Effects of phosphorus fertilizer application rate on transformation processes of phosphorus fractions in the purple alluvial soil of a riparian zone

Effects of phosphorus(P)fertilizer application rate on soil transformation processes of P fraction are still unclear in the riparian zone.Purple alluvial soils in the riparian zone of the Three Gorges Reservoir were collected to conduct a 21-day incubation executed by two hydrological environments(drying and flooding)and ten application rates of P fertilizer.Transformation percentages of P fertilizer(TPPF)were calculated as content differences of soil P fractions between fertilizer addition and none fertilizer addition divided by soil total P increases caused by fertilizer addition.TPPF to inorganic P extracted by sodium hydroxide(NaOH-Pi)and hydrochloric acid(HCl-Pi)increase by 20.91%(9.71%)and 24.26%(40.72%)under the drying(flooding)environment.Instead,TPPF to the other fractions decrease.Phosphorus fertilizer input mainly has indirect positive and negative effects on organic P via precipitated P under the drying and flooding environments and finally has indirect positive effects on labile P(p<0.001).Percentage changes of water-soluble inorganic P(H2O-Pi)and HCl-Pi under the flooding environment are higher than that under the drying environment,and percentage changes of organic P extracted by sodium hydrogen carbonate(Na HCO3-Po)and NaOH-Pi show an opposite trend(p<0.01).?(differences in soil P fraction content between flooding and drying incubations)H2O-Pi is negatively correlated with?NaHCO3-Po,and?NaHCO3-Po is positively correlated with?NaOH-Pi(p<0.001).In conclusion,P fertilizer is transformed more into precipitated P than into other P fractions with an application rate increase.Phosphorus fertilizer input mainly increases organic P via precipitated P under the drying environment and decreases organic P via precipitated P under the flooding environment,and organic P is further transformed into labile P.With P fertilizer input,P release caused by flooding is derived from NaHCO3-Po release triggered by NaOH-Pi release.The results can be helpful for the understanding of P fertilizer migration processes from the riparian zone soil to the Three Gorges Reservoir under rain leaching and flooding.

Dynamics of soil inorganic phosphorus fractions at aggregate scales in a chronosequence of Chinese fir plantations

Successive cultivation of Chinese fir(Cunninghamia lanceolata) would markedly affect the distribution and accumulation of soil inorganic phosphorus(Pi).However,how different chronosequence phases of Chinese fir plantations exerting influences on the quality and quantity of soil Pi fractions in aggregate-scale remain poorly understood. This study researched the dynamic changes of aggregate-related Pi fractions encompassing occluded-P(O-P), aluminum-bound P(Al-P), iron-bound P(Fe-P), and calcium-bound P(Ca-P) in topsoil(0-20 cm) from different stand aged(9-, 17-, and 26-yr) Chinese fir plantations and one nearby abandoned land(CK) in Rongshui County,Guangxi, China. In this study, soil aggregates were classified into micro-aggregates(< 0.25 mm), small macro-aggregates(1-0.25 mm), medium macroaggregates(2-1 mm), and large macro-aggregates(> 2 mm) by one wet-sieving process. As the primary aggregate fractions correlated with better soil aggregate stability, the large macro-aggregates took the highest proportion in all aggregate sizes regardless of various stand ages of Chinese fir plantations. Besides, the 17-yr plantations of Chinese fir displayed the highest stability of aggregates structure. Compared with CK, all four soil Pi fractions from three different stand ages of Chinese fir plantations generally showed increasing trends.Irrespective of chronosequence phases, Al-P was mainly carried by small macro-aggregates. O-P showed the opposite tendency to Al-P, which had the lowest content in small macro-aggregates. Fe-P and Ca-P showed an even distribution in all aggregates.The contribution rates and stocks of each Pi fraction exhibited close relevance to the content of soil aggregates. As revealed from the results, planting of Chinese fir before 17-yr was beneficial to prompt the formation of large macro-aggregates and the level of soil P. But after 17-yr, successive monoculture planting of Chinese fir would reduce the stability of soil aggregates and render the losses of soil P. The dynamics of soil total phosphorous(TP) and Pi fractions contents were highly related to the stand ages of Chinese fir plantations, but less related to the distribution of soil aggregate sizes. As the major carriers for soil P stocks, the large macro-aggregates played a vital role in the cycles and reserves of soil P.

Effect of long-term fertilization on phosphorus fractions in different soil layers and their quantitative relationships with soil properties

Investigating the dynamics and distribution of soil phosphorus(P) fractions can provide a basis for enhancing P utilization by crops. Four treatments from a 29-year long-term experiment in black soil with maize cropping were involved in this study: no fertilizer(CK), inorganic nitrogen and potassium(NK), inorganic nitrogen, phosphorus, and potassium(NPK), and NPK plus manure(NPKM). We analyzed soil P fractions in different soil layers using a modified Hedley sequential method. The long-term NPKM treatment significantly increased total P by 0.6–1.6 times in the different soil layers. The Olsen-P concentration far exceeded the environmental threshold for soil Olsen-P(50.6 mg kg) in the NPKM treatment in the 0–60 cm soil profile. Moreover, the concentrations and proportion of labile and partially labile inorganic P(Pi) fractions(i.e., Na HCO-extracted Pi, Na OH-extracted Pi, and dilute HClextracted Pi) to the sum of all P fractions(Pt) in the 0–60 cm soil profile were higher in the NPKM treatment than in the NPK treatment, indicating that manure could promote the transformation of non-labile into more labile forms of P in soil, possibly by manure reducing P fixation by soil particles. Soil organic matter, Mehlich-3 extractable iron(Fe), and organic-bound aluminum were increased by fertilization, and were the main factors influencing the differences in the P fractions in the 0–20 cm soil layer. Soil mineral components, i.e., free Fe oxide and Ca CO, were the main factors influencing the P fractions in the subsoil. The soil P transformation process varied with soil layer and fertilization. Application of manure fertilizer can increase the labile(Olsen) P concentrations of the various soil layers, and thus should reduce the mineral P fertilizer requirement for crop growth and reduce potential environmental damage.

Soil phosphorus fractions and their availability over natural succession from clear-cut of a mixed broadleaved and Korean pine forest in northeast China

To assess phosphorus(P)status of forest soil under naturally restored vegetation,P fractions in the 10-cm soil layer were quantified at different successional stages on the clear-cut site of mixed broadleaved and Korean pine forest.Four communities of shrub,softwood broad-leaved forest,softwood and hardwood broad-leaved forest,and hardwood broad-leaved forest represented different successional stages.A soil sample from a primary broad-leaved and Korean pine stand was the control.A sequential P fractionation scheme extracted empirically defined pools of P and path analysis used to partition the direct and indirect contribution of soil P fractions to available P.The results show that available P increased significantly with long-term succession,while both sodium bicarbonate-extractable P(NaHCO_(3)-P)and sodium hydroxide-extractable P(NaOHP)fractions were reduced in early successional stages and increased in late stages.Compared to the primary forest,concentrations of P fractions in the four stages significantly decreased except for HCl-P,indicating that soil P supplements over the long-term did not return to primary forest levels.The results of related analysis also showed that NaHCO_(3)-P_(i)levels were significantly related to available phosphorus.According to the path analysis coefficient,NaHCO_(3)-P_(i)exhibited the highest effect on available P among eight P fractions;the indirect effects of other P fractions via NaHCO_(3)-P_(i)were larger than those with other P fractions.Overall,this study suggests that soil P bioavailability gradually improved during natural vegetation restoration on clear-cut sites mainly through the increase of NaHCO_(3)-P,where phosphorous is immediately available,and subsequently available phosphorus Na OH-P.

Characteristics of inorganic phosphorus fractions and their correlations with soil properties in three non-acidic soils

Understanding the characteristics and influences of various factors on phosphorus(P)fractions is of significance for promoting the efficiency of soil P.Based on long-term experiments on black soil,fluvo-aquic soil,and loess soil,which belong to Phaeozems,Cambisols,and Anthrosols in the World Reference Base for Soil Resources(WRB),respectively,five fertilization practices were selected and divided into three groups:no P fertilizer(CK/NK),balanced fertilizer(NPK/NPKS),and manure plus mineral fertilizer(NPKM).Soil inorganic P(Pi)fractions and soil properties were analyzed to investigate the characteristics of the Pi fractions and the relationships between Pi fractions and various soil properties.The results showed that the proportion of Ca_(10)-P in the sum of total Pi fractions was the highest in the three soils,accounting for 33.5%in black soil,48.8%in fluvo-aquic soil,and 44.8%in loess soil.Long-term fertilization practices resulted in periodic changes in soil Pi accumulation or depletion.For black soil and fluvo-aquic soil,the Pi accumulation was higher in the late period(10–20 years)of fertilization than in the early period(0–10 years)under NPK/NPKS and NPKM,whereas the opposite result was found in loess soil.The Pi accumulation occurred in all Pi fractions in black soil;mainly in Ca_(8)-P,Fe-P,and Ca_(10)-P in fluvo-aquic soil;and in Ca_(2)-P,Ca_(8)-P,and O-P in loess soil.Under CK/NK,the soil Pi was depleted mainly in the early period in each of the three soils.In addition to the labile Pi(Ca_(2)-P)and moderately labile Pi(Ca_(8)-P,Fe-P,Al-P),the Ca_(10)-P in black soil and fluvo-aquic soil and O-P in loess soil could also be used by crops.Redundancy analysis showed that soil properties explained more than 90%of the variation in the Pi fractions in each soil,and the explanatory percentages of soil organic matter(SOM)were 43.6%in black soil,74.6%in fluvo-aquic,and 38.2%in loess soil.Consequently,decisions regarding the application of P fertilizer should consider the accumulation rate and the variations in Pi fractions driven by soil properties in non-acidic soils.

Interaction of soil microbial communities and phosphorus fractions under long-term fertilization in paddy soil

Understanding the impact of biological activities on the soil phosphorus(P)distribution under long-term fertilizer application can facilitate better soil P fertility management.Therefore,the primary objectives of this study were to investigate the effect of long-term(since 1981)fertilizer application on the soil P fractions and microbial community and to evaluate correlations between the microbial community structure and P distribution.The following treatments were implemented in a long-term field trial:no fertilization(CK),inorganic N and K(NK),inorganic P and K(PK),inorganic N,P and K(NPK)and manure+NPK(MNPK)fertilization.The study showed that the soil pH,soil organic carbon and total and available N and P concentrations were considerably higher in the MNPK treatment than in the CK treatment.The soil microbial biomass C,N and P concentrations were also significantly higher in the MNPK treatment than in the CK treatment.Among fertilization treatments,theβ-1,4-glucosidase,α-1,4-glucosidase,urease,acid phosphatase and phosphodiesterase activities were the highest in the MNPK treatment.Compared to inorganic fertilization,the MNPK treatment increased the labile soil P fractions and decreased the residual soil P concentration.Continuous fertilization significantly affected the soil microbial composition.The total phospholipid fatty acid(PLFA)concentrations in the NK,PK,NPK and MNPK treatments were 23.3,43.1,48.7 and 87.7%higher,respectively,than in the CK treatment.A significant correlation was observed between the microbial community and soil P fractions.Moreover,the aggregated boosted tree(ABT)model showed that among the various soil biochemical properties,the total PLFA concentration was the factor that most influenced the active P pool,accounting for 35.4%of the relative influence of all soil biochemical properties examined.These findings reveal that combined manure and inorganic fertilizer application is a better approach than applying inorganic fertilizer alone for sustaining long-term P fertility by mediating soil biological activity.

The distribution and availability of phosphorus fractions in restored cut slopes soil aggregates:a case study of subalpine road,Southwest China

The distribution and availability of phosphorus(P)fractions in restored cut slope soil aggregates,along altitude gradients,were analyzed.Samples were collected at 3009,3347,3654 and 3980 m of altitude.We examined soil aggregates total phosphorus(TP),available phosphorus(AP)and phosphorus activation coefficient(PAC),and discovered that there was no significant difference in TP levels between all four altitudes samples(p>0.05).However,there was a significant difference in AP at 3009,3347 and 3980 m of altitude(p<0.05).At the altitudes of 3009,3347 and 3654 m,the AP accumulation in small size aggregates was more advantageous.Overall,PAC dropped steadily as soil aggregates sizes increased,as shown:PAC(3654 m)>PAC(3347 m)>PAC(3009 m)>PAC(3980 m).In all particle size soil aggregates,the distribution of the P fractions was as follows:total inorganic phosphorus(TPi)>total organic phosphorus(TPo)>residual phosphorus(R-P),at 3009,3347 and 3654 m,but a different registry was observed at 3980 m of altitude:TPo>TPi>R-P.Through correlation and multiple stepwise regression analysis,it was concluded that active NaHCO_(3)-Pi was the main AP source.It was also suggested that more attention should be given to the ratio of small particle size aggregates to increase soil AP storage.In order to improve the activation capacity and supply of soil P,along with promotion of the healthy development of soil ecosystem on slope land,it was suggest that inorganic P fertilizer and P activator could be added to soil at both low(3009 m)and high altitudes(3980 m).

Effects of Biochar and Wood Vinegar on Labile Phosphorus Pool in Soda Saline-Alkaline Soil

A pot experiment was conducted to research the effect of biochar and wood vinegar on labile phosphorus fractions in saline-alkali soil.There were eight treatments,including CK(0 kg•hm-2 biochar+0 kg•hm-2 wood vinegar),C1(0.6 t•hm-2 biochar),C2(0.6 t•hm-2 wood vinegar),C3(1.2 t•hm-2 wood vinegar),C4(1.8 t•hm-2 wood vinegar),C5(0.6 t•hm-2 biochar+0.6 t•hm-2 wood vinegar),C6(0.6 t•hm-2 biochar+1.2 t•hm-2 wood vinegar),and C7(0.6 t•hm-2 biochar+1.8 t•hm-2 wood vinegar).The results showed that biochar without wood vinegar and the co-application of biochar and wood vinegar significantly increased soil total phosphorus content.Meanwhile,compared with CK,all of treatments increased resin phosphorus and sodium bicarbonate-extracted inorganic phosphorus(NaHCO3-Pi)contents in saline-alkali soil.Especially,the contents of resin phosphorus and NaHCO3-Pi under C5,C6,and C7 treatments were higher than those of C2,C3,and C4 treatments,respectively,indicating that the increases of labile phosphorus contents under the co-application of biochar and wood vinegar were better than those of the alone application of biochar and wood vinegar.Each treatment increased the proportion of labile phosphorus pool in saline-alkali soil and the proportion of labile phosphorus pool increased with the increase of the amount of wood vinegar.In addition,the application of biochar and wood vinegar increased the 100-grain weight of rice,and C6 treatment had the best effect,increasing the 100-grain weight by 134.35%.Therefore,the application of biochar and wood vinegar in saline-alkali soil could improve the soil phosphorus availability,increase the weight of rice grains,thereby realizing the resource utilization of agricultural waste and the sustainable development of agriculture.

Impacts of soil properties on phosphorus adsorption and fractions in purple soils

Information on phosphorus(P) adsorption and its impacts on the redistribution of the P fraction in soil profiles are important for environmental management under intensive agricultural practices.To clarify the dominant factors influencing soil phosphorus adsorption in an Entisol(locally known as purple soil), P adsorption experiments were conducted in Sichuan Basin of southwestern China for cropland and woodland soils with acidic, neutral and calcareous origins throughout their profile. After various doses of P were added during incubation experiments, soil P fractions were also analyzed. The results showed that there were no significant differences in Fe-oxides and P adsorption along the vertical gradients. Agricultural practices and lower p H conditions reduced the P adsorption capacity of purple soils throughout the soil profiles. For acidic and neutral purple soil profiles, the P adsorption capability was mainly influenced by Fe-oxides and soil texture. Ca-bound P and Fe-Al-bound P represented the majority of the total inorganic P of calcareous soils.There was a saturation of adsorption capacity by sesquioxide and a high risk of dissoluble reactive P(NH_4 Cl-P) being released out of the soil profile in acidic and neutral purple soils after the greatest P addition, indicated by the higher proportions of NH_4 Cl-P(over 40%) and decreasing Fe-Al-P fraction.P fractions migrated with greater difficulty in calcareous purple soil profiles as Ca-P fraction peaked over 65% when adding a P dose at or greater than 80 g P kg^(-1), indicating the high potential of P adsorption.The X-Ray Diffraction analysis also verified the formation of brushite. Adaptive management practices should be designed to alleviate P losses for acidic and neutral purple soils.

Dissolved organic carbon,a critical factor to increase the bioavailability of phosphorus during biochar-amended aerobic composting

Considerable research efforts have been devoted to increase phosphorus(P)availability during aerobic composting.However,there is little discussion weather the dissolved organic carbon(DOC)controls the transformation among P-fractions.Thus,we investigated the changes in DOC compositions and P-fractions during biochar-amended composting(wet weight basis,5%and 10%).TP content continuously increased since the'concentration effect'during aerobic composting.NaHCO_(3)-Pi,NaOH-Pi and HCl-Pi were main P-fractions,and biochar can improve P-bioavailability by transforming NaOH-Pi and HCl-Pi into NaHCO_(3)-Pi.Structure equation models(SEMs)indicated that biochar enhanced the P-bioavailability through regulating the decomposition of DOC.Our results at least hint that the activation mechanism on P under the influence of DOC during biochar-amended composting.

Responses of soil phosphorus pools accompanied with carbon composition and microorganism changes to phosphorus-input reduction in paddy soils

In rice-wheat rotation systems, changes in soil phosphorus(P) pools and microorganisms in rice-growing seasons have been studied;however, further investigations are required to test whether these indexes exhibit different responses in wheat-growing seasons. Additionally, such studies need to include potential variations in soil carbon(C) structure and microbial community composition. In this study, a long-term rice-wheat rotation P-input reduction experiment was conducted to observe the variations in soil P pools and C composition in the 7th wheat season and to investigate the responses of soil enzyme activity and microbial communities. Four P fertilization treatments were included in the experiment, i.e., P application for rice season only(PR), for wheat season only(PW), and for both rice and wheat seasons(PR+W) and no P application in either season(Pzero). Compared with PR+W treatment, Pzero treatment significantly decreased(P < 0.05) labile and stable P pools. Different P fertilization regimes altered soil microbial community composition and enzyme activity, whereas C composition did not vary. However, PW treatment resulted in relatively more O-alkyl-C than PR treatment and the highest number of microorganisms. Besides, the higher ratios of fungi/bacteria and Gram-positive bactetia/Gram-negative bactetia were related to labile C pools, particularly O-alkyl-C, as opposed to recalcitrant C. Our results clarified the status of soil P pools, C chemistry, and the response of microorganisms under dry-farming conditions in the P input-reduced rice-wheat rotation system.

Abiotic and biotic drivers of struvite solubilization in contrasting soils

Phosphorus(P) limitation in the coming decades calls for the utilization of alternative fertilizers in agriculture. Struvite is a promising P source, but its potential role as a fertilizer is dependent on different physical, chemical, and biological properties, which are very heterogeneous in soil, complicating the prediction of the best soil conditions for its application. Here, we evaluated the solubility of struvite in soil, its redistribution into P fractions, and its potential abiotic and biotic drivers in 62 globally distributed soils with contrasting properties through an incubation assay. We found that after 40 d, about 35% of struvite P was redistributed into soil fractions more accessible to plants and microbes. Phosphorus redistribution from struvite was driven by a complex suite of soil physical, chemical, and microbial properties as well as environmental factors that varied across soils. Soil texture played a critical role in determining the redistribution of P in struvite-amended soils in soluble(H2O extraction), labile(NaHCO3 extraction), and moderately labile(NaOH extraction) fractions.In addition, the soil solution cation concentration was one of the most important drivers of available struvite-derived P fractions. The great importance of texture and cations in determining struvite-derived P fractions in soil was contrasted with the relatively minor role of pH. At the microbial level, the number of bacterial operational taxonomic units(OTUs) from the unfertilized soils that correlated with struvite-derived P fractions was higher than that of fungi. The number of OTUs that correlated with the struvite-derived soluble P fraction was dominated by fungi, whereas the number of OTUs that correlated with the struvite-derived labile P fraction was dominated by bacteria. Overall, this study provided a predictive framework for the potential use of struvite as a P fertilizer in contrasting soils.

Positive effects of biochar application and Rhizophagus irregularis inoculation on mycorrhizal colonization,rice seedlings and phosphorus cycling in paddy soils

Phosphorus(P)is an essential element for plant growth but is often limiting in ecosystems;therefore,improving the P fertilizer use efficiency is important.Biochar and arbuscular mycorrhizal fungi(AMF)may enhance P cycling in paddy soils that contain high content of total P but low content of available P(AP).In this study,the effects of biochar addition and Rhizophagus irregularis inoculation on the organic and inorganic P contents and phosphatase activities in paddy soils,rice seedling growth,and AMF colonization were investigated.Compared with no biochar addition,biochar addition enhanced the percentage of spore germination at day 7,hyphal length,most probable number,and mycorrhizal colonization rate of R.irregularis by 32%,662%,70%,and 28%on average,respectively.Biochar and R.irregularis altered soil P cycling and availability.Biochar and R.irregularis,either individually or in combination,increased soil AP content by 2%–48%.Rice seedlings treated with biochar and R.irregularis produced greater biomass,improved root morphology,and increased nutrient uptake compared with those of the control without biochar and R.irregularis.The results suggest that combined application of biochar and R.irregularis is beneficial to rice cultivation in paddy soils with high content of total P but low content of AP.

Seven years of biochar amendment has a negligible effect on soil available P and a progressive effect on organic C in paddy soils

Little attention has been paid to how long-term application of crop straw and its biochar affects soil phosphorus(P)transformation and carbon(C)fractions.We conducted a 7-year field experiment including control treatment(chemical fertilizer only,CK),straw return(2.25 t ha^(−1)),and different amounts of biochar addition(11.25 t ha^(−1)(0.5%BC)and 22.5 t ha^(−1)(1.0%BC),to investigate influence of these amendments on soil C structure,P fractions,and their interaction with microorganisms.The 13C nuclear magnetic resonance and soil P sequence fractionation were applied to capture changes of soil C compositions and P pool.Compared to CK,straw and biochar amendments decreased alkyl C/O-alkyl C,which is conducive to increased soil organic C.The 0.5%BC and 1.0%BC treatments enhanced recalcitrant aromatic C by 69.0%and 131%,respectively.Compared to CK(101.2±33.32 mg kg^(−1)),the 0.5%BC and 1.0%BC treatments had a negligible effect on soil available P,while negative effects were observed in straw treatment(59.79±9.023 mg kg^(−1)).Straw and biochar amendments increased primary P and occluded P,whereas had negligible effect on organic P.Redundancy analysis and correlation analysis indi-cated that C compositions and P pool correlated to microbial community composition and enzyme activities,and aromatic C was the most related factor.Moreover,structural equation modeling indicated available P was most related to phosphatase activity and C composition.Our findings reveal the changes of soil P and C response under long-term crop straw and its biochar amendment,and can contribute toward improving understanding of the effect of biochar and straw return in future agriculture management.