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Background and aims: Long-term nitrogen (N) and phosphorus (P) fertilization could immensely alter plant-soil-microbial properties, thereby impacting the priming effect (PE). However, previous studies mostly simulated PE responses to fertilization by adding nutrient in the laboratory, which could not represent PE changes under long-term fertilization-induced ecosystem alteration. Our aim is to clarify the PE alteration in soils with long-term fertilization history in an alpine meadow. Methods: Soil samples (0–10 cm) were collected from a 9-year field fertilization experiment (including four treatments: control, + N with urea, + P with triple superphosphate, + NP with both fertilizers), and incubated for 30 days with 13C-labeled glucose amendment (2% SOC). Plant-soil-microbial properties were measured before/after incubation. Results: Glucose addition induced a positive PE in all soils with a range from 0.56 to 1.37 mg C g−1 soil. N fertilization did not affect PE intensity due to the microbial adaptation and fast utilization of the added glucose for metabolic needs. P fertilization caused P accumulation in soils, and decreased available N and pH. Such changes inhibited microbes, and glucose activated microbial activities, causing higher PE intensity. Conclusion: Long-term N fertilization did not significantly affect PE, while P fertilization stimulated PE intensity. Overall, we highlight that P fertilization may induce higher risk of CO2 release, which deserves more attention when applying P fertilizers in this alpine meadow. [ABSTRACT FROM AUTHOR]

Background and aim: Seed inoculation with effective rhizobia (Rh) strains and phosphorus (P) application are sustainable agricultural practices that enhance soybean grain yield. However, adoption of these practices in northern Ghana is hindered by unpredictable yield responses and poor understanding of the factors that cause yield variation. We compared soybean yield from inputs managed trials such as Rh inoculants and P sources. Methods: Soybean trials were conducted on-station and on-farm with one of three Rh inoculants [Bradyrhizobium japonicum (Bj), B. elkanii (Be), and B. diazoefficiens (Bd)], and with one of three P sources [no-P, Triple Superphosphate (TSP), and a mixture of rock-P (low solubility) and TSP (water-soluble P)]. Yield was compared at harvest. The random forest (RF) model was used to predict yield, and factors of yield variation were determined using forward redundancy analysis (RDA). Results: The soybean yield was consistently higher in the Rh × P treatments compared to the control in on-station and on-farm experiments. The treatments that received P fertilizer (RP and TSP) showed a higher grain yield than the control. The on-station experiment yielded more accurate results than the on-farm dataset, with a trained coefficient of determination (R2) of 0.95 and 0.87, respectively. The yield variation was explained by the Rh × P fertilizer, P sources, Rh strains, and exchangeable soil Mg. Conclusion: The exchangeable magnesium in the soil contributed significantly to the variation in yield. Further research is recommended to study the mechanisms that underline the impact of magnesium on soybean growth. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) fertilization affects plant diversity and ecosystem function by changing the abundance and composition of functional soil microorganisms and genes. Understanding the mechanisms regulating the soil carbon (C), nitrogen (N), sulfur (S), and P cycle across different P fertilizer inputs is crucial to the management of P in sustainable agroecosystems. Methods: We investigated whether soil functional microorganisms affected the coupling of the abundance of soil C, N, P, and S genes under long-term (up to 14 years) P fertilizer input (0, 21.8, 43.6, and 87.2 kg P ha−1 yr−1) on the Loess Plateau of China. Results: Long-term P fertilizer input resulted in the increased abundance of soil functional microorganisms and the expression of soil C cycle genes but decreased soil P cycle genes. The relative abundance of ecological clusters (including bacteria, fungi, and archaea) was significantly correlated with functional genes related to the C, N, P, and S cycles. Soil Actinobacteria, Proteobacteria, Cyanobacteria, Bacteroidetes, and Chloroflexi were the keystone taxa mediating soil nutrient cycling in wheat fields. Both Mantel's test and structural equation modeling indicated that the shifts in soil available C and P were the major factors driving the coupling of soil functional microorganisms and genes. Conclusions: The changes in soil microorganisms and genes can drive soil nutrient cycling and promote crop growth, suggesting that their relationship can provide new insight for understanding the microbial mechanisms of soil P turnover in sustainable agroecosystems. [ABSTRACT FROM AUTHOR]

Background: We are facing the challenge of sustainable phosphorus (P) use due to high P inputs in farmland and low P-use efficiency of crops, which leads to critical soil P imbalances and accelerates consumption of limited P resources. Organic P is an essential component of the soil P cycle, and if managed properly, may compensate partly for decreased usage of P fertilizers. However, organic P dynamics in the rhizosphere has received little attention even though it is important for P availability to plants. Scope: We review biological turnover of organic P in soils, focusing on the processes driven by roots and microbial communities and their interactions in the rhizosphere. We also consider recent progress in understanding of organic P acquisition strategies that integrate soil carbon (C) cycling. We address several perspectives to achieve more sustainable P use in agriculture via rhizosphere management aimed at recycling and re-using soil organic P. Conclusions: Organic P mineralization by microorganisms may be limited by low P and/or C availability. In these processes, plants interact with microorganisms to alter stoichiometric ratios of C to P in the rhizosphere soils or microbial community, thus impacting on turnover of organic P into inorganic P for plant absorption, which is manifested in plant-microbial facilitation/competition in the rhizosphere. We highlight future research in improving rhizosphere management of agroecosystems by optimizing nutrient inputs and enhancing rhizosphere interactions to manipulate P and C dynamics towards sustainable organic P use. [ABSTRACT FROM AUTHOR]

Aims: Zn is always co-fertilized with N and P fertilizers to increase crop yield production in agriculture. Although strong interactions between Zn and P have been recognized, how Zn affects soil P transformation mediated by microorganisms is not completely clear. Methods: We planted rice plants in soils with different combinations of P and Zn supply, and analyzed the P transformation, bacterial and fungal communities, enzyme activities and gene expressions in rhizosphere soil. Results: Zn application promoted rice growth and P uptake, increased available P, but decreased the proportion of organic P in rhizosphere soil after Zn supply under moderate P condition. Although Zn application did not affect either bacterial or fungal diversity, it clearly elevated PSB abundances including Saccharimonadales, Sphingomonas, Flavisolibacter, Gemmatirosa, subgroup_6, and subgroup_7, but significantly decreased the abundances of pathogenic fungi Curvularia and Fusarium under moderate P condition. Furthermore, the acid phosphatase activity increased 12.70%, the phoC, phoD, ppk, and pqqc expression levels increased to 1.88-fold, 4.99-fold, 2.86-fold, and 5.07-fold, respectively, after Zn supply under moderate P condition. Conclusion: Zn application could facilitate the turnover of organic P into inorganic form and improve P availability by increasing PSB abundances, acid phosphatase activity, and functional gene expression levels. This positive effect of Zn on soil P transformation strongly depended on the environmental P conditions, as no obvious changes were displayed under high P condition. Therefore, Zn co-fertilized with appropriate P is an effective strategy to enhance P availability in rice rhizosphere soil to improve plant growth and P uptake. [ABSTRACT FROM AUTHOR]

Background and aims: Plant-derived metabolites play a crucial role in mediating plant–microbe interactions affecting plant development, health and ability to withstand biotic and abiotic stresses. However, how the key plant metabolites, e.g., flavonoids and fatty acids secreted by roots, regulate soil microbial communities to promote plant phosphorus (P) nutrition, growth and development remains unclear. Methods: We determined whether the addition of different concentrations (0, 50 or 500 μmol kg−1) of myristic acid (fatty acid), quercetin, naringenin or luteolin (flavonoids) to the soil to improved soil organic P utilization efficiency and enhanced plant growth by changing microbial community. Results: Flavonoids could directly regulate rhizosphere bacterial community structure, with a significant increase in the relative abundance of Micrococcaceae and Nocardioidaceae by the addition of 50 μmol kg−1 of naringenin, luteolin, 500 μmol kg−1 of quercetin, naringenin or luteolin. The addition of myristic acid had weaker impact on bacterial community structure. The altered bacterial community structure lead to the increased alkaline phosphatase activity in the rhizosphere to promote the mineralization of organic P, which could facilitate plant growth and P uptake to different extents. Conclusion: Our results indicate that the addition of flavonoids enhanced organic P mineralization by selecting individuals which secreted more phosphatases. These findings can provide guidance for effective manipulation of composition of plant-microbial communities to increase plant P nutrition and/or efficiency of use of P fertilizers. [ABSTRACT FROM AUTHOR]

Background and aimes: Plant roots secrete acid phosphatases (ACPs) to mineralize rhizosphere organic phosphorus (Po) for absorption. However, the ecological effects of such exudates on the rhizobacterial community and function remain unclear. Methods: Purple acid phosphatase 10c (OsPAP10c) is the major root-secreted ACP under both Pi-sufficient and Pi-deficient conditions in rice. To study the effect of root-secreted ACP on rhizosphere phosphorus (P) cycling and succession of the bacterial community, the previously reported OsPAP10c mutant and overexpression lines were planted in paddy soils with or without P fertilizer (+ P or -P). Results: The results showed that the expression of OsPAP10c significantly influenced ACP activity in rhizosphere soil, which changed the bacterial composition by 6.72% to 9.54%. The expression of OsPAP10c helped to recruit P-solubilizing bacteria (PSB) at the filling stage under -P conditions. However, OsPAP10c increased bacterial P competition potentials and rhizosphere alkaline phosphatase (ALP) at the elongation and filling stages under + P conditions. Interestingly, overexpression of OsPAP10c relaxed bacterial P demand pressure and increased the relative abundance of bacteria with nitrogen, sulphur, and iron potential functions, which benefited rice nutrient uptake and growth at the early stages. Conclusion: In conclusion, this study indicated that P fertilizer and root-secreted ACPs cooperatively regulate rhizosphere P cycling potential by modifying the rhizobacterial composition. [ABSTRACT FROM AUTHOR]

Background: Precipitation of Zn phosphates may limit Zn availability in cogranulated P fertilizers. We assessed whether the Zn availability of Zn could be improved by post-granulation acid treatment. Methods: Uncoated Zn-fortified monoammonium phosphate granules were compared with sulfuric acid-coated granules in which Zn was either cogranulated or dissolved in the acid coating. Spatially resolved XRF and XANES was used to assess the distribution and speciation of Zn in the granules (before and after incubation in soil) and in the exposed soil. The amount of Zn remaining in the granule was determined after incubation in various soils. The effect of acid coating rate on corn yield was determined in a highly Zn-deficient soil in a pot trial. Results: The speciation of Zn in the untreated granules was dominated by Zn phosphates. In the sulfuric acid treatments, sulfate species accounted for ~ 45% (if cogranulated) or ~ 80% (if coated) of the Zn. After one week incubation in soil, 10–86% of the added Zn remained in the residual granule, mostly as sparingly soluble compounds. The Zn speciation in the soil near the granule was dominated by Zn phosphates irrespective of treatment, but Zn moved further away from the application site in the acid treatments, as more Zn was released from the granule. In the pot trial, the dry matter yield increased by 70% at a coating rate of 0.75% H2SO4 compared to the uncoated control. Conclusions: Post-granulation acid treatment of Zn-fortified P fertilizers is an effective way to enhance the phytoavailability of fertilizer Zn. [ABSTRACT FROM AUTHOR]

Background: Phosphorus (P) is an essential nutrient for plant growth, taking part in primary cellular metabolic processes as a structural component of key biomolecules. Soil processes as adsorption, precipitation, and coprecipitation can affect P bioavailability, leading to limited plant growth and excessive use of P fertilizers, with adverse impacts on the environment and progressive depletion of P reserves. To cope with P stress, plants undergo several growth, development, and metabolic adjustments, aimed at increasing P-acquisition and -utilization efficiency. Recently, strigolactones (SLs) have emerged as newly defined hormones that mediate multiple levels of morphological, physiological and biochemical changes in plants as part of the P acclimation strategies to optimize growth. Therefore, understanding the soil processes affecting P availability and P acquisition strategies by plants can contribute to improved agronomical practices, resources optimization and environmental protection, and the development of plants with high P use efficiency for enhanced agricultural productivity. Scope: In this review, we discuss the range of abiotic processes that control P retention in soil and how different concentrations or degrees of P bioavailability can trigger various responses in plants, while critically highlighting the inconsistent conditions under which experiments evaluating aspects of P nutrition in plants have been conducted. We also present recent advances in elucidating the role of SLs in the complex P signalling pathway, with a special focus on what has been discovered so far in the model plant tomato (Solanum lycopersicum L.). [ABSTRACT FROM AUTHOR]

Background and aims: The stoichiometric ratio of carbon (C): phosphorus (P) acquisition is strongly correlated with soil available C:P ratio. However how the stoichiometric relationship between acquiring C and P through microbial metabolism affects bioavailable P is poorly understood in semi-arid agricultural ecosystems. Methods: Our objective was to investigate the underlying mechanisms of the P availability in typical P-limited steppe soil from Kazakhstan in response to mineral nutrient (Na2HPO4) with and without Dactylis glomerata L. leaves addition in a 38-day incubation experiment. Results: Four bioavailable P fractions content (CaCl2-P, Citrate-P, Enzyme-P, and HCl-P) were improved. Sole application of P fertilizer decreased the maximal velocity (Vmax) of P acquisition enzyme (phosphomonoesterase) but increased microbial C limitation, resulting in increasing the ratio of C to P acquisition but decreasing the ratio of available dissolved organic C: Olsen-P. In contrast, plant residues returning (the application of sole D. glomerata leaves and the combined application of D.glomerata and mineral P) increased Vmax of C (β-1, 4-glucosidase, β-D-cellobiosidase, β-1, 4-xylosidase) and P acquisition enzymes, however decreasing microbial C and P limitation through improving microbial metabolism. Furthermore, the spearman correlation and piecewiseSEM analysis suggested that microbial C limitation and EEAC:P had a negative effect on P availability, illustrating that the decreasing of microbial C limitation can improve soil bioavailable P. Conclusion: The decomposition of organic residues eliminated microbial P limitation and increased P availability by allocating C and P acquisition enzymes to balance the stoichiometric ratio of microbial C and P demand. [ABSTRACT FROM AUTHOR]

Aims: Litter decomposition affects soil organic carbon storage, and nutrient addition alters exogenous nutrient availability in soil, thereby affecting the endogenous nutrient concentration and extracellular enzyme activity in litter. However, how above- and belowground litter decomposition responds to nutrient addition is not fully understood. Methods: We conducted a 7-yr field experiment with 5 levels (0, 1, 2.5, 5, and 12.5 g P m−2 yr−1) of phosphorus fertilization (P). Starting in the 6th year, we determine litter decomposition, nutrient elements, and enzyme activity to explore the response mechanisms of above- and belowground litter decomposition to P addition. Results: All levels of P addition increased the rate of aboveground litter decomposition, but only 2.5 g P m−2 yr−1 increased that of belowground litter. P addition increased the litter initial P and Mn contents, while decreased the C/P and N/P ratios of aboveground litter, which stimulated the activities of β-1,4-glucosidase and β-1,4-N-acetylglucosaminidase, thereby increasing the aboveground litter decomposition rate. The belowground litter decomposition was mainly inhibited by lignin content, and 2.5 g P m−2 yr−1 addition significantly decreased lignin content and increased the phenol oxidase activity, thereby accelerating the decomposition. P addition promoted the accumulation of P and the release of cellulose from aboveground litter and promoted the accumulation of calcium and the release of carbon from belowground litter. Conclusions: Different mechanisms of above- and belowground litter decomposition under P addition were driven by litter quality and enzyme activity, but moderate P addition increased semiarid grassland litter decomposition, which may contribute to low soil C sequestration. [ABSTRACT FROM AUTHOR]

Aims: Understanding the accumulation and mineralization of soil organic carbon (SOC) in aggregates under long-term fertilization conditions is of great significance in comprehending the dynamic changes in farmland C pools on the Loess Plateau. Methods: The long-term field experiment has been established for 26 years and includes six fertilization treatments: no fertilization (CK), organic fertilizer (M), organic and nitrogen fertilizers (MN), organic and phosphorus fertilizers (MP), NP and MNP. We determined nutrient content, mineralization characteristics, temperature sensitivity (Q10), and extracellular enzyme activities of soil aggregates (< 0.25 mm, 0.25–1 mm, 1–2 mm, > 2 mm). Results: (1) M, MN, MP, and MNP significantly increased the SOC content of aggregates by 92.58%, 82.84%, 73.55% and 83.23% compared to NP. The SOC in < 0.25 mm aggregates was significantly highest than other particles. (2) Organic fertilizer treatments (M, MN, MP, and MNP) significantly increased the cumulative mineralization of different-sized aggregates by 97.10–178.75% compared to NP. The average mineralization rate and the cumulative mineralization of < 0.25 mm aggregates was the lowest. (3) The mineralization of aggregates is directly and significantly affected by the available soil nutrients and enzyme activities. (4) Fertilization and aggregate size had significant effects on Q10 and the Q10 of MNP was lower than that of M, MP, and MN. Conclusion: < 0.25 mm aggregates had the strongest C sequestration effect. MNP reduced the amount of mineralization by regulating enzyme activities and promoted the accumulation of SOC in farmland on the Loess Plateau by increasing the percentage of < 0.25 mm aggregates. [ABSTRACT FROM AUTHOR]

Background and aims: Intercropping is an effective practice for increasing crop diversity and achieving sustainable agricultural development, especially in areas with limited agricultural land. Although the nitrogen turnover and trade-off responses of plant–soil systems to intercropping have been extensively studied, quantitative information on the association between P and crop productivity is lacking. Therefore, in this study, we aimed to elucidate the effects of intercropping on plant P concentration, uptake, and use efficiency and soil P availability.We conducted a quantitative meta-analysis using a database containing 453 comparisons from 56 peer-reviewed studies.Intercropping significantly increased the soil available P concentration and phosphatase activity by 14.68% and 11.74%, respectively, compared with monocropping. However, the effects of intercropping on other P characteristics and grain yield were not significant. Among the evaluated influencing factors, crop type (cereal or legume) had the greatest effect on soil P availability, followed by soil pH and P fertilizer input. Regression analysis revealed that plant P concentration and uptake were significantly and linearly correlated with soil available P concentration and phosphatase activity. Notably, in maize–legume intercropping systems, maize exhibited increased P concentration and uptake and increased grain yield, whereas legumes exhibited constrained growth.Overall, we determined that intercropping improves soil P availability, depending on the ecological environment, nutrient management, and intercropping system. This study serves as a valuable reference for effective P fertilizer input in cereal–legume intercropping systems under different management practices.Methods: Intercropping is an effective practice for increasing crop diversity and achieving sustainable agricultural development, especially in areas with limited agricultural land. Although the nitrogen turnover and trade-off responses of plant–soil systems to intercropping have been extensively studied, quantitative information on the association between P and crop productivity is lacking. Therefore, in this study, we aimed to elucidate the effects of intercropping on plant P concentration, uptake, and use efficiency and soil P availability.We conducted a quantitative meta-analysis using a database containing 453 comparisons from 56 peer-reviewed studies.Intercropping significantly increased the soil available P concentration and phosphatase activity by 14.68% and 11.74%, respectively, compared with monocropping. However, the effects of intercropping on other P characteristics and grain yield were not significant. Among the evaluated influencing factors, crop type (cereal or legume) had the greatest effect on soil P availability, followed by soil pH and P fertilizer input. Regression analysis revealed that plant P concentration and uptake were significantly and linearly correlated with soil available P concentration and phosphatase activity. Notably, in maize–legume intercropping systems, maize exhibited increased P concentration and uptake and increased grain yield, whereas legumes exhibited constrained growth.Overall, we determined that intercropping improves soil P availability, depending on the ecological environment, nutrient management, and intercropping system. This study serves as a valuable reference for effective P fertilizer input in cereal–legume intercropping systems under different management practices.Results: Intercropping is an effective practice for increasing crop diversity and achieving sustainable agricultural development, especially in areas with limited agricultural land. Although the nitrogen turnover and trade-off responses of plant–soil systems to intercropping have been extensively studied, quantitative information on the association between P and crop productivity is lacking. Therefore, in this study, we aimed to elucidate the effects of intercropping on plant P concentration, uptake, and use efficiency and soil P availability.We conducted a quantitative meta-analysis using a database containing 453 comparisons from 56 peer-reviewed studies.Intercropping significantly increased the soil available P concentration and phosphatase activity by 14.68% and 11.74%, respectively, compared with monocropping. However, the effects of intercropping on other P characteristics and grain yield were not significant. Among the evaluated influencing factors, crop type (cereal or legume) had the greatest effect on soil P availability, followed by soil pH and P fertilizer input. Regression analysis revealed that plant P concentration and uptake were significantly and linearly correlated with soil available P concentration and phosphatase activity. Notably, in maize–legume intercropping systems, maize exhibited increased P concentration and uptake and increased grain yield, whereas legumes exhibited constrained growth.Overall, we determined that intercropping improves soil P availability, depending on the ecological environment, nutrient management, and intercropping system. This study serves as a valuable reference for effective P fertilizer input in cereal–legume intercropping systems under different management practices.Conclusion: Intercropping is an effective practice for increasing crop diversity and achieving sustainable agricultural development, especially in areas with limited agricultural land. Although the nitrogen turnover and trade-off responses of plant–soil systems to intercropping have been extensively studied, quantitative information on the association between P and crop productivity is lacking. Therefore, in this study, we aimed to elucidate the effects of intercropping on plant P concentration, uptake, and use efficiency and soil P availability.We conducted a quantitative meta-analysis using a database containing 453 comparisons from 56 peer-reviewed studies.Intercropping significantly increased the soil available P concentration and phosphatase activity by 14.68% and 11.74%, respectively, compared with monocropping. However, the effects of intercropping on other P characteristics and grain yield were not significant. Among the evaluated influencing factors, crop type (cereal or legume) had the greatest effect on soil P availability, followed by soil pH and P fertilizer input. Regression analysis revealed that plant P concentration and uptake were significantly and linearly correlated with soil available P concentration and phosphatase activity. Notably, in maize–legume intercropping systems, maize exhibited increased P concentration and uptake and increased grain yield, whereas legumes exhibited constrained growth.Overall, we determined that intercropping improves soil P availability, depending on the ecological environment, nutrient management, and intercropping system. This study serves as a valuable reference for effective P fertilizer input in cereal–legume intercropping systems under different management practices. [ABSTRACT FROM AUTHOR]

Aims: Many soils in the developed world have been fertilized with phosphate for several decades. Appreciable phosphate has accumulated in such soils. This is referred to as "legacy P". The benefits of legacy P are not widely appreciated. Here, we report the effects of legacy P on buffering capacity and the consequent effects on the effectiveness of plant growth, and its effects on the continuing reaction between soil and P and the consequent effects in decreasing the decline of P effectiveness with time. Methods: We produced five levels of legacy P by incubating the soil with added phosphate at high temperatures for 30 days. We then measured the effect on sorption/desorption and on plant growth in response to further additions of phosphate. Results: Legacy P decreased soil buffering capacity, decreased hysteresis of desorption, and increased the amount of P in a similar state to that of the recently sorbed P. There were analogous effects of plant growth; effectiveness of P fertiliser increased; the decline in effectiveness with time decreased; and the amount of soil P accessible to plants increased. We think that soil tests reflect only the amount of soil P accessible to plants. Soil testing services which include estimates of phosphate buffering reflect its decrease and the consequent increase in fertilizer effectiveness. We propose a simple test to reflect the rate of decline in effectiveness with time. Conclusions: Managing phosphate applications using soil tests alone underestimates phosphate status and leads to over application of phosphate. It is necessary to also include estimates of the change in phosphate buffering and the change in the rate of decline in effectiveness with time. A simple way to estimate the rate of decline is suggested. [ABSTRACT FROM AUTHOR]

Background and aims: Humic acid-enhanced phosphate fertilizer (HAP) is an efficient, widely used fertilizer in China produced by incorporating trace amounts of humic acid (HA) into conventional phosphate fertilizer (CP). However, the mechanism of its increased efficiency has remained unclear, limiting its optimization. Methods: Maize (Zea mays L. cv ZD 958) was cultivated in root boxes to evaluate the effects of localized HAP, CP, or HA on biomass production, phosphorus (P) uptake, distribution of roots and available P in soil, and activity of C-acquiring and P-acquiring enzymes. Meanwhile, the effects of HAP, CP, and HA in fertosphere were isolated through their uniform application in confined growth tubes and quantifying root traits. Results: HAP significantly increased available P content and soil area with high P content, and elevated the ratio of soil C- and P-acquiring enzyme activity. Total maize biomass and root distribution area treated with localized HAP were 12.9% and 29.7% higher than that with local CP application, and root biomass was positively correlated with soil available P. Uniform HAP supply significantly increased the maize biomass and P uptake compared to CP uniform treatments, and the biomass and P uptake were highly correlated with root length. HA alone had no impact on above indices. Conclusions: The presence of HA in HAP increased the area and strength of P supply, and P in HAP guaranteed the adequate nutrient supply for maize enabling HA to stimulate growth. Thus, efficacy of HAP was resulted from the synergistic effects of HA and P fertilizer. [ABSTRACT FROM AUTHOR]

Background and scope: Enriching phosphorus (P) fertilizers with phosphate-solubilizing microorganisms (PSM) can be a promising strategy to enhance P-use efficiency in agriculture. However, the effects of these microorganisms when applied in mixtures or coating P fertilizers needs further investigation. In this work, we coated a Rock Phosphate (RP) or soluble P fertilizer (Triple Superphosphate -TS) with Trichoderma harzianum, to enhance plant P uptake and growth of corn (Zea mays).The addition of T. harzianum to RP and TS reduced soil pH and increased the activity of soil acid and alkaline phosphatases which are important mechanisms involved in P mobilization by PSM. Trichoderma harzianum increased plant root length, root surface area and total root dry mass (17%). Trichoderma harzianum also increased plant P content (34%) and total dry matter content (22%) of plants fertilized with soluble phosphate (TS).Our main findings provide evidence that coating fertilizers with T. harzianum can be an effective way to enhance plant growth and P-use efficiency in agricultural systems. Importantly, we show that joint application with fertilizer did not impair important mechanisms of P mobilization by T. harzianum. Further research, in the field and under different environmental conditions, is necessary to validate the technology.Results: Enriching phosphorus (P) fertilizers with phosphate-solubilizing microorganisms (PSM) can be a promising strategy to enhance P-use efficiency in agriculture. However, the effects of these microorganisms when applied in mixtures or coating P fertilizers needs further investigation. In this work, we coated a Rock Phosphate (RP) or soluble P fertilizer (Triple Superphosphate -TS) with Trichoderma harzianum, to enhance plant P uptake and growth of corn (Zea mays).The addition of T. harzianum to RP and TS reduced soil pH and increased the activity of soil acid and alkaline phosphatases which are important mechanisms involved in P mobilization by PSM. Trichoderma harzianum increased plant root length, root surface area and total root dry mass (17%). Trichoderma harzianum also increased plant P content (34%) and total dry matter content (22%) of plants fertilized with soluble phosphate (TS).Our main findings provide evidence that coating fertilizers with T. harzianum can be an effective way to enhance plant growth and P-use efficiency in agricultural systems. Importantly, we show that joint application with fertilizer did not impair important mechanisms of P mobilization by T. harzianum. Further research, in the field and under different environmental conditions, is necessary to validate the technology.Conclusion: Enriching phosphorus (P) fertilizers with phosphate-solubilizing microorganisms (PSM) can be a promising strategy to enhance P-use efficiency in agriculture. However, the effects of these microorganisms when applied in mixtures or coating P fertilizers needs further investigation. In this work, we coated a Rock Phosphate (RP) or soluble P fertilizer (Triple Superphosphate -TS) with Trichoderma harzianum, to enhance plant P uptake and growth of corn (Zea mays).The addition of T. harzianum to RP and TS reduced soil pH and increased the activity of soil acid and alkaline phosphatases which are important mechanisms involved in P mobilization by PSM. Trichoderma harzianum increased plant root length, root surface area and total root dry mass (17%). Trichoderma harzianum also increased plant P content (34%) and total dry matter content (22%) of plants fertilized with soluble phosphate (TS).Our main findings provide evidence that coating fertilizers with T. harzianum can be an effective way to enhance plant growth and P-use efficiency in agricultural systems. Importantly, we show that joint application with fertilizer did not impair important mechanisms of P mobilization by T. harzianum. Further research, in the field and under different environmental conditions, is necessary to validate the technology. [ABSTRACT FROM AUTHOR]

Background: Cowpea is a grain legume of major importance in sub-Saharan Africa where it is cultivated by smallholder farmers on poor soils and production is often constrained by the parasitic weed Striga gesnerioides. Method: Experiments were conducted to assess the potential of rhizobium inoculation to mitigate Striga infection and increase cowpea productivity. We infested soils with S. gesnerioides and assessed the impact of treatments combining cowpea genotypes and bradyrhizobium inoculation on Striga dynamics and cowpea yield. In total, 20 cowpea genotypes were included, of which nine were resistant to Striga and 11 were susceptible. In the first experiment these were factorially combined with three inoculation options (two bradyrhizobium strains USDA3384 and IRJ2180A, and uninoculated control) in a screen-house using potted sterile soils. Second, the same trial was repeated in the field with basal phosphorus applied at sowing and a fourth treatment of fertilizer-N (urea) included testing whether N was limiting cowpea growth. The field trial also included a separate treatment with no input that served as a negative check. Result: Significant genotype x treatment interactions were observed in nodule counts, Striga attachment, emergence, and cowpea shoot growth in the screen-house. There were few nodules across all cowpea lines. Striga counts were the lowest for resistant varieties with no emerged plants. Rhizobial inoculants depressed Striga counts with consistent differences across cowpea genotypes. Inoculation with IRJ2180A performed the best against Striga attachment in resistant genotypes, and against Striga emergence in susceptible genotypes. In the field trial, cowpea grown without inputs had the least number of nodules. The genotype x treatment interaction was significant: resistant cowpea genotypes were free of emerged Striga while there was much more Striga emergence without input addition with susceptible genotypes. A significant genotype x treatment interaction was observed on cowpea grain yield. Yield response to inoculation was clearest with resistant genotypes inoculated with the strain IRJ2180A. Conclusion: The integrated use of Striga-resistant cowpea lines, basal phosphorus fertilizer and elite bradyrhizobium inoculants is a promising approach to mitigate Striga infection and increase cowpea productivity. [ABSTRACT FROM AUTHOR]

Background and aims: It has been confirmed that the declines in arbuscular mycorrhizal fungi (AMF) populations and agroecosystem diversity are largely due to nutrient enrichment caused by fertilization. Replacing chemical-only fertilization with organic fertilization is widely considered a possible approach for maintaining soil biodiversity and a healthy functioning ecosystem. Here we aim to examine the effects of organic fertilizer on AMF occurrence. Methods: We conducted a meta-analysis of 162 field experiments from 54 published studies conducted over the last 20 years. Our dataset included two groups: organic fertilization (OF) vs chemical-only fertilization (CF) and OF vs no fertilization (NF). Results: We found that organic fertilizer increased AM fungal biomass and was less detrimental to AMF richness than mineral-only fertilization. AMF responses to organic fertilizer were generally positive when AMF and host plants had a strong mutualistic symbiosis such as in phosphorus-deficient soil, drought and semi-drought areas, at low latitudes, and at testing sites that contained two or more plant species or included legume. In conditions other than these, the responses were generally negative. Organic carbon input, increased soil phosphorus and the ratio of fertilizer N and P jointly explain the effects of organic fertilizer on AMF occurrence. Conclusions: Our analysis indicates that, although some limiting factors exist, application of organic fertilizer can be an effective practice to protect AM symbiosis from the negative effects of nutrient enrichment in current cropping systems. [ABSTRACT FROM AUTHOR]

Aims: Phosphorus (P) fertilizers are often considered an important source of cadmium (Cd) in crop plants. However, increased plant Cd concentrations are not strictly related to the Cd content of P fertilizers. Considering this, we hypothesized that, alternatively, reduction of arbuscular mycorrhizal colonization by P fertilization enhances Cd accumulation in plants. Methods: Wheat and canola as mycorrhizal and non-mycorrhizal species, respectively, were grown under greenhouse conditions with and without soil sterilization. Phosphorus fertilizers with 0.09, 5, and 28 mg Cd kg−1 were applied at different rates with varied zinc (Zn) fertilization. Results: In wheat, all three P fertilizers markedly increased shoot and grain Cd concentrations as P supply was increased, irrespective of the Cd concentration in the fertilizers. These increases were pronounced with soil sterilization or at low zinc supply. Adding mycorrhizal fungi to sterilized soil substantially decreased shoot Cd concentrations. We found a strong negative relationship in wheat between mycorrhizal colonization and shoot Cd concentration, for both high- and low-Cd fertilizers. In contrast to wheat, shoot Cd concentrations in canola showed virtually no response to P supply or soil sterilization. High Zn application also reduced plant Cd concentrations, especially at high P rates. Conclusion: Our findings demonstrate the critical importance of mycorrhizal colonization in reducing Cd accumulation in wheat, and suggest that factors suppressing root mycorrhizal activity including P fertilization, will increase Cd uptake in mycorrhizal plants. [ABSTRACT FROM AUTHOR]

Aims: While reported short-term microbial responses to nutrient enrichment experiments are common, we provide results from a six-year data set in response to field manipulations of soil phosphorus (P) availability. We hypothesized that long-term shifts in P economics should result in the persistent suppression of P-acquiring extracellular enzymes when compared with ambient soils, as opposed to acclimation by the microbial community. Methods: P availability was experimentally increased, either directly by addition of phosphate fertilizer or indirectly by raising soil pH with lime in relatively P rich (i.e., glaciated) and P poor (i.e., unglaciated) forest soils. Soil chemistry, phosphatase enzymes (phosphomonoesterase, PM and phosphodiesterase, PD), and microbial structure (PLFA analysis) were measured annually for six years. Results: Since the start of the experiment, the microbial communities have become more distinct across treatments. PD enzyme activity was more responsive to the treatments than PM, especially in the glaciated elevated P treatment where ambient P availability was greatest. The treatments dramatically suppressed P-acquiring enzyme activity with no indication of acclimation. Conclusions: These results suggest that the initial conditions and ambient nutrient supply of an ecosystem will have a strong influence on its response sensitivity to continuous nutrient enrichment. [ABSTRACT FROM AUTHOR]

Aims: Struvite (MgNH4PO4·6H2O), 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. [ABSTRACT FROM AUTHOR]

Aims: Phosphate chemical fertilizers are costly and raise concerns about environmental pollution through industrial production. The use of phosphate rock (PRs) emerges as a more sustainable alternative for agriculture. The aim of this work was to isolate phosphate rock-solubilizing bacteria (PRSB) from maize mycorrhizosphere, having growth promoting traits and that will be arbuscular mycorrhizae fungi (AMF) compatible. Methods: Bacteria were isolated from the mycorrhizosphere of maize and tested for rock phosphate solubilization, production of organic acids, phosphatases and phytase activities, and growth promotion traits. The capacity of some strains to enhance the dry weight of maize plants was determined in a growth chamber experiment. The compatibility of the selected strains with Rhizophagus irregularis under in vitro conditions was also tested. Results: Out of 118 isolates from maize, eight belonging to Asaia lannaensis, Rahnella sp., Pantoea sp., and Pseudomonas sp. were found to be the best PRSB. On solid media, all strains mobilized P from tricalcium phosphate, hydroxyapatite, and PRs. A. lannaensis was the only PRSB showing visible solubilization of AlPO4 and FePO4. All the PRSBs solubilized PR by producing D-gluconic acid and 2-ketogluconic acid and by lowering the pH. Most strains presented IAA and siderophore production and different biofilm formation and motility capacities. All strains improved the dry weight of maize seedlings compared with non-inoculated plants. The results proved that PRSBs were able to grow on R. irregularis hyphae as the sole in vitro C source. Conclusions: Bacteria isolated from the mycorrhizosphere of maize shows effective solubilization of phosphorus from PR with different reactivity levels. The traits of these bacteria as growth promoters and their biocompatibility with AMF show their potential as inoculants. Improvement of the agronomic effectiveness of PRs is relevant for developing countries that use PRs directly as P-fertilizers (less expensive than soluble P-fertilizers) for sustainable agriculture. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus deficiency often limits crop productivity, while phosphate rock, which is used to produce phosphorus fertilisers, is a non-renewable resource. Formation of cluster roots is an adaptation to nutrient-poor soils in Lupinus species, including L. albus. Lupinus species also produce nodules, which require a large investment of phosphorus. Our aim is to test whether nodulation promotes cluster-root formation in L. albus. Methods: Seedlings of L. albus, either inoculated with rhizobia or non-inoculated, were grown in nutrient solution with a low phosphorus supply. Non-inoculated plants were provided with the same amount of nitrogen in the form of nitrate as the nodulated ones acquired, from both air and nutrient solution, based on preliminary experiments. We measured biomass, phosphorus and nitrogen concentrations as well as photosynthesis just prior to each harvest. Results: Nodulated plants and non-nodulated control plants produced the same amount of biomass. Nodulated plants had, on average, 86% more cluster roots than non-nodulated ones at the four harvests. As hypothesised, nodulation significantly promoted cluster-root formation; it also enhanced rates of photosynthesis. Conclusions: Nodulation promoted cluster-root formation and photosynthesis, presumably because nodules are significant sinks for phosphorus and photosynthates. Our results do not provide evidence for a trade-off between investment of resources in nodules and cluster roots. [ABSTRACT FROM AUTHOR]

Aims: The low phosphorus (P) fertilizer use efficiency in weathered, P deficient soils calls for better fertilizer formulations. We previously formulated nanoparticles containing P (NP-P) that were a successful fertilizer in nutrient solution. This study was set up to test the fate and the bioavailability of nanofertilizer-P and of that of native (colloid) P naturally present in soil. Methods: The NP-P consisted of nano-ferrihydrite (~ 10 nm) loaded with phosphate (P-nFh) and stabilized with either natural organic matter (NOM) or hexametaphosphate (HMP). Natural colloid concentrations were increased with KOH addition, as deflocculating agent, to soil; all tests used samples from P deficient, highly weathered soils. Results: Pot trials with rice seedlings did not reveal larger P uptake in the NP-P amended soils compared to equal doses of soluble PO4 or soluble HMP. Total Fe concentrations in soil solutions were unaffected by NP-P addition, whereas natural colloidal Fe and P markedly increased by KOH addition. The bioavailability of native colloidal P, mobilized by KOH addition, could not be assessed due to lack of growth, likely related to collapse of the soil structure. Conclusions: This study showed that P-loaded iron oxyhydroxide NPs insufficiently enhanced soluble P in soil to offer benefits over soluble fertilizers, likely because of a combined effect of lower diffusivity of NPs compared to Pi and lower bioavailability of NP-P than Pi. Smaller particles or small labile organic colloids might offer an improvement in both aspects. [ABSTRACT FROM AUTHOR]

Background and Aims: Rare earth elements (REE) are a group of the periodic table formed by 17 chemical elements (lanthanoids plus yttrium and scandium). They have been used in different field applications. In agriculture, they can be found in some phosphate fertilizers at levels one or two orders of magnitude higher than those found in normal agricultural soils. Citrus plants are known to present high levels of REE when compared to most other species, however, there is little information about bioavailability of REE in phosphate fertilizers for citrus plants. This work focuses on the study of REE behavior by the application of increasing doses of single superphosphate fertilizer in Rangpur lime (Citrus limonia Osbeck) plants in a greenhouse study. Methods: The technique used was instrumental neutron activation analysis (INAA). Results: The results showed that the fertilizer has caused significant increases in the content of REE in the citrus plant tissues, with higher concentrations in leaves than in branches. The highest substrate-leaf transfer factor was observed for La (0.0047), though the concentrations in the plants followed the same order found in the substrate, i.e. Ce > La > Sm > Eu > Sc. Conclusion: There was an increase of rare earth elements concentrations in Rangpur lime plants by superphosphate fertilizer application. [ABSTRACT FROM AUTHOR]

Background and aims: The effects of phosphorus and zinc applications on phosphorus and zinc concentrations in plants grown in different soil types have rarely been investigated. The aim of this study was to evaluate the effects of different soil types and phosphorus and zinc addition on growth and mineral element composition of red cabbage (Brassica oleracea var. capitata L. cv. Red Drumhead).Methods: Plants were grown for six weeks in three different soils (a freely drained Cambisol, an imperfectly drained Cambisol, and a Stagnosol) in a glasshouse. Each soil was amended with one of 25 combinations of phosphorus and zinc fertiliser. Soil characteristics, growth, and mineral element concentrations in shoots were assessed.Results: Soil type significantly affected shoot growth and concentrations of phosphorus, zinc, potassium, calcium, magnesium and manganese, but not iron concentration of red cabbage. Across soils, the observed responses were attributed to soil phosphorus, potassium, calcium, magnesium, and sulphur concentrations, organic matter content, and mineral composition, mainly kaolinite and plagioclase.Conclusions: Soil type effects on mineral element composition of red cabbage could have important implications for increasing mineral element concentration in crops to alleviate mineral element deficiencies in human diets. [ABSTRACT FROM AUTHOR]

Aims: Potato (Solanum tuberosum L.) has a large phosphorus (P)-fertiliser requirement. This is thought to be due to its inability to acquire P effectively from the soil. This work tested the hypothesis that early proliferation of its root system would enhance P acquisition, accelerate canopy development, and enable greater yields.Methods: Six years of field experiments characterised the relationships between (1) leaf P concentration ([P]leaf), tuber yield, and tuber P concentration ([P]tuber) among 27 Tuberosum, 35 Phureja and 4 Diploid Hybrid genotypes and (2) juvenile root vigour, P acquisition and tuber yield among eight Tuberosum genotypes selected for contrasting responses to P-fertiliser.Results: Substantial genetic variation was observed in tuber yield, [P]leaf and [P]tuber. There was a strong positive relationship between tuber yields and P acquisition among genotypes, whether grown with or without P-fertiliser. Juvenile root vigour was correlated with accelerated canopy development and both greater P acquisition and tuber biomass accumulation early in the season. However, the latter relationships became weaker during the season.Conclusions: Increased juvenile root vigour accelerated P acquisition and initial canopy cover and, thereby, increased tuber yields. Juvenile root vigour is a heritable trait and can be selected to improve P-fertiliser use efficiency of potato. [ABSTRACT FROM AUTHOR]

Background: Phosphorus (P) fertilizer is usually applied in excess of plant requirement and accumulates in soils due to its strong adsorption, rapid precipitation and immobilisation into unavailable forms including organic moieties. As soils are complex and diverse chemical, biochemical and biological systems, strategies to access recalcitrant soil P are often inefficient, case specific and inconsistently applicable in different soils. Finding a near-universal or at least widely applicable solution to the inefficiency in agricultural P use by plants is an important unsolved problem that has been under investigation for more than half a century.Scope: In this paper we critically review the strategies proposed for the remobilization of recalcitrant soil phosphorus for crops and pastures worldwide. We have additionally performed a meta-analysis of available soil 31P-NMR data to establish the potential agronomic value of different stored P forms in agricultural soils.Conclusions: Soil inorganic P stocks accounted on average for 1006 ± 115 kg ha−1 (57 ± 7%), while the monoester P pool accounted for 587 ± 32 kg ha−1 (33 ± 2%), indicating the huge potential for the future agronomic use of the soil legacy P. New impact driven research is needed in order to create solutions for the sustainable management of soil P stocks. [ABSTRACT FROM AUTHOR]

Background and aims: The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil.Methods: We applied 33P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated.Results: The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO3 extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil.Conclusion: We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently. [ABSTRACT FROM AUTHOR]

Aims: Glyphosate use has increased in recent decades with the adoption of minimum tillage techniques and the emergence of glyphosate-tolerant crop cultivars. There is evidence that glyphosate residues are common in cropping soils at sowing, but any potential impact of these residues on crop growth is not known. This study aimed to determine concentrations of soilborne glyphosate that are phytotoxic to common crop species and investigate any interactions between glyphosate residues and phosphorus (P) fertiliser.Methods: A pot study examined the impact of soilborne glyphosate residues on the growth of wheat (Triticum aestivum L.) and narrow leaf lupin (Lupinus angustifolius L) seedlings in a sandy soil with a low P buffering capacity in the absence or presence of P fertiliser applied as a liquid to the topsoil. A second pot study investigated whether the phytotoxic effects of soilborne glyphosate residues on lupin growth in the presence of P fertiliser could be mitigated by banding the P fertiliser (as superphosphate) as per standard practice by farmers.Results: Wheat was more tolerant of glyphosate residues than lupin, with glyphosate levels up to 14.8 mg kg−1 having no effect on wheat shoot growth at 48 days after sowing (DAS), while lupin shoot growth at 48 DAS had an ED10 (i.e. a 10% yield reduction) of glyphosate at 6.4 mg kg−1 in the absence of P fertiliser. When P fertiliser was applied, wheat shoot biomass had an ED10 of 5.8 mg glyphosate kg−1 soil while lupins had an ED10 of 3.4 mg glyphosate kg−1 soil. When P fertiliser (superphosphate) was banded at sowing, lupins grown adjacent to band were unaffected by glyphosate whereas the shoot weights of lupins planted above the band were significantly reduced by 68% in soil containing 1.3 mg kg−1 glyphosate and 81% in soil containing 3.4 mg kg−1 glyphosate.Conclusions: Where P fertiliser was applied, growth reductions in lupin seedlings were observed at soil glyphosate concentrations that have been observed in farmers’ fields, suggesting that glyphosate residues may be problematic in sandy soils with low P buffering capacities. Banding of P fertiliser exacerbated, rather than mitigated, the phytotoxicity of glyphosate residues to lupins where P fertiliser was banded directly beneath the seed. [ABSTRACT FROM AUTHOR]

Aims : Dried sewage sludge (SS) and the by-products of four SS thermal conversion processes (pyrolysis, incineration and two types of gasification) were investigated for phosphorus (P) availability. Methods : A sequential extraction was used to determine the distribution of P among different P pools. After mixing materials with soil, availability of the P was determined with soil P extractions and in a growth experiment with wheat. Results : Thermally converted SS contained a greater proportion of P within recalcitrant pools than dried SS. Despite having very different P pool distributions, the incinerated and dried SS provided similar amounts of P to plants. Plant P supply from dried and incinerated SS was lower than the comparable soluble P treatment (50 mg P kg), but higher than a soluble treatment at a lower rate (20 mg P kg). Plant P uptake in gasified and pyrolysed treatments was only marginally greater than uptake in a control (no P) treatment. Plant P uptake correlated most closely with diffusive gradients in thin films (DGT) P analysis of soil-material mixes. Phosphorus availability in the dried and incinerated SS treatments increased over time. Conclusions : We propose that the dried and incinerated SS have potential as slow release P fertilisers in low pH soils. [ABSTRACT FROM AUTHOR]

Aims: Soil hydrolysable P can be a main P source for biota in P-limited tropical rain forests. Soil hydrolysable P occurs in various chemical fractions, including, monoester P, diester P, pyrophosphate and phytate, which need enzymatic hydrolysis into orthophosphate before their assimilation into biota. We examined whether P-limited plants and microbes preferentially hydrolyzed specific fraction of soil hydrolysable P and whether those in different successional stages had different abilities to hydrolyze various soil hydrolysable P. Methods: We measured four classes of phosphatase (phosphomonoesterase, PME; phosphodiesterase, PDE; pyrophosphatase, PyP; and phytase, PhT) activities for fine-roots and soils in nitrogen (N) and P fertilized primary and secondary tropical rain forests in Sabah, Malaysia. Results: P fertilization reduced PME, PyP and PhT activities for fine-roots and PME and PyP activities for soils. Fine-roots in primary forests had higher PME and PyP activities whereas those in secondary forests had higher PhT activities. Conclusions: We suggest that P-limited trees and microbes depend more on hydrolysable P degraded by one step of enzymatic reaction (monoester P, pyrophosphate, and phytate) as a P source. We also suggest that trees have different soil-organic-P acquisition strategies in association with their life history strategies. [ABSTRACT FROM AUTHOR]

Aims: The objectives of this study were to evaluate (1) the fertilizer potential of bone char, (2) the effects of wood biochar on plant-available phosphorus (P), and (3) the role of root-mycorrhizae-biochar interactions in plant P acquisition from a P-fixing soil. Methods: Incubation and pot experiments were conducted with a P-fixing soil and maize with or without root hairs and arbuscular mycorrhizae (AM) inoculation. Olsen-, resin-P and plant P accumulation were used to estimate P availability from bone char, co-pyrolyzed bone char-wood biochar, and separate bone char and wood biochar additions produced at 60, 350 and 750 °C, and Triple Superphosphate (TSP). Results: Maize inoculated with AM showed similar P accumulation when fertilized with either 750 °C bone char or TSP. Pyrolyzing bone did not increase extractable P in soil in comparison to unpyrolyzed bone, apart from a 67 % increase in resin-extractable P after additions of bone char pyrolyzed at 350 °C. Despite greater Olsen-P extractability, co-pyrolysis of bone with wood reduced maize P uptake. Wood biochars reduced resin-P from bone char by 14-26 %, whereas oven-dried wood increased resin-P by 23 %. Conclusions: Bone char is an effective P fertilizer, especially if root-AM interactions are simultaneously considered. Biochar influences plant access to soil P and requires careful management to improve P availability. [ABSTRACT FROM AUTHOR]

The author comments on the results of a study conducted by researcher M. Long and colleagues entitled "Nitrogen deposition promotes phosphorus uptake of plants in a semi-arid temperate grassland." He discusses the chemical interaction between phosphorus and nitrogen fertilizers and suggests to consider the different nitrogen forms when studying this interaction. The types of nutrient co-limitation are explained, namely simultaneous co-limitation, independent co-limitation and serial limitation.

Aims: Phosphorus (P) is an essential nutrient necessary for maintaining crop growth, however, it's often used inefficiently within agroecosystems, driving industry to find new ways to deliver P to crops sustainably. We aim to combine traditional soil and crop measurements with climate-driven mathematical models, to give insight into optimising the timing and placement of fertiliser applications. Methods: The whole plant crop model combines an above-ground leaf model with an existing spatially explicit below-ground root-soil model to estimate plant P uptake and above ground dry mass. We let P-dependent photosynthesis estimate carbon (C) mass, which in conjunction with temperature sets the root-growth-rate. Results: The addition of the leaf model achieved a better estimate of two sets of barley field trial data for plant P uptake, compared with just the root-soil model alone. Furthermore, discrete fertiliser placement increases plant P uptake by up to 10 % in comparison to incorporating fertiliser. Conclusions: By capturing essential plant processes we are able to accurately simulate P and C use and water and P movement during a cropping season. The powerful combination of mechanistic modelling and experimental data allows physiological processes to be quantified accurately and useful agricultural predictions for site specific locations to be made. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal fungi (AMF) play a key role in the functioning of agricultural ecosystems. Therefore, understanding how the application of fertilizers, a common management practice, affects AMF communities is of major importance. Here we aimed to: (i) experimentally test whether different amounts and forms of phosphorus (P) fertilizer affect AMF diversity and community composition associated with the roots of apple trees ( Malus domestica); (ii) identify differences in tolerance to P fertilization between AMF taxa. Methods: We used 454-pyrosequencing of the small subunit rRNA gene amplicons to quantify AMF diversity and community composition in root samples obtained from a three year field experiment, with two inorganic, three slow-release P fertilization and one control treatment. Results: The slow-release fertilizer treatments showed significantly higher AMF richness and differed in community composition compared to the inorganic fertilizer treatments. The distribution of AMF OTUs showed a significantly nested pattern. Additionally, AMF communities in the inorganic fertilizer treatments were a subset of the communities in the slow-release fertilizer treatments. Conclusions: We demonstrate that application of slow-release fertilizers promoted AMF diversity in the roots of cultivated apple trees in comparison to the other treatments. The application of inorganic fertilizers elevated levels of plant-available P in the soil and selected only a small subset of abundant AMF, resulting in a lower AMF diversity. This may result in AMF communities dominated by inferior AMF mutualists. [ABSTRACT FROM AUTHOR]

Background and aims: Single superphosphate (SSP) is a major source of phosphorus (P) used in grazing systems to improve pasture production. The aim of this experiment was to determine the fate of fertiliser P in clover pastures under field conditions. Methods: A procedure was developed to radiolabel SSP granules with a P radiotracer, which was then applied to the soil surface (equivalent to ~12 kg P ha) of a clover pasture. Recovery of fertiliser P was determined in clover shoots, fertiliser granules and soil fractions (surface layer: 0-4 cm and sub-surface layer: 4-8 cm). Results: The P diffusion patterns of the P-labelled SSP granules were not significantly different to those of commercial SSP granules ( P > 0.05). Recovery of fertiliser P in clover shoots was 30-35 %. A considerable proportion of the fertiliser P (~28 %) was recovered in the surface soil layer and was largely inorganic P. Conclusions: Recovery of fertiliser P by clover plants was up to 35 % in the year of application. Much of the fertiliser P in soil fractions was inorganic P, which highlights the importance of inorganic P forms and dynamics in soils under clover pasture on a single season timeframe at these sites. [ABSTRACT FROM AUTHOR]

Aims: The readily available global rock phosphate (P) reserves may be depleted within the next 50-130 years warranting careful use of this finite resource. We develop a model that allows us to assess a range of P fertiliser and soil management strategies for Barley in order to find which one maximises plant P uptake under certain climate conditions. Methods: Our model describes the development of the P and water profiles within the soil. Current cultivation techniques such as ploughing and reduced till gradient are simulated along with fertiliser options to feed the top soil or the soil right below the seed. Results: Our model was able to fit data from two barley field trials, achieving a good fit at early growth stages but a poor fit at late growth stages, where the model underestimated plant P uptake. A well-mixed soil (inverted and 25 cm ploughing) is important for optimal plant P uptake and provides the best environment for the root system. Conclusions: The model is sensitive to the initial state of P and its distribution within the soil profile; experimental parameters which are sparsely measured. The combination of modelling and experimental data provides useful agricultural predictions for site specific locations. [ABSTRACT FROM AUTHOR]

Aims: Plant root system architecture adapts to the prevailing soil environment and the distribution of nutrients. Many species respond to localised regions of high nutrient supply, found in the vicinity of fertiliser granules, by elevating branching density in these areas. However, observation of these adaptations is frequently limited to plants cultured in idealised materials (e.g., hydrogels) which have a structure-less, homogenous matrix, which are spatially limited and in the case of rhizotron observation provide only 2D data that are not fully quantitative. Methods: In this study, in vivo, time resolved, micro-focus X-ray CT imaging (μCT) in 3D was used to visualise, quantify and assess root/fertiliser interactions of wheat plants in an agricultural soil during the entire plant life cycle. Two contrasting fertilisers [Triple superphosphate (TSP) and struvite (Crystal Green®)] were applied according to 3 different treatments, each providing an equivalent of 80 kg PO ha (struvite only, TSP only and a 50:50 mixture) to each plant. μCT scans (60 μm spatial resolution) of the plant roots were obtained over 14 weeks. Results: This is the first time that in situ root/soil/fertiliser interactions have been visualised in 3D from plant germination through to maturity. Results show that lateral roots tend to pass within a few millimetres of the phosphorus (P) source. At this length scale, roots are able to access the P diffusing from the granule. Conclusions: Quantitative analysis of root/fertiliser interactions has shown that rooting density correlates with granule volume-loss for a slow release, struvite fertiliser. [ABSTRACT FROM AUTHOR]

Soil phosphate research has been hampered by the persistence of superseded ideas and language. Consequently few have recognised the two phosphate-sparing effects of previous phosphate fertilizer application: one caused by the decreased buffering capacity; the other caused by the eventual cessation of the diffusive movement of phosphate into the adsorbing particle. This is one cause of excessive phosphate applications and thence to contamination of water. [ABSTRACT FROM AUTHOR]

Aims: This paper assessed the effect that the vertical stratification of nutrients in conservation cropping systems of Australia has on phosphorus (P) and nitrogen (N) fertiliser use efficiency. Methods: Intact soil cores from two long-term tillage experiments, located on a Vertosol and on a Calcarosol were used to assess if tillage system (zero tillage - ZT vs conventional tillage - CT) and soil water influence fertiliser use efficiency (using P and N) of wheat under controlled growth conditions. Results: Adding P increased shoot growth and P uptake on the Calcarosol, provided the surface remained moist and N was applied. The percentage of plant P derived from fertiliser (Pdff) was greater on the Calcarosol regardless of tillage practice. Pdff increased when the soil remained wet or when N was added. The percentage of N derived from fertiliser (%Ndff) was not affected by tillage practice on the Vertosol but when the soil surface was allowed to dry, it was significantly greater under ZT than CT on the Calcarosol. Adding P increased N fertiliser recovery but tillage practice had no effect. Conclusion: The effect of tillage practice on P and N fertiliser use efficiency depends on soil and topsoil water status. [ABSTRACT FROM AUTHOR]

Aims: Phosphorus (P) removed in grains causes losses of P from fields each year. Reducing grain P may therefore improve the P efficiency of cropping systems. This study quantified impacts of reduced seed-P concentrations on rice seedling vigor and final yields and investigated whether this was influenced by soil P supply or genotype. Methods: Seed batches with P concentrations ranging from 0.9 to 3.5 mg g were produced by growing rice in field plots ranging from severely P-deficient to fully fertilized and used in glasshouse and field experiments to investigate effects on seedling vigor and final grain/straw yield. Results: 'Genotype by seed-P concentration' interactions were significant for seedling vigor but grain yield was generally not affected. This suggested some genotypes were sensitive to reduced seed-P concentration during the seedling stage while others with seed-P concentrations as low as 0.9 mg g maintained rapid early vigor and high grain yield. Conclusions: Results indicate it may be possible to reduce seed-P concentrations without having negative effects on seedling vigor or yield. The development of cultivars with reduced seed-P concentration, particularly if combined with rapid seedling root growth, could be a valid option to improve the sustainability of phosphate fertilizer use. [ABSTRACT FROM AUTHOR]

Aims: Few direct tests of phosphorus (P) limitation on highly-weathered soils have been conducted, especially in mature, native Eucalyptus stands. We tested whether growth in a mature >80-year old stand of Eucalyptus tereticornis in Cumberland Plain Woodland was limited by P, and whether this P-limitation affected leaf photosynthetic capacity. Methods: P was added to trees at the native woodland site at 50 kg ha year in each of 3 years, and stem and leaf responses were measured. Results: Leaf P concentrations before fertilisation were < 1 mg g and N:P ratios ranged between 16 and 23. Addition of 50 kg ha year of P increased leaf P concentration significantly (+50 %) compared to non-fertilised trees, for two but not for the 3 years. Despite higher leaf P in fertilised trees, photosynthetic capacity was unaffected. However, there was a 54 % increase in tree stem basal area growth during the first and second years of P fertilisation, statistically significant in the second year of the experiment. Conclusions: Our evidence shows that E. tereticornis is P-limited on Cumberland Plain soils. This has implications for forest responses to rising atmospheric [CO], because photosynthesis in elevated [CO] may become further constrained by required phosphate pools within the photosynthetic apparatus. [ABSTRACT FROM AUTHOR]

Aims: Soil biota regulate essential ecosystem processes but our understanding of how soil fertility constrains biotic interactions remains limited. We investigated belowground responses to short-term phosphorus (P) fertilization in a P-limited woodland. Methods: Ten Eucalyptus tereticornis were randomly selected and five fertilized with superphosphate equivalent to 50 kg P ha over 6 months. We estimated aboveground (understory) and belowground plant biomass, and collected samples for soil chemistry, arbuscular mycorrhizal (AM) root colonization, soil fungal abundance and community composition, and extraction of nematodes and microarthropods. Results: P-fertilization increased root biomass, abundance of non-AM fungi, and abundances of Collembola, and altered fungal community structure, but was associated with a decrease in predatory nematodes. Structural equation modelling indicated that effects on Collembola and fungal abundances were mediated by direct effects of the fertilizer treatment and/or indirect effects via root biomass responses. However, fungal community compositional changes and reductions in predatory nematodes resulted primarily due to fertilization-mediated changes in soil pH. Conclusion: Our study shows that understory plant communities and soil biota are P-limited at the study site but that some biotic groups appear to be more sensitive to changes in soil pH than to increases in P availability. [ABSTRACT FROM AUTHOR]

Aims: To estimate the production of external ectomycorrhizal mycelia (EMM) in Norway spruce forests with varying nitrogen (N) and phosphorus (P) levels, and to relate this to the N retention capacity of ectomycorrhizal fungi (EMF) and N leaching. Methods: Seasonal changes in EMF production (in ingrowth mesh bags) and soil water N (in suction lysimeters) were analyzed after fertilization with N or N combined with P. The EMF N retention capacity was estimated by the addition of isotopically labeled N to the mesh bags. Results: No relationship was found between the seasonal variation in EMF growth and N leakage from the soil. However, in the mesh bags, the total assimilation of N by EMF was almost halved by N fertilization, while twice as much N leached through. Conclusions: We found a high specific N assimilation capacity per unit weight of EMF mycelia. This was unaffected by N fertilization, but the total assimilation of N by EMF was drastically reduced due to reduced production of EMM. However, N-retaining processes other than N assimilation by EMF must be taken into account to explain the losses of N after fertilization. [ABSTRACT FROM AUTHOR]

Background and aims: Although foliar fertilisation using liquid forms of phosphorus (P) is not a new concept, its adoption has been hindered by a limited understanding of the variability in performance of fluid forms of foliar P applied to broadacre crops. There is a need to identify how the surface structure of leaves influences the absorption and subsequent translocation of foliar-applied P in above ground plant parts. Methods: This study examined the surface properties of wheat leaves using scanning electron microscopy and measured the recovery of foliar-applied fertiliser that was labelled with either P or P from both the adaxial (upper) and abaxial (lower) leaf sides into untreated plant parts. Results: We found that the adaxial leaf surface absorbed and translocated more foliar-applied P away from the treated leaf than the abaxial surface, likely related to the higher abundance of trichomes and stomata present on that side of the leaf. The recovery of the foliar-applied fertiliser varied with rate and timing of application; ranging from <30 % to as much as 80 % of the adaxial-applied fertiliser translocated from the treated leaf into the wheat ear. Conclusions: This study demonstrated that the differences in surface morphological features between leaf sides influenced the combined absorption and subsequent translocation of foliar-applied P in the above ground plant parts. This is due to a direct effect on the foliar pathway and/or due to differences in wettability affecting both the leaf coverage and drying time of fertilisers on the leaves. Although foliar fertilisation in this study contributed less than 10 % of the total P in the plant, it provided a more efficient pathway for P fertilisation than soil-applied P. [ABSTRACT FROM AUTHOR]

Background and aims: Limited information is available on how cadmium (Cd) applied in phosphate fertilizer interacts with soil and environmental conditions over time to affect crop Cd concentrations. Methods: Field studies from 2002 to 2009 at seven locations evaluated the cumulative effects of P fertilizer rate and Cd concentration on seed Cd concentration of durum wheat ( Triticum turgidum L.) and flax ( Linum usitatissiumum L.). Results: Soil characteristics and environment affected Cd availability. Durum wheat grain Cd increased with P fertilizer rate but effect on flaxseed Cd concentration was smaller. Cadmium concentration in fertilizer had a greater effect on flaxseed than durum wheat Cd concentration. Seed Cd concentration of both crops was greatest with the highest rate P fertilizer containing the highest Cd concentration. There was not a strong cumulative effect of fertilization over the 8 years of the study, indicating attenuation of Cd availability over time. Conclusions: Cadmium in phosphate fertilizer increases Cd available for crop uptake, but crop Cd concentration is also affected by soil characteristics and annual environmental conditions. Type of crop produced and soil and environmental characteristics that affect phytoavailability must be taken into account when assessing the Cd risk from P fertilization. [ABSTRACT FROM AUTHOR]

Aims: Evidence shows that tillage modifies soil properties, especially phosphorus (P) dynamics. Our objective was to disentangle long-term effects of P-fertilization and tillage on arbuscular mycorrhizal fungal (AMF) proliferation and community structure. Methods: Changes in the community structure of AMF and in the density of their hyphae and spores induced by moldboard plow (MP) or no till (NT), and fertilization with 0, 17.5, or 35 kg P ha were sought in the 0-15 cm and 15-30 cm soil layers after soybean harvest, at a long-term (17 years) experimental site in a humid continental zone of eastern Canada. The relationships among AMF, soil and plant attributes were examined. Results: The 0-15 cm and 15-30 cm soil layers had different properties under NT, but were similar under MP, after 17 years, and MP increased soil available P levels. Phosphorus fertilization increased P levels in soil and in soybean. Treatment effects on AMF spore and hyphal density at 0-15 cm were greater than that at 15-30 cm, whereas effects on AMF community structure did not change with soil depths. At 0-15 cm, P-fertilization increased AMF spore density and reduced AMF hyphal density, and MP reduced AMF spore density. A total of eight AMF phylotypes were detected. Phosphorus fertilization reduced AMF phylotype richness and Shannon diversity index. Soil P availability increased under MP and hence the influence of P-fertilization treatments on the frequency of AMF phylotype detection varied with tillage system; it declined with P-fertilization under MP, but increased under NT. Conclusions: Phosphorus fertilization shifts resource partitioning in AMF propagules rather than in their hyphae, and degrades the genetic diversity of AMF in soil; tillage increases soil P availability and hence aggravates the impact of P-fertilization. [ABSTRACT FROM AUTHOR]

Background and aims: Malnutrition resulting from zinc (Zn) and iron (Fe) deficiency has become a global issue. Excessive phosphorus (P) application may aggravate this issue due to the interactions of P and micronutrients in soil crop. Crop grain micronutrients associated with P applications and the increase of grain Zn by Zn fertilization were field-evaluated. Methods: A field experiment with wheat was conducted to quantify the effect of P applications on grain micronutrient quality during two cropping seasons. The effect of foliar Zn applications on grain Zn quality with varied P applications was tested in 2011. Results: Phosphorus applications decreased grain Zn concentration by 17-56%, while grain levels of Fe, manganese (Mn) and copper (Cu) either remained the same or increased. Although P applications increased grain yield, they restricted the accumulation of shoot Zn, but enhanced the accumulation of shoot Fe, Cu and especially Mn. In 2011, foliar Zn application restored the grain Zn to levels occurring without P and Zn application, and consequently reduced the grain P/Zn molar ratio by 19-53% than that without Zn application. Conclusions: Foliar Zn application may be needed to achieve both favorable yield and grain Zn quality of wheat in production areas where soil P is building up. [ABSTRACT FROM AUTHOR]

Background: Crop production in China has been greatly improved by increasing phosphorus (P) fertilizer input, but overuse of P by farmers has caused low use efficiency, increasing environmental risk and accumulation of P in soil. From 1980 to 2007, average 242 kg P ha−1 accumulated in soil, resulting in average soil Olsen P increasing from 7.4 to 24.7 mg kg−1. China is facing huge challenges to improve P use efficiency through optimizing corresponding technology and policies. The problem is exacerbated because people have been shifting their diet from plant-based to animal-enriched foods. This results in higher P load in the food chain and lower P use efficiency. Scope: A multidisciplinary approach has been used to improve P management at the field and national level in China. Management strategies based on the soil and on the plant rhizosphere have been developed to increase efficient use of P. A national soil testing and fertilizer recommendation program has been used since 2005 to control build-up and maintenance of P levels. Interactions between root growth and the rhizosphere have been manipulated in intercropping systems and plant genetic traits have been exploited. Phosphorus surplus is highly associated with animal concentrated feed. Conclusions: The P-saving potential by the integrated P management strategies of P flow reaches 1.46 Mt P in 2050 compared to 2005. [ABSTRACT FROM AUTHOR]