Excessive fertilization has led to a high risk of phosphorus (P) leaching and related problems in the North China Plain, where the most typical cropland soil is fluvo-aquic soil. The main factors controlling environmental P behavior and the acting time sequence of these factors in soil after long-term P fertilizer application have not been well recognized. A clear understanding is essential for effective P management.
Materials and methodsEffects of Fe minerals, calcium carbonate, and organic matter (OM) on P immobilization in fluvo-aquic soil were studied systematically through farmland investigation and aging experiments.
Results and discussionPhosphorus associated with Ca was the primary fraction in fluvo-aquic soil. Even though there was no significant correlation between the total contents of P and Ca in soils, formation of P-Ca phases facilitated by Ca2+ in soil solution was a mechanism of P retention when soil received excess P fertilizer. Positive correlations between the contents of P and Fe and total organic carbon (TOC) indicate that Fe minerals and OM have significant effects on P immobilization. Through the aging experiments, P was found to primarily adsorb on goethite and gradually forms Ca-P compounds. Organic fertilizer caused P release and inhibition of P adsorption in the initial stages; however, OM derived from organic fertilizer might facilitate P immobilization in the long term through the formation of a P-Ca-OM complex.
ConclusionsAlthough superfluous application of P fertilizers leads to the gradual formation of Ca-P in fluvo-aquic soils, there is still a risk of P loss because P is not immediately adsorbed by Fe minerals. Moreover, application of organic fertilizers increases the risk of P loss. These results provide an important scientific basis for initiating P management policies for fluvo-aquic soils.
相似文献Variation in soil microbial metabolism remains highly uncertain in predicting soil carbon (C) sequestration, and is particularly and poorly understood in agroecosystem with high soil phosphorus (P) variability.
Materials and methodsThis study quantified metabolic limitation of microbes and their association with carbon use efficiency (CUE) via extracellular enzymatic stoichiometry and biogeochemical equilibrium models in field experiment employing five inorganic P gradients (0, 75, 150, 225, and 300 kg P ha?1) in farmland used to grow peas.
Results and discussionResults showed P fertilization significantly increased soil Olsen-P and NO3?-N contents, and enzyme activities (β-1,4-glucosidase and β-D-cellobiosidase) were significantly affected by P fertilization. It indicated that P fertilization significantly decreased microbial P limitation due to the increase of soil available P. Interestingly, P application also significantly decreased microbial nitrogen (N) limitation, a phenomenon primarily attributable to increasing NO3?-N content via increasing biological N fixation within the pea field. Furthermore, P fertilization increased microbial CUE because the reduction in microbial N and P limitation leads to higher C allocation to microbial growth. Partial least squares path modeling (PLS-PM) further revealed that the reduction of microbial metabolic limitation is conducive to soil C sequestration.
ConclusionsOur study revealed that P application in agroecosystem can alleviate not only microbial P limitation but also N limitation, which further reduces soil C loss via increasing microbial CUE. This study provides important insight into better understanding the mechanisms whereby fertilization mediates soil C cycling driven by microbial metabolism in agricultural ecosystems.
相似文献This study compares the dynamic effects of straw and biochar on soil acidity and phosphorus (P) availability in the rice growth period to reveal how straw and biochar affect the availability of phosphorus in soil and utilization of P for rice crop.
Materials and methodsIn the pot experiment, rice straw, canola stalk, and corresponding biochars were mixed uniformly with the Ultisol. Soil samples were collected at four stages of rice growth to analyze the dynamic changes of soil acidity and P availability. The availability of phosphate in straw/biochar-amended soils were evaluated using a combination of chemical extraction and diffusive gradients in thin films (DGT) technique.
ResultsSoil pH, KCl-P, Olsen-P, DGT-P, and Al-P deceased with the rice growth, while Fe-P increased. Biochar increased soil pH and P availability more than straw returning, especially in the mature stage, while the DGT-P only increased in the tillering stage. The DGT-induced fluxes in sediments (DIFS) model revealed that all treatments increased the capacity of soil solid phase supplementing P to pore water in the filling and mature stages. The content of total P in different rice tissues followed the order of grain?>?straw?>?root, and RB350 treatment had the highest P content in rice tissues. In the mature stage, soil pH had positive correlations with KCl-P and Olsen-P, and soil Fe-P had positive correlations with total P of root and straw.
ConclusionsApplication of biochar made at 550 ℃ resulted in a larger increase in available P in soil, while biochar made at 350 ℃ had more effect on the chemical forms of P. The canola stalk biochar showed a larger influence on the P availability than rice straw biochar. Biochar treatments had a larger effect on inhibiting soil acidification and improving P availability than straw returning directly.
相似文献The purpose of this study was to evaluate the influence of suspended particulates on P loading captured during a single storm event. The Everglades Agricultural Area of Florida comprises 280,000 ha of organic soil farmland artificially drained by ditches, canals, and pumps. Phosphorus (P)-enriched suspended particulates in canals are susceptible to transport and can contribute significantly to the overall P loads in drainage water.
Materials and methodsA settling tank experiment was conducted to capture suspended particulates during tropical storm Isaac in 2012 from three farms approximately 2.4 to 3.6 km2 in size. Farm canal discharge water was collected in a series of two 200-L settling tanks over a 7-day drainage period, during tropical storm Isaac. Water from the settling tanks was siphoned through Imhoff settling cones, where the suspended particulates were allowed to settle and collected for P fractionation analyses, and compared to intact sediment cores collected from the canals.
Results and discussionThe discharged suspended particulates contained higher organic matter content, total P, and labile P fractions compared to the drainage canal sediments. Based on the equilibrium P concentrations, drainage canal sediments behave as a source of P to the water column. A 7-day continuous drainage event exported 4.7 to 11.1 t of suspended solids per farm, corresponding to 32 to 63 kg of particulate P being lost to downstream ecosystems. Drainage associated to this single 7-day storm event exported up to 61 % of the total annual farm P load.
ConclusionsIt is evident from this study that short-term, high-intensity storm events can skew annual P loads due to the export of significantly higher suspended particulate matter from farm canals. Exported particulates rich in P, if captured and replenished back on farmlands, would be a sustainable farming practice that can provide a supplemental source of nutrients.
相似文献The purposes of present study were to display the vertical distribution of soil organic carbon (SOC), nitrogen (N), and phosphorus (P) stoichiometry; identify the biogeographic characteristics of SOC, N, and P stoichiometry along an aridity gradient across the desert ecosystem of Hexi Corridor; and determine how biogeographic distribution patterns of SOC, N, and P stoichiometry are related to vegetation, soil texture, geography, and climate.
Materials and methodsWe investigated the distribution and characteristics of SOC, N, and P stoichiometry based on samples collected from Hexi Corridor during 2011–2012 with total 400 plots of 80 sites. This region presents a precipitation gradient from about 250 mm in the east to less than 50 mm in the west. The measured variables included belowground and aboveground biomass, pH, bulk density, sand, clay, silt, SOC, N, and P contents. ANOVA analysis, reduced major axis, redundancy analysis, Person’s correlation, and regression analysis were used to analysis the variation of SOC, N, and P stoichiometry and related biogeographic factors.
Results and discussionIn present study, SOC, N, and P contents decreased significantly with increasing soil depth. C/N did not change significantly, while C/P and N/P decreased significantly. SOC and N, SOC and P, and N and P were well constrained within 0–100 cm. SOC, N, and P contents in 0–20 cm were higher than them in other studies. Vegetation, soil texture, climate, and geography could explain 91.6% of the total variance of soil stoichiometry. The impact of latitude and longitude on SOC, N, and P stoichiometry was mainly caused by the redistribution of precipitation, while the impact of altitude mainly resulted from the variation of temperature. With increasing aridity, SOC, N, and P contents and C/N/P ratios reduced consistently with inconsistent decrease rates.
ConclusionsOur results suggested that the interaction of vegetation structure, soil condition, and shortage of precipitation should be the main driver for the lower contents and much shallower distributions of SOC, N, and P of Hexi Corridor. The increasing aridity should be the critical factor that is responsible for the decrease of SOC, N, and P contents and C/N/P ratios. This study contributes to the understanding of soil stoichiometry in the desert ecosystem.
相似文献With increasing urban area and population, global cities are playing a more important role in the alteration of the global biogeochemical cycles. The aims of this study are to understand the concentrations and stoichiometric relations of biogenic elements (C, N, and P) in urban soils, further to reveal the effects of C, N, and P accumulation on the urban environment.
Materials and methodsWe collected 317 surface (0–10 cm) soil samples taken from Nanjing, China, a typical city with more than 2000 years of history. These soil samples were located in different urban zones of Nanjing with different land use histories. The soil C, N, and P concentrations were determined. The stoichiometric relations of soil C, N, and P were investigated in urban soils. Meanwhile, some studies on sources of C, N, and P in diverse urban settings from literature were combined to explore the universal rule of C, N, and P cycling and their ecological and environmental effects in urban area.
Results and discussionCompared to rural soils, more C, N, and P are accumulated in the urban soils, which also change their stoichiometric relations. The concentrations of OC, TN, and TP in urban top soils are 17.0 ± 9.69 g kg?1, 1.53 ± 0.92 g kg?1, and 1.31 ± 0.67 g kg?1, respectively. The mean atomic ratio of C:N:P is 37:3:1 in the surface of urban soils that strictly differs from natural soils in China and the whole world. The mean of C:N ratio in urban soils is similar to that of agriculture, grassland, and forest soils. However, the ratios of C:P and N:P in urban soils are much lower than that in agricultural, forest, and grassland soils. This implies that P is extremely enriched in the urban soils. The high C in urban soils are considered coming from natural and anthropogenic sources. The high N and P mainly come from anthropogenic sources.
ConclusionsThe well-constrained C:N:P ratio in rural soils does not apply for urban soils. The abnormal C:N:P ratio of urban soils is the result of unbalanced accumulation of C, N, and P from human activities. Urban soils are already an important storage of carbon. High N and P in urban soils may bring threat of surface water eutrophication and ground water contamination. These effects are expected to increase with the city development time.
相似文献The construction of riparian buffer strips has become increasingly important due to the effective phosphorus (P) retention of the strips, thus preventing eutrophication in freshwater ecosystems. The key mechanism is P sorption in soils. To provide some suggestions for increasing the sorption ability of P, the relationships between P sorption behavior and both land use patterns and distance from the shoreline were determined.
Materials and methodsIn April, July, and October 2013, field investigations were carried out along the shoreline of Lake Chaohu. Eleven sections, including 36 sampling sites at different distances from the shoreline, were chosen, and these sections contained different types of riparian buffer strips, such as grassland, farmland, forest, wetland, and forest/grassland. The P species, sorption parameters, and dominant vegetation species were analyzed.
Results and discussionThe total P (TP) and P sorption maximum (Qmax) showed no recognizable seasonal variation and were closely correlated with the distance from the shoreline. The further the distance from the shoreline, the higher the TP and Qmax values, suggesting that soil traits could determine the P sorption extent. However, the Olsen-P content and equilibrium P concentration (EPC0) fluctuated greatly, with the peak occurring in spring and the minimum occurring in summer in the majority of the sampling sites. In addition, positive relationships existed between the TP content and the Qmax value as well as the Olsen-P content and the EPC0 value. Canonical correlation analysis (CCA) further showed that the Olsen-P content and EPC0 values were closely related to the dominant vegetation species, indicating that land use patterns played a decisive role in regulating the P sorption strength and the level of available P.
ConclusionsTo effectively adsorb P (increase Qmax) and prevent P leaching (reduce the EPC0), we recommend changing the land use patterns (more constructed wetlands and forests with grass) in riparian buffers.
相似文献Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (Pi) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which Pi fraction exerts the greatest influence on P desorption capacity.
Materials and methodsFive soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with Pi fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.
Results and discussionThe content and proportions of dicalcium phosphate fraction (Ca2-P), octacalcium phosphate fraction (Ca8-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in Pi increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca8-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg?1 desorbed P per 1 mg kg?1 increase of initial Olsen-P. Ca2-P exerted the conclusive effect on P desorption in the first four extractions, but Ca8-P played a more important role in the 16 extractions.
ConclusionsCa8-P was the greatest potential pool for P desorption after Ca2-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.
相似文献The carbon (C), nitrogen (N), and phosphorus (P) concentrations of leaves can reflect soil nutrient supply conditions and changes in soil. An understanding of species adaptability and nutrient use efficiency in extreme ecosystems can help land managers choose effective methods to improve management and community structure of introduced plants which may induce biological invasion and limit the regeneration of native species.
Materials and methodsWe selected the Leucaena leucocephala forests in three ages (9, 15, and 26 years old) in the Jiangjiagou Gully to study the relationships between (i) soil factors and forest age and (ii) leaf nutrient concentrations. Soil factors and leaf nutrients were measured in nine sampling quadrats of 10?×?10 m of each plot. We used ANOVA to examine differences in leaf variables and soil factors at different ages of L. leucocephala forest. Pearson’s correlation analysis and linear regression analysis were conducted to identify the relationships between soil factors and leaf variables. Then, we used analysis of covariance to examine combined effects of forest ages and soil factors on leaf variables.
Results and discussionLeaf N was significantly correlated with available P, while leaf P was significantly correlated with both available P and available N. Leaf N and P had no significant relationship with soil total N and P. Leaf C:N:P stoichiometries had a higher significant correlation with total N, available N, and soil water content.
ConclusionsOur findings illustrate that available N and available P are the main limitations for L. leucocephala, though available P imposed a stronger limitation than available N. Moreover, soil water content played an indispensable role on nutrient accumulation and the soil ecological environment. Our results provide useful information to improve L. leucocephala community structure and reduce soil degradation in a dry-hot valley.
相似文献Phosphorus influence on arsenic bioavailability in soils and its toxicity to plants is widely recognized. This work compares competitive influence of P on As bioavailability in dry and flooded soils.
Materials and methodsPot experiments were carried out in dry and flooded soils, respectively. Bioavailable As in soils was measured using diffusive gradients in thin films (DGT), soil solution concentration, and three single chemical extraction methods.
Results and discussionP concentration at 50 mg/kg promoted wheat growth in dry soil. At concentrations above 50 mg/kg, P competition inhibited wheat growth and enhanced As toxicity. In flooded soil, the rice height and biomass decreased with the increase of P addition. P concentrations above 800 mg/kg were lethal to the rice. The content of As absorbed by wheat and rice roots as well as shoots increased with the increase of P concentration. The bioavailability of As in wheat- and rice-grown soils, determined by all methods, also increased with the increase of P concentration. The correlation analysis between the bioavailable As measured by the all three methods and the content of As in plants showed a significant positive correlation. The Pearson correlation coefficient for the DGT method was higher comparing to all other methods. DGT-induced fluxes in soils (DIFS) modeling further showed sharp decreases of Tc (the characteristic time to reach equilibrium between available solid As pool and soil solution As from DGT perturbation) and increases of desorption and adsorption rate constants (k1 and k?1) of As in P-amended soils, reflecting that the kinetic release of As from available solid As pools became much easy from P competition.
ConclusionsP competition in both dry and flooded soils could significantly increase bioavailability of As and further increase its toxicity. Competition effect was more pronounced in flooded soil. DGT is a more accurate method for As bioavailability evaluation in both dry and flooded soils.
相似文献Phosphorus (P) mobility in soil is controlled by its forms and soil sorption capacity. The P forms and soil sorption capacity are both affected by nitrogen (N) and carbon (C) addition. This paper aimed to (i) analyze effects of N and straw application on the different forms and content of P in the soil and its leachates in greenhouse soil, and (ii) explain variations in soil P transformation and transport in terms of contributing soil factors.
Material and methodsIn this study, the impacts of N and straw application on the transformation and transport of soil P were investigated after 17 years in a greenhouse. Four fertilization regimes were implemented: farmer standard fertilization practice (CK), straw incorporation treatment (SC), optimized N fertilizer application (ON), and combined straw and optimized N fertilizer application (SN). P forms and its contents were determined in the selected leached water and its related soil samples.
Results and discussionCompared with CK, ON treatment significantly (p < 0.05) decreased total phosphorus (Pt) and the proportion of organic phosphorus (Po) in soil, while straw amendment did not affect soil Pt content. SC, ON, and SN all decreased soil available phosphorus (Pa) but enhanced P transformation, as evidenced by the increase in the ratio of Pa to Pt and microbial phosphorus (MBP) and alkaline phosphatases (ALP) in soil. After SN implementation, soil P adsorption capacity increased significantly and was associated with higher soil organic matter (SOM) and CaCO3. ON showed lower Pt in the leachate than CK, but SC did not lead to significantly different. Under the SN regime, Pt loss by leaching decreased by 29.4% compared with CK and significantly reduced proportion of total dissolve P (DPt) in leachate.
ConclusionsOur study highlights that straw and optimized N fertilizer in SN treatment not only generates lower P loss by leaching but also promotes the transformation of soil P, which were attributed to higher soil Pa in greenhouse soil. This finding further indicates that P transformation and transport in the different fertilizer regimes was primarily linked to pH and SOM in greenhouse soil.
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