Effect of Citrate Concentration on the Extraction Efficiency of Selected Micronutrients from Soil

This study was carried out with the objective of evaluating the effect of citrate concentration on the extraction efficiency of some micronutrients from soil. Composite surface soil samples (0–20 cm) were collected from Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa and Humbo Districts) and Dire Dawa Administrative Council in purposive sampling. The treatments were arranged in completely randomized design (CRD) with three replications. A greenhouse pot experiment with soybean plant was conducted to determine the correlation between soil test methods and the selected micronutrients, such as iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in the leaves of the plant. The results showed that, among the different citrate concentrations with strontium chloride (SrCl₂) tested for the determination of available Fe, Mn and Zn, the highest correlation coefficients (r = 0.82, p < 0.05), (r = 0.96, p < 0.001) and (r = 0.98, p < 0.001) were found between the diethylenetriamine pentaacetic acid (DTPA) method and 0.02 M strontium chloride (SrCl₂)-0.025 M citric acid extractant, respectively. Therefore, 0.02 M SrCl₂-0.025 M citric acid extractant is considered to be the most effective for the determination of Fe, Mn and Zn in soils of the studied areas. Similarly, high correlation coefficients (r = 0.97, p < 0.001) were found between DTPA and 0.02 M SrCl₂-0.05 M citric acid and (r = 0.88, p < 0.01) between DTPA and 0.02 M SrCl₂-0.025 M citric acid extractants for the determination of available Cu from soils. Hence, the 0.02 M SrCl₂-0.05 M citric acid extractant was shown to be the best for the determination of Cu in soils of the studied areas. However, considering the use of universal extractant, the 0.02 M SrCl₂-0.025 M citric acid extractant could easily be adopted as a procedure for the determination of Fe, Cu, Mn and Zn for both agricultural and environmental purposes. The greenhouse experiment confirmed the result.     

Transformation of Phosphorus in Forest and Savannah Agro-Ecological Alfisols incubated with Different Phosphorus Fertilizers,in Ekiti state,Southwestern Nigeria

Experiments on incubation with phosphorus (P) changes in two Nigerian Alfisols, were evaluated on the effectiveness of P sources (ground phosphate rock, GRP-9% P, Pace-setter Organo-Mineral Fertilizer (PR-fortified P-S-OM, 11% P and single superphosphate, SSP-7.7% P, for reference). All samples were adjusted to water tension measured at M Ψ w = 0.03 MPa. Changes in applied P were evaluated at 2, 6, 12 and 24 weeks after which data were analyzed using analysis of variance and correlations. Over 24 weeks of incubation, SSP transformed mostly into iron (Fe)-bound P and GPR produced the highest inorganic phosphate ions and transformed largely into the soluble and more chemically stable residual P, in both soils. This fraction, had high and positive correlations (r = 0.69, p < 0.05) with soil properties and constituted a major source and sinks of plant available P. Thus, GPR contributing beneficial effects of residual phosphates.     

Catalase and Phosphatase Activities During Hydrocarbon Removal from Oil-Contaminated Soil Amended with Agro-Industrial By-products and Macronutrients

Microbiological activities are essential in the bioremediation of polluted soils. The enzymatic activities of microorganisms are usually used as a biological indicator of soil health. The aim of this work was to observe the catalase, acid phosphatase (AcP), and alkaline phosphatase (AlP) activities in soil that was amended with agro-industrial by-products and macronutrients during the process of total petroleum hydrocarbon (TPH) removal. To this end, microcosm tests were performed with soil and agro-industrial by-products ratios of 100:2:2, for soil:sugarcane bagasse pith:filter cake mud (SSF); 100:2, for both soil:sugarcane bagasse pith (SS); and for soil filter cake mud (SF). The macronutrients—carbon, nitrogen, and phosphorus—in the experimental treatments were adjusted to 100:10:1 with a solution of NH₄NO₃ and K₂HPO₄. The best TPH removal (51.4%) was obtained with SSF at 15 days. In addition, a significant correlation was observed between TPH removal and AlP as well as AcP (r = 0.74, p < 0.0001; r = 0.70, p < 0.0107, respectively). Fungi growth was also correlated with both AlP (r = 0.97, p < 0.0001) and AcP (r = 0.95, p < 0.0001) activities. Besides, bacterial and fungi growth showed a correlation with TPH (r = 0.86, p < 0.001; r = 0.77, p < 0.0034, respectively). It could be said that the agro-industrial by-products and macronutrients contributed to pollutant removal from the oil-polluted soil at relatively short amount of time. In addition, the enzymatic activities were increased after the treatment; in this study, the high sensitivity enzyme was AlP, and it could be used as an indirect indicator of oil pollutant removal.     

Comparative evaluation of Ca chloride and Ca phosphate for extractable sulfur in soils with a wide range in pH

Deficiency of sulfur (S) is becoming widespread in the rainfed systems of India, and there is increasing need for diagnosing the deficiency. Calcium chloride and Ca phosphate are commonly used for extracting available S in soils. Because of cost and the ease of availability locally, we prefer using Ca chloride as an extractant over Ca phosphate, for extracting available S. However, there is paucity of data on the comparative evaluation of the two extractants to extract available S, especially in soils having a wide range in natural pH (from acidic to alkaline range). It is recognized that soil pH plays a dominant role in the adsorption–desorption and extractability of sulfate‐S in soils. We compared the extraction of S by Ca chloride and Ca phosphate in 86 Indian soils having a wide range in pH (4.5 to 10.6). Sulfur in the extracts was determined by ICP‐AES. Considering all the 86 soil samples tested, there was an excellent agreement between the values of extractable S determined by using the two extractants (r = 0.96, p < 0.001). However, the correlation coefficient (r) between the values of extractable S by the two reagents, although highly significant, varied among the groups of soil samples according to the range in soil pH. The highest correlation coefficient (r = 0.99, p < 0.0001, n = 17) was found for soils with pH in the alkaline range (8.5–10.6), and the lowest correlation coefficient (r = 0.71, p < 0.0001, n = 58) was obtained with a set of soil samples with pH in the acidic range (4.5–6.5). For soil samples having pH in the near‐neutral range (6.7–7.3), an excellent agreement was observed (r = 0.93, p < 0.0001, n =11) between the extractable‐S values obtained by the two extractants. While Ca phosphate extracted higher amount of S compared to Ca chloride in soil samples with pH in the acidic range, the two extractants were equally effective for soil samples with pH in the neutral or alkaline range. Our results suggest that for most of the soils in the semiarid tropical regions, which have pH in the neutral to alkaline range, Ca chloride can replace Ca phosphate as an extractant for removing available S in such soils.     

Change Point in Phosphorus Release from Variously Managed Soils with Contrasting Properties

Abstract

Investigating the relation between concentration or release of phosphorus (P) into soil solution (CaCl₂‐P, determined by 0.01 M CaCl₂ extraction of soils) and soil test phosphorus (Olsen P, or 0.5 N NaHCO₃‐extractable soil phosphorus) for 10 widely ranging and variously managed soils from central Italy, a change point was evident where the slopes of two linear relationships meet. In other words, it was possible to distinguish two sections of the plots of CaCl₂‐P against Olsen P, for which increases of CaCl₂‐P per unit of soil test P increase were significantly (p<0.05) greater above than below these change points. Values of change point ranged from 14.8 to 253.1 mg kg^?1 Olsen P and were very closely correlated (p<0.001) to phosphorus sorption capacity of soils. Similar change points were also previously observed when Olsen P (and also Mehlich 3 P) of surface soils was related to the P concentration of surface runoff and subsurface drainage. Because insufficient data are available relating P in surface soils and amount of P loss by overland, subsurface, or drainage flow, using the CaCl₂ extraction of soil can be convenient to determine a change point in soil test P, which may be used in support of agricultural and environmental P management.     

Nitrous oxide and nitric oxide fluxes from cornfield,grassland, pasture and forest in a watershed in Southern Hokkaido,Japan

Abstract

To develop an advanced method for estimating nitrous oxide (N₂O) emission from an agricultural watershed, we used a closed-chamber technique to measure seasonal N₂O and nitric oxide (NO) fluxes in cornfields, grassland, pastures and forests at the Shizunai Experimental Livestock Farm (467 ha) in southern Hokkaido, Japan. From 2000 to 2004, N₂O and NO fluxes ranged from –137 to 8,920 µg N m^?2 h^?1 and from –12.1 to 185 µg N m^?2 h^?1, respectively. Most N₂O/NO ratios calculated on the basis of these N₂O and NO fluxes ranged between 1 and 100, and the log-normal N₂O/NO ratio was positively correlated with the log-normal N₂O fluxes (r ² = 0.346, P < 0.01). These high N₂O fluxes, therefore, resulted from increased denitrification activity. Annual N₂O emission rates ranged from –1.0 to 81 kg N ha^?1 year^?1 (average = 6.6 kg N ha^?1). As these emission values varied greatly and included extremely high values, we divided them into two groups: normal values (i.e. values lower than the overall average) and high values (i.e. values higher than average). The normal data were significantly positively correlated with N input (r ² = 0.61, P < 0.01) and the “higher” data from ungrazed fields were significantly positively correlated with N surplus (r ² = 0.96, P < 0.05). The calculated probability that a high N₂O flux would occur was weakly and positively correlated with precipitation from May to August. This probability can be used to represent annual variation in N₂O emission rates and to reduce the uncertainty in N₂O estimation.     

鄂东南崩岗区花岗岩风化岩土体抗剪强度的异向性

旨在从岩土力学性质的角度为崩岗侵蚀提供理论依据,采用直接剪切实验,对鄂东南崩岗区典型花岗岩风化岩土体剖面不同方向上原状土的抗剪强度进行测定,并分析了花岗岩风化岩土体抗剪强度在剖面尺度上的异向性及其影响因素。结果表明,饱和条件下,花岗岩风化岩土体黏聚力和内摩擦角的变化范围分别为3.19～19.26 kPa和26.50°～32.42°,其中B_2层黏聚力最大,而各层次间内摩擦角的差异并不明显(p0.05);黏聚力和内摩擦角均存在明显的异向性,其中水平方向总体大于垂直方向,且黏聚力的异向性较内摩擦角更明显。不同方向上抗剪强度的影响机理不同,其中,垂直于剖面方向上,黏聚力主要受毛管孔隙度(r=-0.97,p0.01)和粉粒含量(r=0.94,p0.05)的影响,而水平方向上仅与粉粒含量(r=0.91,p0.05)显著相关;而液限对水平方向上的内摩擦角影响显著(r=-0.99,p0.05)。对于花岗岩风化岩土体抗剪强度的异向性而言,其主要受自然含水率(r=-0.98,p0.01)、有机质(r=-0.93,p0.05)和塑限(r=-0.97,p0.05)影响。研究结果对于从力学稳定性角度揭示崩岗的发生机理具有重要意义。     

Effects of Long-Term Fertilization on the Form of Inorganic Phosphorus and the Characteristic of Adsorption and Desorption in Black Soil

Changes of inorganic phosphorus forms and the characteristics of phosphorus adsorption and desorption were studied under a long-term fertilization experiment in black soil. Results showed that the forms of inorganic phosphorus ranged as O–P < Ca₂–P < Ca₈–P < Al–P < Ca₁₀–P < Fe–P. Therefore, Fe–P was the main inorganic phosphorus form in this study. The capacity of phosphorus adsorption with phosphate treatments was higher than with no-phosphorus treatments. The optimal fitted equation was the Langmuir equation. Phosphorus desorption was related to the binding energy. Positive correlation between phosphorus adsorption and desorption without phosphorus addition was found; however, negative correlations among the phosphate treatments had been observed.     

Silicon availability of the nursery bed soils and effects of silicon fertilizer applied on the growth and silicon uptake of rice Oryza sativa L. seedlings

(pp. 41–46)

Silicon availability in 36 commercial nursery bed soils was evaluated by four methods the phosphate buffer (pH 6.2, 40 mmol L^?1), incubation, supernatant and acetate buffer (pH 4.0, 1 mol L^?1) Methods. The influence of silicon availability in the nursery bed soils on the silicon uptake of rice Oryza sativa L. cv. Hitomebore seedlings and the effect of silicon fertilizer application were examined in a glass house in 2002.

The results revealed that the best correlation between silicon content in rice seedlings and available silicon in soils was obtained with the phosphate buffer-solution method (r = 0.86). More precise evaluation of available silicon was achieved by grouping soils based on these phosphate absorption coefficients (PAC). The correlation coefficients between silicon content in rice seedlings and available silicon in soils were 0.92 and 0.72 for volcanic soils (PAC > 1500) and non volcanic soils (PAC < 1500), respectively.

We concluded that the phosphate buffer method is the most easily adjusted method for estimation of silicon availability in nursery bed soils, and silicon fertilizers should be applied when silicon availability in non-volcanic nursery bed soils goes below 200 mg kg^?1, whereas the level is less than 350 mg kg^?1 in volcanic soils.     

Methane production potentials of twenty-eight rice soils in China

 Soil CH₄ production potentials were investigated by incubating air-dried soils under anaerobic conditions in the laboratory. Twenty-eight soils from different fields and locations were collected for this study. Soil CH₄ production during a 100-day incubation differed greatly and were significantly correlated with soil organic content (r=0.61, P<0.01). The statistical significance increased when soils were grouped according to soil reduction rates. A significant correlation was also found between CH₄ production and total N content (r=0.64, P<0.01) and between CH₄ production and soil particle sizes of 0.25–0.05 mm (r=0.48, P<0.05). A negative exponential correlation was found between CH₄ production and aerobic soil pH (r=–0.74, P<0.01). The 28 soils were stratified into four groups on the basis of variation in CH₄ production rates which were associated with the soil reduction rate and soil organic content. The faster the Eh of soil fell, the more CH₄ was formed. Adding rice straw to Hangzhou and Beijing soils increased CH₄ production. The increase in CH₄ production was more pronounced in the soil with the lowest organic matter content and slowest reduction rate than in the soil with highest organic matter and fastest reduction rate. Inorganic fertilizer had no significant influence on CH₄ production potentials of either type of soil. Received: 26 November 1997     

Comparison of Iron Oxide–Impregnated Paper Strips with Other Extractants in Determining Available Soil Phosphorus

Abstract

Iron oxide–coated strips (P_i) can serve as a sink to continuously remove phosphorus (P) from solution. In this way, P extraction is analogous to the P absorption by plant roots. The objective of this study was to compare the iron oxide–coated paper strips with other chemical extraction methods to estimate the plant P availability for corn (Zea mays) growing in the greenhouse in some soils of Hamadan province of Iran. Sixteen soil samples with different physicochemical properties were analyzed for available P using Olsen, Colwell, Mehlich‐1, 0.01 M CaCl₂, AB‐DTPA, and 0.1 M HCl methods and p_i. Furthermore, the effects of two P levels (0 and 200 mg P kg^?1) on the plant indices (P uptake, relative yield, and plant responses) were studied in a greenhouse experiment using 10 soil samples. The results showed that the amount of extractable P decreased in the order of 0.01 M CaCl₂<AB‐DTPA<p_i<Olsen<Colwell<Mehlich‐1<0.1 M HCl. The amount of P extracted by the p_i method was significantly correlated with other extractants. The amounts of P extracted by all chemical methods were significantly correlated. The results of a pot experiment showed that the amount of P extracted by the p_i method was significantly correlated with the plant P uptake. However, the other methods were not significantly correlated with P uptake. The results of this experiment showed that p_i method was able to predict the plant availability of soil P.     

Phosphorus desorption and isotope exchange kinetics in agricultural soils

To improve phosphorus (P) fertilization and environmental assessments, a better understanding of release kinetics of solid-phase P to soil solution is needed. In this study, Fe (hydr)oxide-coated filter papers (Fh papers), isotopic exchange kinetics (IEK) and chemical extractions were used to assess the sizes of fast and slowly desorbing P pools in the soils of six long-term Swedish field experiments. The P desorption data from the Fh-paper extraction of soil (20 days of continual P removal) were fitted with the Lookman two-compartment desorption model, which estimates the pools of fast (Q₁) and slowly (Q₂) desorbing P, and their desorption rates k₁ and k₂. The amounts of isotope-exchangeable P (E) were calculated (E_1min to E_{>3 months}) and compared with Q₁ and Q₂. The strongest relationship was found between E_{1 min} and Q₁ (r² = .87, p < .01). There was also an inverse relationship between the IEK parameter n (the rate of exchange) and k₁ (r² = .52, p < .01) and k₂ (r² = .52, p < .01), suggesting that a soil with a high value of n desorbs less P per time unit. The relationships between these results show that they deliver similar information, but both methods are hard to implement in routine analysis. However, Olsen-extractable P was similar in magnitude to Q₁ (P-Olsen = 1.1 × Q₁ + 2.3, r² = .96), n and k₁ were related to P-Olsen/P-CaCl₂, while k₂ was related to P-oxalate/P-Olsen. Therefore, these extractions can be used to estimate the sizes and desorption rates of the different P pools, which could be important for assessments of plant availability and leaching.     

N2O and CH4 fluxes from a volcanic grassland soil in Nasu,Japan: Comparison between manure plus fertilizer plot and fertilizer-only plot

Abstract

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N₂O) and methane (CH₄) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha^?1 year^?1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha^?1 year^?1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N₂O and CH₄ fluxes using closed chambers. Annual N₂O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha^?1, respectively. Annual N₂O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N₂O emissions following manure application. N₂O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH⁺ ₄ concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and NO^? ₃ concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH⁺ ₄ concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH₄ emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha^?1, respectively. No significant difference was observed in annual CH₄ emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH₄ emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH₄ fluxes were correlated with NH⁺ ₄ concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both NH⁺ ₄ concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.     

Evaluation of sodium tetraphenylboron (NaBPh4) as a soil test of potassium availability

Non-exchangeable potassium (K_nex) contributes to soil K availability and several extractants are used to access its contribution. This study evaluated sodium tetraphenylboron (NaBPh₄) as a soil test of K availability in 20 soils from Northern Greece. Winter wheat (Triticum aestivum L. var. ‘Yecora’) was sown in a greenhouse pot experiment and five cropping cycles were carried out until K-depletion. Soils were analyzed with NH₄OAc and NaBPh₄ (1 and 5 min incubation periods). Critical levels of K ranged between 130–140 and 330–340 mg K kg^?1 of soil for NH₄OAc and NaBPh₄ (1 min incubation period), respectively, and between 32 and 35 g K kg^?1 of wheat dry matter. NaBPh₄-K (1 min) related better with K concentration and uptake compared to NH₄OAc for each cropping cycle (r² = 0.45–0.83 and 0.44–0.89) and for all soils (r² = 0.58 and 0.51). Similar results obtained in soils low in exchangeable K (r² = 0.41 and 0.39). Correlation between NH₄Oac- and NaBPh₄-extractable K was weaker among soils below the critical level (r = 0.70) compared to those above (r = 0.93). Inclusion of illitic K and cation exchange capacity in a multiple linear regression between NH₄OAc- and NaBPh₄-extractable K showed that they significantly contributed to NaBPh₄-extractable K.     

Measuring and simulating pH buffer capacity of calcareous soils using empirical and mechanistic models

ABSTRACT

We studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100–6500 mM H⁺ kg^–1), in a 0.01 M CaCl₂ background and an equilibration time of 24 h. The pHBC (mM H⁺ kg^–1 pH^?1) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO₃ equivalent (calcite) (r = 0.94), sand (r = ?0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.     

Chemical fractionation of phosphorus in calcareous soils of Hamedan,western Iran under different land use

We investigated the effects of land uses on P distribution and availability in selected calcareous soils under different management practices. KCl‐P (labile P), NaOH‐P (Fe‐Al‐bound P), HCl‐P (Ca‐bound P), and residual P (Res‐P) fractions at 0–30 cm depth were determined for soils planted to garlic, orchard, pasture, potato, leafy vegetables, and wheat. Trends in P distribution between chemical fractions were similar between land uses. Ca‐bound P was the most abundant P fraction in the soils, constituting between 61% and 78% of the total P, whereas P associated with labile was less abundant (< 2%). Soils under leafy vegetables and wheat along with pasture presented the highest and lowest values in all fractions of P, respectively. Labile P generally was highest for leafy vegetables and potato. Labile P and Fe‐Al‐bound P comprised < 1.4% and 8% of total P, respectively. Residual P ranged from ≈ 14% (potato and garlic) to 31% (pasture). Long‐term fertilization increased P allocation to inorganic fractions, as Ca‐bound P contained 78% of total P for potato and garlic and 74% for leafy vegetables but 61% for pasture. A strong positive correlation between labile P and Fe‐Al‐bound P (r = 0.534, p < 0.01), labile P and Ca‐bound P (r = 0.574, p < 0.01), Ca‐bound P and Fe‐Al‐bound P (r = 0.504, p < 0.01), Olsen‐P and CaCl₂‐P (r = 0.821, p < 0.01) was found. Principal‐component analysis showed that the first four components accounted for most of the variation, 32.5%, 16.9%, 12.9%, and 7.9% of total variation, respectively.     

Silicon influences cadmium translocation by altering subcellular distribution and chemical forms of cadmium in peanut roots

Effects of silicon (Si) on subcellular distribution and chemical forms of Cd in two contrasting peanut cultivars, Qishan 208 (low seed Cd cultivar) and Haihua 1 (high seed Cd cultivar), were investigated by a hydroponics experiment at low Cd level (0.2 μM CdCl₂). Two cultivars differ in Cd translocation, subcellular distribution and chemical forms. In comparison to Qishan 208, Haihua 1 shows higher translocation factors (TFs); this may be resulted from higher Cd in the soluble fraction, and a larger proportion of inorganic Cd (extracted by 80% ethanol) and water-soluble Cd (extracted by d-H₂O) in roots. Pretreatment with Si decreased Cd in the cell wall, and enhanced Cd in the soluble fraction for both cultivars. However, effects of Si on chemical forms and TFs are cultivar dependent. Si enhances Cd translocation and the d-H₂O extractable Cd in Haihua 1. Positive correlations were observed between TF and Cd in the soluble fraction (r = 0.71, P < 0.05), and between TF and d-H₂O extractable Cd in root (r = 0.89, P < 0.001). Therefore, larger proportion of d-H₂O extractable Cd may be responsible for high TF in Si pretreated plants of Haihua 1.     

A New Method of Preparing Gel for DGT Technique and Application to the Soil Phosphorus Availability Test

There are different methods for soil phosphorus (P) availability assessment. Researchers have recently introduced a new method called diffusive gradients in thin films (DGT) to evaluate P availability in soils. The aim of this study was manufacturing DGT gel using copolymerization of acrylamide and allylic double bonds agarose to replace the patented agarose as a cross-linker. We evaluated the efficacy of the prepared gel and used the assembled DGT with that gel in 10 calcareous soils. We compared the available P measured with the assembled DGT in those soils to Olsen’s P measured in the same soils. Corn plant (Zea mays L.) was also grown in those soils in a greenhouse for two months. Results showed that the diffusion coefficient of P ions in the gel with 0.3% of allylagarose at 25 °C was 6.9 * 10^–6 cm².s^?1, implying that P ions were allowed to diffuse freely through the prepared diffusive gel. Measured P by the assembled DGT showed a close linear correlation (r² = 0.98) with the P concentrations measured in soil solutions extracted by the Olsen method. This demonstrates the prepared allylagarose cross-linked gels’ efficiency and thus the reliability of the assembled DGT in easily and rapidly measuring the soil’s available P. The P, as measured by the assembled DGT in the examined soils, indicated a little lower correlation coefficient (r = 0.77) than those measured by the Olsen method (r = 0.88). However, the CE values measured by DGT showed a good correlation with P uptake by the roots (r = 0.88, p ≤ 0.01). The best correlation between CE and P content in corn occurred for the measurements made after 48 h of DGT placement in soils. The 20-h measurements had about the same r value, indicating that 20 h is sufficient for the placement of DGT assembly in the soil before its removing and measuring the available P. According to our findings, acrylamide—allylagarose gel as a diffusive gel in DGT was found to be suitable for P measurements in both aqueous solutions and soil.     

Effect of Soil Organic Matter on Adsorption of Nitrification Inhibitor Nitrapyrin in Black Soil

ABSTRACT

Experiments were conducted to study the adsorption kinetics and isothermal adsorption mechanism of nitrification inhibitor nitrapyrin onto the black soil of northeastern China. The nitrapyrin adsorption kinetics of the black soil were fitted with a quasi-second-order kinetics equation before and after organic matter removal (R² ≥ 0.8320, p < .05). The adsorption isotherm was obtained by the Langmuir equation (R² ≥ 0.9400, p < .05). Isothermal adsorption requires less energy and is a spontaneous endothermic reaction with an L-type isothermal curve (n > 1), dominated by surface physical adsorption. With the decrease of organic matter content in black soil, the adsorption mechanism of nitrapyin changed from distribution mechanism to surface adsorption. The black soil’s organic matter content exhibited a quadratic relation with the maximum adsorption capacity and adsorption constant (Kf) at the different temperatures, reaching significant levels (R² ≥ 0.6484, p < .05).     

宁夏灌淤土对磷吸附的初步研究

本文报道了宁夏灌淤土12个代表性土样对磷的等温吸附与解吸特性。实测吸附曲线与Preundlich、Langmuir和Temkin三种等温吸附方程都很吻合。全部供试样品的相关系数变化在0.931-0.999之间,均达极显著水平(p<0.01)。其中Langmuir等温式与本实验资料最为吻合。供试土壤对磷的最大吸附量(X_m)变化在172-460μgP/g之间,平均为347±28μgP/g。影响其大小的因子主要是物理性粘粒和CaCO₃,含量,均达极显著正相关。灌淤土不同土层的吸磷量大小依次为:剖面24>23>21>22,而解吸磷能力大小依次为:剖面23>22>21>24。磷的解吸量与吸附量之间呈极显著正相关。根据本试验数据,土壤对磷的等温吸附曲线可以用来预测土壤需磷量。