Phosphorus status of some saline and non-saline hydromorphic soils of the Niger Delta of Nigeria

Summary The phosphorus status of some mangrove and fresh-water hydromorphic soils of the Nigerian Niger Delta was evaluated by determining the relative abundance of various P forms and the P-sorption capacity indices. Total P was high in all soils ranging from 352 to 2055 mg/kg, with a mean of 1011 mg/kg. The saline mangrove-swamp soils had generally higher values than the fresh-water soils. Organic P formed about 34% of total P. The relative abundance of the inorganic P forms was in decreasing order, active P, occluded P and residual P. The relative distribution of active P followed the decreasing order, Fe–P, Al–P and Ca–P.The adsorption capacity was generally low in all soils. The amount of P sorbed from the addition of 150 mg/100g of soil ranged from zero to 13 mg/100g, giving an average of about 7% of added P sorbed.The abundance of active P and low content of occluded P were attributed to the poorly drained and unweathered nature of the soils. The low P adsorption suggests little capacity of the soils to fix P. The relatively high content of active P and the low P sorption capacity generally indicate high availability of P to plant in these soils.     

Legacy phosphorus in subtropical wetland soils: Influence of dairy, improved and unimproved pasture land use

Wetlands provide various ecosystem services. One of these services includes nutrient storage in soils. Soils retain and release nutrients such as phosphorus (P). This dynamic can be controlled by soil characteristics, overlying water quality, environmental conditions and historical nutrient loading. Historical nutrient loading contributes to a legacy of P stored in soils and this may influence present day P dynamics between soil and water. We quantified P characteristics of wetland soils and determined the availability and capacity of soils to retain additional P loadings. We sampled surface (0-10) and subsurface (10-30) wetland soils within dairy, improved and unimproved pastures. Surface soils had much greater concentrations of organic and inorganic P. Wetland soils in dairy had greatest concentrations of Ca and Mg, probably due to inputs of inorganic fertilizer. They also had much greater total P, inorganic P, and P sorption capacity; however, these soils were P saturated and had little capacity to retain additional P loading. Improved and unimproved pasture wetland soils had greatest amounts of organic P (>84%) and a capacity to store additional P loadings. Using multivariate statistics, we determined that rather than being different based on land use, wetland soils in improved and unimproved pasture were dissimilar based upon organic matter, organic P fractions, residual P, and soil metal (Fe and Al) content. The legacy of stored P in soils, particularly wetland soils from dairies, combined with best management practices (BMPs) to reduce nutrient loading to these systems, could contribute to a short-term release of soil-stored P to overlying wetland water.     

中亚热带不同母质发育森林土壤磷组分特征及其影响因素

本研究以福建三明砂岩和花岗岩发育的米槠林土壤和杉木林土壤为对象,分析土壤磷组分、铁铝氧化物、微生物生物量以及磷酸酶活性等指标,研究母质和森林类型对土壤磷组分的影响程度和机制.结果表明:母质和森林类型显著影响土壤不同磷组分含量.总体上,砂岩发育土壤全磷含量、活性无机/有机磷、中等活性无机/有机磷以及惰性磷含量均显著高于花...     

Influence of poultry manure on phosphorus availability and the standard phosphate requirement of crop estimated from quantity-intensity relationships in different soils

Twelve samples comprising of non-calcareous, calcareous and acidic soils were used to study P availability parameters and standard phosphate requirement (SPR) in the presence and absence of poultry manure (PM). Adsorption of P and phosphate potential decreased while Olsen extractable P increased by PM addition, the extent varying with the type of soil. The calculated SPR to attain soil solution concentration of 0.2 microg P ml(-1) was invariably higher in fine textured soils. Acid and calcareous soils registered higher SPR compared to non-calcareous soils. PM addition lowered the SPR in all the soils. The observed P supplementation through PM ranged from 11.6% to 100% signifying no fertilizer P need in the latter. Calibration curves were drawn for calculating the SPR for a given soil solution P concentration without and with the addition of PM.     

Apple replant disease: the influence of soil phosphorus and other factors on the growth responses of apple seedlings to soil fumigation with chloropicrin

The effects of fumigating field soils before replanting apple are frequently predicted from bioassays where apple seedlings are grown in pots, some containing untreated soil and the others containing chloropicrin-fumigated soil. The results from 418 such bioassays made during eight years are discussed with reference to the effects of certain physical and chemical soil features. Soil phosphorus (P) content and pH had large effects on growth in fumigated (but not untreated) soils; they therefore had large effects on the growth response to soil fumigation. There were no indications of important effects due to soil content of potassium or magnesium or to soil texture. In fumigated soils, the height of seedlings was generally greater, the greater the soil P content, but in untreated soils it was mostly independent of P (range 1 – 156 mg P litre^-1soil). The differing effects of native P on growth in untreated or fumigated soils were attributed respectively to the presence and absence of vesicular-arbuscular mycorrhizas: their absence in fumigated soils was considered (for apple) to be an artefact in the seedling bioassay. The results for untreated soils indicated that the apple mycorrhizal system was very efficient in retrieving P when there was little available. Growth responses to soil fumigation were usually greater in acidic than in alkaline soils for any given level of P. When soils were P-amended before testing, the effects of native P and pH virtually disappeared and the proportion of orchard soils with economically significant growth responses increased from 39% to 67%.     

The productivity of pine plantations in relation to previous land use

Summary The improved growth of pine plantations on pasture soils compared with that on soils which previously supported native eucalypt forest is primarily explained in terms of soil phosphorus. Pasture development has resulted in a decrease in the P adsorption maximum of about 300 g g^–1 soil, a figure which agrees with the increase in total P due to the application of superphosphate. P adsorption isotherms were used to calculate additions of P to give comparable levels of soil solution P in eucalypt and pasture soils. The growth of pine seedlings in soils thus amended showed a strong N×P interaction. When P was non-limiting, addition of N raised productivity of the eucalypt soil above that of the pasture soil. It is postulated that the different nature of the N×P interaction in eucalypt and pasture soils results from differences in the nitrogen cycle in the two soils.     

Distribution ofUrtica dioica L. in relation to edaphic factors

Summary Soils withU. dioica (a soils) were compared with soils 1–6 m away (b soils) with seemingly identical conditions except for absence of Urtica. The a soils had a higher EDTA–Cu concentration than b soils. The values for mineralised N, anion exchanged P, CEC, conductivity, Zn, Ca, Mg, K, organic matter and pH were alike in a- and b soils. Inorganic P was a limiting factor for Urtica when the P level, in general, was low (in this material not roadside soils). In the roadside soils the level of inorganic P was, in general, high and the content in a- and b soils was alike.     

Changes in heated and autoclaved forest soils of S.E. Australia. II. Phosphorus and phosphatase activity

The effect of soil heat and autoclaving on labile inorganic P (Bray I), microbial P (P-flush) and on phosphatase activity was studied by heating five forest soils in the laboratory, which simulated the effects of heat during bushfires. Top soil was heated to 60 °C, 120 °C and 250 °C or autoclaved for 30 minutes. Soils were analysed immediately after heating and during seven months of incubation to assess immediate and longer-term effects of heating.Labile inorganic P increased immediately after heating and autoclaving soils, with the highest amount recorded for the 250 °C treatment. Phosphorus associated with microbial biomass decreased with heat, and none or small amounts were detected in soils heated to 250 °C and autoclaved, because high temperatures killed the microbial population. Most of the P released from microbes acted as a source of labile inorganic P in soils low in inorganic P, and some of the released P was fixed by the soil. In one soil high in inorganic labile P and with undetectable amounts of microbial-P, the increase in Bray P on heating could only be assigned to solubilisation of other sources of total P Because high temperatures denature enzymatic proteins, phosphatase activity diminished with the increase in temperature, and no activity was detected in 250 °C and autoclaved soils.Phosphorus released by heating decreased during incubation in three of the five soils studied, approaching values observed in unheated soils. Simultaneously, an increase in microbial P was observed in these heated soils, indicating that the partial recovery of microbial biomass acted as a sink for the decrease in Bray-P measured. Phosphatase activity recovered only partially during incubation of heated soils.     

Sorption and bioavailability of phosphorus during the drainage period of flooded-drained soils

Summary Changes in P sorption and bioavailability were studied with 4 soils previously flooded and drained as occurs in rice-based cropping systems. Phosphorus sorption was measured at 15 and 119 days after drainage and the bioavailability of added and native soil-P was determined at 9, 16, 30, 45, 70 and 135 days in both flooded-drained and unflooded soils. The P sorptivity and bonding energy of sorption increased under flooded-drained soil conditions. At 119 days after drainage the P sorptivity and bonding energy of sorption decreased as compared to 15 days after drainage. The P sorptivity of the flooded-drained soils, however, did not reach the same levels as existed in the soils prior to flooding. The bioavailability of P during the drainage period remained low and did not measurably change up to 70 days after drainage. At 135 days after drainage the bioavailability of P increased significantly, but did not reach the level found in the corresponding unflooded soils.     

Effect of moisture and oxidation status of alkaline rice soils on the adsorption of soil phosphorus by an anion resin

Summary Considerable effort was devoted to experimentally explaining the greater amount of anion resin-adsorbable P (ARAP) in water-saturated alkaline soils relative to moist soils with the purpose of explaining the phenomenon of increased P availability in flooded rice soils. ARAP increased when waterlogged conditions were imposed on soils, but the increase in ARAP occurred before reducing conditions were obtained. Reducing conditions did not increase ARAP. The increase in ARAP in the water-saturated alkaline soils was attributed to the enhanced P diffusion resulting from a decrease in tortuosity, thus indicating that increased P availability upon flooding could be due to increased P diffusion.Paper number 4533 of the Journal Series of the North Carolina Agricultural Experiment Station.Paper number 4533 of the Journal Series of the North Carolina Agricultural Experiment Station.     

Phosphorus status of some ethiopian soils

The capacity to sorb P varied among some Ethiopian soils. Volcanic ash soils sorbed the maximum P while Fluvisols and Regosols sorbed the least. Sorption of P was significantly correlated with exchangeable and extractable forms of Fe and Al as well as pH and organic matter. But is was not related to the clay content of the soils. The role of Al was more important than that of Fe even though more dithionite and oxalate extractable Fe than Al was found in all soils.     

磷高效利用野生大麦基因型筛选及其根际土壤无机磷组分特征

通过土培盆栽试验,研究了16份野生大麦种质资源在相同供磷水平下磷素吸收利用的基因型差异,探讨磷高效野生大麦根际土壤无机磷组分特征.结果表明：拔节期和扬花期磷素干物质生产效率（CV=11.6%、12.4%）、成熟期磷素籽粒生产效率（CV=13.7%）基因型间差异较大.不同生育时期磷高效基因型IS-22-30和IS-22-25生物量、磷积累量和磷素干物质生产效率均显著高于低效基因型IS-07-07,且高效基因型的籽粒产量分别是低效基因型的3.10和3.20倍.不施磷、施磷30 mg·kg^-1条件下,不同磷素利用效率野生大麦根际土壤有效磷和水溶性磷含量均显著低于非根际土壤,且高效基因型较低效基因型根际土壤水溶性磷亏缺量更大.根际与非根际土壤无机磷组分含量为Ca₁₀-P＞O-P＞Fe-P＞Al-P＞Ca₂-P＞Ca₈-P.在拔节期和扬花期,施磷30 mg·kg^-1条件下,磷高效基因型根际土壤Ca₈-P含量显著高于低效基因型,而Ca₂-P含量显著低于低效基因型;不施磷条件下,高效基因型根际土壤Ca₂-P和Ca₈-P含量均显著高于低效基因型,且根际土壤Ca₁₀-P均减少.施磷30 mg·kg^-1条件下,根际土壤Fe-P和O-P含量均表现为高效基因型显著高于低效基因型,Al-P含量则呈现相反的趋势;不施磷条件下,高效基因型根际土壤Al-P、Fe-P和O-P含量均显著低于低效基因型.低磷胁迫下,高效基因型活化吸收Ca₂-P、Al-P的能力强于低效基因型.     

Granite Rock Outcrops: An Extreme Environment for Soil Nematodes?

We studied soil nematode communities from the surface of granite flatrock outcrops in the eastern Piedmont region of the United States. The thin soils that develop here experience high light intensity and extreme fluctuations in temperature and moisture and host unique plant communities. We collected soils from outcrop microsites in Virginia (VA) and North Carolina (NC) in various stages of succession (Primitive, Minimal, and Mature) and compared soil properties and nematode communities to those of adjacent forest soils. Nematodes were present in most outcrop soils, with densities comparable to forest soils (P > 0.05). Nematode communities in Mature and Minimal soils had lower species richness than forest soils (P < 0.05) and contained more bacterial-feeders and fewer fungal-feeders (P < 0.05). Primitive soils contained either no nematodes (NC) or only a single species (Mesodorylaimus sp., VA). Nematode communities were similar between Mature and Minimal soils, according to trophic group representation, MI, PPI, EI, SI, and CI (P > 0.05). Forest soils had a higher PPI value (P < 0.05), but otherwise community indices were similar to outcrop soils (P > 0.05). Outcrop nematode communities failed to group together in a Bray-Curtis cluster analysis, indicating higher variability in community structure than the Forest soils, which did cluster together. A high proportion of the nematodes were extracted from outcrop soils in coiled form (33-89%), indicating that they used anhydrobiosis to persist in this unique environment.     

Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes—flooded, moist, and dry—for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron‐bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence.     

Biological immobilization of fertilizer phosphorus

Summary Comparable uncultivated and cultivated Coastal Plain soils of New Jersey were analyzed for total inorganic and total organic soil P. Inorganic P was found to be greatly increased as a result of intensive fertilization. Organic P increased in most soil series examined, and up to 30 per cent of gains in total P in cultivated soils could be accounted for as increases in soil organic P. C: organic-P ratios in uncultivated soils were much higher than those usually encountered in soils containing humified organic matter. Cultivation has led to a considerable lowering of these ratios, as a result of decreases in organic-C contents and increases in organic-P contents.Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers University. The author is now with the Agricultural State University, Wageningen, Netherlands     

The rise and fall of arbuscular mycorrhizal fungal diversity during ecosystem retrogression

Ecosystem retrogression following long‐term pedogenesis is attributed to phosphorus (P) limitation of primary productivity. Arbuscular mycorrhizal fungi (AMF) enhance P acquisition for most terrestrial plants, but it has been suggested that this strategy becomes less effective in strongly weathered soils with extremely low P availability. Using next generation sequencing of the large subunit ribosomal RNA gene in roots and soil, we compared the composition and diversity of AMF communities in three contrasting stages of a retrogressive >2‐million‐year dune chronosequence in a global biodiversity hotspot. This chronosequence shows a ~60‐fold decline in total soil P concentration, with the oldest stage representing some of the most severely P‐impoverished soils found in any terrestrial ecosystem. The richness of AMF operational taxonomic units was low on young (1000's of years), moderately P‐rich soils, greatest on relatively old (~120 000 years) low‐P soils, and low again on the oldest (>2 000 000 years) soils that were lowest in P availability. A similar decline in AMF phylogenetic diversity on the oldest soils occurred, despite invariant host plant diversity and only small declines in host cover along the chronosequence. Differences in AMF community composition were greatest between the youngest and the two oldest soils, and this was best explained by differences in soil P concentrations. Our results point to a threshold in soil P availability during ecosystem regression below which AMF diversity declines, suggesting environmental filtering of AMF insufficiently adapted to extremely low P availability.     

Increasing the organic carbon stocks in mineral soils sequesters large amounts of phosphorus

Despite the fact that phosphorus (P) is critical for plant biomass production in many ecosystems, the implications of soil organic carbon (OC) sequestration for the P cycle have hardly been discussed yet. Thus, the aims of this study are, first, to synthesize results about the relationship between C and P in soil organic matter (SOM) and organic matter inputs to soils, second, to review processes that affect the C:P ratio of SOM, and third, to discuss implications of OC storage in terrestrial ecosystems for P sequestration. The study shows that the storage of OC in mineral soils leads to the sequestration of large amounts of organic phosphorus (OP) since SOM in mineral soils is very rich in P. The reasons for the strong enrichment of OP with respect to OC in soils are the mineralization of OC and the formation of microbial necromass that is P‐rich as well as the strong sorption of OP to mineral surfaces that prevents OP mineralization. In particular, the formation of mineral‐associated SOM that is favorable for storing OC in soil over decadal to centennial timescales sequesters large amounts of OP. Storage of 1,000 kg C in the clay size fraction in the topsoils of croplands sequesters 13.1 kg P. In contrast, the OC:OP ratios of wood and of peatlands are much larger than the ones in cropland soils. Thus, storage of C in wood in peatlands sequesters much less P than the storage of OC in mineral soils. In order to increase the C stocks in terrestrial ecosystems and to lock up as little P as possible, it would be more reasonable to protect and restore peatlands and to produce and preserve wood than to store OC in mineral soils.     

Effects of microorganism on carbon,nitrogen and phosphorus of Dodonaea viscosa and the soils from different elevations in Yuanmou,Yunnan, China

Aims Understanding the effects of soil microorganism at different elevations on plant C:N:P stoichiometry can help us to understand the plant-soil interactions in the context of climate change. Our aim was to quantify the independent and interactive effects of soil microbial communities and temperatures on the C, N, and P in the leaves of Dodonaea viscosa—a global widespread species. Methods Rhizosphere soils of D. viscosa were collected from two elevation zones in Yuanmou County, Yunnan Province. A 2 × 3 factorial experiment with six replications was conducted using climate chambers. The leaf C, N and P contents and the soil properties were measured after three months of the treatments. Important findings Compared with the autoclaved treatment, inoculated rhizosphere soils from both high and low elevations had higher nutrient absorption, especially P uptake. Temperature produced no significant effect on leaf C:N:P stoichiometry, but the interactive effect of temperature and microbial treatment appeared significant. For inoculated rhizosphere soils from high elevation, temperature had no significant effect on leaf C:N:P stoichiometry. For inoculated rhizosphere soils from low elevation, leaf N and P contents under low temperature were significantly lower than those with warmer soils. The promoting effect of soil microorganisms on nutrient uptake may be due to the direct effect of beneficial microorganisms (e.g., mycorrhizal fungi), but not through the alteration of nutrient cycling process. Because D. viscosa in the inoculated rhizosphere soils absorbed more N and P from the soil than those in autoclaved soil, the available N and P in inoculated rhizosphere soils were lower than those in autoclaved soils. As predicted future temperature will be lower in the studied region, the growth of D. viscosa may be negatively affected through plant-microbe feedbacks.     

On the tropical soils; The influence of organic matter (OM) on phosphate bioavailability

Application of organic manure (OM) and crop residues in agricultural soils can potentially influence positively or negatively the availability of soil phosphorus (P) through soil mineralization, sorption, or desorption of soil-bound P. Traditionally, the addition of OM can reduce the capacity of the soil colloids to adsorb P, thus increasing the release of P in soil solution, but also added OM can increase the adsorption site and increase the fixation or sorption of P to soil colloids, thus reducing the availability of P in soil solution and loss to the environment. The highly weathered tropical soils (HWTS) are susceptible to P insufficiency because HWTS have high P adsorption and fixation; this is mainly due to high concentration of P adsorbent. The main P adsorbents in HWTS include Al, Fe, Ca, and clay minerals, which are principally the same binding or adsorbent for OM compounds, but in excess, are toxic (Al and Fe) to crops. Thus, the presence of OM in HWTS can compromise the adsorption and availability of P in agricultural soils following phosphatic fertilizer applications. In this study, the influence of OM on P adsorption and availability was characterized to have a clear understanding of how OM influences P availability in agricultural soils, especially in highly weathered tropical soil. It is clearly outlined that the application of OM and crop residues can positively or negatively influence the availability of P in agricultural soils for plant uptake and dictate the P that is available for loss to the environment. Thus, the addition of organic matter as a strategy to increase P bioavailability for plant uptake must be treated with care because their contribution is not strait forward to be positive in many agricultural soils.     

A new method for estimating gross phosphorus mineralization and immobilization rates in soils

Phosphorus availability in soils is controlled by both the sizes of P pools and the transformation rates among these pools. Rates of gross P mineralization and immobilization are poorly known due to the limitations of available analytical techniques. We developed a new method to estimate P transformation rates in three forest soils and one grassland soil representing an Alfisol, an Ultisol, and Andisol, and a Mollisol. Three treatments were applied to each soil in order to separate the processes of mineral P solubilization, organic P mineralization, and solution P immobilization. One set of soils was retained as control, a second set was irradiated with -rays to stop microbial immobilization, and a third was irradiated and then autoclaved, also stop phosphatase activity. All three sets of samples were then incubated with anion exchange resin bags under aerobic conditions. Differences in resin P among the three treatments were used to estimate gross P mineralization and immobilization rates. Autoclaving did not affect resin-extractable P in any of the soils. Radiation did not alter resin-extractable P in the forest soils but increased resin-extractable P in the grassland soil. This increase was corrected in the calculation of potential P transformation rates. Effects of radiation on phosphatase activity varied with soils but was within 30% of the original values. Rates of P gross mineralization and immobilization ranged from 0.6–3.8 and 0–4.3 mg kg-soil^-1 d^-1, respectively, for the four soils. The net rates of solubilization of mineral P in the grassland soil were 7–10 times higher than the rates in forest soils. Mineralization of organic P contributed from 20–60% of total available P in the acid forest soils compared with 6% in the grassland soil, suggesting that the P mineralization processes are more important in controlling P availability in these forest ecosystems. This new method does not require an assumption of equilibrium among P pools, and is safer and simpler in operation than isotopic techniques.