that long-term continuous cropping can directly lead to the accumulation of P fractions, but it can also affect the abundance of actinomycetes through SOM enrichment, which indirectly leads to the accumulation of non-labile P. This study provides a theoretical basis for future soil P fertilizer management and vegetable production sustainability.

Dynamics of phosphorus fractions and potential bioavailability along soil profiles from seasonal-flooding wetlands in a Chinese estuary

Soil phosphorus fractions in wetland ecosystems have received increasing attention due to its high eutrophication risks. Soil samples were collected to 40 cm depth in three sampling seasons to investigate the seasonal dynamics of organic and inorganic phosphorus fractions, bioavailability, and relationship between those and soil properties in a seasonal-flooding wetland in the Yellow River Estuary. The results showed that inorganic phosphorus (IP) and organic phosphorus (OP) contents exhibited much higher levels in the top 10 cm soils, and declined along soil profiles in spring. IP kept constant along soil profiles in fall, while OP decreased in summer and fall. They were greatly affected by water content (WC), pH, Cl^-/SO₄^2-, soil organic matter (SOM), and electrical conductivity (EC). Middle labile organic phosphorus (MLOP) and non-labile organic phosphorus (NLOP) accounted for higher percentages of total OP in summer and fall respectively than labile organic phosphorus (LOP) in spring. MLOP and NLOP levels showed a decrease along soil profiles in spring and in spring/fall, respectively, while NLOP significantly increased with depth in summer. Ca-P was the dominant IP fraction in all soils in three sampling seasons, declined with depth in spring/fall and increased in summer. Comparatively, soluble/loosely-P(S/L-P) generally decreased with depth along soil profiles in three sampling seasons. And residual P (Res-P) kept little change with depth in spring. Fe/Al-P levels decreased firstly and then increased with depth in spring and summer. Available phosphorus and potential bioavailable phosphorus contents decreased with depth in spring and summer not in fall, and had a strong significant positive correlation with WC and SOM. Alkaline phosphatase not acid phosphatase was the key factor influencing soil MLOP levels. Generally, the fractions and bioavailability of phosphorus as well as phosphatase in this region were affected by soil depth, sampling seasons, and soil properties (e.g., WC, pH, Cl^-/SO₄^2-, SOM, and EC).

Impacts of long-term inorganic and organic fertilization on phosphorus adsorption and desorption characteristics in red paddies in southern China

Soil phosphorus (P) adsorption and desorption occur in an important endogenous cycle linked with soil fertility problems and relevant to the environmental risk assessment of P. In our study, the effect of long-term inorganic and organic fertilization on P adsorption and desorption characteristics in relation to changes in soil properties was evaluated by selecting three long-term experimental sites in southern China. The selected treatments at each site were CK (unfertilized), NPK (synthetic nitrogen, phosphorus and potassium) and NPKM (synthetic NPK plus manure). The adsorption and desorption characteristics of P were evaluated using Langmuir and Freundlich isotherms. The results showed that long-term application of NPK plus manure significantly increased soil organic carbon (SOC), total P and available P at all three sites compared with the NPK and CK treatments. All three treatments fit these equations well. The maximum adsorption capacity (Qm) of P increased with NPKM treatment, and the binding energy of P (K) and the maximum buffering capacity (MBC) showed increasing trends. NPKM showed the highest Qm (2346.13 mg kg-1) at the Jinxian site, followed by Nanchang (221.16 mg kg-1) and Ningxiang (2219.36 mg kg-1). Compared to CK and NPK, the NPKM treatment showed a higher MBC as 66.64, 46.93 and 44.39 L kg-1 at all three sites. The maximum desorption capacity (Dm) of P in soil was highest with the NPKM treatment (157.58, 166.76, 143.13 mg kg-1), showing a better ability to release P in soil. The correlation matrix showed a significant positive correlation of SOC, total and available P with Qm, Dm and MBC. In conclusion, it is suggested that manure addition is crucial to improve P utilization in red paddy soils within the recommended range to avoid the risk of environmental pollution.