Influence of long-term application of composted or stockpiled feedlot manure with straw or wood chips on soil cation exchange capacity

The influence of annual applications of composted (CM) or stockpiled (SM) beef feedlot manure with straw (ST) or wood-chip (WD) bedding on cation exchange capacity (CEC) of a clay loam soil in southern Alberta was examined after 1, 8, and 15 years. The hypotheses in our study were that soil CEC should be greater for amended than unamended soils; manure type and bedding should have no effect on soil CEC; and soil CEC should increase with greater manure application rate. After fifteen applications, the CEC was significantly greater for amended than unamended soils. Manure type had no significant (P > 0.05) effect on soil CEC after fifteen applications, and the mean soil CEC was 5% greater for WD than ST. Mean CEC was significantly greater by 7 to 12% for the 77 than the 13 and the 39 Mg ha^?1 rates after fifteen applications. The soil CEC was increased by 0.061 cmol_c kg^?1 for a unit increase in application rate (Mg dry wt. ha^?1 yr^?1), and 96% of the variation in CEC for amended soils could be explained by application rate. Overall, bedding, rate, or adjusting both bedding type and manure rate (but not manure type), may be possible practices for feedlot producers to manage soil CEC.     

Addition of phosphorus to soils with low to medium phosphorus retention capacities. II. effect on soil phosphorus extractability

Abstract

Knowledge of the change in soil extractable phosphorus (P) as a consequence of soil P fertilization could be useful in discriminating soils with a potential for soil P release to runoff or movement of P along the soil profile. In this research, soils with low to medium P retention capacity were equilibrated for 90 days with soluble P (KH₂PO₄) at rate of 100 mg P kg^‐1 soil. After this period, soil samples both with and without the P addition were analyzed using six conventional methods: 1) Olsen, 2) Bray 1,3) Mehlich3,4) Egner, 5) Houba, dilute CaCl₂ solution, and 6) distilled water, and three “innovative”; P‐sink methodologies: 1) Fe oxide‐coated paper strip, 2) anion exchange resin membrane, and 3) cation‐anion exchange resin membrane. The soils without P addition had low levels of extracted P as determined by all nine procedures. Net increases in the amount of P extracted from the soils with added P ranged from 4.2 mg kg^‐1 (CaCl₂ extraction) to 57.6 mg kg^‐1 (cation‐anion resin membrane extraction). Relationships between change in extracted P and i) physical and chemical characteristics, and ii) soil P sorption properties are also presented and discussed.     

Effects of soil flooding on P transformations in soils of the Mesopotamia region,Argentina

In the Mesopotamia region (Argentina), rice is cropped on a wide range of soil types, and the response of rice to fertilizer application has been inconsistent even in soils with very low levels of available phosphorus. Phosphorus transformations in flooded soils depend on soil characteristics that may affect phosphorus availability. This study was conducted to determine which soil characteristics were related to the changes in P fractions during soil flooding. Soils were chosen from ten sites within the Mesopotamia region that are included in five different soil orders: Oxisols, Ultisols, Alfisols, Mollisols, and Vertisols. Soil phosphorus (P) was fractionated by a modified Hedley method before and after a 45 d anaerobic‐incubation period. Changes in the inorganic P extracted with resin depended on soil pH and were related to the exchangeable‐Fe concentration of soils (extracted with EDTA). Inorganic P extracted with alkaline extractants (NaHCO₃ and NaOH) increased due to soil flooding. This increase was related to the organic‐C (OC) percentage of soils (r² = 0.62, p < 0.01), and ranged from 13 to 55 mg kg^–1. Even though previous studies showed that P associated with poorly crystalline Fe played an important role in the P nutrition of flooded rice, in this study, there was no relationship between ammonium oxalate–extractable Fe and P changes in soils due to flooding. Our results suggest that in the Mesopotamia region, changes in P fractions due to soil flooding are related to soil OC, soil pH, and soluble and weakly adsorbed Fe.     

Effects of organic matter addition on phosphorus availability to flooded and nonflooded rice in a P‐deficient tropical soil: a greenhouse study

Addition of organic matter (OM) to flooded soils stimulates reductive dissolution of Fe(III) minerals, thereby mobilizing associated phosphate (P). Hence, OM management has the potential to overcome P deficiency. This study assessed if OM applications increases soil or mineral fertilizer P availability to rice under anaerobic (flooded) condition and if that effect is different relative to that in aerobic (nonflooded) soils. Rice was grown in P‐deficient soil treated with combinations of addition of mineral P (0, 26 mg P/kg), OM (0, ~9 g OM/kg as rice straw + cattle manure) and water treatments (flooded vs nonflooded) in a factorial pot experiment. The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; blanket N and K was added in all treatments. Fresh addition of OM promoted reductive dissolution of Fe(III) minerals in flooded soils, whereas no such effect was found when OM had been incubated for 6 months before flooding. Yield and shoot P uptake largely increased with mineral P addition in all soils, whereas OM addition increased yield and P uptake only in flooded soils following fresh OM addition. The combination of mineral P and OM gave the largest yield and P uptake. Addition of OM just prior to soil flooding increased P uptake but was insufficient to overcome P deficiency in the absence of mineral P. Larger applications of OM are unlikely to be more successful in flooded soils due to side effects, such as Fe toxicity.     

The effect of soil pH manipulation on chemical properties of an agricultural soil from northern Idaho

Abstract

Selected chemical properties of an artificially acidified agricultural soil from northern Idaho were evaluated in a laboratory study. Elemental S and Ca(OH)₂were used to manipulate the soil pH of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll), which had an initial pH of 5.7. A 100 day incubation period resulted in a soil pH manipulation range of 3.3 to 7.0. Chemical properties evaluated included: N mineralization rate, extractable P, AI, Mn, Ca, Mg and K and CEC. N mineralization rate (assessed by anaerobic incubation) decreased with decreasing soil pH. Nitrification rate also decreased as NH₄ ⁺‐N accumulated under acid soil conditions. Sodium acetate extractable P was positively linearly correlated (R²= 0.87) with soil pH over the entire pH range evaluated. Potassium chloride extractable Al was less than 1.3 mg kg^‐1of soil at pH values higher than 4.4. Consequently, potential Al toxicity problems in these soils are minimal. Extractable Mn increased with decreasing soil pH. Soil CEC, extractable Mg, and extractable K all decreased with increasing soil pH from 3.3 to 7.0. Extractable Ca levels were largely unaffected by changing soil pH. It is likely that the availability of N and P would be the most adversely affected parameters by soil acidification     

Effects of soil flooding and organic matter addition on plant accessible phosphorus in a tropical paddy soil: an isotope dilution study

Plant growth experiments were conducted to reveal the mechanism by which organic matter (OM) and soil flooding enhance phosphorus (P) bioavailability for rice. It was postulated that reductive dissolution of iron‐(III) [Fe(III)] oxyhydroxides in soil releases occluded phosphate ions (PO₄), i.e., PO₄ that is not isotopically exchangeable in the original soil prior to flooding. Rice was grown in P‐deficient soil treated with factorial combinations of addition of mineral P (0, 50 mg P kg^?1), OM (0, ≈ 20.5 g OM kg^?1 as cattle manure +/– rice straw) and water treatments (flooded vs. non‐flooded). The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; nitrogen and potassium were added in all treatments. The soil exchangeable P was labeled with ³³PO₄ prior to flooding. The plant accessible P in soil, the so‐called L‐value, was determined from the ³³P/³¹P ratio in the plants. The L‐values were inconsistently affected by flooding in contrast with the starting hypothesis. The OM and P addition to soil clearly increased the L‐value and, surprisingly, the increase due to OM application was larger than the total P addition to soil. An additional isotope exchange study in a soil extract (E‐value) at the end of the experiment showed that the E‐value increased less than the total P addition with OM. This suggests that plants preferentially take up unlabeled P from the OM in the rhizosphere compared to labeled labile inorganic P. The effects of soil flooding on P bioavailability is unlikely related to an increase of the quantity of bio‐accessible P in soil (L‐value) but is likely explained by differences in P mobility in soil.     

Sodium hypochlorite oxidation reduces soil organic matter concentrations without affecting inorganic soil constituents

Oxidative treatment can isolate a stable organic matter pool in soils for process studies of organic matter stabilization. Wet oxidation methods using hydrogen peroxide are widely used for that purpose, but are said to modify poorly crystalline soil constituents. We investigated the effect of a modified NaOCl oxidation (pH 8) on the mineral composition of 12 subsoils (4.9–38.2 g organic C kg^?1) containing varying amounts of poorly crystalline mineral phases, i.e. 1.1–20.5 g oxalate‐extractable Fe kg^?1, and of different phyllosilicate mineralogy. Post‐oxidative changes in mineral composition were estimated by (i) the determination of elements released into the NaOCl solution, (ii) the difference in dithionite‐ and oxalate‐extractable Si, Al and Fe, and (iii) the specific surface areas (SSAs) of the soils. The NaOCl procedure reduced the organic C concentrations by 12–72%. The amounts of elements released into the NaOCl extracts were small (≤ 0.14 g kg^?1 for Si, ≤ 0.13 g kg^?1 for Al, and ≤ 0.03 g kg^?1 for Fe). The SSA data and the amounts of dithionite‐ and oxalate‐extractable elements suggest that the NaOCl oxidation at pH 8 does not attack pedogenic oxides and hydroxides and only slightly dissolves Al from the poorly crystalline minerals. Therefore, we recommend NaOCl oxidation at pH 8 for the purpose of isolating a stable organic matter pool in soils for process studies of organic matter stabilization.     

Phosphorus source,organic matter,and arbuscular mycorrhiza effects on growth and mineral acquisition of chickpea grown in acidic soil

Abstract

Plants grown in acidic soil usually require relatively high amounts of available phosphorus (P) to optimize growth and productivity, and sources of available P are often added to meet these requirements. Phosphorus may also be made available at relatively high rates in native soil when roots are colonized with arbuscular mycorrhizal fungi (AMF). Addition of P to soil usually reduces root‐AMF colonization and decreases beneficial effects ofAMF to plants. In glasshouse experiments, soil treatments of P [0 P (Control), 50 mg soluble‐P kg^?1 as KH₂PO₄ (SP), and 200 mg P kg^?1 as phosphate rock (PR)], organic matter (OM) at 12.5 g kg^?1, AMF (Glomus darum), and various combinations of these (OM+SP, OM+PR, AMF+SP, AMF+PR, AMF+OM, AMF+OM+SP, and AMF+OM+PR) were added to steam treated acidic Lily soil (Typic Hapludult, pH_w=5.8) to determine treatment effects on growth and mineral acquisition by chickpea (Cicer areitinum L.). The various treatment applications increased shoot dry matter (DM) above the Control, but not root DM. Percentage AMF‐root colonization increased 2‐fold or more when mycorrhizal plants were grown with AMF, OM+SP, and OM+PR. Regardless of P source, plant acquisition of P, sulfur (S), magnesium (Mg), calcium (Ca), and potassium (K) was enhanced compared to the Control, and mineral enhancement was greater in PR compared to SP plants. Mycorrhizal plants also had enhanced acquisition of macronutrients. OM+SP and OM+PR enhanced acquisition of P, K, and Mg, but not Ca. Concentrations of Fe, Mn, Cu, and Al were generally lower than Controls in SP, RP, AMF+PR, AMF+SP, and OM plants, and mycorrhizal plants especially had enhanced micronutrients. Relative agronomic effectiveness values for shoot DM and shoot P, Ca, and Mg contents were considerably higher for PR, including OM+PR, AMF+PR, and AMF+OM+PR, than for SP. PR and OM applications to AMF plants are low‐cost attractive and ecologically sound alternatives to intensive use of P fertilizers for crops grown in acidic soils.     

Predicting phosphorus sorption isotherm parameters in soil using data of routine laboratory tests

Knowledge of phosphorus(P) sorption dynamics across different soil types could direct agronomic and environmental management of P. The objective of this study was to predict P isotherm parameters for a national soil population using data of routine laboratory tests. Langmuir and Freundlich sorption parameters were calculated from two different ranges(0–25 and 0–50 mg P L~(-1)) using an archive of representative agricultural soil types from Ireland.Multiple linear regression(MLR) identified labile forms of aluminium(Al) and iron(Fe), organic matter(OM), cation exchange capacity(CEC), and clay as significant drivers. Langmuir and Freundlich sorption capacities, Freundlich affinity constant, and Langmuir buffer capacity were predicted reliably, with R~2 of independent validation 0.9. Sorption isotherm parameters were predicted from P sorbed at a single concentration of 50 mg P L~(-1)(S_(50)). An MLR prediction of P sorption maximum in the 0–50 mg P L~(-1) range was achieved, to an accurate standard, using S_(50), OM, and Mehlich-3 Fe(R~2 of independent calibration and validation being 0.91 and 0.95, respectively). Using Giles' four shapes of isotherms(C, L, H, and S), L non-strict-and C-shaped isotherm curves accounted for 64% and 27% of the soils, respectively. Hierarchical clustering identified a separation of isotherm curves influenced by two ranges of Mehlich-3 Al. Soils with a low range of Mehlich-3 Al(2.5–698 mg kg~(-1)) had no incidence of rapid sorption(C shape). Single point indices, Al, or available soil data make the regression approach a feasible way of predicting Langmuir parameters that could be included with standard agronomic soil P testing.     

Divergent Relationships of Phosphorus Soil Tests in Temperate Grassland Soils

Abstract

Various soil tests are used to estimate phosphorus (P) availability for both crop uptake and potential loss to water. Conversion equations may provide a basis for comparison between different tests and regions, although the extent to which information can be interchanged is uncertain. The objective was to determine and quantify relationships between specific soil test extractants for samples taken annually in October and February over 4 years from four sites in each of eight soil series under grassland. The extractants comprised Mehlich‐3, Morgan, Olsen, Bray‐1, lactate–acetate, CaCl₂ (1∶2 and 1∶10 soil–solution ratios), and resin. The results showed distinct relationships for each soil series, for which individual lines regression models (different intercepts and slopes) were superior to a single conversion equation across all soils. The ensuing difference between soils was large and ranged from 1.9 to 8.0 and 9.2 to 15.6 mg kg^?1 P for Morgan and Olsen, respectively, at 20 mg kg^?1 Mehlich‐3 P. Generally, the environmentally oriented tests CaCl₂ and resin correlated best with Morgan. Some soil‐specific limitations were also observed. CaCl₂ was less efficient than Morgan, and Morgan less efficient than Mehlich‐3 on a high Fe–P soil derived from Ordovician‐shale diamicton, compared with the general trend for other soils. This finding suggests that further disparity may arise where evaluation of critical, or other, limits across regions involves even a limited sequence of tests.     

Relationship of Phosphorus Fractions with Soil Properties in Mothbean Growing Acid Soils of North Western Indian Himalayas

Phosphorus (P) availability in acid soils is affected and hence it is important to monitor the distribution of P in acid soils. Here, the relationship was investigated taking 81 surface (0–0.20 m) soil samples into consideration collected from 21 mothbean cultivated areas and were analyzed for different phosphorus fractions in relation to their physical and chemical properties. Results revealed that available P ranged from 8.19 to 15.46 kg ha^–1 which lies in a slightly low-to-medium range. Available P was significantly positively correlated with organic carbon and cation exchange capacity (CEC). The content of soil total P increased significantly with organic carbon and was found in range between 201.00 and 596.11 mg kg^–1 which was in suffice category. Various phosphorus fractions under study viz., Al–P, Fe–P and Ca–P ranged between 20.23–32.28, 34.80–51.44 and 8.57–15.00 mg kg^?1, respectively. Among the various P fractions, organic carbon was positively correlated with Fe–P and Ca–P.     

The effect of soil flooding on the transformation of Fe oxides and the adsorption/desorption behavior of phosphate

As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N₂ atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Fe_ox), mainly at the expense of dithionite‐soluble Fe (Fe_DCB), as well as oxalate‐extractable P (P_ox), but decreased the ratio of P_ox/Fe_ox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was P_ox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Fe_ox and P_ox fractions under non‐flooded and flooded conditions. The degree of the changes in Fe_ox, P_ox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed.     

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.     

Availability of soil boron fractions to M.26 apple rootstock

The availability of various boron (B) fractions in soil to M.26 apple (Malus spp.) rootstock was examined. The study was carried out in a greenhouse on soils with diverse chemical and physical properties. The following B fractions were determined: (i) B in soil solution, (ii) B non‐specifically adsorbed on soil surface, (iii) B specifically adsorbed on soil colloid surfaces, (iv) B occluded in Mn oxyhydroxides, (v) B occluded in noncrystalline aluminum (Al) and iron (Fe) oxides, (vi) B occluded in crystalline Al and Fe oxides, (vii) B fixed with soil silicates, and (viii) total soil B. In the studied soils there were: 0.07–0.17 mg kg^‐1 B in soil solution, 0.01–0.03 mg kg^‐1 B non‐specifically adsorbed on soil surface, 0.04–0.08 mg kg^‐1 B specifically adsorbed on soil colloid surfaces, 0.28–0.67 mg kg^‐1 B occluded in manganese (Mn) oxides, 4.03–17.22 mg kg^‐1 B occluded in noncrystalline Al and Fe oxides, 8.93–50.62 mg kg^‐1 B occluded in crystalline Al and Fe oxides, 12.2–42.5 mg kg^‐1 B fixed with soil silicate, and 52.9–82.2 mg kg^‐1 total B. Simple correlation analysis showed positive correlation between B contents in M.26 apple rootstocks and amounts of B in soil solution (r=0.77), B non‐specifically adsorbed on soil colloid surfaces (r=0.65), B specifically adsorbed on soil surface (r=0.76) and B occluded in Mn oxyhydroxides (r=0.77). No relation was found between plant B contents and amounts of B occluded in non‐crystalline and crystalline Al and Fe oxides, B fixed with soil silicates and total B. The results indicated that extraction of B by 0.1 M NH₂OH HCl solution adequately represented amounts of B in soil solution, B non‐specifically and specifically adsorbed on soil compound surfaces and B occluded in Mn oxyhydroxides to assess availability of B to apple trees.     

Ammonia toxicity in aerobic rice: use of soil properties to predict ammonia volatilization following urea application and the adverse effects on germination

Recent studies indicate that aerobic rice can suffer injury from ammonia toxicity when urea is applied at seeding. Urea application rate and soil properties influence the accumulation of ammonia in the vicinity of recently sown seeds and hence influence the risk of ammonia toxicity. The objectives of this study were to (i) evaluate the effects of urea rate on ammonia volatilization and subsequent seed germination for a range of soils, (ii) establish a critical level for ammonia toxicity in germinating rice seeds and (iii) assess how variation in soil properties influences ammonia accumulation. Volatilized ammonia and seed germination were measured in two micro‐diffusion incubations using 15 soils to which urea was applied at five rates (0, 0.25, 0.5, 0.75 and 1.0 g N kg^?1 soil). Progressively larger urea rates increased volatilization, decreased germination and indicated a critical level for ammonia toxicity of approximately 7 mg N kg^?1. Stepwise regression of the first three principal components indicated that the initial pH and soil texture components influenced ammonia volatilization when no N was added. At the intermediate N rate all three components (initial pH, soil texture and pH buffering) affected ammonia volatilization. At the largest N rate, ammonia volatilization was driven by soil texture and pH buffering while the role of initial pH was insignificant. For soils with an initial pH > 6.0 the risk of excessive volatilization increased dramatically when clay content was <150 mg kg^?1, cation exchange capacity (CEC) was <10 cmol_c kg^?1 and the buffer capacity (BC) was <2.5 cmol_c kg^?1 pH^?1. These findings suggest that initial pH, CEC, soil texture and BC should all be used to assess the site‐specific risks of urea‐induced ammonia toxicity in aerobic rice.     

Influence of applied zinc and organic matter on zinc desorption kinetics in calcareous soils

Zinc (Zn) desorption from an exchange complex to solution, the release of Zn from organic matter (OM), crystalline minerals and other precipitates into the solution phase, is the process that controls Zn mobility in soils. An experiment was conducted to determine the pattern of Zn desorption and the soil characteristics affecting it. Desorption of Zn in 15 calcareous soils from southern Iran, treated with 10 mg Zn kg soil^?1 as zinc sulfate (ZnSO₄?7H₂O) and 10 g organic matter (OM) kg^?1 as feedlot cattle manure, equilibrated and extracted with diethylenetriamine pentaacetic acid (DTPA), was studied. Eight kinetic models were evaluated to describe the rate of Zn desorption of soil extracted with DTPA. There was a rapid rate of desorption during the first 4 h followed by a slower rate during the next 12 h. Two-constant rate and simple Elovich models were determined as the best models describing Zn desorption kinetics. Zinc desorption increased as Zn was applied, whereas it decreased with applied OM. The constants of the simple Elovich (β_s) and two-constant rate equations (a and b) were closely correlated with cation-exchange capacity (CEC), OM and pH, which affect Zn solubility, sorption–desorption and diffusion in soils.     

Response of phosphorus fractions to land-use change followed by long-term fertilization in a sub-alpine humid soil of Qinghai–Tibet plateau

Purpose

Identification of phosphorus (P) species is essential to understand the transformation and availability of P in soil. However, P species as affected by land use change along with fertilization has received little attention in a sub-alpine humid soil of Tibet plateau.

Materials and methods

In this study, we investigated the changes in P species using Hedley sequential fractionation and liquid-state ³¹P-NMR spectroscopy in soils under meadow (M) and under cropland with (CF) or without (CNF) long-term fertilization for 26 years in a sub-alpine cold-humid region in Qinghai–Tibet plateau.

Results and discussion

Land-use change and long-term fertilization affected the status and fractions of P. A strong mineralization of organic P (OP) was induced by losing protection of soil organic matter (SOM) and Fe and Al oxides during land-use change and resulted in an increase of orthophosphate (from 56.49 mg kg^?1 in M soils to 130.07 mg kg^?1 in CNF soils) and great decreases of orthophosphate diesters (diester-P, from 23.35 mg kg^?1 in M soils to 10.68 mg kg^?1 in CNF soils) and monoesters (from 336.04 mg kg^?1 in M soils to 73.26 mg kg^?1 in CNF soils). Long-term fertilization boosted P supply but failed to reclaim soil diester-P (from 10.68 mg kg^?1 in CNF soils to 7.79 mg kg^?1 in CF soils). This may be due to the fragile protection from the combination of SOM with diester-P when long-term fertilization had only improved SOM in a slight extent.

Conclusions

These results suggest that SOM plays an important role in the soil P cycling and prevents OP mineralization and losses from soil. It is recommended that optimization of soil nutrient management integrated with SOM was required to improve the P use efficiency for the development of sustainable agriculture.

     

Effects of iron,calcium, and organic matter on phosphorus behavior in fluvo-aquic soil: farmland investigation and aging experiments

Purpose

Excessive fertilization has led to a high risk of phosphorus (P) leaching and related problems in the North China Plain, where the most typical cropland soil is fluvo-aquic soil. The main factors controlling environmental P behavior and the acting time sequence of these factors in soil after long-term P fertilizer application have not been well recognized. A clear understanding is essential for effective P management.

Materials and methods

Effects of Fe minerals, calcium carbonate, and organic matter (OM) on P immobilization in fluvo-aquic soil were studied systematically through farmland investigation and aging experiments.

Results and discussion

Phosphorus associated with Ca was the primary fraction in fluvo-aquic soil. Even though there was no significant correlation between the total contents of P and Ca in soils, formation of P-Ca phases facilitated by Ca²⁺ in soil solution was a mechanism of P retention when soil received excess P fertilizer. Positive correlations between the contents of P and Fe and total organic carbon (TOC) indicate that Fe minerals and OM have significant effects on P immobilization. Through the aging experiments, P was found to primarily adsorb on goethite and gradually forms Ca-P compounds. Organic fertilizer caused P release and inhibition of P adsorption in the initial stages; however, OM derived from organic fertilizer might facilitate P immobilization in the long term through the formation of a P-Ca-OM complex.

Conclusions

Although superfluous application of P fertilizers leads to the gradual formation of Ca-P in fluvo-aquic soils, there is still a risk of P loss because P is not immediately adsorbed by Fe minerals. Moreover, application of organic fertilizers increases the risk of P loss. These results provide an important scientific basis for initiating P management policies for fluvo-aquic soils.

     

Effect of iron oxide on phosphate sorption by calcite and calcareous soils

Pure calcite (AR grade CaCO₃) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (x_m) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg^?1 as the amount of coating increased from 0.00 to 16.0 g Fe₂O₃, kg^?1 CaCO₃. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.     

Soil‐Test Methods for Florida Sands Treated with an Aluminum–Water Treatment Residual and Various Phosphorus Sources

Use of aluminum (Al)–rich water treatment residuals (Al‐WTR) has been suggested as a practice to immobilize excessive phosphorus (P) in Florida soils that could represent an environmental hazard. Fertilizer P requirements can differ in WTR‐amended and unamended soil, so careful selection of soil‐testing methodology is necessary. Acidic extractants can dissolve WTR sorbed P and overestimate plant‐available P. We evaluated the suitability of the Mehlich 1 P (M‐1P) and other agronomic soil‐test procedures in an Al‐WTR‐treated Florida soil. Bahiagrass (paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were grown in succession in a Florida topsoil amended with four sources of P at 44 kg P ha^?1 (P‐based rates) and 179 kg PAN ha^?1 [nitrogen (N)–based rates] and three WTR rates (0, 10, and 25 g kg^?1 oven‐dry basis). Both water‐extractable P (WEP) and iron (Fe) strip P (ISP), but not M‐1P, values of soil sampled at planting of each grass were greater in the absence than in the presence of WTR. Total plant P uptake correlated with WEP (r² = 0.82^***) and ISP (r² = 0.75^***), but not M‐1P (r² = 0.34^***). Correlations of the dry‐matter yield, P concentration, and P uptake of the first bahiagrass were also better with WEP and ISP than with M‐1P values. However, regression of plant responses with M‐1P improved after the first crop of bahiagrass. Both WEP and ISP values were better predictors of available soil P than M‐1P in a field study with same four P sources surface applied to established bahiagrass at the same two P rates, with and without WTR. Both WEP and ISP are recommended as predictors of P adequacy in soils treated with WTR, especially for soils recently (< 5 months) treated with Al‐WTR.