An evaluation of three Thai phosphate rocks for agronomic use based upon their chemical and mineralogical properties

Ratchaburi phosphate rock (Rat-PR), Kanchanaburi-PR (Kan-PR), and Roi-Et-PR (Roi-PR) from Thailand, and North Carolina-PR (NCR-PR), were evaluated in the laboratory for agronomic use. NCR-PR consisted mostly of apatite (unit-cell a-value 9.336 Å, c-value 6.889 Å). Rat-PR contained apatite (a-value 9.428 Å and c-value 6.882 Å) and calcite as the main minerals. Kan-PR consisted mostly of apatite (a-value 9.406 Å and c-value 6.888 Å), crandallite, and calcite. Roi-RP consisted mostly of quartz and variscite. Dissolution kinetics of PRs in 2% formic acid (2% FA), 2% citric acid (2% CA), neutral ammonium citrate (NAC), alkaline ammonium citrate (AAC), and deionized (DI)-water were determined. The dissolution rate of phosphate from PRs in 2%FA, 2%CA, NAC, and DI-water was NCR-PR > Rat-PR > Kan-PR > Roi-PR. As Roi-PR is very poorly soluble, it is clearly unsuitable for direct application to soil.     

Evaluation of maturity and stability parameters of composts prepared from farm wastes

A composting experiment was carried out to study changes in physical [color, odor, temperature, organic matter (OM) loss], chemical [C:N ratio, water-soluble organic carbon (C_w):organic N (N_org) ratio, NH₄ ⁺-N and NO₃ ^?-N, humic acid (HA):fulvic acid (FA) ratio, humification index (HI) and cation-exchange capacity (CEC):total organic carbon (TOC) ratio)] and biological [seed germination index (GI)] parameters to assess compost maturity and stability over a period of 150 days. Five composts were prepared using a mixture of different farm wastes with or without enrichment of N, rock phosphate (RP) and microorganism (MO) inoculation. All the composts appeared to change to a granular and dark grey color without foul odor, and attained a constant temperature with no measurable changes (ambient level) at 120 days of composting. Correlation analysis showed that the optimal values of the selected parameters for our experimental conditions are as follows: organic matter loss > 42%, C:N ratio < 15, HA:FA ratio > 1.9, HI > 30%, CEC:TOC ratio > 1.7 and C_w:N_org ratio < 0.55. Composts enriched with N + RP or N + RP + MO matured at 150 and 120 days, respectively, whereas composts without any enrichment or enrichment with N or RP + MO did not mature even at 150 days of composting.     

Citric acid loaded nano clay polymer composite for solubilization of Indian rock phosphates: a step towards sustainable and phosphorus secure future

Non-renewable nature of rock phosphate (RP) reserves coupled with open ended nature of P cycle makes it imperative for maximum utilization of available P resources. In this context, use of Indian RPs from Purulia and Udaipur along with citric acid loaded nanoclay polymer composite (CA-NCPC) as P source to costly diammonium phosphate (DAP) was investigated through an incubation experiment followed by a greenhouse experiment with wheat-rice cropping sequence in a Luvisol (pH 5.14, available P 13.5 mg kg^?1). Soil available P, crop yield parameters and dynamics of soil P fractions were taken to judge the efficacy of CA-NCPC in solubilizing RPs. Application of CA-NCPC and DAP resulted in 82% and 69% increase in available P over control, respectively under incubation study. Direct effect of treatment receiving CA-NCPC + RP on yield and P uptake by wheat was comparable with DAP but residual impact of CA-NCPC + RP (16.7 g pot^?1) was better than DAP (13.8 g pot^?1) in rice. The changes in inorganic P fractions were also significant as inclusion of RP increased calcium-P from 16.1 to 61.5 mg kg^?1. Results indicated potentiality of RPs treated with CA-NCPC as an alternate P source which could prove promising amidst P scarcity.     

Agronomic Evaluation of Calcined Crandallite from Three Brazilian Phosphate Deposits

Abstract

Samples from the weathering mantle containing crandallite of three Brazilian phosphate deposits, Tapira, Catalão, and Juquiá, were characterized, calcined, and agronomically evaluated. The calcination process increased total phosphorus (P) and neutral ammonium citrate soluble (NAC) P contents of all samples. The NAC solubility of original Tapira, Catalão, and Juquiá was about 5% of total P, whereas for calcined samples it was 54, 16, and 53%, respectively. In a greenhouse study, rates of P were applied at 0, 10, 20, 40, 80, and 120 mg P kg^?1 from the calcined materials and MCP (monocalcium phosphate) to an Ultisol cropped with upland and flooded rice for 65 days. The results showed that the calcined P samples increased dry‐matter yield and P uptake with increasing rates of P applied for both crops. Tapira and Juquiá were more effective for flooded than for upland rice. The calculated values of relative agronomic effectiveness of Tapira, Catalão, and Juquiá with respect to MCP were 57, 48, and 53% in dry‐matter yield for upland rice and 64, 50, and 69% for flooded rice, respectively.     

Agronomic Effectiveness of Cationic Phosphate Impurities Present in Superphosphate Fertilizers as Affected by Soil pH

Abstract

The general concept that low‐water‐soluble phosphorus (P) fertilizers should be more agronomically effective when applied to acidic soils was developed based on sources containing mainly calcium (Ca)‐P compounds, but it may not hold true for sources with different chemical composition. To obtain information related to this issue, two important iron (Fe)–potassium (K)–P compounds present in superphosphates [Fe₃KH₈(PO₄)₆ · 6H₂O, H8, and Fe₃KH₁₄(PO₄)₈ · 4H₂O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg^?1 as neutral ammonium citrate (NAC)+H₂O‐soluble P. Reagent‐grade monocalcium phosphate (MCP) was used as a standard P source with high water solubility with an additional rate of 120 mg P kg^?1 included. Also, mixtures of both Fe‐K‐P compounds and MCP were prepared to provide 0, 25, 50, 75, and 100% of the total P as MCP. All sources were applied to a clayey loamy acid soil (pH 5.3) classified as Rhodic Kanhapludult. The soil was incubated at two rates (0 and 10 g kg^?1) of lime, which resulted in pH 5.4 and 6.8. Upland rice was cultivated to maturity. The H14 compound confirmed to be a highly effective source of P for the rice plants at both soil pH, as opposed to the H8, which was poorly effective when applied alone. When mixed with water‐soluble P (WSP), the H8 was able to provide P to the plants with the maximum yield of upland rice reached with 54.8 and 80.5% of WSP for pH 5.4 and 6.8, respectively. The high agronomic performance of the H14 compound clearly indicates that this low‐water‐soluble P source cannot be deemed as ineffective at high soil pH.     

Genetic Variations of Brassica Cultivars for P Acquisition in a P Stress Environment and Comparison of P Sources for Sustainable Crop Management

To compare the growth performance of Brassica in a phosphorus (P) stress environment and response to added P, six Brassica cultivars were grown in pots for 49 days after sowing, using a soil low in P [sodium bicarbonate (NaHCO₃)–extractable P = 3.97 mg kg^?1, Mehlich III–extractable P = 6.13 mg kg^?1] with (+P = 60 mg P kg^?1 soil) or without P addition (0P). Phosphorus‐stress markedly reduced biomass accumulation and P uptake by roots and shoots. However, root–shoot ratio remained unaffected, implying that relative partitioning of biomass into roots and shoots had little role to play in shoot dry matter (SDM) production by cultivars. Biomass correlated significantly (P < 0.01) with total P uptake. Under P stress, the cultivars that produced greater root biomass were able to accumulate more total P content (r = 0.95^**), which in turn was related positively to SDM and total biomass (r > 0.89^**) and negatively to P‐stress factor (r = ?0.91^**). There was no correlation between P efficiency (PE) (relative shoot growth) and plant P, but PE showed a very significant correlation with shoot P content and SDM. Wide differences in growth and better performance of cultivars such as ‘Brown Raya’ and ‘Con‐1’ under P stress encouraged screening of more germplasm, especially in the field, to identify P‐tolerant cultivars.

In another study, potential relative agronomic effectiveness (RAE) of sparingly soluble P sources was investigated by growing two contrasting cultivars. The P sources incorporated into soil at 0, 10, 25, 50, and 100 mg P Kg^?1 were (i) powdered Jordan rock P (RP), (ii) triple superphosphate (TSP), (iii) powdered low‐grade TSP [TSP(PLG)], (iv) a mixture of RP + TSP compacted into pellets at 50:50 P ratio [RP + TSP(PelC)], and (v) a mixture of powdered RP + TSP at 50:50 P ratio [RP + TSP(PM)]. The RP was low in RAE and only 5 and 29% as effective as TSP in producing dry matter (DM) of P‐sensitive ‘B.S.A.’ and P‐tolerant ‘Brown Raya’ cultivars, respectively. There were no significant differences between TSP and RP + TSP(PelC) in DM yield of ‘Brown Raya,’ whereas, in the case of ‘B.S.A.’ RP + TSP(PM) was significantly less effective than RP + TSP(PelC) compared with TSP. Combined utilization of superior genome and P sources [such as TSP(PLG) and RP + TSP(PelC)] produced from low‐grade RP (that cannot be used either for direct application or acidulated P fertilizers) can be used as an alternative strategy for sustainable crop production, especially in resource‐poor environments. Further field trials at the level of cropping systems are needed.     

Neutral Ammonium Citrate Extraction of Biosolids Phosphorus

Abstract

Matching biosolids application rates to crop phosphorus (P) needs requires quantifying the P fertilizer replacement value of biosolids. Neutral ammonium citrate (NAC) extraction of P, used for assessing available P in mineral fertilizers, was evaluated for 35 different biosolids. Biosolids NAC‐P was not statistically different (p=0.05) from total P using strong acid digestion (EPA 3051‐P). High P recovery by NAC was attributed to dissolution of P‐containing iron (Fe)/aluminum (Al) oxides under the aggressive extracting conditions (0.88 M citrate at 65°C). Citrate effectively dissolves P‐binding Fe/Al hydrous oxides, the very components that reduce phytoavailability when biosolids are land applied. Greenhouse studies with pasture grass (Paspalum notatum Flugge) grown in P‐deficient soils amended with biosolids revealed P phytoavailability was not correlated (r²=0.10) with biosolids NAC‐P. Phytoavailability was inversely correlated (r²=0.66) with biosolids total Al+Fe content. The NAC extraction, designed for commercial fertilizers, is inappropriate for quantifying biosolids phytoavailable P.     

A comparison of 5 soil phosphorus extraction methods applied to different soils of South of Iran

Phosphorus (P) fertilization is commonly based on soil testing, for which a variety of different soil P extraction methods are in use. In this research, the correlation and calibration of five extraction techniques for available P were studied: Soltanpour and Schwab, Olsen, EDTA-Na₂, Paauw and Morgan in 168 different soil samples from 63000 ha of Sirjan pistachio orchards of Kerman province, Iran. The Morgan reagent extracted the most P and then EDTA-Na₂> Olsen> Soltanpour and Schwab> Paauw extracted more phosphorus, respectively. Positive and significant correlation (P < 0.05) existed among all extractants. The correlation coefficients between different extractants and plant P concentration indicated that, EDTA-Na₂ (P < 0.01), Olsen and Paauw methods (P < 0.05) had positive and significant correlation with leaf P concentration and thus with due attention to acceptable relationship with plant indices, the Olsen and EDTA-Na₂ methods could be used to advise on available P.     

Gradient differences in soil metal solubility and uptake by shoots and roots of wheat (T. aestivum)

The aim of this research was to identify and quantify gaps in currents methods and models for predicting the plant availability of selected nutrient and contaminant metals (Cu, Ni, Zn, Cd) in soil. This study investigated relationships between the relative solubility of Cu, Ni, Zn, and Cd determined by six extraction methods with short-term uptake by shoots and roots of wheat (Triticum aestivum). For Cu, Ni, and Cd, relationships between solubility and plant uptake were found to be different for shoots and roots, with Cu and Ni solubility being more closely correlated with root uptake compared with shoot uptake. Correlation coefficients for Cd concentrations in shoot and root tissue for all six solubility methods were poor (r ²?<?0.5), while corresponding results for Zn explained more than 50 % of shoot variation but less than 50 % of root variation. Soil Cu solubility explained up to 85 % of variation in root uptake compared with 42–55 % for shoot uptake. These results clearly demonstrated that purely chemical and passive diffusion mechanisms were inadequate predictors of Cd uptake by shoots and roots, together with Cu uptake by shoots. Thus further attempts at refining soil metal bioavailability assays based solely on chemical extraction without consideration of plant responses are unlikely to improve prediction of plant uptake.     

Changes in Chemical Composition of Australian Waxflowers Due to Soil Applications of Nitrogen and Assessment of Nitrogen Status by Tissue Analysis

Abstract

Three field experiments were conducted to investigate the effects of soil‐applied nitrogen (N) on plant chemical composition, nutrient removal, and the use of plant analysis to assess N status of Australian waxflowers. Experiments were conducted in commercial plantings of Chamelaucium uncinatum cultivar Alba and a Chamelaucium hybrid (C. floriferum × C. uncinatum) known locally as Walpole wax, at 3 sites in South Australia. Nitrogen, as ammonium nitrate, was applied at rates up to 160 g plant^?1 over several side dressings during the growing season. To assess plant nutrient status, stem tips (25–40 mm long tips of stems) were sampled during the growing season and whole stems at harvest.

Nitrogen concentration in both stem tips and whole stems was sensitive to variations in N supply; however, the magnitude of the effect varied between sampling times and sites. In stem tips sampled during spring, the increase in N concentrations ranged from 19.8% at site 2 to 74.6% at site 1. Nitrogen concentrations in stem tips were consistently greater than concentrations in whole stems. The application of N decreased phosphorus (P) concentrations in whole stems and copper (Cu) concentrations in stem tips and whole stems. There was no consistent effect of applied N on potassium (K), calcium (Ca), magnesium (Mg), boron (B), zinc (Zn), and manganese (Mn) concentrations in either plant part sampled. Nutrient removal by flowering stems, in order from greatest to least, was N > K > Ca > P > Mg > Mn > B > Zn > Cu.

Based on 1800 plants ha^?1, it was estimated that for N, P, and K, 121.9, 15.4, 60.1 kg ha^?1, respectively, was removed in harvested stems. Based on poor sensitivity, the lack of a sharp transition zone between deficient and adequate N concentrations and the lack of consistent relationships between N concentration in stem tips and yield response, it is concluded that N concentration in stem tips is not a useful indicator of the N status of waxflower plants.     

Rice Yields Enhanced through Integrated Management of Cover Crops and Phosphate Rock in Phosphorus‐deficient Ultisols in West Africa

The relatively low solubility and availability of phosphorus (P) from indigenous phosphate rock could be enhanced by legumes in the acid soils of humid forest agroecosystems. Crotalaria micans L. was grown in a screenhouse without P or with P from triple superphosphate (TSP) and Malian Tilemsi Rock P. The P response of 20 cover crops was field‐evaluated using TSP and Rock P. In both experiments, the fertilized cover crops were followed by upland rice without mineral N or P application. Mean rice grain yield and agronomic residual P‐use efficiency were similar for both P sources. In the field, 1‐year fallow treatment of Canavalia ensiformis (velvet bean) supplied with Mali Rock P gave the highest rice grain yield of 3.1 Mg ha^?1, more than 180% that of 2‐year continuous unfertilized rice (cv. ‘WAB 56‐50’). Among continuous rice plots, ‘NERICA 2’ (interspecific rice) supplied with Rock P produced the highest yield (2.0 Mg ha^?1), suggesting that ‘NERICA 2’ might have greater potential to solubilize rock P. Results indicate that when combined with an appropriate legume, indigenous rock‐P can release sufficient P to meet the P requirement of the legume and a following upland rice crop in rotation.     

Evaluation of agronomic effectiveness of phosphate rocks for aluminum‐tolerant soybean cultivar

Abstract

The effect of liming on the agronomic effectiveness of three phosphate rocks (PRs) Pesca and Huila from Colombia and Sechura from Peru as compared with TSP was evaluated in a greenhouse experiment for an Al‐tolerant soybean cultivar grown on an acid Ultisol. On both unlimed (pH 4.4) and limed (pH 5.0) soils, the agronomic effectiveness of P sources in terms of increasing seed yield followed the order of TSP > Sechura PR > Huila PR > Pesca PR > check, an order similar to that of solubility of P sources. Liming slightly decreased the effectiveness of Pesca PR, whereas liming had no effect on Huila PR. A significant increase in agronomic effectiveness was observed upon liming for Sechura PR and TSP. Soil‐available P as extracted by the Pi method was closely related to the amount of N fixed by soybean crop that, in turn, was related to the soybean seed yield. Values of relative agronomic effectiveness (RAE) of PRs with respect to TSP were calculated by assuming the check = 0% and TSP = 100%. On unlimed soil, the RAE values of PRs were: Pesca PR = 31%, Huila PR = 42%, Sechura PR = 84%. On the limed soil, the RAE values were: Pesca PR = 8%, Huila PR = 24%, Sechura PR = 66%. It can be concluded that the use of PR with respect to that of TSP for soybean crop is more favorable in the unlimed soil than in the limed soil, provided that the soybean plant is relatively Al‐tolerant.     

Sonochemical Degradation of Chlorinated Phenolic Compounds in Water: Effects of Physicochemical Properties of the Compounds on Degradation

This study examined a comparative degradation of various chlorinated phenolic compounds including phenol, 4-chlorophenol (4-CP), 2,6-dichlorophenol (2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP) using 28, 580, and 1,000 kHz ultrasonic reactors. The concentration of hydrogen peroxide was also determined in order to investigate the efficacy of different sonochemical reactors for hydroxyl radical production. Clearly, it was observed that the 580 kHz sonochemical reactor had maximum efficacy for hydroxyl radical production. The degradation of all the compounds followed the order; 580 kHz (91?C93%) > 1,000 kHz (84?C86%) > 28 kHz (17?C34%) with an initial concentration of 2.5 mg L^?1 at a reaction time of 40 min with ultrasonic power of 200 ± 3 W and aqueous temperature of 20 ± 1°C in each experiment. Overall, the degradation of those phenolic compounds followed the order, PCP > 2,3,4,6-TeCP > 2,4,6-TCP > 2,6-DCP > 4-CP > phenol at various frequencies in the presence/absence of a radical scavenger (tert-butyl alcohol). It was revealed that the correlations between the compound degradation rates and the physicochemical parameters, R ² = 0.99 for octanol?Cwater partition coefficient, R ² = 0.95 for water solubility, R ² = 0.94 for vapor pressure, and R ² = 0.88 for Henry??s law constant, excluding PCP, were very good in the entire range of each parameter.     

Spatial occurrence and geochemistry of soil salinity in Datong basin,northern China

Purpose

Soil quality assessment is tremendously important for agronomic and environmental concern. The objective of this study was to spatially evaluate soil salinity and its geochemistry at regional scale.

Materials and methods

A soil quality assessment study was conducted over a 1,000 km² field in Datong basin, northern China via collecting and determining 163 topsoil samples. A combined approach of statistical methods and hydrochemical tools was applied for a comprehensive analysis in this study.

Results and discussion

In the study area, the nonsaline lands (total dissolved solids (TDS) <0.08 %, Ca-HCO₃ type soils) that are located in the pluvial plains consist of coarse-medium sands and deep unsaturated zone (depth >10 m). The slightly (0.08 %?<?TDS?<?0.2 %, Ca-Na-HCO₃-NO₃ type soils) and the moderately (0.2 %?<?TDS?<?1 %, Ca-Na-SO₄ type soils) saline lands are located in the alluvial plains and the central basin composed of fine sediments like fine sands, loams and silts, and intermediately deep unsaturated zone (depth 2–10 m). By contrast, due to irrigation, the very (1 %?<?TDS?<?2 %) and the extremely (TDS >2 %) saline areas with Na-SO₄/Na-Cl type soils are locally found in some desolate lands comprised of silty clays and shallow unsaturated zone (depth <2 m) in the central basin.

Conclusions

As a result of water-rock/sediments interactions, effects of landscapes and anthropogenic activities, soil salinity is characterized by strong spatial variability in Datong. The new insights into the basin-scale distribution pattern of soil salinity in inland basins of silicate terrain under arid climatic conditions should be applicable in other similar regions of the world.     

Can the arbuscular mycorrhizal fungus Glomus intraradices actively mobilize P from rock phosphates?

Plants colonized by arbuscular mycorrhizal (AM) fungi have been shown to respond positively to the application of insoluble forms of inorganic phosphorus (P) such as rock phosphates (RPs). The mechanism(s) underlying such responses remain(s) unknown and although it has been hypothesized, there is no experimental support for the production of chelating agents by AM fungal hyphae. Here we investigate whether AM fungi can solubilize P from RPs and transfer it to plant roots. Using root-organ cultures of Daucus carrota L. inoculated or not with Glomus intraradices Schenk & Smith and containing P from different RP sources, we predicted that: (1) roots inoculated with G. intraradices would take up more P than those uninoculated; that (2) the amount of P taken up by roots through G. intraradices would be positively correlated with the RP reactivity; and that (3) G. intraradices would have access to RP through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The RP reactivity was positively correlated with P uptake. However, mycorrhizal roots grew initially slower and did not respond differently to any P treatment than those uninoculated. There was no evidence of localized changes in pH in proximity of G. intraradices hyphae, indicating that responses to RP by mycorrhizal plants observed in previous studies do not appear to result from the release of H⁺ ions alone or in combination with organic acid anions.     

Kinetics of nutrient release from different organic residues using a laboratory system

Organic residues play a vital role in maintaining soil fertility in arid and semi-arid regions. Knowledge of the nutrient release from organic residues will help in optimizing nutrient efficiency in agricultural crop production systems. This study was conducted to assess the continuous release of phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) from eight different organic residues (sheep manure, beet, waste material, rape, poultry manure, sunflower, potato and garlic) using successive extractions with distilled water. The residues were shaken for 1 h and equilibrated for longer intervals (1, 3.5, 18, 42, 72, 192, 768, 1248, 1608, 1968 and 2328 h) with successive extractions. Cumulative nutrient release curves by different organic residues versus time showed an initial rapid phase followed by a slow phase. The average percentage of nutrients released and the average release rate of nutrients found using a power model was different and were in the order K > P > Ca > Mg and Ca > Mg > P > K, respectively. According to MINTEQ software, the partitioning of total P between HPO₄ ^2? and H₂PO₄ ^? is sensitive to the type of organic residue. On average (pooled over all extractions), between 13% (rape) to 40% (poultry) and 27% (poultry manure) to 79% (beet) of total P in aqueous solutions present as HPO₄ ^2? and H₂PO₄ ^?, respectively. Among the various organic residues and in the first stage of release, sunflower residue, beet residue, poultry manure and garlic residue had the highest rate constant for Ca, Mg, P and K, respectively, indicating the high potential availability of these nutrients in the early stage of application to soils.     

Managing Citrus Trees to Optimize Dry Mass and Nutrient Partitioning

Abstract

Non‐bearing “Hamlin” orange trees on “Swingle citrumelo” rootstock (32 months‐old) grown on a Candler fine sand (hyperthermic, coated Typic Quartzipsamments) were harvested to estimate dry mass, nitrogen (N), phosphorus (P), and potassium (K) accumulation and partitioning into various parts of the tree. The above parameters were evaluated for trees grown under low or high fertilization rates, using either water soluble granular (WSG), controlled release formulation (CRF), or liquid fertilizer delivered through irrigation water, i.e., fertigation (FRT). Trees were irrigated using under tree sprinklers with a wetting area diameter of 3.0 m. Total dry mass per tree followed the order: CRF > FRT = WSG and FRT > CRF > WSG for the low and high fertilization rates, respectively. Effects of fertilizer source on dry mass of individual tree parts followed the above response pattern with few exceptions. Dry mass of tree parts in relation to total tree dry mass decreased in the order: trunk > branch > leaves > roots. Therefore, the woody portion of the tree represented the major proportion of tree dry mass. Total N content in trees varied from 28.4 to 50.4 g and 41.4 to 82.3 g with different fertilizer sources at the low and high fertilization rates, respectively. The tree total N content decreased in the order: CRF > FRT > WSG and FRT > CRF > WSG at the low and high fertilization rates, respectively. Nitrogen in the leaves represented the major proportion of tree N, regardless of N source or fertilization rate. Total K content of the tree was slightly lower than total N content. Effects of fertilization source on total K content was similar to that of total N content. Total P content in trees was considerably lower than that of either N or K content. Fertilization sources and rates had negligible effects on the P content.     

Phosphorus Availability and Transformation as Affected by Repeated Phosphorus Additions in an Ultisol

Phosphorus (P) solubility and transformation in soils determine its availability to plants and loss potential to the environment, and soil P dynamics is impacted by fertilization and soil properties. A Ultisol sample was interacted with 20 mg L^?1 P solution from one to ten times. The P-reacted soils were then analyzed for water-soluble P (0.01 M calcium chloride (CaCl₂)–extractable P); plant-available P (Olsen P); ammonium chloride P, aluminum P, iron P (NH₄Cl-P, Al-P, Fe-P, respectively); and occluded P (Oc-P). The degree of P saturation (DPS) was calculated from ammonium oxalate–extractable Al, Fe, and P. The amount of P sorbed by the soil was highly correlated with the frequency of P addition with high percentage of P adsorbed initially and gradually decreased as the P addition continued. The relative abundance of the five P fractions in the P-reacted soil was in the order of Fe-P (36.5 percent) > Al-P (35.6 percent) > Oc-P (22.8 percent) > Ca-P (2.7 percent) > NH₄Cl-P (2.3 percent). Both Olsen P and CaCl₂-P were significantly increased by the repeated P addition process and highly correlated in an exponential function. The DPS was increased above the so-called critical point of 25 percent after the first P saturation process and kept increasing as the P addition continued. The P availability and adsorption in the soil were controlled by soil free and amorphous Al and Fe. The results suggest that repeated P application will build soil P to an excessive level, and consequently result in poor P-use efficiency and high P-loss potential to surface and groundwater.     

Evaluation of Physicochemical Methods for Treatment of Cu, Pb, Sb, and Zn in Canadian Small Arm Firing Ranges Backstop Soils

This paper presents the results of physicochemical treatment on Pb-, Cu-, Sb-, and Zn-contaminated Canadian small arm firing range (SAFR) backstop soils in order to evaluate the potential of such methods for remediation of SAFR backstop soils. Remediation target for the treatment assays was to attain the Québec Department of Environment commercial C criterion or more realistically, to reach the soil burial D criterion. Two treatment lines (TL) were evaluated. TL-1, consisting of jig and Wilfley table (WT) treatments on the 0.5–3 mm and 53–500 μm soil size fractions (SF), respectively, and chemical leaching on the <53 μm SF and TL-2, consisting of jig on the 1–4 mm SF, spiral, and WT treatments on 250 μm–1 mm SF, and Kelsey jig assays on the <250 μm SF. For both TL, the untreated SF (>3 mm for TL-1; >4 mm for TL-2), and the gravimetric separation concentrates could be sent for recycling in smelter facilities. Results showed that the finer SF (<53 μm SF for TL-1; <250 μm SF for TL-2) were very difficult to treat. Even with metal removed mass proportions up to 78% for Pb, concentrations were still very high after chemical leaching; and the Kelsey jig showed deceiving metal removed mass proportions (up to 47% for Pb). In both TL, the jig and the WT showed Pb removed mass proportions up to 98% and treated mass proportions up to 77% in their respective SF. Whole process efficiencies in the cleaned soils showed that TL-1 led to the remediation of up to 65% of the initial total soil, and TL-2, 36%. TL-1 and TL-2 results showed that the WT effectively treated soils of 53 μm–1 mm SF, and the jig, soils of the 1–4 mm SF. Our study shows that gravimetric concentration techniques are very promising for the treatment of SAFR backstop soils, and further research has to be done in order to treat the SF lower than 53 μm.     

Effect of Crop Rotations and Continuous Fertilization on the Status of Silicon (Si) Available in Soil in a 97-Year Permanent Experiment

ABSTRACT

This work aims to study the status of silicon (Si) as a plant nutrient in the soil of Bahtim long-term field experiment in Egypt under the effect of crop rotations system and continuous fertilization. The experiment has been set up since 1912 based on two main factors: (1) crop rotations: mono-cropping (MC), two-year rotation (2Y-R), and three-year rotation (3Y-R), and (2) Fertilization: mineral nitrogen N, phosphorus P, potassium K, and organic farmyard manure FYM. Available N, P, K, and Si in soil were estimated. Productivity of soil was evaluated using Berseem (Trifolium alexndrinum L.) cultivated and harvested in 2019. The plant-available Si (PAS) in soil decreased significantly compared to the control C in case of MC by 70.26%, 2Y-R by 85.09%, and 3Y-R by 92.65% in the direction of N > NP > NPK. Mineral fertilization decreased the PAS significantly by 12.84% N, 29.52% NP, 78.45% NPK compared to the control C in the order of MC > 2Y-R > 3Y-R. Berseem yield (t ha^?1) increased significantly compared with the control C following the order C < N < NP < NPK. The most significant increase in the yield was recorded for the NPK treatments by 224.04%, and 200% in case of MC, 2Y-R, 3Y-R, respectively.