Survey of the plant-available silicon status of agricultural soils in Louisiana

Adequate silicon nutrition in plants has shown positive effects on the growth and yield of the crop and physico-chemical properties of the soil. Hence, this study was initiated to survey the plant-available silicon in the agricultural soils of different parishes of Louisiana. Soil samples were collected from 212 representative agricultural fields of 27 agrarian parishes of Louisiana. Poor correlations between deionized water, calcium chloride, and other extractants suggest that the unbuffered calcium chloride extraction may reflect only a transient status of soil soluble silicon similar to deionized water extraction procedure. Also, acetic acid-2 extraction procedure may reflect the net effects of the sorption/desorption reactions by extracting the readily as well as the slowly releasable silicon that control solubility, thus giving a true measure of current availability. Compared to the previously established critical soil silicon levels, several agricultural fields of Louisiana were deemed to be low in plant-available silicon.     

Relationship between mineral composition or soil texture and available silicon in alluvial paddy soils on the Shounai Plain,Japan

Abstract

To evaluate the relationship between the amount of available Silicon (Si) in paddy soils and their mineral properties on the Shounai Plain in Japan, which is formed from several parent materials, we evaluated the amount of available Si, the particle size distribution, the oxide composition of crystalline minerals and the amount of oxalate-extractable Si (Si_o), iron (Fe_o) and aluminum (Al_o) in the soil. The amount of available Si in the soil and the oxide content of the crystalline minerals differed among four soil groups that were distinguished by their clay mineral composition. There was no difference in the particle size distribution among the soil groups. The amount of available Si was positively related to the SiO₂/Al₂O₃ ratio of clay, the CaO concentration of silt and fine sand, and the amounts of Si_o, Fe_o and Al_o in the soil. The amount of available Si in the soils was negative correlated with the Na₂O and K₂O concentrations of silt, the K₂O concentration of fine sand, and the coarse sand content. These results suggest that the amount of available Si in soils is affected by the weathering resistivity of their minerals and that the particle size distribution and mineral composition are related to the available Si of the soils. Mineralogical properties, including the particle size distribution and mineral composition such as the SiO₂/Al₂O₃ ratio × clay fraction content and the amounts of CaO and MgO in silt-sized particles, were positively correlated with the amount of available Si in the soil, but these correlations were not found for fine sand-sized particles. The Si_o, Fe_o and SiO₂/Al₂O₃ ratio × clay fraction contents contributed approximately 50% to the amount of available Si in the soils. The amount of available Si in the soil was divided into two groups according to the location of the paddy field. The amount of soil-available Si in the alluvial plain was affected by the geology upstream through the mineral composition.     

硅钼蓝比色法测定石灰性土壤的有效硅含量

This paper deals with the determination of available Si content in calcareous soils with Mo blue colorimetric analysis method. The experimental results showed that two acid reagents of sodium acetate buffering solution (pH 4) and 0.025 mol/L citric acid generally had a strong ability of extracting soil available Si, and their soil filtrates were colorless. On the contrary, two alkaline extractants of 20 mg/mL sodium carbonate and 0.5 mol/L sodium bicarbonate only got a relevantly lower soil available Si and their extracts appeared deep color of organic and other pigments, which could be decolorized by adding certain amounts of P-free activated charcoal (about 0.1 g/g soil). In the procedure of Mo blue colorimetry, adding proper amount of oxalic acid and K(SbO)C₄H₄O₆ could eliminate the interference of P to Si and Si to P, respectively. The concentration of acids was not the major factor suppressing the interferences between P and Si in the colorimetric analysis. In the medium of 0.2-0.8 mole H⁺/L sulfuric acid, the intensity of the silicomolybdate blue color did not vary with acidity, no matter whether (NH₄)₂Fe(SO₄)₂ or ascorbic acid was used as reductive reagent. About 10 minutes was needed to form a fully blue complex at 20-25℃. After 30 minutes, the blue color would slowly change into light one, and hence, the colorimetric process should be finished within a short time.     

A contemporary overview of silicon availability in agricultural soils

Our current understanding of silicon (Si) availability in agricultural soils is reviewed and knowledge gaps are highlighted. Silicon is a beneficial rather than essential plant nutrient and yield responses to its application have been frequently demonstrated in Si‐accumulator crops such as rice and sugarcane. These crops are typically grown on highly weathered (desilicated) soils where soil solution Si concentrations are low. Increased yields are the result of simultaneous increases in plant tolerance to a wide range of biotic (plant pathogens, insect pests) and abiotic (water shortage, excess salts, metal toxicities) stresses. Traditionally, soil solution Si is viewed as being supplied by dissolution of primary and secondary minerals and buffered by adsorption/desorption of silicate onto Al and Fe hydrous oxide surfaces. In recent years it has become recognized that phytogenic cycling of Si [uptake of Si by plants, formation of phytogenic silica (SiO₂ · nH₂O) mainly in leaves and subsequent return of this silica to soils in plant litter] is the main determinant of soil solution Si concentrations in natural forests and grasslands. Considerable diminution of the phytogenic Si pool in agricultural soils is likely due to regular removal of Si in harvested products. A range of extractants (unbuffered salts, acetate‐based solutions, and acids) can provide valuable information on the Si status of soils and the likelihood of a yield response in rice and sugarcane. The most common Si fertilizers used are industrial byproducts (e.g., blast furnace slag, steel slag, ferromanganous slag, Ca slag). Since agriculture promotes soil desilication and Si is presently being promoted as a broad spectrum plant prophylactic, the future use of Si in agriculture is likely to increase. Aspects that require future research include the role of specific adsorption of silicate onto hydrous oxides, the significance of phytogenic Si in agricultural soils, the extent of loss of phytogenic Si due to crop harvest, the role of hydroxyaluminosilicate formation in fertilized soils, and the effect of soil pH on Si availability.     

土壤有效钾提取方法评价

本文综述了土壤有效钾的提取方法,并根据不同浸提方法的测定结果与作物反应与标准方法之间的相关性进行了评价。结果表明有多种方法与参比项有显著的相关性。并推荐单独提取土壤有效钾时用1moL·l-1中性NH4OAC法,也可用CEM法或2moL·l-1冷HNO3法,同时需要提取其他有效养分时可用ASI法或M-3法。个别土壤还可用其他方法。但在石灰性土壤上不能用Bray-1法和M-1法。     

小麦蚕豆间作对红壤有效磷的影响及其与根际pH值的关系

在云南红壤上采用田间小区试验,通过测定分蘖～拔节期、孕穗～抽穗期、灌浆～乳熟期不同土层深度小麦根际土壤有效磷(available phosphorus)含量和根际pH值,比较研究了小麦蚕豆间作对小麦根际土壤有效磷含量和pH值的影响,探讨了间作小麦根际pH与根际土壤有效磷之间的相互作用.结果表明,与小麦单作相比,小麦蚕豆间作显著地促进了小麦产量的提高.同时,小麦蚕豆间作促进了小麦根际土壤有效磷含量的提高,分蘖～拔节期、孕穗～抽穗期0-10 cm、10-20 cm土层单、间作差异显著;间作显著降低了分蘖～拔节期10-20 cm土层、孕穗～抽穗期0-10 cm、10-20 cm、20-30 cm土层小麦根际土壤pH.分蘖～拔节期、灌浆～乳熟期,单、间作小麦根际土壤有效磷含量与根际pH呈负相关关系.试验表明,在红壤上间作小麦根际土壤有效磷含量的提高与间作降低根际pH有密切关系.     

土壤中有效结合态氨的一种测定方法

Dynamics of fixed NH₄⁺ in NH₄⁺-treated soils incubated with glucose at 37±2 ℃ during the course of incubation and factors affecting it were studied. Results showed that content of fixed NH₄⁺ in soil reached a minimum on day 7 after incubation and then increased gradually regardless of the amount of glucose added and the kind of soil tested. However, the amount of fixed NH₄⁺ released from the soil at the given time varied with both the amount of glucose added and the kind of soil examined. In cases glucose was added at a rate of 10.0g C/kg soil, the amount of fixed NH₄⁺ retained in soil after 7 days of incubation was almost identical to that found by Neubauer test. Addition of K⁺ depressed the release of fixed NH₄⁺ significantly. Based on the results obtained a method for determining the content of available fixed NH₄⁺ in soils was proposed and the amount of N as available fixed NH₄⁺ in two soils measured by this method on an area profile-depth basis was presented.     

Soluble selenium content of agricultural soils in Japan and its determining factors with reference to soil type,land use and region

Abstract

To evaluate labile selenium (Se) content in agricultural soils in Japan and to investigate its determining factors, 178 soil samples were collected from the surface layer of paddy or upland fields in Japan and their soluble Se contents were determined. Two grams of soil was extracted with 20 mL of 0.1 mol L^?1 sodium sulfate (Na₂SO₄) solution for 30 min in boiling water, and the released Se was reduced to Se (IV) after organic matter decomposition. The concentration of Se (IV) was then determined by high performance liquid chromatography (HPLC) with a fluorescence detector after treatment with 2,3-diaminonaphthalene (DAN) and extraction with cyclohexane. Soluble Se content ranged from 2.5 to 44.5 μg kg^?1 with geometric and arithmetic means of 11.4 and 12.8 μg kg^?1, respectively, and corresponded to 3.2% of the total Se on average. The overall data showed log-normal distribution. In terms of soil type, Non-allophanic Andosols and Volcanogenous Regosols had relatively high soluble Se content, and Wet Andosols and Lowland Paddy soils had relatively low soluble Se content. In terms of land use, upland soils had significantly higher soluble Se content than paddy soils (p < 0.01). The soluble Se content had significant positive correlation with total organic carbon (TOC) content of the extract, soil pH and total Se content (p < 0.01). In conclusion, total Se content in combination with soil pH was the main determining factor of the soluble Se content of agricultural soils in Japan.     

石灰用量对污染红壤和黄泥土中有效态铜锌含量的影响

采用外源加入重金属铜锌硝酸盐的方法,制成铜、锌单一及复合污染的三级污染红壤和黄泥土（Cu 200mg/kg、Zn 400 mg/kg）,稳定一个月,施入低（0.50 g/kg）、中（1.50 g/kg）和高（2.50 g/kg）3种不同用量的石灰,稳定两个月后测定土壤有效态铜、锌含量和pH值,以阐明石灰用量对不同污染土壤中重金属有效态含量的影响。结果表明,随石灰用量的增加,复合污染红壤中有效态铜含量较对照依次降低31%、76%和87%;而石灰用量对黄泥土中有效态铜影响的差异不显著;两种土壤中有效态锌含量均随石灰用量的增加而显著减少;复合污染较单一污染相比,有效态铜及有效态锌的含量差异不显著。在复合污染下,低、中量石灰使黄泥土中有效态铜含量较红壤减少89%和63%,有效态锌减少27%和65%。但加入高量石灰,两种土壤差异不显著。石灰能够降低单一与复合污染铜、锌有效态的含量,但其效果因土壤类型而异,在红壤上选择施用高量石灰而在黄泥土上则适宜施用低中量石灰,以取得最佳的修复效果和效益。     

Evaluation of nitrogen status of agricultural soils in Java,Indonesia

Abstract

To evaluate the content of nitrogen (N) fractions of agricultural soils in Java, Indonesia, in relation to soil type and land use, 46 surface soil samples, 23 from paddy and 23 from upland, were collected throughout Java to include various types of soils. Soil N was separated into four fractions according to form and availability: inorganic extractable nitrogen (Iex-N), fixed ammonium nitrogen (Ifix-N), organic mineralizable nitrogen (Omin-N) and organic stable nitrogen (Osta-N). The total-N content was determined by the dry combustion method. The Iex-N content was determined by extraction with a 2 mol L^?1 potassium chloride (KCl) solution and the Ifix-N content by extraction with an hydrofluoric and hydrochloric acid (HF-HCl) solution after removal of organic-N. The Omin-N content was evaluated as the potentially mineralizable N based on a long-term incubation method. The Osta-N content was calculated as the difference between the contents of total-N and the three other fractions. The total-N content was 2.06 g kg^?1 on average. The contents of Iex-N, Ifix-N, Omin-N and Osta-N were 25.8, 99.1, 103 and 1,832 mg kg^?1, respectively, and corresponded to 1.3, 4.8, 5.0 and 88.9% of the total-N. Hence, available (Iex-N and Omin-N) and stable (Ifix-N and Osta-N) fractions accounted for 6.3% and 93.7% of the total-N, respectively. Correlation analysis indicated that the contents of total-N and Osta-N had positive correlation with (Alo + 1/2Feo) as an index of amorphous minerals (p < 0.01), suggesting strong influence of volcanic materials for the accumulation of organic matter in Java soils. The content of Ifix-N had a positive correlation with nonexchangeable potassium (K) content (p < 0.01), suggesting the contribution of 2:1 clay minerals which can fix both ammonium (NH₄⁺) and K⁺ in their interlayer sites. On the contrary, Omin-N did not have any significant correlation with soil properties, implying the importance of management for the improvement of the available N level in soils, rather than intrinsic soil properties. Soil N status further showed strong topographical trends depending on the elevation where soil developed. The contents of total N, Iex-N, Ifix-N, Omin-N and Osta-N in Java soils were on average 80, 69, 90, 65 and 80% of those in Japanese soils, respectively, suggesting that the soil N level in Java was lower than that in Japan, probably due to accelerated decomposition of organic matter, especially degradable fractions, reflecting high temperature, but that the level was relatively high for tropical soils due to the effect of volcanic materials. In conclusion, these results should be taken into account for the sustainable management of soil N in agricultural fields in Java, Indonesia.     

石灰用量对酸性土壤pH值及有效养分含量的影响

采用室内培养法,设置不施生石灰和生石灰用量0.3、0.9、1.8、2.4、4.8 g/kg,共6个用量梯度,研究不同生石灰用量对酸性土壤pH值动态变化、有效养分含量的影响及土壤pH值与有效养分含量之间的相关性。结果表明,生石灰的施入,可以显著提高土壤pH值,改善土壤酸度。培养到第90 d,生石灰用量4.8、2.4、1.8g/kg处理较对照分别提高了2.88、1.16和0.74个pH单位。施用生石灰对土壤全氮含量影响不大,但对土壤无机氮影响显著。生石灰用量在0~2.4 g/kg范围内,土壤硝态氮含量随生石灰用量的增加而显著增加,增幅为12.4%~146.8%,当生石灰用量2.4 g/kg时,土壤硝态氮含量显著降低。土壤铵态氮的变化趋势则刚好相反,随着生石灰用量的增加而减少;土壤有效磷含量随着生石灰用量的增加先升高后降低;对于土壤速效钾来说,当生石灰用量0.9 g/kg,其含量随着石灰用量的增加而显著降低,降幅为2.9%~21.7%。施用生石灰可以显著提高土壤有效Ca含量,且随生石灰用量的增加而显著增加,增幅为32.3%~543.0%。生石灰的施用显著降低了土壤有效Fe、Mn、Cu、Zn的含量,且当生石灰用量≥2.4 g/kg时,土壤有效Mn、Zn含量均已处于极其缺乏的状况。土壤pH值与土壤全氮、铵态氮、速效钾、有效Fe、Mn、Cu、Zn呈显著线性负相关,与有效Ca呈极显著线性正相关,与土壤硝态氮、有效磷和有效Mg则符合二次函数,各相关系数均达到极显著水平。土壤养分与土壤酸度有着较好的相关性,在施用石灰改良酸性土壤时,要特别注意其施用量及土壤有效Mn、Zn等微量元素的及时补充。     

Total selenium content of agricultural soils in Japan

To evaluate the selenium (Se) level in agricultural soils in Japan and to investigate its determining factors, 180 soil samples were collected from the surface layer of paddy or upland fields in Japan and their total Se contents were determined. Finely ground soil (50 mg) was wet-digested with HNO₃ and HClO₄ solution and the released Se was reduced to Se(IV). The concentration of Se(IV) was then determined by high-performance liquid chromatography with a fluorescence detector after treatment with 2,3-diaminonaphthalene and extraction with cyclohexane. The total Se content ranged from 0.05 to 2.80 mg kg⁻¹ with geometric and arithmetic means of 0.43 and 0.51 mg kg⁻¹, respectively. The overall data showed a log-normal distribution. In terms of soil type, volcanic soils and peat soils had relatively high Se content and regosols and gray lowland soils had relatively low Se content. In terms of land use, upland soils had significantly higher Se content than paddy soils. Among regions, soils in the Kanto, Tohoku, Hokkaido and Kyushu regions had relatively high content. The total Se content had a significant positive correlation with the organic carbon content ( P  < 0.01) and the equation for the estimation of total Se content with organic carbon suggested that on average approximately 48% (0.24 mg kg⁻¹) of the total Se was in inorganic forms and approximately 52% (0.25 mg kg⁻¹) was in organic forms. Soil pH, on the contrary, did not show a significant relationship with the total Se content. In conclusion, the organic matter content, in combination with volcanic materials, was the main determining factor of the total Se content of agricultural soils in Japan.     

Phosphorus and potassium fertility of some riceland soils in Indonesia

Abstract

Contents of soil phosphorus and potassium vary appreciably in different localities of the Indonesian Archipelago. Data collected for riceland soils from seven irrigation areas (five on Java and one each on Sumatra and Sulawesi) show that average available phosphorus contents in the tilled layer may range from 23 ppm P at the Sumatra location to 203 ppm Pat the Sulawesi location. Average exchangeable potassium contents ranged from less than 0.2 meq/100g. K in the Sumatran soils to over 1.0 meq/100g. in potash‐rich soils of Java. Distinct regional differences in soil fertility of the magnitude observed indicate that blanket fertilizer recommendations cannot be made if rice production is to be increased without wasting chemical fertilizers which are relatively scarce and expensive in Indonesia. Increased emphasis must be placed on soil testing and soil fertility research in order to achieve the national goal of self‐sufficiency in food stuffs.     

电感耦合等离子体发射光谱法测量土壤中有效锌含量的不确定度评估

对电感耦合等离子体发射光谱法(ICP-OES)测定土壤有效锌含量的不确定度进行评定,分析了整个检测过程产生不确定度的来源,对称样量、浸提液体积、标准系列溶液配制、线性标准曲线拟合、测量重复性等产生的不确定度分量进行计算,量化给出扩展不确定度。待测土壤中有效锌含量最终结果表示:w(Zn)=(1.12±0.10)mg/kg,包含因子k=2,置信概率为95%。测量过程中,标准溶液制备所产生的不确定度最大。因此,在ICP-OES法测定土壤样品有效锌时应足够重视标准溶液制备与曲线拟合过程,以减小测量不确定度。本文研究结果为控制ICP-OES法测定土壤有效锌数据质量提供了理论依据。     

Improved SMP buffer method for determining lime requirements of acid soils

Abstract

Single buffer‐two pH and two‐buffer adaptations were compared as double buffer features of the SMP method using a group of 54 soils of wide range in lime requirement (LR). Data from both methods were highly correlated both with each other and with Ca(OH)₂‐titrated acidity.

Formulas for LR based on the schematics of similar triangles relating differences in measured pH vs corresponding acidities for the double buffer system were developed. A regression equation relating buffer‐indicated LR and Ca(OH)₂ titrated acidity was used to adjust the quick‐test double buffer‐indicated values to levels nearer the actual ones. A recommended SMP double buffer procedure, and a formula for computing LR from soil‐buffer pH's measured by the double buffer, quick‐test method are presented.     

攀西烟区紫色土pH值与土壤养分的相关分析

对四川攀西烟区有代表性的30个紫色土样品的pH值、有机质及有效养分含量进行了测定。结果表明，攀西烟区紫色土的pH值在5．13～8．14范围内，有半数左右的土壤偏碱性；有机质、碱解氮、有效锌和有效锰的含量均随pH值的升高而降低，交换性钙的含量随pH值的升高而升高，而pH值与速效磷、速效钾、交换性镁、速效铜、速效硼间的相关性则不显著。烟区紫色土的有机质和碱解氮含量偏低，速效磷、速效钾含量中等，交换性钙、交换性镁含量丰富；部分pH值较高的土壤可能会缺乏铜、锌等微量元素；在不同pH值的土壤上硼营养均严重亏缺，建议生产中增施硼肥。     

Silicon concentrations in soil and bark in Irish Sitka spruce forests

The relationship between plant‐available silicon (Si) soil concentrations and bark Si concentrations in coniferous species is poorly understood. The objectives of this research were to generate baseline data on Si concentrations in soils and bark of Sitka spruce (Picea sitchensis) seedlings in Ireland and to understand better the relationship between soil and bark Si concentrations. Seedlings were harvested from eight plantation forestry sites and two tree nurseries, and Si concentrations in the bark tissue as well as plant‐available Si concentrations in soils (CaCl₂ extractant) were measured. Bark Si concentrations varied significantly between sites and were lowest [mean 790 (± 242 SD) mg kg^?1 dry plant tissue] on acidic, organic rich peat soils, while the highest Si concentrations occurred in seedlings [mean 3688 (± 633 SD) mg kg^?1 dry plant tissue] grown on soils with low C concentration and higher pH values (≈ 4.5 to 5.5 in H₂O). Plant‐available Si soil concentrations were not related to soil C concentrations. There was a negative (but statistically not significant) relationship between plant–soil concentrations and soil pH. A significant negative relationship was observed between plant‐available soil Si concentrations and bark Si concentrations, which may be related to the presence of soil from mixed soil horizons forming the mounds that seedlings were planted on. Uptake and sequestration of Si by seedlings may have been related to the rate of growth of the seedlings, as bark Si concentrations were highest on sites that were expected to have greater seedling growth rates. The negative relationship between bark and plant‐available Si soil concentrations suggest that uptake of Si by Sitka spruce is rejective at higher concentrations.     

基于常规土壤有效磷(Olsen法)分析的高效测试技术研究

提高常规方法土壤测试的效率是我国测土配方施肥亟待解决的技术问题。通过30个有代表性的土样研究了与现代化测试技术手段相应的土壤有效磷(Olsen-P)的分析过程的改进和提高,结果显示:700 nm波长比色测定土壤有效磷比882 nm波长测定有显著正偏差,土壤有效磷的比色测定应该用882 nm波长以消除土壤可溶有机质影响;改进的钼锑抗显色剂10 min可稳定显色,大大缩短了比色测定需要等待的时间,且测定结果与原有测定过程测定结果一致。同时改进的显色剂稳定时间长,24 h的测定结果和10 min测定结果没有差异。土壤有效磷测定显色过程采用稀释加液器和比色测定中采用泵吸式进样器,可以大大提高土壤测试效率。     

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.