Validation of Soil Phosphate Removal by Alkaline and Acidic Reagents in a Vertosol Soil using XANES Spectroscopy

There is a paucity of information on the soil phosphorus (P) forms removed by alkaline and acidic reagents in Vertosols. The first aim of this study was to identify which soil phosphates are removed by a two-step sequential fractionation (0.1 M NaOH and 1 M HCl) and by a dilute acid extractant (0.005 M H₂SO₄; Bureau of Sugar Experiment Stations (BSES) soil P test) on an “untreated” Vertosol using P K-edge x-ray absorption near-edge structure (XANES) at the Australian Synchrotron. There was supporting evidence that the 0.1 M sodium hydroxide (NaOH), 1 M hydrochloric acid (HCl), and 0.005M sulfuric acid (H₂SO₄) extractants remove soil phosphates according to the chemical solubility of known P minerals. The XANES spectra revealed the 1 M HCl and 0.005 M H₂SO₄ extractants remove calcium (Ca) phosphates from Vertosols, suggesting the latter extractant could be used as an alternative for a rapid and cost-effective measure of Ca phosphates in Vertosols.     

Comparison of extractable phosphorus from two sulfuric acid methods with the Mehlich phosphorus test number one

Abstract

All mineral phosphates in soil dissolve more completely when HCl is mixed with H₂SO₄ than with the HCl alone. It was hypothesized that a new extracting solution of H₂SO₄ alone with the same ionic strength or the same acidity as the Mehlich P1 extractant would extract similar amounts of soil phosphorus (P) as the Mehlich P1 soil test. Thirty six acid soils from Alabama, Georgia, North Carolina, South Carolina, and Colorado were used in this study. These acid soils reflect wide ranges in parent materials, texture, pH, organic matter, and available soil P. They were analyzed for available soil P with the Mehlich P1 soil test and with the two H₂SO₄ methods: Method A has an extracting solution of same ionic strength (0.0875M) as the Mehlich P1 extractant, and Method B was an extracting solution of the same acidity (0.0375M) as the Mehlich P1 extractant. Correlations between the results of Mehlich P1 with Method A and Method B were 0.994 and 0.997, respectively. The measured test precision was <3.5% for all three methods. The new H₂SO₄ methods are simple and faster to conduct under routine operations than the original Mehlich P1 extractant, and because of the high correlations, the H₂SO₄ methods should predict crop response to P as well as the original Mehlich P1 extractant for acid soils.     

Influence of the Soil Solution Composition on Retention and Release of Sulfate in Acid Forest Soils

The potential for sulfate retention is an important soil feature for buffering of atmospheric acid deposition. We studied the effects of increasing additions of different neutral salts and acids on mobilization and retention of SO₄ ²- in acid forest soils. Soils containing up to 11 mmol SO₄ ²- kg^-1 were equilibrated with H₂O, NaCl, MgCl₂, and HCl. Release of SO₄ ²- was highest with H₂O and NaCl additions and lowest when HCl was used. Increasing the ionic strength of the added solutions caused decreasing SO₄ ²- concentrations in equilibrium solution. Decreasing pH in equilibrium solution was found to be the reason for the decrease in release. Even when the pH was < 4, the SO₄ ²- release decreased. We assume that this finding resulted from the fact that in the soils studied the SO₄ ²- sorption was controlled by the high contents of Fe oxides/hydroxides. Experiments with Na₂SO₄, MgSO₄, and H₂SO₄ demonstrated that the B horizons already containing high amounts of SO₄ ²- were still able to retain SO₄ ²-. Sulfate retention increased in the order Na₂SO₄ < MgSO₄ < H₂SO₄, which corresponds to increasing H⁺ availability. The higher SO₄ ²- retention along with MgSO₄ compared to Na₂SO₄ may be caused by higher potential of Mg to mobilize soil acidity compared to Na.     

Relationship of Soil Phosphorus Pools with Bray 1 Phosphorus in Some Acid Soils of Central Southern Cameroon

We measured phosphorus (P) chemical pools of genetic horizons of five representative pedons from central southern Cameroon. Our objectives were to assess the relative abundance of P pools and to empirically model their interrelations and contributions to a P availability index. The fractionation scheme followed a modified Hedley sequential procedure with anion exchange resin, 0.5 M sodium bicarbonate (NaHCO₃; Pi and Po), 0.1 M sodium hydroxide (NaOH; Pi and Po), 0.5 M hydrochloric acid (HCl; Pi), and 2 M sulfuric acid (H₂SO₄) after soil ignition at 550 ^oC. Resin P, sodium bicarbonate (NaHCO₃-P; Pi and Po), and HCl-Pi–extractable pools accounted for 1.0, 5.7 and 0.7 % of total P (TP) respectively. The NaOH-P and residual P pools measured through 2 M H₂SO₄ emerged as the largest and most variable pools, accounting for 86.2% of TP. The relative abundance of extracted P pools decreased in the order resin P < NaHCO₃-P ≤ HCl-P < NaOH-P < H₂SO₄-P. Bray 1 P was significantly correlated with all P pools except NaHCO₃-Pi, NaOH-Pi, and residual pools.     

Extraction of phosphorus,potassium, calcium,and magnesium from soils by an ion‐exchange resin procedure

Abstract

A procedure for the simultaneous extraction of phosphorus, potassium, calcium and magnesium from soils, by an ion‐exchange resin procedure applicable to large‐scale advisory soil testing, is described. The important steps are the disaggregation of soil by shaking in water during 15 minutes with a glass marble, the transference of the elements from the soil to a sodium bicarbonate treated mixture of anion and cation exchange resins during a 16‐hour shaking period, the separation of the resin from the soil by sieving and extraction of the elements from the resin.

The results of resin extractable calcium, magnesium and potassium were comparable to the results of these elements extracted with 1M NH₄OAc, to calcium and magnesium extracted with 1M KCl, and to potassium extracted with 0.025M H₂SO₄.

For phosphorus the resin extractable values were not comparable to the results obtained by the former routine method, based on the extraction with 0.025M H₂SO₄. The results of resin extractable P presented closer correlation with cotton response to phosphorus application in 28 field experiments (r = 0.85**) as compared with 0.025M H₂SO₄ extractable P (r = 0.68**), and also with P uptake by flooded rice in a pot experiment with eight lowland soil samples (r = 0.98**), as compared with extraction with 0.0125M H₂SO₄ in 0.050M HCl, for which the correlation was not significant. The reasons for the superiority of the extraction of P with the described procedure are discussed.     

Estimation of critical limit for zinc in rice soils

Abstract

Twenty surface soil samples were collected from Nainital Tarai (foothills of Himalya) where “Khaira”; disease (Zn deficiency of rice) is prevalent. Rice (Oryza sativa L. variety IR‐8) was grown in pots for 8 weeks after transplanting. Experiments were conducted to determine the suitability of five soil Zn extractants: dilute acid (HCl + H₂SO₄) mixture; DTPA‐(NH₄) ₂CO₃, pH 7.3; dithizone; NH₄OAc, pH 4.6; and 2N MgCl₂ to predict Zn deficiency. Critical values for soil available Zn were established for rice by the old and new Cate and Nelson procedures¹.

Zinc extracted from the soils with dithizone; NH₄OAc, pH 4.6; 0.2N MgCl₂. and DTPA‐(NH₄) ₂CO₃ pH 7.3 was significantly correlated with the uptake of Zn by the rice plants. The correlation between Zn extracted with the dilute acid (HCl + H₂SO₄) mixture and plant Zn was not statistically significant. The ex‐tractants which extracted greater quantities of Zn gave higher critical values and vice versa. It is concluded that all extracting solutions except the dilute acid (HCl + H₂SO₄) mixture were found to he suitable for predicting available Zn in rice soils of Tarai.     

Salts and acids as determinants of the solution composition of acidic forest soils — anion effects

The study aimed at evaluating whether salt-induced mobilization of acidity may be modified by the type of anion. For this purpose, the effects of different neutral salts on the solution composition of acid soils were investigated. The results were compared with those of the addition of acids. Two topsoil (E and A) and two subsoil horizons (Bs and Bw) were treated with NaCl, Na₂SO₄, MgCl₂, MgSO₄, HCl, and H₂SO₄ at concentrations ranging from 0 to 10 mmol dm^?3. With increasing inputs of Cl^? the pH of the equilibrium soil solution dropped, the concentrations of Al and Ca increased, and the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios decreased. These effects were the least pronounced when NaCl was added and the most at the HCl treatments. According to the release of acidity, the topsoils were more sensitive for salt-induced soil solution acidification whereas on base of the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios, the salt effect seems to be more important for the subsoils. Addition of S0₄^2? salts and H₂SO₄ induced higher pH and lower Al concentrations than the corresponding Cl^? treatments due to the SO₄^2? sorption, especially in the subsoils. The Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios were higher than those of the corresponding Cl^? treatments. In subsoils even after H₂SO₄ additions these ratios were not higher than those of the NaCl treatments. The results indicate (I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider the ionic strength and the cation type but also the anion type, (II) that salt-induced soil solution composition may be more crucial in subsoils than in topsoils, and (III) that in acid soils ongoing input of HNO₃ due to the precipitation load may induce an even more acidic soil solution than the inputs of H₂SO₄ of the last decade.     

SO42-和Cl-对稻田土壤养分及其吸附解吸特性的影响

利用长期定位试验 ,比较了长期施用含SO₄^2-和Cl^- 化肥 22年后稻田土壤的 pH值、养分状况及其吸附解吸特性。结果表明 ,长期施用含SO₄^2-化肥 ,土壤有机质、速效氮和速效钾的含量较高 ,但全量氮磷钾的含量较低 ;长期施用含Cl^- 化肥 ,土壤全量氮磷钾和速效磷的含量较高 ,但pH值相对较低。长期施用含上述二种阴离子的化肥后 ,土壤对H₂PO₄^-的最大吸附量均较大 ,且在Cl^- 处理下土壤对H₂PO₄^-吸附的结合能较大 ,而SO₄^2-处理下土壤在同等吸附量时对H₂PO₄^-的解吸量相应较多。长期施用含SO₄^2-的化肥亦使土壤对钾素的供应强度较大 (ΔK0的绝对值较大 )、缓冲能力增强 (AR0值较高 ) ,而长期施用含Cl^- 的化肥时则与SO₄^2-相反     

Comparison of Analytical Methods for Quantifying the Levels of Lead,Cadmium, Chromium,and Nickel in Mineral Fertilizers and Industrial By-products

The control of contaminants in fertilizers and industrial by-products is fundamental to safe food production, and it requires low-cost, reliable test methods. The aim of this study was to evaluate the performance of the USEPA 3051a and alternative analytical methods [concentrated hydrochloric acid (HCl), 10 percent HCl, 10 percent sulfuric acid (H₂SO₄), and 50 mmol L^?1 diethylenetriaminepentaacetic acid (DTPA)] for quantifying the levels of lead, cadmium, chromium, and nickel in zinc and/or copper sources. The sample digestions with concentrated HCl, H₂SO₄, and nitric acid (HNO₃) (USEPA 3051a) were heated. Extraction without heating and stirring was employed in 10 percent HCl and 50 mmol L^?1 DTPA methods. The Graybill’s modified F-test, t-test for mean error, and the linear correlation coefficient analysis were used to compare test method performance. Equivalent results to USEPA 3051a were found with the following methods: DTPA for the extraction of lead in zinc sources and concentrated HCl and H₂SO₄ for the extraction of cadmium and chromium in copper sources. However, the absolute values of cadmium, chromium, and nickel recovered by the use of H₂SO₄ were greater regardless of the source. The greater extraction of contaminants in the evaluated methods suggests that there is need to review the official method if the aim is to quantify the total levels of these elements in raw materials and mineral fertilizers.     

Evaluation of an anion‐exchange membrane for extracting plant available phosphorus in soils

Abstract

Anion‐exchange resins (AER) have been used to determine plant available phosphorus (P) since the fifties and their results have shown strong relationships with plant growth and P uptake irrespective of soil properties. However, this procedure is still not widely used by laboratories because of difficulties in handling resin beads under routine conditions. New kinds and different shapes of resins are being produced each with specific characteristics that must be evaluated before use in laboratory procedures. Thus the objective of this work was to evaluate an AER manufactured in membranes reinforced with a Modacrylic fabric. These anion‐exchange membrane (AEM) sheets are commercially available, making them suitable for soil testing. The membranes were cut in pieces (1.0×7.5 cm) identified as AEM‐strips. The AEM‐strips were soaked in 0.5M HCl for a few days and transferred, after being rinsed with deionized water (DI), to 0.5M NaHCO₃ to convert them to HCO₃ ^‐ form. The AEM‐strips and resin beads in nylon bags recovered 98.4 and 98.0% of the P content in an aqueous P solution, respectively. Three eluent solutions were evaluated with different shaking times. The 0.1M H₂SO₄ and 1.0M NaCl in 0.1M HCl were equally suitable for the molybdenum blue color development without any pH adjustment, while the pH of the 0.5M HCl was too low. The elution of P from the AEM‐strips was independent of time with a 15‐min shaking being adequate for removal of all P from the strips. A comparison of soil sample preparation demonstrated that it was not necessary to vigorously grind or sieve the soil to improve the repeatability of the results. The AEM‐strips were compared with other methods (Pi impregnated filter paper, Mehlich I and Bray 1) using 32 soils from Guatemala with widely varying physico‐chemical and mineralogical properties. Phosphorus extracted by the AEM and Pi procedures (similar principle) were highly correlated and gave similar results irrespective of soil type. The acid extraction (Mehlich I and Bray 1 methods) attacked soil components (apatites) resulting in higher and inconsistent amounts of P extracted which may not be available to plants; the correlation between these methods within soils of similar properties was good, but when all soils were considered together the relationship was not significant. This demonstrated that the acid extraction method for P is not suitable for soils containing apatites, while those based on a sink for P (AEM and Pi) can be applied irrespective of the type of soil.     

酸和氧化还原剂对二氧化锰溶解度的影响

由于土壤中锰的有效性随pH和Eh的变化而变化,利用土壤测试方法得到的锰素营养丰缺指标,通常难以代表田间锰素营养的实际状况.然而,在应用土壤pH和氧化锰溶解度的关系时,某些文献的不确切解释,引起一些误解.本实验研究了在浓HCl、HNO3和H2SO4及其稀溶液的不同浓度情况下对二氧化锰-水钠锰矿(MnO2)的溶解能力和机理,以及三种卤素还原剂(KCl、KBr和KI)在两种pH值条件下对MnO2的还原能力,从实验上和理论上进一步阐明了pH和Eh对MnO2溶解度的影响.实验结果表明,在浓HCl中,MnO2能被Cl-迅速还原而溶解.而在浓HNO3和H2SO4溶液中,MnO2不能被酸所直接溶解,只能被酸中的H2O缓慢还原,放置两年后反应仍未到达终点.在稀酸溶液中,当H+强度小于0.5 mol L-1(pH＞1.0)时,三种强酸对MnO2都无明显的溶解能力;当H+强度＞1.0 mol L-1时,HCl对MnO2的溶解能力显著地高于HNO3和H2SO4.三种卤盐溶液对MnO2的还原能力为KI＞KBr＞KCl,并随pH的降低和浓度的升高而增强.当pH＞3时,KCl对MnO2的还原能力极弱;而无论pH高低(pH3或pH5),KI在很低浓度(0.001 mol L-1)时都能有效地还原MnO2.上述结果说明,如果二氧化锰不被还原,仅改变pH则很难被溶解.然而,在较高pH条件下,如有强还原剂存在,也有相当量的MnO2被还原.低Eh和pH条件下最有利于MnO2的还原.     

Relationships among soil p test values for soils of differing pedogenesis

Abstract

Surface samples of 78 soils from the continental U.S. and Puerto Rico were obtained from the U.S. Soil Conservation Service National Soil Survey Laboratory. Phosphorus was extracted by the Bray PI (0.03N NH₄F in 0.025N HCl), Mehlich No. 1 (0.05N HCl in 0.025N H₂SO₄), and Olsen bicarbonate (0.5N NaHCO₃) tests. Soil chemical, physical, and taxonomic data were obtained from the National Soil Survey Laboratory. On the basis of soil taxonomy and weathering, soils were divided into calcareous, slightly weathered, and highly weathered groups. Linear regression analysis was used to compare obtained soil P test values. Coefficients of determination (r²) ranged from 0.30 to 0.89. The lower coefficients were obtained between Mehlich No.l and Olsen bicarbonate tests, as these extractants were developed for differing soil types. Using independent data sets, the regression equations provided accurate estimates of soil test P by one method from another.     

不同农业土壤中有效磷的变化与磷平衡的关系

Maintaining soil phosphorus(P) at adequate levels for plant growth requires assessing how the long-term P balance(viz., the difference between P inputs and outputs) results in changes in soil test P. The hypothesis that routinely measured soil properties can help predict the conversion factor of P balance into Olsen P was tested at 39 sites in agricultural areas of the Mediterranean region in Spain. A set of soil samples from each site was analyzed for Olsen P, inorganic P(P extracted using 0.5 mol L~(-1) H_2SO_4), pseudototal P(P extracted using 0.5 mol L~(-1) H_2SO_4 following ignition at 550℃), and organic P(the difference between pseudototal P and inorganic P). Organic and Olsen P were uncorrelated in most of the 39 soil sets, which suggests that organic P content changed little with P inputs and outputs. The slopes of the regression lines of Olsen P against pseudototal and inorganic P, which were used as two different measures of the conversion factor, ranged widely(from 0.03 to 0.25 approximately), with their average values(about 0.10) being similar to those found in long-term experiments conducted in temperate areas. Neither conversion factor was significantly correlated with any routinely measured soil property; however, the conversion factor for inorganic P was significantly lower for calcareous soils than for noncalcareous soils. Our negative results suggest the need to isolate the influence of soil properties from that of management systems and environmental factors relating to P dynamics in future studies.     

Anionic constituents of acid rain and microbial activity in soil

Soil amended with 1% glucose was treated with H₂SO₄, fuming H₂SO₄, HCl, H₃PO₄, HNO₃, fuming HNO₃ or with combinations of fuming and non-fuming H₂SO₄ and HNO₃ to lower the bulk soil pH to values ranging from 5.0 to 2.0. There was a difference in the amount of toxicity caused by the different acids at the same bulk pH of soils. Acidification to pH 2.8 or 2.9 prolonged the lag phase of glucose degradation; fuming HNO₃ had the greatest effect, and fuming H₂SO₄ was only slightly more toxic than non-fuming H₂SO₄. At pH 2.3–2.4, fuming HNO₃, alone or in combination with H₂SO₄, inhibited CO₂ evolution. Both fuming and non-fuming HNO₃ also reduced the amount of C mineralized to a greater extent than did fuming and non-fuming H₂SO₄. The amounts of C mineralized from soils treated with combinations of H₂SO₄ and HNO₃ were intermediate between those from soils treated with each of these acids alone. HCl and H₃PO₄ had a similar effect on prolonging the lag as did non-fuming H₂SO₄. H₃PO₄ was less toxic than the other acids and sometimes increased the total amount of C mineralized. The “anionic effect” of acid rain must, therefore, be considered in addition to the effect of the proton. When the soil was inoculated with a suspension of microbiologically-active soil, more C was mineralized, in general, and the inhibitory effects of acidification on C mineralization were less pronounced than in soil that had not been inoculated. The addition of montmorillonite, but not of kaolinite, enhanced the growth of Aspergillus niger in soils amended with 2:1 combinations of H₂SO₄ and fuming HNO₃ however, growth was inhibited completely at pH 3.4.     

THE ORIGIN OF SOIL POLYSACCHARIDE: TRANSFORMATION OF SUGARS DURING THE DECOMPOSITION IN SOIL OF PLANT MATERIAL LABELLED WITH 14C

Incubation of soil with ¹⁴C-rye straw for 448 days resulted in the evolution of about 50 per cent of the carbon of the substrate as CO₂ The two main sugars of the straw, glucose and xylose, were degraded to approximately the same extent (70 per cent). The same results were obtained whether the soil was derived from granitic or basic igneous parent material. There was very little transformation of the substrate to galactose, mannose, arabinose, rhamnose, or fucose, and a much slower rate of degradation than with soil incubated with ¹⁴C-glucose over a similar period. Hydrolysis of the soil samples by a preliminary treatment with 5 N H₂SO₄, before treatment with 24 N H₂SO₄, followed by heating with N H₂SO₄ did not release significantly greater amounts of sugar than treatment with 24 N H₂SO₄ and N H₂SO₄ alone. Separate analysis of the hydrolysates showed that 90 per cent of each of galactose, mannose, arabinose, xylose, rhamnose, or fucose had been extracted by 5 N H₂SO₄, but only 50 per cent of the glucose. Fractionation of the straw-soil mixture after 224 days incubation showed that the specific activity of the glucose was higher in the humin fraction than in the fulvic acid, as would be expected if the remaining ¹⁴C were still in the form of unchanged plant material. This evidence that plant polysaccharide persists in soil could explain the presence of much of the xylose in the soil organic matter.     

Aluminium and sulphate in acidic soils and groundwaters on the Swedish west coast

Acidic groundwaters and soils in Halland County (Hailands län), southwest Sweden, have been investigated with respect to conditions of soluble aluminium (Al) and sulphate (SO₄ ^2?. Basic Al-sulphate, Fe-oxide, Al-oxide, Al-hydroxide and clay minerals, are discussed and evaluated in their roles for governing Al and SO₄ ^2? in the groundwaters. Based on this investigation, it is suggested that Al³⁺ solubility is controlled by amorphous Al-hydroxide. The SO₄ ^2? in the groundwaters will depend primarily on the H₂SO₄ input. The H₂SO₄ load enhances soil mineral weathering which enhances the production of Fe-oxides, i.e. anion exchange surface sites, to which groundwater SO₄ ^2? attain adsorption equilibra. The factors that control solubility of Al and SO₄ ^2? are both influenced by the acidity in the soil catenas which in the area largely depend on the H₂SO₄ input. Clay minerals such as illite, smectites, halloysite, and variable composition Al-silicates do not exert strong control on Al in the groundwaters investigated.     

Extraction of soil‐available phosphate,nitrate, and sulphate ions using ion exchange membranes and determination by ion exchange chromatography

Abstract

In recent years, ion exchange membranes (IEM) have been used successfully to determine the availability of soil nutrient elements for plants. In general, the procedures proposed are applied to the determination of a single ion, and in only a few of these studies, the selectivity of these IEM was considered. Therefore, this work was conducted (a) to find the most suitable extraction conditions for phosphate (H₂PO₄ ^‐), nitrate (NO₃ ^‐), and sulfate (SO₄ ^2‐) in soils by IEM and their subsequent determination by ion chromatography, (b) to test the effectiveness and selectivity of IEM, (c) to compare the results obtained by IEM with the common procedure for determining the availability of the soil nutrient elements, and (d) to verify whether a relation exits between the concentration of phosphorus (P) extracted by IEM and the plant P requirement. The soil samples used for this study were Humic Cambisols located in four forest plots under natural conditions and four plots fertilized with 100 kg P ha^‐1 as triple superphosphate. The efficacy of the IEM was high (85% for SO₄ ^2‐, and 92% for H₂PO₄ ^‐ and NO₃ ^‐). Statistically significant correlations were obtained between the H₂PO₄ ^‐ extracted by IEM and the H₂PO₄ ^‐ obtained by the Bray P1 procedure (r²=0.936) and with the H₂PO₄ ^‐ extracted using Saunders and Williams (1955) procedure (r²=0.370). The correlation obtained between the amount of NO₃ ^‐ extracted with IEM and that obtained using 2M potassium chloride (KCl) was also highly significant (r²=0.828). The IEM extraction allowed to know in a single extraction process and a single subsequent measurement by ion chromatography the concentrations of soil available H₂PO₄ ^‐, NO₃ ^‐, and SO₄ ^2‐ ions, which are of great plant nutrition interest. Phosphorus extractable with IEM yielded a close relationship with biomass production and could be used for determining the P requirement of these forest trees.     

A rapid method of evaluating the zinc status of coastal plain soils

Abstract

A study was made to evaluate Zn removed by extraction with a 0.075 N acid mixture (0.05 N HCl + 0.025 N H₂SO₄). A ratio of soil to extracting solution of 1 to 4 and an extracting time of 15 minutes was selected. Data obtained by the method was significantly correlated with dithizone (0.01%) extraction. The method was found to be acceptable for evaluation of the Zn status of Southern Coastal Plain soils and easily adapted to routine use in soil testing. A significant correlation was obtained between extractable soil Zn and leaf blade content of Zn for Zn‐deficient and non‐deficient corn plants.     

Using Organic Matter with Chemical Amendments to Improve Calcareous Sodic Soil

Abstract

Kangping soil in northeast China is a sodic soil characterized by a high pH and excessive sodium. The high pH and excessive sodium in sodic soils generally cause loss of soil structure, reduce hydraulic conductivity (HC), increase soil hardness, and make the soil unproductive land. After we mixed organic matter (rice straw) and chemical amendments (H₂SO₄, CaSO₄, and FeSO₄), a column experiment was conducted to evaluate the physical and chemical properties of the soil influenced by the changes in HC, penetrability of soil s`urface, pH, electrical conductivity, CO₃ ^2‐, HCO₃ ^?, Ca²⁺, Na⁺, sodium adsorption rate (SAR), available phosphorus (P) and iron (Fe), and leached P.

Organic matter decreased the concentrations of CO₃ ^2‐, HCO₃ ^?, and Na⁺ in soil solution and increased the total volume of the leachate. Organic matter also reduced the amount of available Fe and increased the available P. However, organic matter did not affect the penetrability of the soil surface as much as soil hardness, HC, and SAR within the short period of this experiment. Among the chemical amendments, H₂SO₄ and FeSO₄ were more effective than CaSO₄ to restore HC, electrical conductivity, Na⁺, and SAR. The chemical amendments, compared with organic matter, significantly leached P from the soil in this study, but the leaching was independent of the concentration of available P in the soil. The CaSO₄ had the strongest effect in increasing leached P from the soil without changing the concentration of available P in the soil. Organic matter with added CaSO₄ leached P from the soil more than all other treatments.