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Plant availability and risk for leaching and/or runoff losses of phosphorus (P) from soils depend among others on P concentration in the soil solution. Water-soluble P in soil measures soil solution P concentration. The aim of this study was to understand the effect of wheat residue char (biochar) addition on water-soluble P concentration in a wide range of biochar-amended soils. Eleven agricultural fields representing dominant soil texture classes of Swedish agricultural lands were chosen. Concentrations of water-soluble P in the soils and in biochar were measured prior to biochar incorporation to soils in the laboratory. Experiments with three dominant soil textures—silt loam, clay loam, and an intermediate loam soil with different rates of biochar addition (i.e., 0.5, 1, 2, and 4 %; w / w ) showed that the highest concentration of water-soluble P was achieved at an application rate of 1 %. At higher application rates, P concentrations decreased which coincided with a pH increase of 0.3–0.7 units. When the 11 soils were amended with 1 % ( w / w ) biochar, water-soluble P concentrations increased in most of the soils ranging from 11 to 253 %. However, much of the water-soluble P added through the biochar was retained (33–100 %). We concluded that wheat residue char can act as a source of soluble P, and low and high additions of biochar can have different effects on soil solution P concentration due to possible reactions with Ca and Mg added with biochar.

While some studies regarding the effect of biofertilizers on plants, including their yield and quality, less is known about how they affect the soil properties, especially the microbial and enzymatic properties. Biofertilizers are promising for enhancing the nutrient availability in agricultural soils and reducing the reliance on inorganic fertilizers. The aim of this four-year-long field experiment was to assess the influence of the use of UGmax biofertilizer, which contains bacterial strains enhancing the soil phosphorus availability, e.g., the Pseudomonas spp. strains from Azotobacter and Penicillium genera, on the soil P forms and acid and alkaline phosphatase activity (AcP, AlP) in the surface soil horizon (Ap). Winter wheat was cultivated in 2005, 2006, and 2008, while winter rapeseed was cultivated in 2007 in a research area (2 hectare) that was selected for the investigation. These plants were selected because they are the main agricultural crops in Poland. UGmax was applied in three successive years after the plants had been harvested. One dose of the biofertilizer (0.7 L per hectare) was applied after the harvesting of wheat had been harvested (2005–2007), while the second dose (0.3 L per hectare) was applied as a top dressing in the spring, when the plants were beginning to grow (2006–2008). Forty soil samples were taken in 2005 (the control year without the application of UGmax). In the following years (2006–2008), 20 soil samples were taken from the area after the UGmax had been applied in the previous year, as well as 20 soil samples from the control area. A grid soil sampling technique (40 m × 25 m) was used to assess the changes in the soil properties across both of the studied areas. The soil samples were taken from the surface (Ap) horizon. Only at the end of the experiment (2008) did the application of UGmax remarkably increase the organic carbon (Corg) and total nitrogen (Nt) content, while the microbial biomass carbon (MBC) content was notably higher in the field with UGmax than in the control. The available P content (Pavail) was significantly higher in the field with UGmax compared to these without the biofertilizer in 2006 and 2008, while no considerable relation was noted for the total phosphorus (Ptot) and water soluble P (Pwater) content in any of the study years. Over the entire period of the experiment, the AcP and AlP were notably lower in the soil samples that were collected from the UGmax field compared to that of the control soil. It was concluded that the application of UGmax exhibited a phosphate-solubilizing activity that could be an encouraging attitude for increasing P bioavailability in arable fields and that further studies ought to be carried out under different soil and climatic conditions in order to confirm such a phenomenon.

Mineral phosphorus (P) fertilizers support high crop yields and contribute to feeding the teeming global population. However, complex edaphic processes cause P to be immobilized in soil, hampering its timely and sufficient availability for uptake by plants. The resultant low use efficiency of current water-soluble P fertilizers creates significant environmental and human health problems. Current practices to increase P use efficiency have been inadequate to curtail these problems. We advocate for the understanding of plant physiological processes, such as physiological P requirement, storage of excess P as phytate, and plant uptake mechanisms, to identify novel ways of designing and delivering P fertilizers to plants for improved uptake. We note the importance and implications of the contrasting role of micronutrients such as zinc and iron in stimulating P availability under low soil P content, while inhibiting P uptake under high P fertilization; this could provide an avenue for managing P for plant use under different P fertilization regimes. We argue that the improvement of the nutritional value of crops, especially cereals, through reduced phytic acid and increased zinc and iron contents should be among the most important drivers toward the development of innovative fertilizer products and fertilization technologies. In this paper, we present various pathways in support of this argument. Retuning P fertilizer products and application strategies will contribute to fighting hunger and micronutrient deficiencies in humans. Moreover, direct soil P losses will be reduced as a result of improved P absorption by plants.

In calcareous soil, the significant portion of applied phosphorus (P) fertilizers is adsorbed on the calcite surface and becomes unavailable to plants. Addition of organic amendments with chemical fertilizers can be helpful in releasing the absorbed nutrients from these surfaces. To check out this problem, a field experiment was conducted for two years to determine the effect of P fertilizers and humic acid (HA) in enhancing P availability in soil and their ultimate effect on growth, yield and P uptake of wheat in calcareous soils. The experiment was comprised of five levels of P (0, 45, 67.5, 90 and 112.5 kg P2O5 ha−1) as a single superphosphate (SSP) and 2 levels of locally produced humic acid (with and without HA) arranged in a two factorial randomized complete block design (RCBD) with three replications. Wheat plant height, spike length, number of grains per spike, 1000-grain weight, grain, straw and biological yield were significantly improved by the addition of HA with SSP. Very often, the performance of 67.5 kg P2O5 ha−1 with HA were either similar or better than 90 or even 112.5 kg P2O5 ha−1 applied without HA. Post-harvest soil organic matter, AB-DTPA extractable and water-soluble P, plant P concentration and its uptake were also significantly improved by the addition of HA with SSP compared to sole SSP application. It was evident that P efficiency could be increased with HA addition and it has the potential to improve crop yield and plants P uptake in calcareous soils.

Background and aims Dark septate endophytes (DSE) are a group of multifunctional fungi that ubiquitously colonize the roots of numerous plants worldwide, benefiting the nutrition and adaptation of hosts to various stressed environments. How DSE benefit phosphorus absorption by their host plants remains unclear. Methods We established pot cultures and compartmentalized microcosms in the greenhouse and used transcriptomic analysis to examine the response of maize to inoculation with a DSE strain, Exophiala pisciphila H93, which has been found to be capable of promoting plant growth and enhancing the tolerance of maize to heavy metals. Results H93 promoted the biomass, phosphorus absorption and photosynthesis of inoculated maize by enhancing phosphorus enzyme activities in the rhizosphere and by decreasing the pH of the rhizosphere compared with non-inoculated controls, either in sufficient or deficient phosphorus conditions in pot cultures. H93 inoculation changed the transcriptional pattern of maize related to 8 metabolic pathways. While H93 did not induce particular phosphate transporter gene expression under deficient phosphorus conditions, it dissolved the sparingly soluble phosphates (tricalcium phosphate) in the rhizosphere. Conclusions Enhanced phosphorus absorption by the host plant by DSE (H93) seemed to occur independently of DSE-induced genes involved in phosphorus absorption. The greatest contribution of DSE to phosphorus utilization of hosts might be their efficiency in transferring sparingly soluble phosphorus into soluble phosphate (Pi).

Arbuscular mycorrhizae (AM) are thought to improve crop growth by enhancing phosphorus (P) uptake via scavenging and enhancing dissolution. However, AM-mediated crop growth responses to P forms of varying solubility are often crop-species and soil-context dependent. The relative importance of AM associations and P source solubility on crop growth is not conclusively understood, and requires controlled factorial experiments to test their relative and interactive effects. We conducted a meta-analysis to evaluate how AM impact crop growth responses to rock phosphate relative to soluble phosphates across diverse crop species and soil characteristics. A total of 83 observations utilizing a 2 × 2 factorial design of relative presence or absence of AM and fertilization with rock phosphate vs. soluble phosphates were identified. We found that AM similarly improved crop growth with rock phosphate and soluble phosphates. A distinguishable crop growth benefit from AM coupled with rock phosphate was observed for soils with a low degree of weathering, at soil pH < 6.5 and > 7.5, and when soils were heat-sterilized prior to inoculation with AM. Shoot biomass of legumes was uniquely greater than non-legumes with rock phosphates and AM as compared to soluble phosphates and AM. However, crop growth under rock phosphate fertilization relative to soluble phosphates was still lower irrespective of AM. This meta-analysis reveals that crop growth is more dependent on P fertilizer solubility than AM. Moreover, AM do not appear to close the solubility gap of rock phosphate vs. soluble phosphate fertilizers to support similar crop growth under rock phosphate relative to soluble phosphates. Studies assessing crop growth responses to AM-crop associations effect on contrasting solubility P fertilizers should expand to the field, and greenhouse experiments should be conducted under realistic field growing conditions, such as agronomically appropriate P application rates.

Aims Struvite (MgNH 4 PO 4 ·6H 2 O), a low water solubility (<3%) mineral that is increasingly recovered from wastewater treatment plants, has potential to be used as a slow release ammonium phosphate fertilizer, especially when blended with highly water soluble phosphorus (P) fertilizers such as monoammonium phosphate (MAP). Methods Maize and soybean were fertilized using a gradient of struvite substitution for MAP, entailing five struvite: MAP blends in a factorial combination with struvite granule size (1.5, 3.0 mm diameter) and fertilizer placement (incorporation, banding). Crop biomass, and P and N uptake (total, concentration) were used to evaluate crop response, and post-harvest soil Mehlich-3 P was measured to assess soluble P loss risk. Results Maize biomass response was similar using up to 50% struvite and similar in soybean using up to 25% struvite. Total P uptake by maize was similar across 0–75% struvite blends, but significantly lower for 100% struvite. Maize apparent fertilizer P uptake and apparent fertilizer P uptake efficiency was greatest for 100% MAP. Despite differences in biomass, soybean apparent fertilizer P uptake and apparent P use efficiency were similar across struvite blends. Soybean P uptake was significantly greater when fertilized with 100% struvite than with 25 and 50% struvite. Inverse correlation of plant P and N concentrations with biomass indicated a biomass dilution effect. Residual soil Mehlich-3 P decreased with increasing struvite substitution of MAP. Conclusions Struvite:MAP blends (25–50% struvite) appear to lower soluble P loss risk compared to MAP without restricting early season (vegetative) growth of maize and soybean, and this can differ by crop species.

Phosphorus (P) is a key element for energy transfer, and biosynthesis of nucleic acids and cell membranes. The objective of this study was to investigate and quantify P utilization by different grain—maize (Zea mays L.) and soybean (Glycine max L.)—and forage-cover crop brachiaria (Brachiaria ruziziensis) plant species in a low fertility highly weathered Oxisol. Two rates of P (25 and 50 mg kg−1) were applied by water-soluble P fertilizer (triple superphosphate) to each of 12 crop cycles, together with a control (no P added). Measurements included plant biomass production and P uptake for each cycle, and analysis of soil P fractions (including labile and non-labile) and enzymes activities (acid phosphatase and β-glucosidase) were done at the beginning of the experiment and after 3, 6, and 12 cycles. Total biomass production and P uptake/removal were significantly higher for brachiaria than maize and soybean, which was reflected in the P use efficiency (PUE), being higher for brachiaria (57%), compared with maize (26%) and soybean (21%). The higher PUE by brachiaria was partly attributed to higher levels of acid phosphatase and β-glucosidase activities which indicated enhanced biological activity and P cycling under brachiaria. Data from the control treatment clearly demonstrated that all three plant species mobilized stable/occluded fractions of P throughout the experiment, however, brachiaria could produce more using less P. The findings of this study indicated the inclusion of brachiaria in crop rotations as a forage or cover crop/green manure may enhance overall P use efficiency.

Leaching of phosphorus fertilizer from loose-structured subtropical soils is a major course of agricultural water pollution in southeastern USA. Soil amendments play a major role in the phosphorus retention in soil through different mechanisms. In the present study we tested the effect of two soil amendments; biochar and coal fly ash in immobilizing the soluble phosphorus fertilizer added to sandy Ultisol soils from subtropical USA. Column leaching tests were conducted with Ultisol soil added with biochar (from avocado branch cut biomass) and coal fly ash at 5 tons/ha rate, under simulated rainfall, to collect the leachate over five pore volumes. The leachate was analyzed for the phosphate phosphorus content. In the end, the soil columns were carefully extracted, sectioned and analyzed for the total phosphorus, after acid digestion. Results showed 50% and 6% drop of soluble phosphorus leaching loss in biochar and coal fly ash added soil respectively. Soil amendments have shifted the loosely bound phosphorus into the Ca/Mg bound and Al/Fe/Mn bound pools which are not readily water extractable. Addition of biochar and coal fly ash together showed a synergistic interaction effect in reducing the leaching loss of phosphorus which needs further investigation to understand the exact mechanism.

Dietary Ca has been reported to influence the amount of phytate excreted from broilers and affect the solubility of P in excreta. To address the effects of dietary Ca and phytate on P excretion, 12 dietary treatments were fed to broilers from 16 to 21 d of age. Treatments consisted of 3 levels of phytate P (0.10, 0.24, and 0.28%) and 4 levels of Ca (0.47, 0.70, 0.93, and 1.16%) in a randomized complete block design. Feed phytate concentrations were varied by formulating diets with 3 different soybean meals (SBM): a low-phytate SBM, a commercial SBM, and a high phytate Prolina SBM having phytate P concentrations of 0.15 to 0.51%. Fresh excreta was collected from cages during 2 separate 24-h periods; collection I commenced after the start of dietary treatments (16 to 17 d) and collection II followed a 3-d adaptation period (19 to 20 d). Ileal samples were also collected at 21 d. Excreta samples were analyzed for total P, water soluble P (WSP), and phytate P, whereas ileal samples were analyzed for total P and phytate P. Results indicated that excreta total P could be reduced by up to 63% and WSP by up to 66% with dietary inclusion of low-phytate SBM. There was a significant effect of dietary Ca on both the excreta WSP and the ratio of WSP:total P. As dietary Ca increased, the excreta WSP and WSP:total P decreased, with the effects being more pronounced following a dietary adaptation period. There was a linear relationship between the slope of the response in WSP to dietary Ca and feed phytate content for excreta from collection II (r² = 0.99). There was also a negative correlation between excreta phytate concentration and excreta WSP during both excreta collections. The response in WSP to dietary manipulation was important from an environmental perspective because WSP in excreta has been related to potential for off-site P losses following land application.