Inoculation of arbuscular mycorrhizal fungi can substantially reduce phosphate fertilizer application to Allium fistulosum L. and achieve marketable yield under field condition

The effects of inoculating arbuscular mycorrhizal (AM) fungi on the growth, phosphorus (P) uptake, and yield of Welsh onion (Allium fistulosum L.) were examined under the non-sterile field condition. Welsh onion was inoculated with the AM fungus, Glomus R-10, and grown in a glasshouse for 58?days. Non-inoculated plants were grown as control. Inoculated and non-inoculated seedlings were transplanted to a field with four available soil P levels (300, 600, 1,000, and 1,500?mg P₂O₅?kg^?1 soil) and grown for 109?days. AM fungus colonization, shoot P concentration, shoot dry weight, shoot length, and leaf sheath diameter were measured. Percentage AM fungus colonization of inoculated plants was 94% at transplant and ranged from 60% to 77% at harvest. Meanwhile, non-inoculated plants were colonized by indigenous AM fungi. Shoot length and leaf sheath diameter of inoculated plants were larger than those of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Shoot P content of inoculated plants was higher than that of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Yield (shoot dry weight) was higher for non-inoculated plants grown in soil containing 1,000 and 1,500?mg P₂O₅?kg^?1 soil than for those grown in soil containing 300 and 600?mg?P₂O₅ kg^?1 soil. Meanwhile, the yields of inoculated plants (200?g plant^?1) grown in soils containing the four P levels were not significantly different. Yield of inoculated plants grown in soil containing 300?mg P₂O₅ kg^?1 soil was similar to that of non-inoculated plants grown in soil containing 1,000?mg P₂O₅?kg^?1 soil. The cost of AM fungal inoculum for inoculated plants was US$ 2,285?ha^?1 and lower than the cost of superphosphate (US$ 5,659?ha^?1) added to soil containing 1,000?mg P₂O₅ kg^?1 soil for non-inoculated plants. These results indicate that the inoculation of AM fungi can achieve marketable yield of A. fistulosum under the field condition with reduced application of P fertilizer.     

Phosphorus Fractionations in Acidic Piedmont Rice Soils

Piedmont lands in Bangladesh, India, Nepal, and many other Asian countries are important rice-growing soils, but most of the soils are potentially phosphorus (P) deficient because of low pH. Phosphorus fractions of rice-growing acidic piedmont soils were determined. Soil samples were amended with 100 and 200 mg P kg^?1 soil, and a control soil without P amendment was maintained. The samples were analyzed for the following fractions: solution P, labile pool [sodium bicarbonate (NaHCO₃) P], alkali-extracted inorganic pool [sodium hydroxide (NaOH) P_i], organic pool (NaOH P_o), acidic pool [sulfuric acid (H₂SO₄)?hydrochloric acid (HCl) P], and residual P. About 98% of the applied P in soils was extracted by the sequential extraction employed in the present experiment. The mean total P concentration in 10 acidic Piedmont soils was 247 ppm, of which only 0.12% was in solution, 8% labile (NaHCO₃), 16% NaOH-extracted inorganic, 32% resistant organic, 18% relatively recalcitrant acidic, and 25% residual. Application of P fertilizer increased mainly the labile P fraction, which would be easily available to wetland rice. Solution P was positively and significantly correlated with pH_KCl (r = 0.64, P < 0.05) and negatively correlated with clay (r = ?0.77, P < 0.01). A negative and significant correlation of NaHCO₃-P was observed with pH_H2O (r = ?0.62, P < 0.05). Solution P showed a negative and significant relationship with NaOH-P_i (r = ?0.63, P < 0.05). A significant and negative relationship of solution P was also observed with acid P (r = ?0.78, P < 0.01) and residual P (r = ?0.82, P < 0.01). The relationship of NaHCO₃-P with NaOH-P_i was positive (r = 0.70, P < 0.05) and significant. Similarly, a positive and significant relationship (r = 0.89, P < 0.01) between NaOH-P_i and acid P was observed, and acid P was positively and significantly correlated with residual P (r = 0.84, P < 0.01).     

Transformation and recovery of fertilizer phosphorus applied to five Quebec Humaquepts

Abstract

Improving phosphorus (P) fertilizer efficiency while minimizing environmental impacts requires better understanding of the dynamics of applied P in soils. This study assessed the fate of fertilizer P applied in Quebec Humaquepts. A pot experiment with five textural Humaquepts, each receiving 0 (P0), 10 (P10), 20 (P20) and 40 (P40) mg P kg^?1 soil was conducted under barley (Hordeum vulgare L.)-soybean (Glycine max L.) rotations. A modified Hedley procedure was used for soil P fractionation. The clayey soils reached a plateau of dry matter at less P applied than the coarser-textured soils. Plant P uptake, soil labile inorganic P (resin-P?+?NaHCO₃-P_i) and moderately labile inorganic P (NaOH-P_i) increased proportionally with P rate. The coarser-textured soils had lower contents of labile and moderately labile P_i, but a larger increase in labile P_i than the finer-textured soils after receiving P additions. The applied P was retained primarily as soil labile P_i, accounting for 43–69% of total soil recovery of applied P, compared to 20–30% recovered as moderately labile P_i, and 7–29% assumed to be sparingly soluble P (HCl-P?+?H₂SO₄-P). The labile P_i recovery of applied P was linearly depressed with clay content, compared to a quadratic relation for the moderately labile P_i recovery. The results suggest the importance of accounting for soil texture along with soil P adsorption capacity when assessing the efficiency of applied P, P accumulation in soils and subsequently P nutrient management.     

Phosphorus fractions in soils from an area with high density of livestock population

The concentrations of total phosphorus and its distribution in fractions of different solubility have been investigated in 6 different organic manures and in 69 soil samples from two counties with high concentrations of livestock population (Cloppenburg and Vechta, Lower Saxony). In the manures, large proportions of total P (means: 24% and 44%) were extracted by H₂O and anion exchange resin so that increases in labile soil P fractions can be expected if these manures are applied. The high total P-concentrations of the soils up to 8173 mg kg^?1 were related to pedogenesis and soil use. Data such as soil P test (H₂O-P, DL-P) values above the P-fertilizer recommendations and considerably larger proportions of soluble and labile P-fractions (7%-47% of total soil P) than in other regions strongly suggested that significant P-losses from the soils are likely. Therefore, reductions of P inputs to soils and measures to reduce the P-solubility and mobility are necessary for water conservation in this region.     

Chemical Fractionation of Trace Elements in Biosolid‐Amended Soils and Correlation with Trace Elements in Crop Tissue

Abstract

A previous study indicated that agricultural biosolid applications increased the concentration of EPA₃₀₅₀‐digestible trace elements in soils on Pennsylvania production farms but could not indicate potential trace‐element environmental availability. This study was conducted to determine if biosolid application had altered the distribution of trace‐elements among operationally defined soil fractions and the relationship of trace element concentrations in soil and crop tissues. Biosolid‐amended and unamended soils from production farms in Pennsylvania were extracted using a modified Bureau Communautaire de Référence (BCR) sequential fractionation technique and analyzed for chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Trace‐element concentrations in crop tissues (soybean silage, sudangrass, corn grain, alfalfa hay, and orchardgrass hay) from the same farms were also determined. Fractionation results indicated that the proportion of Cr, Cu, Ni, Pb, and Zn that is potentially bioavailable is quite small in unamended soils. Biosolid applications significantly (P≤0.1) increased concentrations of Cu in all soil fractions (average increase over unamended soil=1.14, 8.27, 6.04, and 5.84 mg kg^?1 for the exchangeable, reducible, oxidizable, and residual fractions, respectively), Ni (0.41, 1.65 mg kg^?1 for the reducible and residual fractions, respectively), Pb (5.12 and 1.49 mg kg^?1 for the reducible and residual fractions, respectively), and Zn (8.28, 7.12, 4.44, and 8.98 mg kg^?1 for the exchangeable, reducible, oxidizable, and residual fractions, respectively) but did not significantly increase Cr in any soil fraction. Concentrations of Cu in all soil fractions were significantly (P≤0.01) correlated with concentrations of Cu in orchardgrass tissue (r=0.70, 0.66, 0.76, and 0.69 for the exchangeable, reducible, oxidizable, and residual soil fractions, respectively). Concentrations of exchangeable and reducible Zn were significantly correlated with Zn in sudangrass tissue (r=0.81 and 0.67), and reducible Zn was significantly correlated with Zn concentrations in orchardgrass tissue (r=0.65). Application of biosolids had little effect on bioavailability of Cr, Ni, or Pb, whereas higher loadings of Cu and Zn led to a shift toward the more labile soil fractions. Loadings of Cu and Zn were much smaller than cumulative loadings permitted under U.S. Environmental Protection Agency (USEPA) Part 503 regulations. Chemical soil fractionation was able to detect increases in labile soil Cu and Zn that relate to increased phytoavailability.     

Phosphorus desorption from calcareous soils with different initial Olsen-P levels and relation to phosphate fractions

Purpose

Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (P_i) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which P_i fraction exerts the greatest influence on P desorption capacity.

Materials and methods

Five soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg^?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with P_i fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.

Results and discussion

The content and proportions of dicalcium phosphate fraction (Ca₂-P), octacalcium phosphate fraction (Ca₈-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in P_i increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca₈-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg^?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg^?1 desorbed P per 1 mg kg^?1 increase of initial Olsen-P. Ca₂-P exerted the conclusive effect on P desorption in the first four extractions, but Ca₈-P played a more important role in the 16 extractions.

Conclusions

Ca₈-P was the greatest potential pool for P desorption after Ca₂-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.

     

Assessing the Effect of Phosphorus Fertilizer Levels on Soil Phosphorus Fractionation in Rhizosphere and Non-Rhizosphere Soils of Wheat

This study evaluated the effects of phosphorus (P) fertilizer levels on inorganic P fractions. Wheat cultivars (Azadi and Marvdasht) were grown in the soils amended with the four rates of P fertilizer levels (no fertilizer, 10, 15, and 25 mg available P kg^?1 soil). Soils were sampled from rhizosphere and non-rhizosphere areas after 6 weeks. The mean of all P fractions was significantly different in various P fertilizer levels. The smallest and the largest amounts of all P fractions were observed in the soil with no P and in 25 mg kg^?1 soil P level, respectively. The Azadi cultivar, as P-efficient, showed the smallest increase in soil P fractions with increasing soil P levels. The means of all P fractions except Al-phosphates (Al-P) were significantly higher in non-rhizosphere soil. There were differences between these cultivars associated with the more inaccessible fractions at the 15 mg P kg^?1 soil level.     

Surface runoff phosphorus (P) loss in relation to phosphatase activity and soil P fractions in Florida sandy soils under citrus production

Phosphorus losses by surface runoff from agricultural lands have been of public concern due to increasing P contamination to surface waters. Five representative commercial citrus groves (C1-C5) located in South Florida were studied to evaluate the relationships between P fractions in soils, surface runoff P, and soil phosphatase activity. A modified Hedley P sequential fractionation procedure was employed to fractionate soil P. Soil P consisted of mainly organically- and Ca/Mg-bound P fractions. The organically-bound P (biological P, sum of organic P in the water, NaHCO₃ and NaOH extracts) was dominant in the acidic sandy soils from the C2 and C3 sites (18% and 24% of total soil P), whereas the Ca/Mg-bound P (HCl-extractable P) accounted for 45-60% of soil total P in the neutral and alkaline soils (C1, C4 and C5 soils). Plant-available P (sum of water and NaHCO₃ extractable P fractions) ranged from 27 to 61 mg P kg⁻¹ and decreased in the order of C3>C4>C1>C2>C5. The mean total P concentrations (TP) in surface runoff water samples ranged from 0.51 to 2.64 mg L⁻¹. Total P, total dissolved P (TDP), and PO₄³⁻-P in surface runoff were significantly correlated with soil biological P and plant-available P forms (p<0.01), suggesting that surface runoff P was directly derived from soil available P pools, including H₂O- and NaHCO₃- extractable inorganic P, water-soluble organic P, and NaHCO₃- and NaOH-extractable organic P fractions, which are readily mineralized by soil microorganisms and/or enzyme mediated processes. Soil neutral (55-190 mg phenol kg⁻¹ 3 h⁻¹) and natural (measured at soil pH) phosphatase activities (77-295 mg phenol kg⁻¹ 3 h⁻¹) were related to TP, TDP, and PO₄³⁻-P in surface runoff, and plant-available P and biological P forms in soils. These results indicate that there is a potential relationship between soil P availability and phosphatase activities, relating to P loss by surface runoff. Therefore, the neutral and natural phosphatase activities, especially the natural phosphatase activity, may serve as an index of surface runoff P loss potential and soil P availability.     

Potential Use of Bioorganic Nutrient Source Dynamics on Cropping Behavior,Soil Properties,and Quality Attributes of Apricot

The comparative efficacy of bioorganic nutrients on cropping behavior and soil properties of apricot trees was studied. Bioorganic nutrient sources, namely, vermicompost (VC), biofertilizers (BF), cow urine (CU), and vermiwash (VW), were evaluated in 13 treatment combinations. The treatment application of VC at 50 kg, BF at 60 g, CU at 12.5%, and VW at 12.5% significantly improved cropping and soil properties over nitrogen–phosphorus–potassium (N–P–K) chemical fertilizers. Available macronutrient contents of soil (viz., N, P, and K) increased by 25.50, 70.90, and 6.44%, respectively. Diethylenetriaminepentaacetic acid–extractable micronutrients (Fe, Cu, Zn, and Mn) increased by 15.45, 35.90, 80.36, and 40.12%, respectively. Microbial biomass of Pseudomonas, Bacillus, Azotobacter chroococcum, and arbuscular mycorrhizal (AM) fungi improved 51.83, 122.78, 60.93, and 2.91 times, respectively. This superior combination also resulted in considerably greater amounts of leaf macro- and micronutrients: N (2.34%), P (0.34%), K (3.71%), iron (Fe; 172.83 mg kg^?1), copper (Cu; 12.79 mg kg^?1), zinc (Zn; 25.49 mg kg^?1), and manganese (Mn; 54.32 mg kg^?1), which might be responsible for better cropping behavior and productivity in apricot trees.     

Legacy phosphorus in calcareous soil under 33 years of P fertilizer application: Implications for efficient P management in agriculture

Phosphorus (P) fertilizers have long been applied in agriculture. However, the influence of long-term P addition on the evolution of soil P fertility and legacy P characteristics have not been well-documented. Herein, literature data were collected from the Chinese National Knowledge Infrastructure Database (CNKI) to explore the evolution of soil P fertility after 33 years of application of P fertilizer; different soil samples were collected from cropland and adjacent uncultivated land to analyse the distribution of P fractions at different soil depths (0–0.8 m) using Guppy's sequential P extraction method. We found that soil Olsen-P significantly increased by 3.6-fold (from 7.2 mg kg⁻¹ in 1981 to 25.9 mg kg⁻¹ in 2013) after 33 years of P application, while total P increased slightly. The ratios of inorganic P fractions in cropland to those uncultivated land followed NaHCO₃-P (1.47) > NaOH-P (1.38) > resin-P (1.37) > residue-P (1.17) > HCl-P (1.11), suggesting that long-term P addition contributed more to labile and moderately labile P rather than non-labile P. Moreover, a principal component analysis could distinguish between cropland and uncultivated land, indicating that long-term application of P fertilizer changed soil P characteristics. Compared to uncultivated land, soil NaHCO₃-P in cropland was closely associated with soil organic C, total nitrogen and carbonate. Collectively, our findings highlight that soil legacy P was notably increased after long-term of P application, and a large portion of the applied P remained in labile and moderately labile forms. Therefore, soil legacy P can be recommended as a useful P management tool.     

Variable inhibition of iron uptake by oat phytosiderophore in five soybean cultivars

Abstract

Greenhouse experiment was conducted to evaluate the effect of arbuscular mycorrhizal fungi (AMF) on plant growth, and nutrient uptake in saline soils with different salt and phosphorus (P) levels. The following treatments were included in this experiment: (i) Soil A, with salt level of 16.6 dS m^?1 and P level of 8.4 mg kg^?1; (ii) Soil B, with salt level of 6.2 dS m^?1 and P level of 17.5 mg kg^?1; and (iii) Soil C, with salt level of 2.4 dS m^?1 and P level of 6.5 mg kg^?1. Soils received no (control) or 25 mg P kg^?1 soil as triple super phosphate and were either not inoculated (control) or inoculated with a mixture of AM (AM1) and/or with Glomus intraradices (AM2). All pots were amended with 125 mg N kg^?1 soil as ammonium sulfate. Barley (Hordeum vulgar L., cv. “ACSAD 6”) was grown for five weeks. Plants grown on highly saline soils were severely affected where the dry weight was significantly lower than plants growing on moderately and low saline soils. The tiller number and the plant height were also lower under highly saline condition. The reduced plant growth under highly saline soils is mainly attributed to the negative effect of the high osmotic potential of the soil solution of the highly saline soils which tend to reduce the nutrient and water uptake as well as reduce the plant root growth. Both the application of P fertilizers and the soil inoculation with either inoculum mixture or G. intraradices increased the dry weight and the height of the plants but not the tiller number. The positive effect of P application on plant growth was similar to the effect of AM inoculation. Phosphorus concentration in the plants was higher in the mycorrhizal plant compared to the non mycorrhizal ones when P was not added. On the other hand, the addition of P increased the P concentration in the plants of the non mycorrhizal plants to as high as that of the mycorrhizal plants. Iron (Fe) and zinc (Zn) uptake increased with AM inoculation. The addition of P had a positive effect on micronutrient uptake in soil with low level of soil P, but had a negative effect in soil with high level of soil P. Micronutrient uptake decreases with increasing soil salinity level. Inoculation with AMF decreases sodium (Na) concentration in plants grown in soil of the highest salinity level but had no effect when plants were grown in soil with moderate or low salinity level. The potassium (K) concentration was not affected by any treatment while the K/Na ratio was increased by AM inoculation only when plant were grown in soil of the highest salinity level.     

Chemical fractions and response of cauliflower (Brassica oleracea var. botrytis) to soil applied boron

The present study was conducted with an objective to estimate the distribution of boron (B) application in various soil fractions and their plant response for assessing the availability in the soil. Two soils (alluvial and red soil) and five levels of B (0, 0.5, 1, 2 and 3?mg B kg^?1 soil) were applied in the pot experiment, and pots were sown with cauliflower (Sabour Agrim) arranged in a completely randomized block design (CRD) with three replications. Result showed that the curd yield of cauliflower increased significantly upto 2?mg B kg^?1 soil irrespective of soils. The percent yield increase was 14.78 and 15.01 in alluvial and red soil over the control, respectively. The initial total B content was 35.88 (alluvial soil) and 15.51 (red soil) mg·kg^?1. The mean content of Fraction I, II, III, IV and V in alluvial soil was 1.11, 1.54, 0.65, 1.49, and 95.18% and in red soil was 2.68, 4.47, 6.62, 2.50, and 83.59% of the total soil B, respectively. For changes in amount of B fractions due to B applications there was significant effect on all the fractions except Fraction II. The increase in apparent B uptake was 0.43?mg B kg^?1 in alluvial soil and 0.25?mg B kg^?1 in red soil over the control (0?mg B kg^?1 soil). Regression equation of yield and B fractions showed the relationship between first four fractions to the yield. Residual fraction was found to be collinear during calculation. Overall the study predicted the bioavailability and dynamics of B in the two distinct soils.     

Impact of Soil Sorption Characteristics and Bedrock Composition on Phosphorus Concentrations in two Bohemian Forest Lakes

Phosphate (PO₄-P) sorption characteristics of soils and bedrock composition were determined in catchments of two mountain lakes, Ple?né Lake (PL) and ?ertovo Lake (CT), situated in the Bohemian Forest (Czech Republic). The aim was to explain higher terrestrial P export to mesotrophic PL compared to oligotrophic CT. Concentrations of Al and Fe oxides were the dominant parameters affecting soil ability to adsorb PO₄-P. Depending on concentrations of Al and Fe oxides, P sorption maxima varied from 9.7 to 70.5 mmol kg^?1 and from 7.4 to 121 mmol kg^?1 in organic and mineral soil horizons, respectively. The catchment weighted mean PO₄-P sorption capacity was 3.4 mol m^?2 and 11.9 mol m^?2 in the PL and CT soils, respectively. The higher PO₄-P sorption capacity in the CT catchment was predominantly associated with higher pools of soil and Fe oxides. The CT bedrock (mica schist) released one order of magnitude less P than the PL bedrock (granite) within a pH range of catchment soils (pH_CaCl2 of 2.5–4.5). The higher ability of PL bedrock to release P and the lower ability of PL soils to adsorb PO₄-P thus contributed to the higher terrestrial P loading of this lake.     

Long-Term Wheat Residue Management and Supplementary Nutrient Input Effects on Phosphorus Fractions and Adsorption Behavior in a Vertisol

The management of crop residues coupled with external nutrient inputs is important for improving and conserving soil fertility and productivity. We assessed the long-term effects of three wheat residue management options (RMO) (residue burning, incorporation, and surface retention) in combination with three supplementary nutrient inputs (SNI) [control, fertilizer, and farmyard manure (FYM)] on phosphorus (P) fractions and adsorption behavior of a Vertisol under soybean–wheat system. Wheat residue incorporation and retention improved the labile inorganic P [sodium bicarbonate (NaHCO₃-P_i)] by 3.2 and 5.0 mg kg^?1 and the labile organic P (NaHCO₃-P_o) by 2.4 and 4.2 mg kg^?1, respectively, as compared to residue burning. The soils under residue incorporation and retention had 38 and 26% more moderately labile organic P [sodium hydroxide (NaOH-P_o)], respectively, than the soil under residue burning. The SNI either as fertilizer or FYM further enhanced NaHCO₃-P_i, NaHCO₃-P_o, and NaOH-P_o. In contrast, less labile P fractions [hydrochloric acid (HCl)-P and residual-P] remained unaffected by RMO and SNI treatments. Residue retention or incorporation decreased P adsorption over the residue burning for all the three nutrient inputs. The P-adsorption data fitted well to the Langmuir equation (R² ranged from 0.970 to 0.994). The P-adsorption maximum (b), bonding energy constant (k), differential P-buffering capacity (DPBC), and standard P requirement (SPR) were lower with residue incorporation or surface retention than with residue burning. The SPR followed the order residue burning > incorporation > retention for RMOs and control > fertilizer > FYM for SNI treatments. The NaHCO₃-P_i, NaHCO₃-P₀, and NaOH-P_o had negative correlation with P-adsorption parameters and showed positive correlation with soybean P uptake. Wheat residue incorporation or retention plus FYM could be an effective strategy for enhancing the P fertility of Vertisols under a soybean–wheat system.     

Seasonality of organic phosphorus mineralization in the rhizosphere of the native savanna grass, Trachypogon plumosus

Savanna ecosystems have low primary productivity, strong seasonality, and acid soils with low phosphorus (P) content. Organic P (Po) comprises around 50% of the total soil P and is plant-available only after mineralization. Rhizosphere processes mediated by plants, microorganisms and arbuscular mycorrhiza (AM) are important for plant P nutrition. We studied P transformation rates, Po-fractionation, acid phosphomonoesterase activity (APA), AM status, dehydrogenase activity (DHA), and bacterial and fungal plate counts in the rhizosphere of the native dominant grass Trachypogon plumosus. We collected samples from three acid savanna soils differing in order and P content (Entisol, Vertisol and Ultisol) at Estación Experimental La Iguana (Northeastern Venezuela) during the dry, rainy and transitional seasons over a 2-year-period. Less available Po fractions (moderately labile, moderately and highly resistant) seem to be involved in short-term P-cycling transformations as they significantly varied with season. During the rainy season plant P content (576-1160 mg P kg⁻¹ dry weight) and APA (44-200 mg PNP kg⁻¹ dry soil) were higher, while microbial number and activity (DHA) were lower. The higher P availability in the Entisol (6-9 mg P kg⁻¹ dry soil) resulted in a better plant nutritional status and inhibited APA. T. plumosus seems to be highly dependent on AM symbiosis (45-71% AM colonized root length, 0.6-8 AM spores g⁻¹ dry soil), especially during the rainy season. Po mineralization processes, mediated by biological associations in the rhizosphere, are crucial for understanding seasonal P-cycling and fertility in acid savanna soils.     

Transformation kinetics of inorganic P forms in relation to calcareous soil properties of western Iran

This study was conducted to investigate the effect of time on chemical forms of P in 10 calcareous soils of western Iran. Phosphorus was added to soils at the rate of 200 mg kg^?1 as KH₂PO₄. The samples were incubated for 1, 7, 15, 30, 60, 90 and 120 days at 25°C and constant moisture. After incubation, P was fractionated by the sequential extraction procedure: soluble and exchangeable P (NaHCO₃-P) Al + Fe-P (NaOH-P), Ca-P (HCl-P) and residual P (Res-P). The distribution of added P into different fractions consisted of two phases involving initial rapid retention followed by a slow continuous retention. In general, the majority of the P applied entered mostly in the HCl-P and Res-P fractions. After 120 days incubation, the HCl-P fraction remained the most dominant in all soils. A combination of silt and sand content of the soils together explained between 88.5 and 83.3% of the variance inNaHCO₃-P and HCl-P transformation rates, respectively, 76.6 and 72.8% of which is explained by silt alone. CaCl₂-P and electrical conductivity (EC) together accounted for 66.3% of the variation in the rate constant of NaOH-P. The release rate of Res-P was not significantly related to soil properties.     

Relationship Between Extractable Metals in Acid Soils and Metals Taken Up by Tea Plants

Abstract

The accumulation of heavy metals in plants is related to concentrations andchemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate‐bound, organic matter‐bound, oxides‐bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mgCukg^?1, 0.03 to 1.09 mg Cd kg^?1, 3.43 to 31.2 mg Pb kg^?1, and 31.0 to 132.0 mg Zn kg^?1. The concentrations of exchangeable and carbonate‐bound fractions of the metals depended mainly on the pH, and those of organic matter‐bound, oxides‐bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L^?1 CaCl₂, NH₄OAc, and DTPA‐TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long‐term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.     

Coffee‐husk biochar application increased AMF root colonization,P accumulation,N2 fixation,and yield of soybean grown in a tropical Nitisol,southwest Ethiopia

Low soil fertility and soil acidity are among the major bottlenecks that limit agricultural productivity in the humid tropics. Soil management systems that enhance soil fertility and biological cycling of nutrients are crucial to sustain soil productivity. This study was, therefore, conducted to determine the effects of coffee‐husk biochar (0, 2.7, 5.4, and 16.2 g biochar kg^?1 soil), rhizobium inoculation (with and without), and P fertilizer application (0 and 9 mg P kg^?1 soil) on arbuscular mycorrhyzal fungi (AMF) root colonization, yield, P accumulation, and N₂ fixation of soybean [Glycine max (L.) Merrill cv. Clark 63‐K] grown in a tropical Nitisol in Ethiopia. ANOVA showed that integrated application of biochar and P fertilizer significantly improved soil chemical properties, P accumulation, and seed yield. Compared to the seed yield of the control (without inoculation, P, and biochar), inoculation, together with 9 and 16.2 g biochar kg^?1 soil gave more than two‐fold increment of seed yield and the highest total P accumulation (4.5 g plant^?1). However, the highest AMF root colonization (80%) was obtained at 16.2 g biochar kg^?1 soil without P and declined with application of 9 mg P kg^?1 soil. The highest total N content (4.2 g plant^?1) and N₂ fixed (4.6 g plant^?1) were obtained with inoculation, 9 mg P kg^?1, and 16.2 g biochar kg^?1 soil. However, the highest %N derived from the atmosphere (%Ndfa) (> 98%) did not significantly change between 5.4 and 16.2 g kg^?1 soil biochar treatments at each level of inoculation and P addition. The improved soil chemical properties, seed yield, P accumulation and N₂ fixation through combined use of biochar and P fertilizer suggest the importance of integrated use of biochar with P fertilizer to ensure that soybean crops are adequately supplied with P for nodulation and N₂‐fixation in tropical acid soils for sustainable soybean production in the long term.     

Nutrient Dynamics: Effect on Cropping Behavior,Nutrient Profile and Quality Attributes of Pomegranate (Punica Granatum L.) Under Rainfed Agroclimatic Conditions

The study was carried out between 2008 and 2010 on 8-year-old pomegranate (Punica granatum L.) trees cultivar ‘Kandhari Kabuli.’ The potential efficiency of bio-organics used along with chemical fertilizers on cropping behavior, quality attributes, nutrient availability, physico-chemical, and biological properties of soil were investigated. Bioorganic nutrient sources, namely, vermicompost (VC), biofertilizers (BF), farm yard manure (FYM), and green manure (GM), along with chemical fertilizers was evaluated in 13 different treatment combinations. Conjoint treatment application of VC at 20 kg tree^?1, BF at 80 g tree^?1, FYM at 20 kg tree^?1, GM as sun hemp (Crotalaria juncea L.) along with 75% of the recommended dose of nitrogen–phosphorus–potassium (N–P–K) chemical fertilizers significantly resulted in maximum fruit set (52.03%) and fruit yield (34.02 kg tree^?1). All of the fruit quality characteristics were also improved significantly when compared to nitrogen–phosphorus–potassium (N–P–K) chemical fertilizers. This superior combination also enhanced physical-chemical and biological properties of the rhizosphere soil. Microbial biomass of in terms of Pseudomonas, total culturable soil fungi, Azotobacter chroococcum, actinobacteria, and arbuscular mycorrhizal (AM) fungi improved 385.57, 60.26, 134.19, 168.02, and 39.87%, respectively, over control. This combination also resulted in considerable greater concentration of leaf macro-and micronutrients: N (2.63%), P (0.25%), K (1.57%), iron (Fe; 197.87 mg kg^?1), copper (Cu; 14.65 mg kg^?1), zinc (Zn; 59.36 mg kg^?1), and manganese (Mn; 200.45 mg kg^?1).     

Contribution of Arbuscular Mycorrhizal and Saprobe Fungi to the Tolerance of Eucalyptus globulus to Pb

The application of Pb inhibited the development of mycelia of the saprobe fungi Fusarium concolor and Trichoderma koningii and the hyphal length of the arbuscular mycorrhizal fungi (AM) Glomus mosseae and G. deserticola in vitro. The application to soil of 1500 mg kg^?1 of Pb decreases the dry weight, total N, P, Mg and Fe concentration and chlorophyll content of the shoot of E. globulus no inoculated with AM fungi. However, G. deserticola increased the dry weight, total nutrient concentration and chlorophyll content of the shoot, and the percentage of AM root length colonization and the succinate dehydrogenase activity of AM mycelia of E. globulus in presence of 1500 mg kg^?1 of Pb, and these increases were higher when G. deserticola was inoculated together with T. koningii. The application to soil of 3000 mg kg^?1 of Pb decreased the shoot dry weight and AM colonization of E. globulus in all treatments tested. Pb was accumulated in the stem more than in the leaves of E. globulus. In presence of 1500 mg kg^?1 of Pb the highest accumulation of this metal in the stem took place when E. globulus was colonized with G. deserticola. In conclusion, the possibility to increase Lead accumulation in stem is very attractive for phytoextraction function, the saprobe fungi, AM and their interaction may have a potential role in elevating phytoextraction efficiency and stimulate plant growth under adverse conditions such as lead contaminated soil.