The phosphorus concentration of common rocks—a potential driver of ecosystem P status

Background

Soil phosphorus (P) availability can be an important regulator of ecosystem processes. Changes in P availability over time have long been studied, but the P concentration of soil parent materials—which determines ecosystem P concentration at the onset of soil formation—have never been systematically explored. Here we ask two questions: 1) how does P concentration vary among soil parent materials? and 2) under what range of conditions do those differences influence soil P concentration?

Methods

We used the Earthchem webportal to compile the P concentration of 263,539 rocks. We then gathered data from 62 sites (MAT ranging from 200–5,000 mm?yr^-1 and soil age from 0.3–4,100 ky) and assessed the correlation between rock and soil P concentration.

Results

We found a 30 fold difference in median P concentration among rock types, ranging from 120 ppm (several ultramafic rocks) to >3,000 ppm (several alkali basalts). Median P was significantly lower in common silica-rich rocks (e.g. granite - 436 ppm) and higher in common iron-rich rocks (e.g. andesite - 1,000 ppm). In sedimentary rocks, which make up 70 % of the ice-free land surface, median P was highest in mudstone (1,135 ppm) and decreased with increasing grainsize (siltstone-698 ppm, sandstone-500 ppm). Where soil P and parent material P were measured in the same site, parent material P explained 42 % of the variance in total soil P (n?=?62), and explanatory power was higher for sites with similar climate.

Conclusion

The variation in P concentration among common rock types is on a comparable scale to the changes in total P, and several P pools, over long-term soil development. Quantifying these differences may be an important step towards characterizing regional and global variation in soil and ecosystem P status.     

Grassland root demography responses to multiple climate change drivers depend on root morphology

Aims

We examine how root system demography and morphology are affected by air warming and multiple, simultaneous climate change drivers.

Methods

Using minirhizotrons, we studied root growth, morphology, median longevity, risk of mortality and standing root pool in the upper soil horizon of a temperate grassland ecosystem for 3 years. Grassland monoliths were subjected to four climate treatments in a replicated additive design: control (C); elevated temperature (T); combined T and summer precipitation reduction (TD); combined TD and elevated atmospheric CO₂ (TDCO₂).

Results

Air warming (C vs T) and the combined climate change treatment (C vs TDCO₂) had a positive effect on root growth rate and standing root pool. However, root responses to climate treatment varied depending on diameter size class. For fine roots (≤ 0.1 mm), new root length and mortality increased under warming but decreased in response to elevated CO₂ (TD vs TDCO₂); for coarse roots (> 0.2 mm), length and mortality increased under both elevated CO₂ and combined climate change drivers.

Conclusions

Our data suggest that the standing roots pool in our grassland system may increase under future climatic conditions. Contrasted behaviour of fine and coarse roots may correspond to differential root activity of these extreme diameter classes in future climate.     

Pathways of soil genesis in the Coast Range of Oregon, USA

Background and Aims

Soil chronosequences on marine terraces along the Pacific Coast of California and Oregon show evidence of podzolization, though soils ultimately evolve to Ultisols. It is not clear if this pathway of soil evolution can be extended to the humid, inland Oregon Coast Range.

Methods

We analyzed soil properties for a fluvial terrace chronosequence sampled along the Siuslaw River (Oregon, USA) about 50 km from the Pacific coast. The seven terraces ranged in age from <3.5 ky to nearly 1,000 ky.

Results

There was no evidence of early podsolization. Instead, evidence was found that andisolization starts early and occurs even in older soils when pedogenic iron accumulation and clay synthesis and illuviation dominate. Soils develop the morphology characteristic of Ultisols sometime between 20 and 70 ky, but high levels of oxalate extractable iron and aluminum satisfy criteria of an andic subgroup. Alfisols are not formed as an intermediary stage.

Conclusions

The lack of Spodosols inland is due to the inland shift from udic to ustic or xeric moisture regime, which favors summer drying and ripening of short-range order minerals rather than deep leaching or translocation. Other factors are higher pH, different organic chemistry and faster calcium cycling under the Douglas fir inland when compared to the Sitka spruce of the coastal terraces.     

Hierarchical responses of plant stoichiometry to nitrogen deposition and mowing in a temperate steppe

Background and aims

Stoichiometric relations drive powerful constraints on many ecosystem processes. However, our understanding of the hierarchical responses of plant C:N:P stoichiometry at different levels of biological organization to global change factors remains limited.

Methods

we examined the plant C:N:P stoichiometric responses to N deposition and mowing (hay making) at both species- and community-level by carrying out a 4-year field experiment in the temperate steppe of northern China.

Results

Our results showed that N addition and mowing resulted in higher plant N concentrations, lower C:N, and higher N:P at both species- and community-level. Mowing had a limited negative influence on the effects of N addition. We observed divergent responses of both plant P concentrations and C:P to N addition at species-level and community-level: N addition led to higher plant P and lower C:P at species-level, but this effect was not observed at the community-level.

Conclusions

Our results indicate that stoichiometric responses at community-level to N addition and mowing diverge from more traditionally examined species-specific responses. Our results suggest that the hierarchical responses of plant stoichiometry to anthropogenic disturbance deserves more attention when we model the interactions of terrestrial ecosystem C, N, and P cycling under scenarios of increasing N availability concomitantly occurring with active land management.     

Soil drainage and phosphorus depletion contribute to retrogressive succession along a New Zealand chronosequence

Background and aims

Models of retrogressive succession have emphasised the role of phosphorus (P) depletion in driving biomass loss on surfaces of increasing geologic age, but the influence of impeded drainage on old surfaces has received much less attention. We tested whether poor drainage contributed to changes in ecosystem properties along a 291,000-year chronosequence in New Zealand (the Waitutu chronosequence).

Methods

Soil and ecosystem properties were measured at 24 evenly distributed points within each of eight 1.5 ha plots located on young, intermediate and old surfaces. Regression analyses tested whether drainage, in addition to P, affected ecosystem functioning. A complementary fertilization experiment tested whether P was indeed limiting on the most nutrient-depleted sites.

Results

Most phosphorus depletion occurred in the early stages of pedogenesis (within 24,000 years), and the older surfaces were similar in soil-P contents, whereas drainage was initially good but became increasingly impeded with surface age. In the fertilizer experiment, species showed positive responses to both nitrogen (N) and P addition on the oldest surfaces, supporting Walker and Syer’s model. However, water table depth was also found to be strongly correlated with plant species composition, forest basal area, light transmission, and litter decomposition when comparisons were made across sites, emphasising that it too has strong influences on ecosystem processes.

Conclusions

Poor drainage influences the process of retrogressive succession along the Waitutu chronosequence. We discuss the implications of our work with regard to other chronosequences, suggesting that topography is likely to have strong influences on retrogressive processes.     

The three dimensional analysis of the Sforzesco brace correction

Background

Scoliosis is a three dimensional deformity, and brace correction should be 3D too. There is a lack of knowledge of the effect of braces, particularly in the sagittal and transverse plane. The aim of this study is to analyse the Sforzesco Brace correction, through all the parameters provided by Eos 3D imaging system.

Method

Design: This is a cross sectional study from a prospective database started in March 2003.Participants: 16 AIS girls (mean age 14.01) in Sforzesco brace treatment, with EOS x-rays, at start, in brace after 1 month and out of brace after the first 4 months of treatment. Outcome measures: All the parameters and the Torsio-Index obtained from 3D Eos System, in and out of brace, in the three planes. Statistical analysis: the variability of the parameters and the mean differences were analyzed and compared using paired T test. ANOVA was used for multiple comparisons. Critical P value was set at 0.05.

Results

In the comparison of in-brace vs start of treatment, the mean Cobb angle changed significantly from 36.44 +/? 4 to 28.99?+??3.9° (p?=?0.01). Significant changes in all the sagittal parameters were found (p?=?0.02). In the axial plane, the Torsio Index changed significantly in-brace for thoracolumbar and lumbar curves (P?<?0.05). The analysis of the single vertebral tilt demonstrated that the effect of the brace is mostly concentrated at specific segments: T4-T5, T10-T12, L1 and L5 in the axial plane and T3-T6 and T10-L1 in the frontal plane.

Conclusion

The Sforzesco brace mostly modifies the middle of the spine and preserves the sagittal balance. The single vertebral orientation in each plane should be considered together with the typically used values to assess brace effect.

     

Soil organic phosphorus transformations in a boreal forest chronosequence

Background and Aims

Soil phosphorus (P) composition changes with ecosystem development, leading to changes in P bioavailability and ecosystem properties. Little is known, however, about how soil P transformations proceed with ecosystem development in boreal regions.

Methods

We used 1-dimensional ³¹P and 2-dimensional ¹H, ³¹P correlation nuclear magnetic resonance (NMR) spectroscopy to characterise soil organic P transformations in humus horizons across a 7,800 year-old chronosequence in Västerbotten, northern Sweden.

Results

Total soil P concentration varied little along the chronosequence, but P compounds followed three trends. Firstly, the concentrations of DNA, 2-aminoethyl phosphonic acid, and polyphosphate, increased up to 1,200–2,700 years and then declined. Secondly, the abundances of α– and β—glycerophosphate, nucleotides, and pyrophosphate, were higher at the youngest site compared with all other sites. Lastly, concentrations of inositol hexakisphosphate fluctuated with site age. The largest changes in soil P composition tended to occur in young sites which also experience the largest shifts in plant community composition.

Conclusions

The apparent lack of change in total soil P is consistent with the youth and nitrogen limited nature of the Västerbotten chronosequence. Based on 2D NMR spectra, around 40 % of extractable soil organic P appeared to occur in live microbial cells. The observed trends in soil organic P may be related to shifts in plant community composition (and associated changes in soil microorganisms) along the studied chronosequence, but further studies are needed to confirm this.     

Wildfire and forest harvest disturbances in the boreal forest leave different long-lasting spatial signatures

Aims

Natural disturbances leave long-term legacies that vary among landscapes and ecosystem types, and which become integral parts of successional processes at a given location. As humans change land use, not only are immediate post-disturbance patterns altered, but the processes of recovery themselves are likely altered by the disturbance. We assessed whether short-term effects on soil and vegetation that distinguish wildfire from forest harvest persist over 60 years after disturbance in boreal black spruce forests, or post-disturbance processes of recovery promote convergence of the two disturbance types.

Methods

Using semi-variograms and Principal Coordinates of Neighbour Matrices, we formulated precise, a priori spatial hypotheses to discriminate spatial signatures following wildfire and forest harvest both over the short- (16–18 years) and long-term (62–98 years).

Results

Both over the short- and the long-term, wildfire generated a wide spectrum of responses in soil and vegetation properties at different spatial scales, while logging produced simpler patterns corresponding to the regular linear pattern of harvest trails and to pre-disturbance ericaceous shrub patches that persist between trails.

Conclusions

Disturbance by harvest simplified spatial patterns associated with soil and vegetation properties compared to patterns associated with natural disturbance by fire. The observed differences in these patterns between disturbance types persist for over 60 years. Ecological management strategies inspired by natural disturbances should aim to increase the complexity of patterns associated with harvest interventions.     

Soil microorganisms respond to five years of climate change manipulations and elevated atmospheric CO2 in a temperate heath ecosystem

Background and aims

Soil microbial responses to global change can affect organic matter turnover and nutrient cycling thereby altering the overall ecosystem functioning. In a large-scale experiment, we investigated the impact of 5 years of climate change and elevated atmospheric CO₂ on soil microorganisms and nutrient availability in a temperate heathland.

Methods

The future climate was simulated by increased soil temperature (+0.3 °C), extended pre-summer drought (excluding 5–8 % of the annual precipitation) and elevated CO₂ (+130 ppm) in a factorial design. Soil organic matter and nutrient pools were analysed and linked to microbial measures by quantitative PCR of bacteria and fungi, chloroform fumigation extraction, and substrate-induced respiration to assess their impact of climate change on nutrient availability.

Results

Warming resulted in higher measures of fungi and bacteria, of microbial biomass and of microbial growth potential, however, this did not reduce the availability of nitrogen or phosphorus in the soil. Elevated CO₂ did not directly affect the microbial measures or nutrient pools, whereas drought shifted the microbial community towards a higher fungal dominance.

Conclusions

Although we were not able to show strong interactive effects of the global change factors, warming and drought changed both nutrient availability and microbial community composition in the heathland soil, which could alter the ecosystem carbon and nutrient flow in the long-term.     

Partitioning of belowground C in young sugar maple forest

Background and aims

Trees allocate a high proportion of assimilated carbon belowground, but the partitioning of that C among ecosystem components is poorly understood thereby limiting our ability to predict responses of forest C dynamics to global change drivers.

Methods

We labeled sugar maple saplings in natural forest with a pulse of photosynthetic ¹³C in late summer and traced the pulse over the following 3 years. We quantified the fate of belowground carbon by measuring ¹³C enrichment of roots, rhizosphere soil, soil respiration, soil aggregates and microbial biomass.

Results

The pulse of ¹³C contributed strongly to root and rhizosphere respiration for over a year, and respiration comprised about 75 % of total belowground C allocation (TBCA) in the first year. We estimate that rhizosphere carbon flux (RCF) during the dormant season comprises at least 6 % of TBCA. After 3 years, 3.8 % of the C allocated belowground was recovered in soil organic matter, mostly in water-stable aggregates.

Conclusions

A pulse of carbon allocated belowground in temperate forest supplies root respiration, root growth and RCF throughout the following year and a small proportion becomes stabilized in soil aggregates.     

Combined use of bulked segregant analysis and microarrays reveals SNP markers pinpointing a major QTL for resistance to Phytophthora capsici in pepper

Key message

Bulked segregant analysis (BSA) using Affymetrix GeneChips revealed candidate genes underlying the major QTL for Phytophthora capsici resistance in Capsicum . Using the candidate genes, reliable markers for Phytophthora resistance were developed and validated.

Abstract

Phytophthora capsici L. is one of the most destructive pathogens of pepper (Capsicum spp.). Resistance of pepper against P. capsici is controlled by quantitative trait loci (QTL), including a major QTL on chromosome 5 that is the predominant contributor to resistance. Here, to maximize the effect of this QTL and study its underlying genes, an F₂ population and recombinant inbred lines were inoculated with P. capsici strain JHAI1-7 zoospores at a low concentration (3 × 10³/mL). Resistance phenotype segregation ratios for the populations fit a 3:1 and 1:1 (resistant:susceptible) segregation model, respectively, consistent with a single dominant gene model. Bulked segregant analysis (BSA) using Affymetrix GeneChips revealed a single position polymorphism (SPP) marker mapping to the major QTL. When this SPP marker (Phyto5SAR) together with other SNP markers located on chromosome 5 was used to confirm the position of the major QTL, Phyto5SAR showed the highest LOD value at the QTL. A scaffold sequence (scaffold194) containing Phyto5SAR was identified from the C. annuum genome database. The scaffold contained two putative NBS-LRR genes and one SAR 8.2A gene as candidates for contributing to P. capsici resistance. Markers linked to these genes were developed and validated by testing 100 F₁ commercial cultivars. Among the markers, Phyto5NBS1 showed about 90 % accuracy in predicting resistance phenotypes to a low-virulence P. capsici isolate. These results suggest that Phyto5NBS1 is a reliable marker for P. capsici resistance and can be used for identification of a gene(s) underlying the major QTL on chromosome 5.     

Parameter set for computer-assisted texture analysis of fetal brain

Background

Magnetic resonance data were collected from a diverse population of gravid women to objectively compare the quality of 1.5-tesla (1.5 T) versus 3-T magnetic resonance imaging of the developing human brain. MaZda and B11 computational-visual cognition tools were used to process 2D images. We proposed a wavelet-based parameter and two novel histogram-based parameters for Fisher texture analysis in three-dimensional space.

Results

Wavenhl, focus index, and dispersion index revealed better quality for 3 T. Though both 1.5 and 3 T images were 16-bit DICOM encoded, nearly 16 and 12 usable bits were measured in 3 and 1.5 T images, respectively. The four-bit padding observed in 1.5 T K-space encoding mimics noise by adding illusionistic details, which are not really part of the image. In contrast, zero-bit padding in 3 T provides space for storing more details and increases the likelihood of noise but as well as edges, which in turn are very crucial for differentiation of closely related anatomical structures.

Conclusions

Both encoding modes are possible with both units, but higher 3 T resolution is the main difference. It contributes to higher perceived and available dynamic range. Apart from surprisingly larger Fisher coefficient, no significant difference was observed when testing was conducted with down-converted 8-bit BMP images.

     

Root distribution of different mature tree species growing on contrasting textured soils in temperate windbreaks

Aim

We studied the vertical and lateral root distribution of tree species from three genera (Populus spp. - poplar, Picea spp. - spruce, Salix spp. - willow) that were planted in temperate windbreaks and assessed the effects of soil texture on root density.

Methods

Root distribution to depths of up to 1 m was assessed using the trench-profile method at different distances from the tree rows (2, 6 and 9 m) in 18 mature (average age, 25 years-old) windbreak-sites that were located on light- or heavy-textured agricultural soils in southeastern Québec, Canada. Roots were classified into three diameter classes: fine (<1 mm), medium-size (1–5 mm), and coarse (>5 mm).

Results

Tree fine-root density in poplar and willow windbreaks was higher than in spruce windbreaks at 2 m from the tree row. Root densities were higher in light compared to heavy soils, but these differences were specific to poplar and spruce. Across species groups and soil types, 67 % of the roots occurred in the uppermost 30 cm. In this soil zone, different soil fertility variables (pH, clay content, CEC) were negatively correlated with root density. Densities of spruce and willow roots at 6 m from the tree row were much lower (and often unobserved) than that of poplar. At 9 m, low root densities were observed at only two sites.

Conclusions

We conclude that tree identity and soil type are important drivers of root distribution in temperate agroforestry systems. These results may have important implications for the management of tree competition in agroforestry systems and several ecosystem services that are provided by roots, including C-sequestration, erosion control and water infiltration.     

Comparative QTL analysis of root lesion nematode resistance in barley

Key message

This study demonstrates for the first time that resistance to different root lesion nematodes ( P. neglectus and P. penetrans ) is controlled by a common QTL. A major resistance QTL ( Rlnnp6H ) has been mapped to chromosome 6H using two independent barley populations.

Abstract

Root lesion nematodes (Pratylenchus spp.) are important pests in cereal production worldwide. We selected two doubled haploid populations of barley (Igri × Franka and Uschi × HHOR 3073) and infected them with Pratylenchus penetrans and Pratylenchus neglectus. Nematode multiplication rates were measured 7 or 10 weeks after infection. In both populations, continuous phenotypic variations for nematode multiplication rates were detected indicating a quantitative inheritance of resistance. In the Igri × Franka population, four P. penetrans resistance QTLs were mapped with 857 molecular markers on four linkage groups (2H, 5H, 6H and 7H). In the Uschi × HHOR 3073 population, eleven resistance QTLs (P. penetrans and P. neglectus) were mapped with 646 molecular markers on linkage groups 1H, 3H, 4H, 5H, 6H and 7H. A major resistance QTL named Rlnnp6H (LOD score 6.42–11.19) with a large phenotypic effect (27.5–36.6 %) for both pests was mapped in both populations to chromosome 6H. Another resistance QTL for both pests was mapped on linkage group 5H (Igri × Franka population). These data provide first evidence for common resistance mechanisms against different root lesion nematode species. The molecular markers are a powerful tool for the selection of resistant barley lines among segregating populations because resistance tests are time consuming and laborious.     

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

Backgrounds and aims

In Mediterranean frequently burnt areas, the decrease of soil fertility leads to regressive vegetation dynamics. Organic amendments could help to accelerate post-fire ecosystem resilience, by improving soil properties and plant nutrition. This study was conducted to assess the potential of a composted biosolid to restore an early post-fire shrubland.

Methods

About 50 Mg.ha^?1 of fresh co-composted sewage sludge and green wastes were surface applied 7 months after fire on a silty-clayey soil. We monitored over a 2-year period organic matter and nutrient transfers to soil, nutrient responses of dominant plant species, and ecosystem contamination by potentially toxic trace elements.

Results

Over the experimental survey, compost rapidly and durably improved soil P₂O₅, MgO and K₂O content, and temporarily increased N-(NO₃ ^? + NO₂ ^?) content. Plant nutrition was improved more or less durably depending species. The most positive compost effect was on plant and soil phosphorus content. Plant nutrient storage was not improved 2 years after amendment, suggesting luxury consumption. No contamination by trace elements was detected in soil and plant.

Conclusions

The use of compost after fire could help for rapidly restoring soil fertility and improving plant nutrition. The increase of soil nutrient pools after amendment emphazised the diversity of plant nutritional traits. Eutrophication risk could occur from high compost and soil P₂O₅ content.     

Quantifying ecosystem rejuvenation: foliar nutrient concentrations and vegetation communities across a dust gradient and a chronosequence

Background and aims

Due to long-term weathering of land surfaces, aeolian nutrient contributions can become essential to maintain ecosystem fertility and avoid retrogression. However, studies that consider the qualitative and quantitative effects of dust deposition on ecosystem development are rare. We addressed this knowledge gap by studying an active Holocene dust flux gradient along a 6,500 year old dune ridge and a nearby chronosequence outside the influence of dust deposition in a super-humid, high leaching environment, on the west coast of the South Island in New Zealand.

Methods

Along both sequences we measured foliar nutrients of two main tree species (Dacrydium cupressinum, Prumnopitys ferruginea) and analysed vegetation communities in survey plots.

Results

Along the dust gradient, foliar phosphorus (P) concentrations increased up to 50 % with increasing dust flux. Across the nearby chronosequence a rapid decline of up to 50 % in foliar [P] occurred within the first 2,000 years after which it plateaued. At the highest dust flux rate, closest to the dust source, foliar [P] matched those of surfaces that are 5,702 to 6,098 years younger than the 6,500 year old dune. Vegetation communities along the dust gradient showed increasing relative abundance of species typical for successional communities on immature soils (Entisols, Inceptisols), while canopy cover and basal area (total, angiosperms, conifers) did not respond to increasing dust deposition. Tree fern basal area, however, positively responded to the dust flux.

Conclusion

We conclude that naturally occurring dust deposition can fertilise ecosystems significantly, creating a foliar nutrient status normally found on land surfaces that are up to 94 % younger and vegetation communities that are typical for successional stages on young soils (Entisols, Inceptisols). We suspect that these observations mainly reflect more plant-available P in the ecosystem as a result of dust fertilisation. Thus, dust deposition can be an important mechanism to avoid or retard the development of an ecosystem toward natural retrogression. This is the first study to directly quantify the fertilising capacity of natural dust deposition by calibrating its rejuvenating effect against a well-dated successional vegetation sequence.     

Nitrogen deposition promotes ecosystem carbon accumulation by reducing soil carbon emission in a subtropical forest

Background and aims

Tropical and subtropical forests are experiencing high levels of atmospheric nitrogen (N) deposition, but the responses of such forests ecosystems to N deposition remain poorly understood.

Methods

We conducted an 8-year field experiment examining the effect of experimental N deposition on plant growth, soil carbon dioxide efflux, and net ecosystem production (NEP) in a subtropical Chinese fir forest. The quantities of N added were 0 (control), 60, 120, and 240 kg ha^?1 year^?1.

Results

NEP was lowest under ambient conditions and highest with 240 kg of N ha^?1 year^?1 treatment. The net increase in ecosystem carbon (C) storage ranged from 9.2 to 16.4 kg C per kg N added in comparison with control. In addition, N deposition treatments significantly decreased heterotrophic respiration (by 0.69–1.85 t C ha^?1 year^?1) and did not affect plant biomass. The nitrogen concentrations were higher in needles than that in fine roots.

Conclusions

Our findings suggest that the young Chinese fir forest is carbon source and N deposition would sequester additional atmospheric CO₂ at high levels N input, mainly due to reduced soil CO₂ emission rather than increased plant growth, and the amount of sequestered C depended on the rate of N deposition.     

l-Theanine elicits umami taste via the T1R1 + T1R3 umami taste receptor

l-Theanine is a unique amino acid present in green tea. It elicits umami taste and has a considerable effect on tea taste and quality. We investigated l-theanine activity on the T1R1 + T1R3 umami taste receptor. l-Theanine activated T1R1 + T1R3-expressing cells and showed a synergistic response with inosine 5′-monophosphate. The site-directed mutagenesis analysis revealed that l-theanine binds to l-amino acid binding site in the Venus flytrap domain of T1R1. This study shows that l-theanine elicits an umami taste via T1R1 + T1R3.     

Plant phosphorus availability index in rehabilitated bauxite-processing residue sand

Background and aims

Soil phosphorus (P) indices that have been originally developed and applied to agricultural soils for predicting P uptake by plants were examined in a pot experiment to determine the most suitable index for P availability in bauxite-processing residue sand (BRS).

Methods

Pot trials with ryegrass were established using BRS that had been amended with various organic (greenwaste compost, biochar and biosolids) and inorganic (zeolite) materials and different levels of di-ammonium phosphate fertiliser. Soil P availability indices tested included anion-exchange membrane (AEM-P), 0.01 M calcium chloride (CaCl₂-P), Colwell-P, and Mehlich 3-P.

Results

AEM-P was found to most closely reflect the available P status in BRS across all treatments, and had the strongest associations with plant P uptake compared to Colwell-P, Mehlich 3-P and CaCl₂-P. AEM-P was more closely correlated with P uptake by ryegrass than other P indices, while Colwell-P was closely related to leaf dry matter. Interestingly, a strong inverse relationship between plant indices and pH in BRS growth media was observed, and an adequate level of plant P uptake was found only in 15 year-old rehabilitated BRS with pH <?8.0.

Conclusions

AEM-P was found to be the most suitable index for evaluating P availability in highly alkaline BRS and pH was an important parameter affecting uptake of P by ryegrass. Importantly, time is required (> 5 years) before improved uptake of P by plants can be observed in rehabilitated residue sand embankments.     

The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types

Background and aims

Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China.

Methods

Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl₂-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point.

Results

The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg^?1 to 21.4 mg kg^?1, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg^?1 to 90.2 mg kg^?1, above which soil CaCl₂-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg^?1 to 71.8 mg kg^?1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content.

Conclusions

The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.