Aims
Fluctuating phosphorus (P) fertiliser costs, water quality issues and on-going debate over global P supply and demand support the need to evaluate and ensure that P is used efficiently in agriculture.Methods
We analysed the P balance of farming systems across southern Australia to south east Queensland in relation to P management and soil properties at farm and sub-farm scales. Phosphorus input, yield of products and soil data were collected from Mediterranean, temperate and sub-tropical farming environments to assess soil chemistry and P Balance Efficiency (PBE; percentage of P inputs harvested as P outputs) of sheep, beef, dairy and cropping systems.Results
The median PBE was 11% for sheep, 19% for beef, 29% for dairy and 48% for cropping. Phosphorus applied in excess of product removal (P balance) ranged from 18.1 for dairy to 6.1 kg P ha?1 yr?1 for cropping. The bicarbonate-extractable (Colwell) P concentration of surface soils increased with fertiliser application and this differed in relation to P Buffering Index (PBI), production history and the rate of P input. Soil test values for 63% to 89% of soil samples from pastures and crops exceeded critical values (CV; defined by PBI, bicarbonate-extractable P and land use) when little yield improvement would be achieved by applying additional P. A greater percentage of these soil test values exceeded environmental thresholds for water contamination.Conclusions
A transition to using lower rates of P fertiliser to maintain soil P fertility at near optimal levels (P maintenance) has not occurred in farming systems represented by these soil samples. Over 50% of the samples had indications of more important constraints (soil acidity, potassium and sulphur deficiency) to yield. Alleviating these constraints is likely to improve PBE. For soils that exceed the CV for P, there is a need to adopt P maintenance practices to improve financial and environmental outcomes. 相似文献Aims
The efficient management of phosphorus (P) in cropping systems remains a challenge due to climate change. We tested how plant species access P pools in soils of varying P status (Olsen-P 3.2–17.6 mg?kg?1), under elevated atmosphere CO2 (eCO2).Methods
Chickpea (Cicer arietinum L.) and wheat (Triticum aestivum L.) plants were grown in rhizo-boxes containing Vertosol or Calcarosol soil, with two contrasting P fertilizer histories for each soil, and exposed to ambient (380 ppm) or eCO2 (700 ppm) for 6 weeks.Results
The NaHCO3-extractable inorganic P (Pi) in the rhizosphere was depleted by both wheat and chickpea in all soils, but was not significantly affected by CO2 treatment. However, NaHCO3-extractable organic P (Po) accumulated, especially under eCO2 in soils with high P status. The NaOH-extractable Po under eCO2 accumulated only in the Vertosol with high P status. Crop species did not exhibit different eCO2-triggered capabilities to access any P pool in either soil, though wheat depleted NaHCO3-Pi and NaOH-Pi in the rhizosphere more than chickpea. Elevated CO2 increased microbial biomass C in the rhizosphere by an average of 21 %. Moreover, the size in Po fractions correlated with microbial C but not with rhizosphere pH or phosphatase activity.Conclusion
Elevated CO2 increased microbial biomass in the rhizosphere which in turn temporally immobilized P. This P immobilization was greater in soils with high than low P availability. 相似文献Background and aims
Phosphorus and nitrogen availability and forms are affected by soil properties as well as by plant species and further modulated by soil microbes. Additionally, close contact of the roots of two plant species may affect concentrations and forms of N and P. The aim of this study was to assess properties related to N and P cycling in the rhizosphere of wheat and legumes grown in monoculture or in wheat/legume mixtures in three soils differing in pH.Methods
Faba bean, white lupin and wheat were grown in three soils differing in pH (4.8, 7.5 and 8.8) in monoculture or in mixed culture of wheat and legumes. Rhizosphere soil was collected at flowering and analyzed for P pools by sequential fractionation, available N as well as community structure of bacteria, fungi, ammonia oxidizers, N2-fixers and P mobilizers by polymerase chain reaction (PCR)—denaturing gradient gel electrophoresis (DGGE).Results
Soil type was the major factor determining plant growth, rhizosphere nutrient dynamics and microbial community structure. Among the crop species, only faba bean had a significant effect on nitrification potential activity (PNA) in all three soils with lower activity compared to the unplanted soil. Soil type and plant spieces affected the community composition of ammonia-oxidizing archaea (AOB), ammonia-oxidizing archaea (AOA), N2-fixers (nifH), P mobilizers (ALP gene) and fungi, but not that of bacteria. Among the microbial groups, the AOA and nifH community composition were most strongly affected by crop species, cropping system and soil type, suggesting that these groups are quite sensitive to environmental conditions. All plants depleted some labile as well as non-labile P pools whereas the less labile organic P pools (NaOH extractable P pools, acid extractable P pools) accumulated in the rhizosphere of legumes. The pattern of depletion and accumulation of some P pools differed between monoculture and mixed culture as well as among soils.Conclusions
Plant growth and rhizosphere properties were mainly affected by soil type, but also by crop species whereas cropping system had the least effect. Wheat and the legumes depleted less labile inorganic P pools in some soils whereas less labile organic P pools (NaOH extractable P, acid extractable P) accumulated in the rhizosphere of legumes. 相似文献Aims and Background
Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response.Methods
Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot?1), (c) low heterogeneous P (9.3 mg pot?1), and (d) high heterogeneous P (28 mg pot?1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum.Results
Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches.Conclusion
Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions. 相似文献Background and aims
Carbon (C) cycling in terrestrial ecosystems is influenced by the distribution of photo-assimilated C in the plant-soil system. Photo-assimilated C allocation in a wheat cropping system was examined to identify the links between soil fertility, C partitioning and soil C sequestration.Methods
A pulse labelling experiment was conducted where 14CO2 was introduced to wheat plants grown in two groups of soils of varying fertility: arable soils spiked with nutrients, and soils with differing land-use histories. Wheat shoot, root and soil samples were taken 1, 14 and 28 days after pulse labelling to examine the fluxes of 14C in the plant-root-soil system.Results
The partitioning of 14C in wheat plant-root-soil system was found to vary with time, nutrient spiked soil fertility and land-use history. At the end of the experiment using spiked soils, a positive correlation was observed between the allocation of 14C in the shoots and soil fertility, whereas in the roots, this relationship was negative. The overall allocation of 14C in the plant-root system differed significantly between the land-use histories; while in the spiked arable soils 14C allocation in the shoots and roots systematically followed their fertility status.Conclusions
There was a weak relationship between C allocation and soil fertility in the soils of different land-use history compared to the strong relationship in the spiked arable soils. This suggests that other factors in the soils under different land uses were more important than nutrient status alone in driving photo-assimilated C allocation. This study demonstrated that soil fertility and land-use history have a crucial role in the allocation of photo-assimilated C in the plant-soil system and are important factors by which C sequestration in soil may be impacted. 相似文献Background & Aims
Previous studies revealed that cotton plants grown on soils with low available-P were accessing significant non-fertilizer P sources. This suggests that cotton can access stable-P pools from soil. This study examined cotton??s ability to utilize sparingly soluble P sources in comparison with wheat and white lupin.Methods
Plants were grown for 45 days in a Vertosol supplied with AlPO4 and hydroxyapatite, and NH4-N or NO3-N. A 32P dilution technique was used to determine the availability and plant uptake of P from these P sources.Results
Three species differed substantially in P acquisition from the P sources. When averaged over N sources, the proportion of P in shoots sourced from AlPO4 was 89%, 54% and 19% for wheat, cotton and white lupin, respectively. When supplied hydroxyapatite, white lupin sourced 75% from the added P, in contrast to 36% for wheat and 17% for cotton. NH4-N nutrition increased the availability of hydroxyapatite to all the species and AlPO4 to cotton and white lupin.Conclusion
Cotton is inefficient in utilizing sparingly soluble P while wheat is efficient in mobilising AlPO4 and white lupin is efficient in using hydroxyapatite. The superiority of wheat in AlPO4 utilization may be related with its high root length density. 相似文献Aims
Aluminum-tolerant wheat plants often produce more root exudates such as malate and phosphate than aluminum-sensitive ones under aluminum (Al) stress, which provides environmental differences for microorganism growth in their rhizosphere soils. This study investigated whether soil bacterial community composition and abundance can be affected by wheat plants with different Al tolerance.Methods
Two wheat varieties, Atlas 66 (Al-tolerant) and Scout 66 (Al-sensitive), were grown for 60 days in acidic soils amended with or without CaCO3. Plant growth, soil pH, exchangeable Al content, bacterial community composition and abundance were investigated.Results
Atlas 66 showed better growth and lower rhizosphere soil pH than Scout 66 irrespective of CaCO3 amendment or not, while there was no significant difference in the exchangeable Al content of rhizosphere soil between the two wheat lines. The dominant bacterial community composition and abundance in rhizosphere soils did not differ between Atlas 66 and Scout 66, although the bacterial abundance in rhizosphere soil of both wheat lines was significantly higher than that in bulk soil. Sphingobacteriales, Clostridiales, Burkholderiales and Acidobacteriales were the dominant bacteria phylotypes.Conclusions
The difference in wheat Al tolerance does not induce the changes in the dominant bacterial community composition or abundance in the rhizosphere soils. 相似文献Background and aims
Nanoscale zero-valent iron (nZVI) application is a promising technology for degradation of chlorinated contaminants in soil. Plants also play an important role in soil remediation and nZVI should not adversely affect plants growing on treated soils. Large amounts of DDT are still found in certain soils and means to remediate these soils are limited. Our aims were to investigate the effect of nZVI on DDT degradation and evaluate possible negative effects of nZVI on plants.Methods
Columns with spiked (20 mg DDT kg?1) soil were percolated with nZVI (1 g nZVI L?1) and leached with five pore volumes of water to assess leaching of nZVI and residual toxicity of leachates and soil to plants using seed germination and plant growth tests (barley, flax).Results
Addition of nZVI led to degradation of 45 % of the added DDT. Percolation with water significantly oxidized and transported iron through the columns. The first leachates had negative effects on plant development, but after leaching with 4 pore volumes, neither soil nor leachates affected plant negatively.Conclusions
nZVI is efficient for degradation of DDT and adverse effects of nZVI on plants seem ephemeral and are alleviated after oxidation mediated by percolating water. 相似文献Aims
A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.Methods
We adopted 4.5 t ha?1, 9.0 t ha?1 biochar and 3.75 t ha?1 straw for each crop season with an identical dose of NPK fertilizers.Results
We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH4 emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N2O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH3 volatilization in the rice season, but stimulated it in the wheat season.Conclusions
Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH4 mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH3 volatilization differently in the flooded rice and upland wheat seasons, respectively. 相似文献Background
Phosphorus (P) deficiency is wide-spread in agricultural soils. In light of increasing P fertilizer costs, it is of interest to assess the capacity of soil microbes to mobilise native soil P and added P. There is currently no method to assess P mobilisation in situ.Methods
The soil P mobilisation potential was assessed by incubating low P soil for up to 30?days with poorly available P sources; C and N were added to increase microbial activity and ensure that only P was limiting microbial growth.Results
The increase in microbial P from day 0 to day 15 showed that microbes were able to mobilise P from FePO4 and phytate. The P mobilisation potential (sum of microbial and resin P) of the rhizosphere soil decreased in the following order: faba bean > chickpea and white lupin > wheat. After 10?days, up to 80% of the mobilised P was microbial P, whereas after 30?days, almost all P mobilised was resin P.Conclusions
The method developed in this study is useful assessing not only potential of a soil to mobilise P but also, by using different poorly available P sources, the mechanisms of P mobilisation. 相似文献Background and aims
As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status.Methods
Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha?1 equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution 31P nuclear magnetic resonance (NMR) spectroscopy.Results
Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate.Conclusions
Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status. 相似文献Background and aims
7Be has been used as a powerful tracer for estimating short-term soil redistribution by virtue of its short half-life. However, the existing conversion model associated with this radionuclide means that it can only be applied to bare soils because vegetation will intercept a large proportion of 7Be fallout. A modified model which takes into consideration the impact factor of vegetation was reported in this paper and the estimation of soil redistribution was compared by using both the conventional and the modified models.Methods
Field experiment on 7Be distribution in above-ground grasses and soils was carried out on a 100 m2 grass-covered slope. The vegetation interception factor (P) was determined and the soil redistribution rates were calculated by using the previous model and the modified model.Results
The result shows that nearly 40 % of the atmospherically deposited 7Be will be sequestered by leaf surfaces of herbaceous plants. Soil loss rates on grassland will be remarkably overestimated by using the previous model.Conclusions
The net soil loss estimated from the modified model is more accurate than that derived from the conventional model and the modified model will be more appropriate to estimate soil redistribution rates on soils with significant vegetation cover by using 7Be technique. 相似文献Background and Aims
The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.Methods
Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.Results
Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.Conclusions
The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice. 相似文献The results show that a resin gel thickness of 0.3 mm gives the best reproducibility and response in the absorption of copper by DGT. The amount of copper extracted in a period of 4 h by the devices from the soil solution corresponds to 13% of the total metal present in the solution.
The DGT allowed a more representative estimation of the amount of Cu available in the soil, more in agreement with the absence of symptoms of phytotoxicity in cultivated species. This shows that the determination of available Cu by DTPA must be handled cautiously because in soils with high Cu content the amount of metal that can have direct influence on absorption by the plant is overestimated. 相似文献