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Recycling of organic wastes for agricultural production has been recommended as a sustainable way to close the phosphorus (P) cycle. This study seeks to characterize the P forms in organic fertilizers derived from agricultural and nonagricultural source materials to understand how these organic fertilizers will affect corn growth and soil available P. Organic fertilizers including turkey litter compost (TLC), biosolid pellets (BSP), and source separated organic compost (SSO) were applied to a sandy loam soil and compared to controls that received no nutrients or chemical fertilizer. Results from sequential chemical extractions and X‐ray absorption near edge structure spectroscopy revealed that most of the P species are inorganic, with SSO and TLC containing primarily Ca‐P and Mg‐P forms, while the P in the BSP treatments was mostly associated with aluminium (Al). The two chemical fertilizer treatments had the greatest impact on corn height at the initial growth stage; however, after 42 days, corn height was similar for the organic fertilizers and chemical treatment. This initial slow response from the organic fertilizer treatments reduced the grain yield compared to chemical treatment. The results of this study suggest that priority should be given to sufficient P availability at the initial growth stage. Overall, organic fertilizer is a promising P source for grain crop production, but calibration and correlation studies are needed to ensure optimum supply of P for the initial growth stage. Core Ideas: Phosphorus forms in the organic fertilizer used in this study were highly variable.Early corn response to organic fertilizer is slower than chemical fertilizer applied at the same total P rate.Turkey litter compost shows the greatest potential as a P source for grain crop production.Increasing the rate of P application reduced the P use efficiency. [ABSTRACT FROM AUTHOR]

Seasonal asymmetric warming is a distinguishing feature of climate change that is not regularly considered when studying the effects of global change on terrestrial ecosystems. The responses of the stability of soil organic carbon (SOC) in calcareous soils to asymmetric and symmetric warming are not clear. A 5-yr warming experiment, using infrared radiators, was performed to evaluate the effects of symmetric and seasonal asymmetric warming on SOC stability in a calcareous soil in the Karst region, southwest China. The bulk soils were fractionated to density fractions (i.e., light and heavy fractions, separated by 1.7 g mL-1 NaI solution) and then recalcitrant fractions with a combination of density fractionation and acid hydrolysis techniques. Soil organic C densities in the warming treatments (1.95-2.02 g kg-1) were close to the control (nonwarming treatment, 1.94 g kg-1). Warming negligibly affected organic C densities in the two density fractions and recalcitrant fractions, except for the recalcitrant C of light fraction (RC-LF). On average, the RC-LF density in the warming treatments was 18.18% higher than the control. Among the warming treatments, the RC-LF density in the symmetric warming treatment was significantly (P < 0.05) higher than the moderately, highly, and extremely asymmetric warming treatments. The findings reveal that short-term warming can enhance the recalcitrance of unprotected C in a calcareous soil. Symmetric warming potentially overestimates the recalcitrance of the unprotected C pool in the surface soil, compared with the projected asymmetric warming scenario. It may be related to the summer-autumn warming-induced increases in the turnover of SOC and biochemical recalcitrance of unprotected C.

No mechanistic model for phosphorus (P) fertilizer recommendation is available for nutrient management in tropical soils. Soil intrinsic P pools, including a weakly and a tightly adsorbed P pool, were proposed to quantify actual soil available P. The goal of this study was to develop a new mechanistic P fertilizer recommendation model based on the two pools. The public data set of a corn (Zea mays L.) field experiment was used to estimate the daily corn P uptake. Seven soils were used to demonstrate the effects of P-sorption site density (PSSD) and desorption rate of the tightly adsorbed P pool on the P fertilizer recommendation. Dynamics of soil P pools in a corn-soil system were modeled based on the transformation between the pools, the daily crop P uptake, and P fertilizer added at the beginning of planting. The weakly adsorbed P pool was required to be positive to represent no constraint of crop P nutrition. Results showed that the derived P recommendation model was a linear model of the total crop P uptake minus the two pools with three different coefficients. The weakly adsorbed P pool was readily available for crop uptake. The coefficients of the total crop P uptake and the tightly adsorbed P pool were >1.0 and <1.0, respectively, and they changed slightly with PSSD but were dependent on the desorption rate. The coefficient of the total crop P uptake showed a maximum 1.679 at the desorption rate 0.0118 d-1.

Soil P testing is critical to ensure the accuracy of fertilizer recommendations and to optimize crop yield while minimizing negative environmental consequences. Olsen-P is the most commonly used soil P test for alkaline calcareous soils found in Idaho and the western United States. The Bray-1 test is commonly used in the Pacific Northwest on neutral to acidic soils but underestimates P in alkaline calcareous soils. Mehlich-3 has been evaluated throughout various regions in the United States. Few data evaluating Mehlich-3 exist for soils in the western United States. Additionally, the comparatively newly developed Haney–Haney–Hossner–Arnold (H3A) test, a component of the soil health tool, has not been widely evaluated on alkaline calcareous soils. Soil samples from the 0- to 30-cm depth were collected from agricultural fields throughout Idaho and analyzed with Bray-1, H3A, Mehlich-3, and Olsen-P extractants. The results indicate that Olsen-P was correlated with Mehlich-3, whereas Bray-1 and H3A were not correlated with Olsen-P. Both Bray-1 and H3A resulted in lower values of extractable P than the Olsen-P test, whereas Mehlich-3 resulted in greater values. A threshold point in CaCO3 (i.e., inorganic C) of 6.7 and 5.1 mg kg-1 for the Bray-1 and H3A was obtained, respectively, which indicated that inorganic C concentrations at or above these levels resulted in a reduction in extractable soil P. Thus Mehlich-3 could be evaluated for use in alkaline calcareous soils, whereas Bray-1 and H3A have notable issues that would limit their applicability. [ABSTRACT FROM AUTHOR]

To reveal the dynamics of phosphate behavior in a calcareous paddy soil chronosequence (after 0, 3, 8, 30, and 70 yr of rice [Oryza sativa L.] cropping), P adsorption–desorption isotherms, chemical fractions, and loss risks were investigated. The contents of P adsorbents (i.e., Fe and Al oxides and Ca salts) in the paddy soils increased with cultivation age, mainly through accelerated primary mineral destruction and weathering in an Alfisol, along with a small portion from irrigation waters. The Langmuir equation gave increasing P adsorption capacities (Qmad) of 520.67, 545.67, 662.78, 860.79, and 834.45 mg kg-1 for 0, 3, 8, 30, and 70 yr. The Qmad was closely correlated with free Fe and Al oxides, amorphous Al oxides, and HCl-replaceable Ca contents. The fraction of Ca–P was 52.04 to 63.64% without P inputs, indicating that Ca salts primarily determined P availability. The preferential forms of P retained by paddy soils were in the following order: Ca–P > Al–P > Fe–P > loosely sorbed P. The contents of Olsen-P in 3- and 8-yr paddy soils were 42.1 and 28.1 mg kg-1, respectively, much higher than for the two older paddy soils and the upland soil (11.6–24.8 mg kg-1). The highest degree of P saturation and equilibrium P concentration were in the two younger paddy soils, indicating the increasing potential environmental risk of P loss in paddy soils in the first few years. Hence, more attention should be given to P loss in newly reclaimed paddy soils. [ABSTRACT FROM AUTHOR]

Karst ecosystems are vulnerable to degradation and constitute a significant proportion of southwestern China. Here, we explore the amendment of these soils with wood biochar in combination with N-P-K fertilizer and swine manure compost with the goal of improving microbial community structure and soil nutrient status of these soils. A pot experiment with six treatments, including control (CK, no amendment), swine manure compost plus N-P-K fertilizer (MF), wood biochar at 2% in soil (W2), wood biochar at 4% in soil (W4), wood biochar-based fertilizer at 2% in soil (W2MF), and biochar-based fertilizer at 4% in soil (W4MF), was set up for 20 months. The results showed that soil organic matter and soil available nutrients N, P, and K in W4MF increased by 63.95, 66.23, 284.96, and 94.56%, respectively, compared with CK. Soil microbial biomass C, N, and P increased in sequence by 60.05, 87.64, and 307.85%, respectively. Soil bacterial and fungal diversity indices (Simpson and Shannon) and richness index (Chao1) were generally higher in biochar-based fertilizer treatments (W2MF and W4MF) than biochar alone (W2 and W4). The bacterial and fungal community structures of biochar based fertilizer treatments differed from those of biochar amendment alone or control (P < 0.05). Linear discriminant (Effect Size) analysis showed that the bacterial biomarkers of the W2MF + W4MF group were mainly the phylum Acidobacteria and class Alphaproteobacteria, and the fungal biomarkers were the phylum Rozellomycota and Glomeromycota. Redundancy analysis revealed strong relationships between microbial community structure and soil organic matter and soil available nutrients N, P, and K (P < 0.05). In conclusion, either sole biochar or biochar-based fertilizer amendment improved karst soil nutrient conditions and induced microbial community structural shifts. The performance was better in biochar-based fertilizer treatment than that in biochar addition alone. [ABSTRACT FROM AUTHOR]

In subsurface systems that have been contaminated with petroleum hydrocarbons (PHCs), the degradation by microbes is limited by nutrient availability, primarily by bioavailable phosphorus (P). Low-molecular-weight organic acids (LMWOA), particularly citrate, have been proposed as a remediation amendment to enhance P mobility, but the effect of citrate on P retention by calcium-rich soils is poorly understood. In this study, the sorption of P in the absence and presence of citrate on calcareous cold soils was investigated under controlled laboratory conditions using a combination of laboratory-based adsorption and desorption studies and synchrotron-based spectroscopic techniques. The results indicate that calcium exerts a strong control on P sorption by forming calcium phosphate minerals, thus limiting the availability of P for transport or microbial uptake. Treatments that reduce reserve and exchangeable Ca increase the relative proportion of adsorbed P. When citric acid is also added to these calcareous soils, their buffering capacity largely inhibits any desorption of P or changes in P speciation until citrate levels exceed P additions by more than 10 to 1. By increasing citrate to P ratios to between 10:1 and 50:1, it is possible to overcome the soil’s buffering capacity, decrease pH, and enhance P desorption via competition with citric acid. This suggests that one can enhance P transport in this soil system, but only when the citrate to P ratio is properly adjusted for the site’s Ca levels. [ABSTRACT FROM AUTHOR]

There are currently no tools available to help predict N mineralization for the silty soils found in southern Idaho receiving repeated manure applications. This experiment aimed to determine the effect of temperature on N mineralization from control and manured soils, develop N mineralization rate correction factors for temperature [ratio of the change in the rate coefficient of mineralization for every 10°C increase (Q10) and temperature factors], and create a simple model for predicting N mineralization as a function of growing degreedays. Manured and control soils underwent a 49-d laboratory incubation at five temperatures (–14, 4, 10, 23, and 30°C); soil inorganic N concentration was determined at 0, 1, 3, 5, 7, 13, 20, 28, 35, 42, and 49 d. Net N mineralization was fitted to a zero-order model, where the rate coefficient (k) values for the manured soil ranged from 0.017 to 1.28 mg kg–1 soil d–1 over the five temperature treatments, whereas k in the control measured 0.028 to 0.53 mg kg–1 soil d–1. The calculated Q10 values from –14 to 30°C were 2.7 and 2.0 for the manured and control soils respectively. At low temperatures (–14 to 4°C), the Q10 for manured soil was 5.1 compared with 1.5 for the control. This suggests that manure additions may lower the temperature threshold for N mineralization under near frozen soil conditions. Manure treatment effects on the temperature factor were not observed, suggesting that manure application history may not need to be considered when developing temperature factor coefficients for N mineralization models. [ABSTRACT FROM AUTHOR]

Potassium application rates based on a reliable soil testing method are critical for maximizing crop yields and minimizing fertilizer costs. Vegetables grown on calcareous soils, however, have no soil test potassium (STK) interpretations in Florida. Therefore, the objectives of this study were to compare Mehlich-3, ammonium bicarbonate-DTpA (AB-DTpA), and water to estimate K availability and calibrate k rates for tomato (Solanum lycopersicum L.) grown on a calcareous soil. The experiment was conducted during the winter seasons of 2014 and 2015. potassium fertilizers were applied through preplant dry fertilizer and drip fertigation at total rate of 0, 56, 93, 149, 186, and 223 kg K ha-1. Regression models were performed to calibrate K rates by tomato relative yield with total K input (initial STK plus full-season K rate). Concentrations of STK were significantly correlated among the three extractants and the highest correlation occurred between Mehlich-3 and AB-DTPA. Due to the high variability, water was ineffective to estimate K availability. Significantly linear relationships were found between total K uptake (TKU) and total K inputs using both Mehlich-3 extracted K (Mehlich-3-K) and AB-DTPA-K. The low STK levels were predicted from 85 to 150 and 70 to 120 mg K kg-1 and the corresponding required K rates ranged from 307 to 151 and 271 to 151 kg K ha-1 using Mehlich-3-K and AB-DTPA-K, respectively. Thus, both Mehlich-3 and AB-DTPA can be used to predict K availability and K rates needed to produce optimal marketable yield for tomato grown on calcareous soils in Florida. [ABSTRACT FROM AUTHOR]

Literature pertaining to the determination of calcite and dolomite is not modern and generally describes slow methods that require expensive specialized apparatus. The objective of this paper is to describe a new method that requires no specialized equipment. The separation of calcite and dolomite was done by placing 0.2000 ± 0.0200 g of calcareous soil, 6-mL glass vial with 4.0 mL of fresh 4 mol L-1 HCl-3% FeCl2 4H2O in a 50-mL Erlenmeyer flask. The Erlenmeyer flask was capped with the tubed rubber stopper and the carbonate meter's (CM) initial weight was recorded to the accuracy of four decimal places. A second weight was recorded after 30 s of reaction, a third weight was recorded after 30 min of reaction, and the last weight was taken after 22 to 24 h. The linear regressions and correlation coefficient results for calcite and dolomite in calcite-dolomite-soil mixtures with the modified carbonate meter (MCM) were excellent. The precision for calcite was <5% in 92.6% of samples and that for dolomite was <10% in 98.8% of samples. Recovery for calcite was 100 ± 10% in 86.4% of samples and recovery for dolomite was 100 ± 10% in 97.5% of samples. The MCM technique efficiently separated calcite and dolomite in calcareous soils. This procedure is recommended for routine analysis of calcite and dolomite concentrations up to 450 g kg-1. The MCM is easy to follow with good precision and recovery. [ABSTRACT FROM AUTHOR]

The release kinetics of phosphate (inorganic p [pi]) at constant proton pressure in a pHstat experiment may be used as a proxy for P mobilization by rhizosphere acidification. pHstat experiments are challenging for calcareous soils because of the strong carbonate buffering. Our objectives were (i) to modify an existing pHstat method for calcareous soils and (ii) to determine plant species richness, plant functional group richness, and identity effects on pool sizes and rate constants (i.e., the fast- and slow-reacting Pools A and B, respectively, and the associated release constants ka and kb). The study was conducted in "The Jena Experiment" comprising grassland mixtures with different functional group composition and species richness. In 27 samples with inorganic C concentrations <10 g kg-1, a constant pH value of 3 after 2 h was reached by removing all released cations with ion-exchange membranes until all carbonates were destroyed. Thereafter, P release kinetics followed a biphasic course: the fast-reacting Pool A contained 86% of the bioavailable Pi extractable with NaHCO3 plus NaOH. The slow-reacting P pool additionally comprised P from dissolution of pedogenic oxides and more stable Ca-phosphates containing 17 to 40% of HCl-extractable Pi. Legumes decreased both pools (Pool A: 40.61 ± 3.83 with legumes vs. 65.24 ± 5.88 mg kg-1 Pi without legumes; Pool B: 36.88 ± 1.89 vs. 48.85 ± 1.81 mg kg-1 Pi) because of their increased P demand and associated ability to access hardly available P fractions. In conclusion, pHstat experiments are suitable for studying P dynamics in soil and reveal an aboveground plant composition feedback on soil P dynamics. [ABSTRACT FROM AUTHOR]

The soil water retention curve (WRC) is one of the most important properties in soil hydraulic studies. Current studies normally focus on fine soils, ignoring the water-holding capacity of coarse fragments (>2 mm) and their effects on soil available water content (AWC). Calcareous concretions (CC) are coarse inclusions distributed widely in soils around the world. This study was conducted to quantify the effects of the proportion and size of CCs on the soil WRC and AWC of a calcic vertisol. The WRCs of CCs were measured using the sand box and ceramic plate method, and the WRCs of fine soils and soil-CC mixtures of various sizes (2-5, 5-8, and 8-30) and proportions (5, 10, 15, and 30% on a total mass basis) of CC were determined with the centrifuge method. The WRCs were fitted with the van Genuchten equation. The results showed that CCs retained a considerable amount of water. The saturated water contents of CCs of 2- to 5-, 5- to 8- and 8- to 30-mm were 0.251, 0.220, and 0.196 cm³ cm-3, respectively. The addition of CCs changed the WRC and pore distribution of soils significantly. The AWC of soil-CC mixtures decreased with increasing CC content. A linear equation, which included the fraction of CCs and water content in CCs, was proposed to estimate the AWC of soils containing CCs accurately. Accounting for CCs in the calcic vertisol improved the accuracy of soil hydraulic property estimations. [ABSTRACT FROM AUTHOR]

Applying manure to crops may alter P speciation in the soil profile and thus affect its availability for plant uptake and transport to surface waters. The goal of this research was to determine how repeated manure amendments affect P speciation within calcareous soil. Soil samples were collected in 2013, 2014 and 2015 from two depths to analyze differences in P composition following annual applications of 17 Mg ha-1 manure, 52 Mg ha-1 manure, or NH4H2,PO4 fertilizer and control plots (no P). To speciate the soil P, sequential chemical extraction, P K-edge X-ray adsorption near-edge structure (XANES) spectroscopy, 31P nuclear magnetic resonance spectroscopy, and microprobe element mapping were used. Total P concentration in the manure-amended soils increased over 3 yr. The highest soil test P concentrations were in the 52 Mg ha-1 plots. Most extractable P in the sequential extraction procedure was removed with the most aggressive extractant, suggesting that the predominant form of P is associated with Ca-P minerals. The XANES results showed that P species were similar among all amendments and years: 54 to 74% Ca-P minerals (e.g., hydroxyapatite), 25 to 35% adsorbed P, and 0 to 19% organic P (predominantly phytic acid). Despite the poorly soluble Ca-P species predominating in all soils, soil test P increased in the manure-amended soils. The P speciation results provide a baseline to compare how long-term changes affect P availability and will be useful for designing long-term scenarios in manure-amended calcareous soils to limit excess soil P that could leach into water. [ABSTRACT FROM AUTHOR]

Total C (TC) in calcareous soils has two components: inorganic C (IC) and organic C (OC). The IC must be measured and subtracted from the TC to obtain OC. Our objective was to develop a simple gravimetric technique to quantify IC. This technique, named the carbonate meter (CM), can be assembled in any soil testing laboratory with a 6-mL glass vial, a no. 1 rubber stopper with one hole, a 6.5-cm glass tube with 0.5 and 0.3-cm outside and inside diameters, respectively and a 50-mL Erlenmeyer flask. Precision and recovery was tested with 0.728 and 2.57% IC standard calcareous soils and pure calcite and dolomite, using 0.2000 ± 0.0200 g of finely ground samples and 4.0 mL of fresh 4 mol L-1 HCl-3% FeCl2x 4H2O. Twelve US calcareous soils with 0.11 to 8.52% IC were used to validate our CM procedure. Inorganic C recoveries after 22 to 24 h for two standard calcareous soils, calcite and dolomite were 100.55, 99.73, 100.45 and 99.58%, respectively. The detection limit (DL) and the lower limit of quantitation (LLOǫ) for calcite were 0.31 and 1.0 g IC kg-1, respectively. The DL and the LLOǫ for dolomite were 0.42 and 1.4 g IC kg-1, respectively. Mean IC recovery with a modified pressure calcimeter (MPC) in reference standards was 56.42%, while the CM recovery was 100.84%. The MPC loses accuracy in calcareous soils with >5.11% IC, whereas the CM had good recoveries up to 8.40% IC. The CM does not require pre-analysis, it is easy, non-tedious and inexpensive, with good precision and accuracy. [ABSTRACT FROM AUTHOR]

Sequential fractionation coupled with phosphatase hydrolysis allows a greater understanding of the effects of animal manure on the chemical distribution of soil P. Concentrations of specific soil P fractions were determined after long-term (>10 yr) poultry litter application at rates of 4.5, 6.7, 9.0, 11.2, and 13.4 Mg manure ha-1 yr-1 to watershed-scale plots (cultivated and grazed-ungrazed pasture) on a calcareous Texas Blackland Vertisol. Soil total extractable P (Pt) and inorganic P (Pi) were quantified following sequential extraction with H2O, NaHCO3, NaOH, and HCl. Hydrolyzable organic P (Pe) and non-hydrolyzable organic P (Pne) were determined in the extracted fractions following enzymatic hydrolysis. Litter application increased Pt regardless of land-use type compared with the control. Concentrations of H2O-extractable Pi in litter-amended plots increased by 9 to 34% (cultivated) and 7 to 30% (pasture) over the control, indicating substantial risk of soluble P runoff. Labile organic P (Po) extracted with H3O and NaHCO3 decreased in the order monoester > nucleic acid > phytate > Pne. An average of 68% of Pt was extractable with HCl. Organic P comprised the majority (95%) of HCl-Pt; however, only trace levels of HCl-Po were hydrolyzable, and litter application increased HCl-Pne up to 217%. Thus, litter application increased levels of both soluble Pi and stable Pne, but the specific response varied with application rate and land management. This study increased understanding of P chemical distribution with time in litter-amended soil with high clay and CaCO3 contents under differing land-use scenarios. [ABSTRACT FROM AUTHOR]

Few multiyear field studies have examined the impacts of a one-time biochar application on net N mineralization and greenhouse gas emissions in an irrigated, calcareous soil; yet this use of biochar is hypothesized as a means of sequestering atmospheric CO2 and improving soil quality. We fall-applied four treatments: stockpiled dairy manure (42 Mg ha-1 dry wt.), hardwood-derived biochar (22.4 Mg ha-1), combined biochar and manure, and no amendments (control). Nitrogen fertilizer was applied in all plots and years based on treatment's preseason soil test N and crop requirements and accounting for estimated N mineralized from added manure. From 2009 to 2011, we measured greenhouse gas fluxes using vented chambers, net N mineralization using buried bags, corn (Zea mays L.) yield, and N uptake, and in a succeeding year, root and shoot biomass and biomass C and N concentrations. Both amendments produced persistent soil effects. Manure increased seasonal and 3-yr cumulative net N mineralization, root biomass, and root/shoot ratio 1.6-fold, CO2-C gas flux 1.2-fold, and reduced the soil NH4/NO3 ratio 58% relative to no-manure treatments. When compared with a class comprising all other treatments, biochar-only produced 33% less cumulative net N mineralization, 20% less CO2-C, and 50% less N2O-N gas emissions, and increased the soil NH4/NO3 ratio 1.8-fold, indicating that biochar impaired nitrification and N immobilization processes. The multi-year nature of biochar's influence implies that a long-term driver is involved, possibly related to biochar's enduring porosity and surface chemistry characteristics. While the biochar-only treatment demonstrated a potential to increase corn yields and minimize CO2-C and N2O-N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH4-N dominated the soil inorganic N pool. Combining biochar with manure more effectively utilized the two soil amendments, as it eliminated potential yield reductions caused by biochar and maximized manure net N mineralization potential. [ABSTRACT FROM AUTHOR]

Phosphorus (P) applied to soil as fertilizer moves away from the point of application mainly through diffusion. Sorption and precipitation reactions may reduce its mobility and availability to plants. Here, we developed a method to visualize diffusion of P from fertilizer in a simple and nondestructive way. A fertilizer granule is added in the center of a soil-filled Petri dish. After a given incubation time, a filter paper impregnated with Fe oxide acting as a P sink is placed on the soil surface. The P captured on the filter paper is visualized using a modified malachite green method, which creates a mirror image of the diffusion zone. The paper is scanned and analyzed using imaging software to quantify the extent and intensity of the diffusion zone. This method was applied to a range of fertilizer formulations in soils with contrasting properties. The extent of diffusion was also assessed through concentric sampling and chemical analysis of soil sections. The measured diffusion was compared with predictions of a numerical diffusion model. The method demonstrated the effects of soil properties and fertilizer formulation on P diffusion. The extent of diffusion strongly depended on soil properties, with least diffusion in soils rich in amorphous oxides and in calcareous soils. Results of the visualization method were in good agreement with chemical analyses and modeling results. This method allows easy comparison of fertilizer sources and enables a better understanding of the physicochemical processes affecting fertilizer P behavior at the soil-fertilizer interface. [ABSTRACT FROM AUTHOR]

Calcium and magnesium are two dominant cations in calcareous soils that undergo precipitation reactions with applied P fertilizers. Unlike Ca, the reactions of Mg with P have not been thoroughly studied. The objectives of this study were to determine the effect of the exchangeable Ca/Mg ratio on the solubility and mobility of P in model calcareous soils and to identify the P species using 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR). A cation exchange resin was saturated to achieve five different saturation ratios: approximately 100% Ca, 60:40 Ca/Mg, 50:50 Ca/Mg, 30:70 Ca/Mg, and 100% Mg. The resin was mixed with quartz sand and CaCO3 to form model calcareous soils. Fertilizer monoammonium phosphate (MAP) was surface applied on soil columns. According to the analysis of 2-mm segments, water-soluble P increased with decreasing Ca saturation while the acid-soluble P decreased with decreasing Ca saturation. The decreasing Ca saturation (or increasing Mg saturation) enhanced deeper penetration of added P. Dicalcium phosphate dihydrate (DCPD) was the dominant P species formed in soils with 100 to 50% Ca saturation. Magnesium phosphate trihydrate (MPTH) was identified as a prominent P phase with a poorly ordered structure in soils with 70 to 100% Mg saturation. The DCPD and MPTH were identified as minor P phases in 30:70 and 60:40 Ca/Mg soils, respectively. Both chemical and NMR results confirmed that Mg, unlike Ca, was not a strong cation for P precipitation. The role of exchangeable Mg in reducing the formation of Ca-P precipitates could have a positive effect on the P availability in soils with low Ca/Mg saturation. [ABSTRACT FROM AUTHOR]

Phosphate release kinetics in soils are of global interest because sustainable plant nutrition with phosphate will be a major concern in the future. Dissolution of phosphate-containing minerals induced by a changing rhizosphere equilibrium through proton input is one important mechanism that releases phosphate into bioavailable forms. Our objectives were (i) to determine phosphate release kinetics during H+ addition in calcareous soils of the Schwäbische Alb, Germany, and to assess the influence of (ii) land-use type (grassland vs. forest) and (iii) management intensity on reactive phosphate pools and phosphate release rate constants during H+ addition. Phosphate release kinetics were characterized by a large fast-reacting phosphatepool, which could be attributed to poorly-crystalline calcium phosphates, and a small slow-reacting phosphate pool probably originating from carbonate-bearing hydroxylapatite. Both reactive phosphate pools--as well as total phosphate concentrations (TP) in soil--were greater in grassland than in forest soils. In organically fertilized grassland soils, concentrations of released phosphate were higher than in unfertilized soils, likely because organic fertilizers contain poorly-crystalline phosphate compounds which are further converted into sparingly soluble phosphate forms. Because of an enriched slow-reacting phosphate pool, mown pastures were characterized by a more continuous slow phosphate release reaction in contrast to clear biphasic phosphate release patterns in meadows. Consequently, managing phosphate release kinetics via management measures is a valuable tool to evaluate longer-term P availability in soil in the context of finite rock phosphate reserves on earth. [ABSTRACT FROM AUTHOR]

Carbonates are an important component of soil found in dry regions. The main aim of this paper is to investigate the origin of C in soil carbonate and to assess the effect of applied organic residues on carbonate dissolution and crystallization. We measured the δ13C of organic carbon (OC), active and total carbonates down to a depth of 260 cm of a calcareous soil developed in a tufa deposit. We found a parallel decrease of the active CaC03-δ13C and OC-δ13C from -10.5 to -13.6%o and from -24.6 to -26.4%0, respectively, in the soil profile. Furthermore, the active CaC03-δ13C and the concentrations of Ca and Mg in the soil solution during incubation of soil samples from the top 0- to 10-cm layer (soil δ13C = -11.5%o) with and without addition of pasteurized chicken manure (PCM, -23.2%o) were determined. The active CaC03-δ13C wasn't affected by time and treatment and with a δ13C 14.1%o higher than the soil organic matter (SOM). The sum of soil solution Ca and Mg concentrations in the PCM treatment decreased in the first days of the incubation and then increased linearly due to released protons by the nitrification processes. The tufa and the soil formed on it have two likely sources for the C in the active carbonate fraction; biogenic carbonates deposited during tufa formation and SOM mineralization and re-crystallization of soil carbonates. Application of an N-rich amendment to this calcareous soil enhanced the dissolution and re-crystallization of calcium carbonate. [ABSTRACT FROM AUTHOR]

Root and microbial respiration is considered to be the main source of CO2, production in soil; however, calcite dissolution in calcareous soils may contribute to the emitted CO2,. The major aim of this research was to quantify the contribution of CaCO3, dissolution to CO2, emission from a soil with and without the addition of an organic residue. Emissions of CO, and its δ13C from incubated noncalcareous (Golan Heights [GH], -26.23‰) and calcareous (Bet She'an [BS], -11.47‰) soils with and without the addition of a pasteurized chicken manure (PCM, -23.2‰) were determined. During 56 d of incubation, 445 and 1804 mg kg-1 CO2-C emitted from BS and GH soils, and PCM application caused additional emission of 2430 and 1884 mg kg-1 CO2-C, respectively. The NO2-N concentrations in the control BS and GH soils were 46 and 133 mg kg-1 and PCM application increased it to 508 and 577 mg kg-1, respectively. The emitted CO2-δ13C from BS and GH soils were -20.0 ± 0.2% and -27.2 ± 0.09%o and application of PCM changed it to -20.6 ± 0.42%o and -23.7 ± 0.16‰, respectively. Consequently, the contributions of the inorganic source to CO2-C emission from BS without and with PCM and from GH with PCM were 113.4,417.5, and 176 mgkg-1 (26.5,14.5, and 5% of the total), respectively. We suggest that oxidation of organic matter, mineralization of organic N, NH4 nitrification, oxidation of organic S, and production of organic acids caused chemical dissolution of calcite and CO2, emission. Ignoring this process will result in overestimation of the respired C. [ABSTRACT FROM AUTHOR]

The aim of this study was to determine the residual effects of Zn applied from five synthetic commercial chelates (Zn-ethylenediaminetetraacetate [EDTA]-hydroxyethyl-ethylenediaminetriacetate (HEDTA], Zn- HEDTA, Zn- diethylenetriaminepentaacetate [DTPA]-HEDTA-EDTA [Zn-D-H-EJ, Zn-EDTA, and Zn- ehtylenediaminedihydroxysulfophenylacetate [EDDHSA]) to two soils: Soil 1 (weakly acidic, with moderate permeability) and Soil 2 (calcareous, with moderate to rapid permeability), in a greenhouse experiment. Beneficial effects of Zn on navy bean (Ph4seolus vulgarss L.) response (dry matter yield, total and soluble Zn concentration, and the utilization of applied Zn) were observed, with significant increases in all of the determined plant parameters, especially in Soil 1, in comparison with the control (no Zn addition). The rates of increase varied among sources depending on the soil. For Soil 1, the greatest increases were usually observed for the Zn-HEDTA fertilizer, while for Soil 2 the greatest increases were exhibited for the Zn-D-H-E and Zn-EDTA sources. The fertilizers that produced the biggest total Zn leaching losses were the three sources that contained EDTA and DTPA, especially in the case of Soil 2. The amounts of easily leachable Zn (estimated using the dilute BaCI2 extraction) were significantly correlated with the amounts of Zn actually leached. The amounts of potentially available Zn and Zn in the water-soluble-plus- exchangeable fraction (as assessed by single and sequential extractions) generally decreased in the second cropping year; this could have been due mainly to Zn leaching and to aging processes, especially in Soil 2. [ABSTRACT FROM AUTHOR]

A better understanding of the internal N cycle in agriculturally used soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective N2O mitigation strategies. The present laboratory study quantifies gross nitrogen transformations in an intensively used agricultural soil of the North China Plain (NCP). It also elucidates the role of nitrification and denitrification in the emissions of the greenhouse gas N2O. In the lab, soil samples adjusted to a water-filled pore space (WFPS) of 40 or 60% were spiked with 15NH4NO3, NH415NO3, or 15NH415NO3 and incubated at 20°C for 10 d. One subset of the samples was amended with glucose. The size and 15N enrichment of the mineral N pools and N2O fluxes were determined at intervals of 0 to 10 d. The studied calcareous soil showed a very rapid nitrification of the applied NH4+, which disappeared during the first 3 d. Glucose enhanced mineralization of native soil organic matter (SOM), stimulated dissimilatory nitrate reduction to ammonium (DNRA), and promoted the immobilization-remineralization cycle. Throughout the incubation, nitrification, and denitrification occurred simultaneously. Nitrification was the dominant N2O-producing process and contributed 83.0 to 95.4% to the totally emitted N2O in the non-glucose soils. In contrast, the N2O emitted from 15NO3- pool increased after adding glucose, indicating that denitrification was C-limited in the studied soil. [ABSTRACT FROM AUTHOR]

Soil test phosphorus (STP) measurements are important for predicting crop P needs and for P loss risk assessments. Previous work indicates that the Bray P1 method extracts less P and does not correlate as well with Mehlich 3 or Olsen STP methods in alkaline or highly calcareous soils. This research was conducted to determine if the Bray P1 test is an appropriate method for the eastern red soil (ERS) region of Wisconsin, where pH typically ranges from 7 to 8 and soils are often calcareous. Soil samples (n = 113) from the ERS region and comparison soils (CS) from Iowa and Kansas (n = 38) with high pH and carbonate content were analyzed for P using the Bray P1, Mehlich 3, and Olsen methods and for soil pH and carbonate content. Results indicate that Bray P1 is strongly correlated with Olsen and Mehlich 3 for all samples in ERS regardless of carbonate content (R2 = 0.83 and 0.98, respectively), but only weakly correlated to Olsen and Mehlich 3 for Iowa and Kansas soils with carbonate contents ⩾ 5 g kg-1 (R2 = 0.01 and 0.08, respectively). Further investigation indicated that carbonate in CS is calcitic while in ERS it is dolomitic. Because dolomite reacts much more slowly than calcite, Bray P1 is not neutralized in ERS during the 5 mm extraction time. For soil with unknown carbonate content, a pH measurement on the Bray P1 filtrate can identify samples where Bray P1 is neutralized and an alternative P extractant should be used. [ABSTRACT FROM AUTHOR]

The objective of this study was to compare the mobility, availability, and relative effectiveness of Zn from liquid Zn-diethylenetriamine-pentaacetate-N-2-hydroxyethyl-ethylenediamine-triacetate-ethylenediamine-tetraacetate (Zn-DTPA-HEDTA-EDTA or Zn-D-H-E) and Zn-aminelignosulfonate (Zn-AML) sources applied to weakly acidic (moderate permeability) and calcareous (moderate to rapid permeability) soils at different Zn levels in a navy bean (Phaseolus vulgaris L.) greenhouse experiment during a 60-d period. Zinc behavior in soil was evaluated by single and sequential extractions. The addition of the two Zn complexes produced a considerable increase in Zn concentration in the water-soluble plus exchangeable and organically complexed fractions. The Zn-D-H-E source resulted in greatly increased mobility of Zn through the soils in comparison with the control (no Zn addition) and the Zn-AML source at the highest dosage (10 mg Zn kg-1); 11 and 32% of total applied Zn was lost in weakly acidic and calcareous soils, respectively, through leaching. Zinc application increased the plant dry matter yield compared with the control treatment in the weakly acidic soil; however, there were no significant differences between the Zn rates of 5 and 10 mg kg-1. All sources of Zn increased the amount of Zn uptake in plants. The Zn-D-H-E was more effective than Zn-AML in the calcareous soil but had a similar effect in the weakly acidic soil. Soluble Zn extracted from plant dry matter with reactive 2-(N-morpholino)ethanesulfonic acid (MES) could be used to diagnose the nutritional status of Zn in navy bean. [ABSTRACT FROM AUTHOR]

The benefits of Mn and Zn fluid fertilizers over conventional granular products in calcareous sandy loam soils have been agronomically demonstrated. We hypothesized that the differences in the effectiveness between granular and fluid Mn and Zn fertilizers is due to different Mn and Zn reaction processes in and around fertilizer granules and fluid fertilizer bands. We used a combination of several synchrotron-based x-ray techniques, namely, spatially resolved micro-x-ray fluorescence (μ-XRF), micro-x-ray absorption near edge structure spectroscopy (μ-XANES), and bulk-XANES and -extended x-ray absorption fine structure (EXAFS) spectroscopy, along with several laboratory-based x-ray techniques to speciate different fertilizerderived Mn and Zn species in highly calcareous soils to understand the chemistry underlying the observed differential behavior of fluid and granular micronutrient forms. Micro-XRF mapping of soil-fertilizer reactions zones indicated that the mobility of Mn and Zn from liquid fertilizer was greater than that observed for equivalent granular sources of these micronutrients in soil. After application of these micronutrient fertilizers to soil, Mn and Zn from liquid fertilizers were found to remain in comparatively more soluble solid forms, such as hydrated Mn phosphate-like, Mn calcite-like, adsorbed Zn-like, and Zn silicate-like phases, whereas Mn and Zn from equivalent granular sources tended to transform into comparatively less soluble solid forms such as Mn oxide-like, Mn carbonate-like, and Zn phosphate-like phases. [ABSTRACT FROM AUTHOR]

Manure characteristics can influence the potential for P transfer in runoff following land application of manures. This research assessed the influence of manure characteristics on P solubility in calcareous soils using manures from poultry (Gallus Domisticus) fed a variety of grain-based diets with the manures containing a range of total P (5.6–16.4 g P kg-1), water-extractable P (WEP, 0.9–4.7 g P kg-1), phytic acid P (0.1–7.6), total N/P ratios (2.6–5.1), and total C/P ratios (19.5–75.7). In addition, mono-ammoniurn phosphate fertilizer and reagent grade inositol hexaphosphate (phytic acid [PA]), were included, as well as a control treatment with no P additions. Treatments were incorporated into two soils (Portneuf [Coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcids] and Millville [Coarse-silty, carbonatic, mesic Typic Haploxerolls]) at three rates (10, 20, and 40 mg P kg-1) and incubated for a total of 18 wk with subsamples taken at 2, 5, 9, and 18 wk. Soil samples were analyzed for inorganic and organic NaHCO3 (Olsen) extractable P and select soils were analyzed at 0 and 12 wk by 31P nuclear magnetic resonance spectroscopy (NMR) for soil P characterization. The percentage of WEP and PA (of total P) in the manures were linearly related (r² = 0.94). Increases in Olsen P over time were positively related to the percentage of monoester P in the treatments. At 2 wk, there was a strong negative correlation between the amount of PA added in the treatments and increases in Olsen P. However, by 18 wk, Olsen P was more closely related to the amount of C or N added with the treatments. Changes in PA content of manures due to dietary modification may influence P sorption on calcareous soils in the short-term while other characteristics such as C/P ratio may exert a stronger influence over changes in soil test P over longer time periods. [ABSTRACT FROM AUTHOR]

Microsprinklers allow precise control of irrigation water applications and offer the potential for higher efficiency of water and fertilizer use compared with flood irrigation. A field experiment was conducted during 1999-2002 in central Arizona (AZ) to evaluate effects of various N rates and fertigation frequencies on fruit yield and quality, leaf N concentration, and residual soil N of ‘Newhall’ navel oranges (Citrus sinensis) on ‘Carrizo’ citrange (Porcirus trifoliata x Citrus sinensis) rootstock (planted in 1997) grown in a Gilman (coarse-loamy, mixed, superactive, calcareous, hyperthermic Typic Torrifluvents) fine sandy loam. The experiment included nonfertilized control plots and factorial combinations of three fertigation frequencies (27, 9, and 3 applications annually) and three N rates (68, 136, and 204 g N tree-1 yr-1). Maximum yields occurred at N rates of 105 to 153 g N tree-1 yr-1 for the fourth to the sixth growing seasons. The yield-maximizing N rates were equivalent to 17 to 34% of currently recommended N rates for citrus grown in AZ. Fruit and juice quality did not show significant response to N rate or fertigation frequency. Leaf N concentrations at yield-maximizing N rates were above the critical leaf tissue N range of 25 to 27 mg g-1, indicating that this range may be too low for these ‘Newhall’ navel orange trees. During all three seasons, higher residual soil NO3 concentrations resulted from the highest N rate. Our results suggest that optimum N rates for microsprinkler-irrigated ‘Newhall’ navel oranges in AZ are lower than currently recommended N rates. [ABSTRACT FROM AUTHOR]

We employed x-ray computed microtomography (X-ray CT) to observe differences in moisture around fertilizer P granules (monoammonium phosphate, MAP) versus injection zones of fluid P fertilizer (technical grade monoammonium phosphate, TG MAP) in a calcareous soil over time. X-ray CT allows nondestructive visualization of small columns containing soils and fertilizers. We were able to visualize the increase in density around the highly hygroscopic fertilizer granule over time. It appeared that both water flow toward the granule and precipitation of P could be responsible for the development of about 1mm thick high density zone immediately adjacent to the granule. The mass flow of water toward the granule may have slowed or restricted the diffusion of fertilizer P from the granule, thus increasing the chances for P fixation through precipitation reactions. Also, the granule became less dense with time indicating the progress of granule dissolution. In contrast, injection of fluid fertilizer (TG-MAP) in soil did not result in moisture changes over time as evidenced by a lack of X-ray CT detectable density differences in the soil column. These data support previous findings that, when P is supplied in granular form, P diffusion and isotopic lability in calcareous soils are reduced compared with equivalent liquid fertilizer formulations, probably due to precipitation reactions induced by osmotically induced flow of soil moisture into the fertilizer granule. [ABSTRACT FROM AUTHOR]

Many of Michigan's loamy soils exhibit varying degrees of fragipan expression, which may be variously influenced by their parent materials. We examined three soils in northern Michigan with varying degrees of fragipan expression to assess development of fragipans formed in acidic and calcareous glacial drift. To accomplish this, soil characterizations were made through field, physical, chemical, and micromorphological observations and analyses. The soils have bisequal horizonation: an upper sequum associated with podzolization processes and lower sequum associated with lessivage. Protofragipans and fragipans are found only in the lower sequum. The soils experience periodic episaturation and contain at least one lithologic discontinuity, often near the protofragipan or fragipan. The protofragipan and fragipans have loamy sand to loam textures, weak platy to subangular blocky structure, higher bulk densities (1.5–1.9 g cm-3) and lower pH values (4.8–6.8) than adjacent horizons, brittle failure, and fine vesicular pores. Eluvial protofragipan and fragipan horizons contain albic materials that tongue into underlying argillic horizons, Illuvial fragipans exhibit clay coats, flows, and bridging. Thin-section characterizations confirm the presence of closely packed fabrics, intergrain bridging by clays, and void pedofeatures. Scanning electron microscopy (SEM) provides evidence of eluviation, reorganization of silt and clay, fluctuating redox conditions, degraded void pedofeatures, and the presence of surficially amorphous (bonding) materials in the protofragipan and fragipans. Soil extraction data do not preclude the presence of a fragic- property (brittleness) agent. Results, therefore, indicate that these protofragipans and fragipans are pedogenic and can form, with vari- able expression, in both acidic and calcareous glacial parent materials. [ABSTRACT FROM AUTHOR]

Plant nutrient uptake from the soil is dependent on fertilizers applied, soil chemicals, and other factors. The purpose of this study is to quantify the effects of applied N fertilizers on P uptake by winter wheat (Triticum aestivum L.) and on the change of soil pH in the root zone related to reductions of inorganic P fractions in the rhizosphere soil. An experiment was conducted using different forms of N fertilizers (i.e., NH4+-N and NO3--N) with three N concentrations (0, 100, and 300 mg kg-1) applied in a calcareous soil. Biomass and total N uptake of the plant increased with the N concentrations and NH4+-N fertilizer resulted in a greater biomass than NO3--N nutrition. Total P uptake in the plant was also higher with NH4+-N fertilizer than with the NO3--N nutrition. Compared with the zero N treatment, the soil pH around the roots decreased by 0.30 and 0.65 units, respectively, with N treatments of 100 and 300 mg kg-1 of NH4+-N fertilizer. The amount of soil inorganic P fractions in the root zone decreased with increasing NH4+-N applied. The NO3--N treatments reduced rhizosphere acidification and had a less impact on the soil inorganic P fractions. The results suggest that enhancing rhizosphere acidification attributable to applications of NH4+-N fertilizer can increase P availability in calcareous soils for plant uptake. [ABSTRACT FROM AUTHOR]

Phosphorus availability is a major factor limiting crop production in highly calcareous soils. Recent field trials on calcareous soils in southern Australia have shown that fluid fertilizers may provide a useful alternative to granular fertilizer products. Fluid sources of P enhance P uptake and yield when compared with granular fertilizers applied at the same rate. This work aimed to compare the behavior of one fluid (technical grade monoammonium phosphate, TG-MAP) and one granular (monoammonium phosphate, MAP) form of P fertilizer in a highly calcareous soil. Changes in soil pH, P diffusion, solubility, and lability (using isotopic dilution techniques) were determined at different distances from the point of application over 5 wk. Furthermore, reaction products in MAP granules were investigated using spectroscopic techniques. The results indicated that P from fluid TG-MAP diffused more and was more available than P supplied as granular MAP. Also, X-ray diffraction (XRD) and energy dispersive X-ray microanalyses (EDXMA) of the MAP granules indicated that a significant percentage (12%) of the initial P remained in the granules even after 5 wk of incubation in the soil. The enhanced P availability of fluid fertilizers observed in field trials compared with granular forms is discussed in relation to differences in the dissolution, diffusion, and reaction processes in soils. [ABSTRACT FROM AUTHOR]

Analyzes the phosphorus-sorption characteristics of calcareous soils and limestone in southern Florida and adjacent farmlands. Soil characteristics; One-point-sorption isotherm and phosphorus saturation; Relationship between phosphorus desorption and phosphorus saturation; Relationship between soil properties and phosphorus sorption.

Develops an experimental procedure for the accurate quantification of [sup 14]carbon-labeled substrate degradation rates in calcareous soils. Characterization of calcareous soils; Inaccuracy of the conventional methods in determining [sup 14]carbon-labeled substrate degradation rates; Measurement of [sup 14]carbon organic acid degradation and alkali trap efficiency.

Studies the soil nitrogen dynamics in organic and mineral soil calcareous wetlands in eastern New York. Classification problems concerning wetlands; Functional differences between organic and mineral soil calcareous wetlands; Regulation of nitrogen cycling in calcareous wetlands.

Investigates the effect of phosphorus transformations on calcareous soil properties of southern western Australia. Positive relationship between clay-related properties and negative relationships between carbonate-related properties; Interrelationships among phosphate fractions and its relationship with available phosphorus.

Studies the release rate and leaching of starch-encapsulated (SE) atrazine in a calcareous soil. Effect of time at all water potentials to the solution concentrations of atrazine; Comparison between the leaching of commercial atrazine and the various granule size of SE atrazine in a sandy calcareous soil.

Presents a study conducted by soil scientists in Indiana to determine if cutans indicate how water moves through the calcareous till and the effect of chemical cementation on the its strength. Materials and methods used; Where samples for study were collected from; Cementation and chemical properties in the till; Results of the study.