Isotope methods for assessing plant available phosphorus in acid tropical soils

Use of isotope methods to measure the availability of phosphorus (P) in soils that are well supplied with P is well established. We have evaluated such methods for acid tropical soils with very small P contents, which are less well studied. The isotopically exchangeable P in soil suspensions (E value) and that in plant growth experiments (L value) were measured in soils that had received varying amounts of P fertilizer in two field experiments in Colombia. We determined the E values over 4–5 weeks of equilibration allowing for the kinetics of isotope exchange. The decrease in radioactivity in the soil solution at a particular time, t, divided by that at the start (r_t/R) was described by three parameters (r₁/R, r_∞/R, and a coefficient n) derived from the time course of isotopic exchange over 100 minutes. Values of E_t were calculated either from measured values of r_t/R or those extrapolated until 12 weeks. Agrostis capillaris was grown on the same soils labelled with carrier‐free ³³P‐orthophosphate ions to obtain L values. Agreement between E values derived from measured and extrapolated values of r_t/R was satisfactory, but errors in n and r_∞/R limited the precision with which we could estimate E values. For most soils, the P concentrations in the soil solution were greater than the detection limit of the malachite green method (0.9 µg l^?1) but smaller than its quantification limit (3.6 µg l^?1). In the soils with the least available P, the P content of the seed limited the determination of the L value. The E values were strongly correlated, but not identical, with the L values measured for the same time of isotopic exchange. We conclude that these approaches are not precise enough to detect in these soils the ability of a plant to access slowly exchangeable forms of P or to quantify the mineralization of organic P. However, these isotope techniques can be used to estimate the total fraction of added fertilizer P that remains available to the plants.     

Evaluation of some chemical methods of soil nitrogen available based on 15Nitrogen technique

Abstract

The large increases in nitrogen (N) fertilizer usage in recent years have led to a recognition of the need for reliable and quick methods of measuring the N‐supplying capacities of soil. Despite this need, there is no well accepted method for testing soils for N availability that has been generally considered to be satisfactory. This study was conducted to determine the N status of the soils of the Bafra Plain and to evaluate some of the more promising methods of determining the index of soil N availability by using a ¹⁵N technique as a standard. Twelve representative soil samples were collected having a broad range of chemical and physical characteristics. In determining the available N contents of these soils, one aerobic incubation method and 12 different chemical methods were compared. In order to evaluate the availability of indigenous soil N to plants and also to investigate the N status of these soils, a greenhouse experiment was conducted with corn as the test plant. Nitrogen was applied as urea at the rate of 0, 50, 100, and 200 ppm with ¹⁵N enriched (2% a.e) urea used at the 50 ppm rate. After eight weeks of growth, plants were harvested. The increased amounts of N were not affected linearly by the dry matter, N content, and N uptake by the corn plants for most of the soils. The most suitable N rate was found to be 50 ppm N under the experimental conditions. In order to select the most suitable chemical methods, the A_N‐value (soil N availability to plant as the applied fertilizer N) was taken as the standard method. Highly significant correlation coefficients were obtained between the A_N‐value and each of the following methods: alkaline hydrolysis (r=0.900 and r=0.938, P<0.001), alkaline permanganate (r= 0.873, r=0.864 and r=0.826, P<0.001), and total N (r=0.850, P<0.001), respectively. These methods appeared worthy of consideration as a routine test for assessing the N availability for these soils.     

Evaluation of four soil test extractants for Zimbabwe soils

Abstract

The objective of this research was to compare the results from anion exchange Resin extraction of P, and the acidified ammonium acetate (AA) extraction of K and Mg with the results obtained using two single extraction procedures, Mehlich 1 (M‐l) and Mehlich 3 (M‐3). Phosphorus extracted from 72 Zimbabwe soils using M‐l and M‐3 was comparable to Resin extracted P in about 80% of the soils. Mehlich 1 extracted about half the amount of P as the Resin method, and M‐3 extracted about one and one‐half times as much. Phosphorus by M‐3 was highly correlated, (r — 0.846), with Resin extracted P from soils having 0.01M CaCl₂ pH values of equal to or greater than 5.9. On soils less than pH 5.9, the r value was 0.502, and for all soils, the r value for M‐3 vs Resin P was 0.615. Mehlich 1 extracted P vs Resin P had a r value of 0.298. Acidified ammonium acetate (AA) extraction of K and Mg was comparable to M‐l and M‐3 extraction of K and Mg in 92% or more of the 72 soils. The K correlation coefficient (r) for AA vs M‐l and AA vs M‐3 was 0.918 and 0.944, respectively. The Mg correlation coefficient (r) for AA vs M‐l and AA vs M‐3 was 0.940 and 0.962, respectively.     

A comparison of methods to determine total,organic, and available phosphorus in forest soils

Abstract

Several methods for the determination of soil phosphorus (P) in acidic forest soils were examined. The Parkinson and Allen digestion method removed more total P than did the ignition method, especially with mineral soils. There were problems with both the Saunders and Williams ignition method and the Bowman and Moir extraction protocol for organic P determination. The problems were more pronounced when used on organic soil samples The Bray P1 was better than the Mehlich 3 method for measuring available P in mineral soils.     

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。     

Determination of available sulphate in some soils of Ghana using five extraction methods

Summary A study was undertaken to measure the sulphate-S in some representative soils cropped to cocoa (Theobroma cacao) and coffee (Coffea canephora var. robusta) in Ghana using five extraction methods at two soil-extractant ratios. The least extracting power was shown by 0.1 N HCL. A soil-extractant ratio of 1:10 extracted higher amounts of SO ₄ ^2– –S than a 1:5 ratio. There were highly significant differences among the extractants and among the soils. From the 15 soil samples, the highest amount of SO ₄ ^2– –S was extracted at the 1:5 ratio and at the 1:10 ratio by H₂O and the KH₂PO_4– extracting solution, respectively. There was no correlation between arylsulphatase activity and the various amounts of extractable SO_4/2– –S, and therefore soil arylsulphatase activity seems less appropriate as an indicator of plant-available inorganic SO ₄ ^2– –S. In the three soil profiles analysed, the amounts of H₂O-extractable SO ₄ ^2– –S decreased with depth while those extracted by sodium acetate buffer increased with depth. The possibility of large amounts of extractable SO ₄ ^2– –S in the subsoils should be considered along with the SO ₄ ^2– –S in the surface samples if an estimation is made of the available –S status of cocoa and coffee rooting zones.     

我国南方地区典型红壤有效磷测定方法研究

通过油菜和水稻的盆栽试验,研究不同耕作方式下红壤有效磷的测定方法。结果表明:不同方法测得的土壤有效磷值差异较大,其中以Olsen法测定的有效磷值最小,各方法测得的土壤有效磷值之间均达到极显著的相关水平;各方法测得的有效磷值与作物吸磷量和生物量的相关性在旱地土壤上均达到极显著水平,在水田土壤上达到显著水平;其中以Bray I法测定的值与作物吸磷量及生长相关性最好,建议将Bray I法作为南方酸性土壤的有效磷测定方法。     

Anion and cation exchange resin membranes to assess the phosphorus status of some Portuguese soils

Abstract

Ion exchange resin methods were applied to 78 different soils to assess their phosphorus (P) status for predicting their response to P fertilization. The techniques used were anion exchange resin membranes eluted with hydrochloric acid (HCl) (AEM) and cation‐anion exchange resin membranes eluted with HCl (CAEM‐HC1), sodium chloride (NaCl) (CAEM‐NaCl) or water with directly color development (CAEM‐H₂O). Greenhouse studies were conducted with the same soils in order to validate laboratory data. Ryegrass was grown with two levels of P: nil and 150 mg P kg^‐1 of soil. Results indicate that soil P levels are significantly correlated (p<0.001) if extracted with AEM or CAEM, both eluted with HCl, although the CAEM technique had extracted larger amounts of P. Concerning the type of elution, results did not show significant differences (p<0.05) between CAEM‐HC1 and CAEM‐NaCl, but both were significantly correlated (p<0.001) with the results obtained with CAEM‐H₂O. All the techniques used to measure extractable P correlated significantly with relative yield and P uptake by ryegrass, showing their ability to predict soil P availability. Nevertheless, CAEM extraction had higher values of r². Among the three techniques for elution, the levels of correlation with the biological parameters were equivalent. From these results, it was concluded that: (i) exchange resins, specially CAEM, is an accurate method to assess the P fertility status of soils, and (ii) the traditional step of elution can be avoided, allowing the process to be less time consuming, thus more suitable for routine use.     

减施磷肥提高设施番茄氮磷钾生理效率并减少土壤速效磷累积

【目的】设施蔬菜生产中过量施肥现象普遍存在,本研究针对设施番茄磷肥过量施用问题,定位研究减施磷肥对番茄产量、干物质量、养分吸收、分配及土壤速效磷状况的影响,旨在为设施栽培磷肥减量提供科学依据。【方法】以习惯施肥为对照 (CK),2015年设磷肥减量50% (P1)、磷肥减量70% (P2) 2个减磷处理,2016年增设不施磷 (P0) 处理,共3个减磷处理。2016年在膨果期、盛果期采集植株样品,测定根、茎、叶、果干重,及各器官氮、磷、钾养分含量;在定植前、盛果期和拉秧期采集0—60 cm土层土壤样品,测定土壤速效磷含量。【结果】在基础速效磷含量较高 (约220 mg/kg) 的土壤,连续两年减磷70%或一年不施磷肥不影响番茄产量,2015年和2016年番茄产量分别为53.9～55.1 t/hm2和50.2～52.7 t/hm2。各减磷施肥处理与CK相比,均显著提高盛果期果实干物质量和N、P、K养分分配率,降低叶片干物质量、干物质分配率和N、P、K养分分配率。膨果期番茄植株62.8%～65.7%干物质分配于叶片,植株氮、磷、钾携出量分别为83.2～89.9 kg/hm2、10.3～11.1 kg/hm2、75.0～85.9 kg/hm2,此时番茄叶片和茎杆是养分的主要累积部位,茎叶氮、磷、钾分配率之和分别为84.4%～86.4%、79.4%～83.4%、76.9%～82.3%,番茄氮、磷、钾吸收比例为1∶0.12∶0.84～0.96。盛果期43.0%～44.6%和37.0%～44.6%的干物质分配于果实和叶片,此时番茄果实和叶片为养分主要累积部位,果实和叶片氮、磷、钾分配率之和分别为84.6%～86.7%、78.5%～82.7%、81.4%～83.9%,植株氮、磷、钾携出量分别为197～226 kg/hm2、33～37 kg/hm2、200～247 kg/hm2。CK处理番茄叶片、果实全钾含量及钾吸收量显著高于减磷处理,可见减施磷肥可降低番茄对钾素的奢侈吸收。经过两年的减磷处理,表层土壤速效磷累积量显著降低,但各处理土壤剖面出现磷素向下迁移,膨果期0—20 cm土层土壤速效磷含量较种植前减少27.0～60.9 mg/kg,20—60 cm土壤速效磷增量在11.8～50.1 mg/kg,减磷处理显著降低20—60 cm土壤速效磷增加量。【结论】在基础磷素含量较高的土壤上,较农民习惯施磷连续两年减少70%的磷肥用量没有影响番茄产量,降低番茄对钾素的奢侈吸收,减缓土壤速效磷累积。两年连续减施磷肥的土壤速效磷含量仍处于较高水平,可见该研究区域设施蔬菜生产减磷潜力仍较大。     

Innovative methods in soil phosphorus research: A review

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state‐of‐the‐art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q‐TOF MS/MS, high resolution‐MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum‐chemical modeling, microbial biomass P, enzymes activity, DGT, ³³P isotopic exchange, ¹⁸O isotope ratios). Required experimental set‐ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.     

Spatial distribution of soil nutrient at depth in black soil of Northeast China: a case study of soil available phosphorus and total phosphorus

Purpose

The spatial variability of soil available phosphorus (AP) and total phosphorus (TP) influences crop yield and the environment. The paper aims to identify the spatial heterogeneity of P (AP and TP) and clarify the main driving mechanisms in a Mollisol watershed of Northeast China.

Materials and methods

Both geostatistical and traditional analysis were used to describe the spatial distribution of P at different depths. P in cultivated fields on the upper slopes was compared with secondary forest areas on the lower slopes within the same watershed.

Results and discussion

The horizontal distribution of P was found to be primarily influenced by structural factors (58–95 %). TP was high at both the summit and the bottom of slopes at all depths, being especially high at the watershed outlet due to erosion on the back slope and deposition at the base. AP was higher on south-facing slopes than on north-facing slopes and typically decreased from the summit to the base of south-facing slopes at the 0–40-cm depths, mainly due to solar radiation, soil loss, and water loss. The vertical distribution of TP typically decreased with increasing depths in farmland but did not show systematic variation in the forest profiles. AP was lower in the middle of the 0–60-cm soil profiles in the farmland, reflecting the influence of fertilization, infiltration, and crop absorption. AP in the 30–60-cm and TP in the 20–60-cm layers were lower in farmland than in the secondary forest, and only 2 % of the area showed a risk of P loss through ground flow and infiltration in the 0–20-cm layer.

Conclusions

The horizontal distribution of P in the 0–60-cm layers was mainly influenced by soil and water loss, deposition, and hydrothermal dynamics, while the vertical distribution of P, especially AP, was more affected by fertilization, infiltration, organic matter, and crop absorption. Secondary forestland that had been converted from farmland was found to effectively hold P, especially in deep soil layers, as the loss of P dissolved in water is not a primary process.     

Soil test for available zinc in acid soils of Venezuela

Abstract

Zinc (Zn) deficiencies have been identified in Venezuela with increasing frequency in recent years. However, there are no established critical values for available Zn in the acid soils of this country. Greenhouse studies were initiated to evaluate five extractants, DTPA, DTPA‐HCl, Na‐EDTA, 0.1N hydrochloric acid (HCl), and Mehlich 1 to predict Zn availability in 14 acid soils with corn as the test crop. Significant and positive correlations were found between Zn extracted among the five extractants. Zinc extracted was not related with soil pH and organic matter content, but with the cation exchange capacity and clay content. The Na‐EDTA extractant was found to be the most suitable as an indicator of Zn‐deficient acid soils, the critical Zn value being 2.4 mg#lbkg^‐1.     

Evaluation of soil sulfate extractants and methods of analysis for plant available sulfur

Abstract

A steady decline in sulfur additions to Atlantic Canadian soils has prompted the need for an accurate method of determining their plant available sulfur status. Three soils were extracted with five soil extractants ‐ 0.01M Ca(H2PO₄)₂‐H₂O in 2M HOAc, 0.1M CaCl₂, Bray‐1 and de‐ionized water. The soil extracts were analyzed for sulfur or sulfate using inductively coupled argon plasma emission spectrometry (ICAP), AutoAnalyzer (AAN), anion exchange‐high performance liquid chromatography (HPLC‐CD) or atomic absorption spectroscopy (AAS). Results were compared with plant response of sulfur treatments to red clover, ryegrass, canola and wheat in a growth room. Instrument reproducibility and crop response indicated the ideal method of determining plant available soil sulfur was HPLC‐CD using the extractant Ca(H2PO₄)₂‐H₂O.     

Drainability of some Dutch clay soils: A case study of soil survey interpretation

Riverine and marine non-calcareous Dutch clay soils have moderate limitations for use as grassland under existing conditions due to high ground-water levels in winter and early spring, which have traditionally been attributed to a very low K_sat of the clay. Physical research, which used soil morphology to define sample size and soil maps to locate test sites within defined mapping units, showed that permanent high ground-water levels were primarily due to low hydraulic gradients and not to a low K_sat. Well-maintained tile drainage, to be associated with low water levels in the ditches in winter, resulted in much lower ground-water levels in the soil, thereby effectively reducing use limitations imposed by existing conditions and improving soil suitability. The latter was specifically characterized in this study in terms of the assessment factor: “drainage status”. Tile drainage resulted in a significant increase of K_sat which was thought to be due to increased drying and cracking of the relatively young riverine soil. In the older marine soils, the increase of K_sat upon tile drainage was due to deep earthworm activity. Existing suitability can thus be improved by using appropriate technology, i.e., tile drainage associated with better water management. The detail by which the technology is defined in soil survey interpretation is critical. The detail should not exceed the generality-level dictated by the variability of regional field data.     

A critical assessment of methods for determining organic phosphorus in savanna soils

 Two newly introduced extraction techniques for determining total organic P (P₀) were compared with the standard high-temperature ignition method in selected savanna soils of Nigeria. The two extraction techniques were: (1) concentrated H₂SO₄ and dilute base sequential extraction (18 N H₂SO₄ and 0.5 N NaOH) and (2) basic EDTA method (0.25 M NaOH plus 0.05 M Na₂EDTA). The concentrated H₂SO₄ and dilute base method extracted significantly higher total P₀ than the high-temperature ignition method and the basic EDTA extraction. The high-temperature ignition and the basic EDTA extraction gave similar total P₀ values (mean=91 mg kg^–1 for ignition and 90 mg kg^–1 for basic EDTA). The precision of the methods, determined by coefficients of variation (CV, %) associated with each P₀ determination method in the soils, was better for the concentrated H₂SO₄ and dilute base extraction method (CV=13%) than the ignition method (CV=18%) and the basic EDTA method (CV=15%). The high C : P₀ ratios determined for the high-temperature ignition and basic EDTA extraction indicated that the two methods underestimated total P₀ in the soils. The concentrated H₂SO₄ and dilute base sequential extraction appears to be suitable for the rapid determination of P₀ in savanna soils because the method can be simplified to a single-step analysis. Received: 14 November 1997     

土壤有效硫评价方法和临界指标的研究

从江西、湖北、河南、北京和黑龙江共采取 18种耕层土壤 ,用玉米和水稻分别进行盆栽试验。选用 6种化学提取剂提取土壤有效硫 ,所提取的硫采用比浊法 (T)和电感耦合高频等离子体原子发射光谱法 (ICP-AES)测定。另外采用阴离子交换树脂膜法和与土壤有机质有关的土壤有效硫评价方法。结果表明 ,各种提取剂不仅能提取土壤无机硫 ,还能把部分有机硫提取出来。NaHCO3提取的有机硫最多 ,其次为KCl-40℃ ,而CaCl2 、Ca(H2PO4)2 、KH2PO4 和Kelowna试剂提取的有机硫相当。在酸性土壤上 ,磷酸盐比氯化物提取出更多的有效硫。不同土壤有效硫指标与植物吸硫量和相对产量相关分析表明 ,Ca(H2PO4)2T是目前最理想和实用的方法。田间试验表明 ,施用硫肥对小麦、玉米、大豆、油菜和水稻都具有不同程度的增产作用。在相对产量为 90 %时 ,用Ca(H2PO4)2 T测定的旱地和水田土壤有效硫临界指标分别为 21.1mgkg-1和 23.8mgkg-1。     

A comparison of 5 soil phosphorus extraction methods applied to different soils of South of Iran

Phosphorus (P) fertilization is commonly based on soil testing, for which a variety of different soil P extraction methods are in use. In this research, the correlation and calibration of five extraction techniques for available P were studied: Soltanpour and Schwab, Olsen, EDTA-Na₂, Paauw and Morgan in 168 different soil samples from 63000 ha of Sirjan pistachio orchards of Kerman province, Iran. The Morgan reagent extracted the most P and then EDTA-Na₂> Olsen> Soltanpour and Schwab> Paauw extracted more phosphorus, respectively. Positive and significant correlation (P < 0.05) existed among all extractants. The correlation coefficients between different extractants and plant P concentration indicated that, EDTA-Na₂ (P < 0.01), Olsen and Paauw methods (P < 0.05) had positive and significant correlation with leaf P concentration and thus with due attention to acceptable relationship with plant indices, the Olsen and EDTA-Na₂ methods could be used to advise on available P.     

A comparison of wet oxidation methods for determination of total phosphorus in soils

For 15 soils with widely different extractability of phosphorus (P) two newly introduced digestion techniques for determining total P (P_t) were compared with the standard perchloric acid digestion procedure. The two digestion techniques were: (1) concentrated H₂SO₄ plus 30 % H₂O₂ at 360 °C, (2) concentrated HCl plus concentrated HNO₃ in the ratio 3:1 (aqua regia) at 140 °C. Almost equal amounts of P_t were extracted by the two methods (mean = 188.7 mg kg^—1 for H₂SO₄/H₂O₂ and 188.4 mg kg^—1 for aqua regia) which were slightly higher than the standard method (mean = 183.8 mg kg^—1). However, there is no statistical difference among the three digestion methods, suggesting that the tested methods should be useful for estimating P_t in soils with high content of organic C, eliminating the danger of explosion when hot concentrated HClO₄ is used.     

Comparison of phosphorus impregnation and bray 1 soil tests for evaluating plant available phosphorus

Abstract

The relationship between soil test phosphorus and crop response has not been studied for maize (Zea mays L.) in some major benchmark soils of Zambia. The suitable soil test procedure for estimating available P needs to be identified. The objective of this study was to compare two soil test methods, impregnation of phosphorus (Pi) and Bray 1, in predicting P requirement of maize grown in Makeni (fine, mixed Isohyperthermic Udic Paleustalf), Maheba (clayey, kaolinitic, isohyperthermic Haplic Acrustox), and Konkola soil series (fine, oxidic, isohyperthermic oxic, Rhodustalf). The three soil series were treated with 0, 262, 524, and 1,048 mg P per pot as triple superphosphate (TSP). Maize was grown in pots, and after 8 weeks the plants were harvested and analyzed for total P concentration. Phosphorus uptake (P uptake) was calculated as a product of P concentration in the plant and maize dry matter yield. The soil was dried, sieved and analyzed for available P. The available P content estimated by Bray 1, and Pi soil tests was correlated with maize dry matter yield, and P uptake. The P which was extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and more significant (r=0.991 * *), than correlation with P extracted by Pi soil test (r=0.958*). The P extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and significant (r=0.990**), as well as correlation with P extracted by Pi soil test (r=0.958**). The correlation of P extracted from Maheba soil series by Pi soil test and maize dry matter yield followed the same trend as for Makeni series with correlation of r=0.990**. The correlation of P uptake and P extracted by Pi soil test was high but less significant (r=0.955*) than that for Makeni soil series. The correlation of P extracted by Bray 1 soil test with maize dry matter yield was high (r=0.973 *) and significant, but the correlation with P uptake was low and not significant (r=0.879 ns). The available P extracted from Konkola soil series by both Bray 1 and Pi soil tests produced poor and not significant correlation with maize dry matter yield, as well as P uptake. The results show that Bray 1 soil test extracted larger amounts of P from all the three soil series than P impregnation (Pi) soil test. The results further demonstrated that Pi soil test was consistently more closely related to P uptake and dry matter yield of maize grown in Makeni and Maheba soil series. Therefore, Pi soil test was more effective than Bray 1 soil test in evaluating soil solution P that the plant usually takes up.