Comparative Evaluation of Inductively Coupled Plasma–Atomic Emission Spectroscopy and Colorimetric Methods for Determining Hot-Water-Extractable Boron in Soils

Frequency of boron (B) deficiency is increasing in rainfed systems, and hence there is a need to diagnose the deficiency. Colorimetric methods are still widely used in soil-testing laboratories in India for measuring B. Little information is available on the comparative evaluation of the colorimetric and inductively coupled plasma (ICP) methods for determining extractable B in soils. We describe results of the comparative evaluation of these methods for measuring extractable B in 57 soil samples with pH values ranging from 5.3 to 9.5. There was a significant correlation between B values determined by the two methods, and the correlation coefficient was greater for soil samples with pH in the neutral to alkaline range. Interaction between soil samples and methods (ICP or colorimetric) was significant except for soil samples in the pH range of 8.0 to 9.5. Precision for B determination was greater with the ICP than with the colorimetric method.     

Pulverizing Soils for Laboratory Analysis

Soil-testing laboratories utilize a range of grinder types to pulverize soils for laboratory analysis. This study was conducted to evaluate the effects of soil particle diameter and laboratory subsample size on analysis variability on nitrate, Bray 1 extractable phosphorus (P), extractable potassium (K), and soil organic matter (SOM). Four soils collected for the Agricultural Laboratory Proficiency Program were pulverized using four types of commercial grinders and analyzed for particle-size distribution, P, and K. In a second study, soils were pulverized to pass sieves of 2.0, 1.0, and 0.50 mm and subsampled for P, K, and SOM. Results of the commercial grinders indicate a range in mean particle diameters from 0.15 to 0.60 mm, with the lowest for the grinder utilizing a hammer mill design. Sieve-size analysis results indicate that the coarsest 2.0-mm fraction had the largest variability for all soil analyses evaluated. Analyte variability decreased with decreasing sieve size. Mean Bray P, K, and SOM-LOI (Loss-on-Ignition) mean concentrations were not statistically significantly different across the sieve sizes evaluated. Laboratory analysis variability for extractable Bray P increased as subsample size was reduced.     

Interlaboratory and Intralaboratory Testing of Soil Sulfate Analysis in Mollisols of the Pampas

Sulfur (S) deficiencies in grain and forage crops have been detected in many agricultural regions of the world, but soil tests are not commonly used as the basis for S fertilizer recommendation programs. Errors of measurements of soil sulfate were determined to assess whether the variation among and within soil-testing laboratories could be a factor that prevent the adoption of soil testing to assess soil sulfate availability. Subsamples of 10 selected soils (Mollisols) from the Pampas (Argentina) were sent in two batches to five soil-testing laboratories. Laboratories were unaware of the existence of subsamples and performed routine sulfate analysis as if these soils came from 60 different fields. Soil sulfate ranged from 3.3 to 20.6 mg kg^?1. One laboratory reported sulfate values greater than the other ones, having a mean bias of 4.1 mg kg^?1 S sulfate (SO₄). The other four laboratories reported similar sulfate values when soils had low sulfate availability (less than 10 mg S kg^?1), even when they used different extractants. Considering only these four laboratories, average interlaboratory coefficients of variations ranged from 6 to 24% for the 10 soils. Within-laboratory mean coefficients of variation (CVs) ranged from 12 to 22%. However, mean absolute errors of all laboratories were less than 1.2 mg kg^?1 S-SO₄. Two laboratories reported different sulfate values for the two batches of shipment (an average difference of 4.7 and 3.8 mg kg^?1 of S-SO₄). Laboratories using different extractants obtained similar results, suggesting that using the same extractant is not a prerequisite to standardize laboratory results in these soils. Differences between laboratories in our study were smaller than in other interlaboratory comparisons for soil sulfate. These differences could be easily detected and corrected if laboratories participate in an interlaboratory control system. The observed low mean absolute errors suggested that, in general, all laboratories achieve acceptable precision when evaluating within the same batch of determinations. Differences between batches of shipment (within laboratory error) stressed the importance of using reference material for internal quality control.     

Modified Soil‐Test Methods for Extractable Phosphorus in Acidic,Neutral, and Alkaline Soils

Abstract

Although numerous soil‐test methods for estimating extractable phosphorus (P) have been developed around the world, their results are difficult to compare because of the very different scale levels used. In the present study, the Bray–Kurtz method (Bray‐P) is used as a reference value. Two other methods [lactate‐P and sodium bicarbonate (NaHCO₃)‐P] were modified to facilitate the comparison of extractable‐P determinations, mainly by adjusting the shaking time. These three methods were applied to 101 soil samples from an extensive region of Argentina with soil pH values ranging from 5.5 to 8.5. The results confirm that the Bray‐P and the two modified methods (lactate‐P and NaHCO₃‐P) determine similar contents of extractable P but are not applicable to all types of soils and conditions. Equations that minimize the statistical error were selected for soil properties such as organic carbon (OC) content, pH, soluble salts, and calcium carbonate content. Correlation coefficients between Bray‐P and NaHCO₃‐P increased to 0.91 and 0.95 in soils with high and low OC levels, respectively. It was also demonstrated that the lactate‐P test is not suitable for soils rich in calcium carbonate or soluble salts. These two modified methods are expected to be useful for testing P values that impact agricultural production.     

Pressurized Hot Water Procedures for Use on Small Farms in Developing Countries

Abstract

Soil analysis for small farms in developing countries is often inconvenient and prohibitively expensive, yet the information gained from these soil tests could result in significant benefits. Based on tests done on a limited range of soils, the pressurized hot water (PHW) extraction coupled with colorimetric or turbidimetric analysis is a promising alternative. Before this extraction and analysis can be used in developing countries, testing is needed across the range of soils found in these countries. At Brigham Young University (BYU), 228 soils from Guatemala and Morocco were analyzed for NO₃‐N, phosphorus (P), and potassium (K) using standard methods (water–CTA, Olsen–molybdic acid and ammonium acetate–atomic absorption, respectively). Results were correlated to values obtained from the PHW extraction coupled with colorimetric or turbidimetric analytical procedures. The relationships between these tests were good (r² values of 0.96, 0.71, and 0.52 for NO₃‐N, P, and K, respectively). In an additional study comparing several P extraction methods for Guatemala soils, relationships between PHW‐extractable P and Olsen‐, Bray I–, and Mehlich I–extractable P (r² values of 0.75, 0.67, and 0.46, respectively) suggest that PHW is a promising P‐extraction procedure for use in Guatemala. Overall, PHW extraction and accompanying analyses are a less expensive alternative to current soil nutrient extraction and analysis procedures for the soils of Morocco and Guatemala.     

Comparison of Copper,Manganese, and Zinc Extraction with Mehlich 1, Mehlich 3, and DTPA Solutions for Soils of the Brazilian Coastal Tablelands

Deficiency of micronutrients is increasing in crop plants in recent years in Oxisols and Ultisols in the tropics. The predominant soils in the coastal tablelands of Brazil are Ultisols and Oxisols, with low cation exchange capacity and kaolinitic clay mineralogy. Soil copper (Cu), manganese (Mn), and zinc (Zn) extracted by the Mehlich 1 solution, currently used in the regional soil-testing laboratories, were compared with those extracted by the Mehlich 3 and diethylenetriaminepentaacetic acid (DTPA) solutions in a greenhouse experiment with 10 soil samples (0–20 cm deep) collected from representative Ultisols and Oxisols from various locations in the region. Corn was grown as a test crop, and its dry matter and micronutrient uptake was measured at 30 days of growth. Soil Cu, Mn, and Zn extracted with the three solutions were significantly correlated (0.65–0.95 range for r values), with the Mehlich 3 solution extracting greater quantities than the Mehlich 1 and DTPA solutions. Zinc and Cu taken up by corn plants were significantly related to their soil-extractable levels measured at harvest with all three of the solutions, except for Zn DTPA. However, similar relations between plant uptake and soil extractable Mn were poor, except for DTPA extracting solution.     

Anion‐exchange membrane,water, and sodium bicarbonate extractions as soil tests for phosphorus

Abstract

Three techniques were evaluated as soil P tests for western Canadian soils: anion‐exchange membrane (AEM), water, and bicarbonate extraction. The AEM, water, and bicarbonate‐extractable total P represented novel approaches to compare to the widely used bicarbonate‐extractable inorganic P (traditional Olsen) soil test. In a range of Saskatchewan soils, similar trends in predicted relative P availability were observed for AEM, water extraction, bicarbonate‐extractable total P, and bicarbonate‐extractable organic P. Correlations between soil test values revealed AEM and water‐extractable P to be most closely correlated, consistent with the similar manner of P removal in the two tests.

Phosphorus availability, as predicted by the tests, was compared to actual P uptake by canola and wheat grown on 14 soils in a growth chamber experiment. P uptake by canola was highly correlated with AEM (r² = 0.86–0.90), water (0.87 ‐0.94), and bicarbonate‐extractable total (0.91) and inorganic (0.92) P. Uptake of P by wheat was not quite as highly correlated with test‐predicted values: AEM (r² = ‐0.73–0.78), water (0.72–0.77), bicarbonate total (0.82), bicarbonate‐inorganic P (0.75).

The similarity in coefficients of determination among test methods indicated nearly identical abilities of the tests to predict soil P availability in the range of soils examined. The AEM and water extractions, unlike bicarbonate, are largely independent of soil type and may prove superior when a wider range of soils is being tested. Bicarbonate‐extractable total P and water‐extractable P suffer limitations in analytical simplicity and cost. In testing for P alone, AEM was considered superior to the other methods due to low cost, simplicity, independence of soil type, and high correlation with plant uptake.     

提取剂和土水比对旱耕地土壤无机和有机磷的提取效应

比较了O lsen(0.5 mol L-1NaHCO3)和B ray-1(0.03 mol L-1NH4F-0.025 mol L-1HC l)提取剂土水比1∶4和1∶20(W/V),对我国5种类型旱耕地土壤(pHKC l3.3~7.4)无机磷(Pi)和有机磷(Po)及外加正磷酸盐态无机磷的提取效应。结果表明,以O lsen提取剂土水比1∶20对土壤Pi和Po的提取效果最佳,其测定结果是评价土壤磷素供应能力(有效磷)和活性有机磷含量较为适宜的指标。测定的土壤大多数(占60%)磷素供应能力较差(O lsen-Pi为4.2~14.0mg kg-1),应适当加强其磷素的投入。测定的土壤活性有机磷(O lsen-PO)含量为1.4~37.9 mg kg-1,占土壤全磷的0.2%~15.8%,大多数(75%)土壤占1%~6%。采用O lsen提取剂时土壤外加Pi的固定率随土水比减小而增高,当土水比1∶4提取时,酸性和强酸性(pHKC l3.3~5.5)土壤对外加Pi的固定率达40%~86%,据此推测实际田间条件下土壤对外加Pi的固定率更大。表明酸性和强酸性旱耕地土壤对外加Pi具有强烈的固定作用。     

Effect of the Extraction Period on the Routine Assessment of Soil P Status by Ion‐Exchange Resin Membranes

The cation–anion exchange resin membrane (CAERM) system is one of the most promising alternative methodologies for the assessment of soil phosphorus (P) availability. Nevertheless, the CAERM method has a recommended period of extraction (16 h) that limits its applicability. With the aim to improve the use of CAERM in routine laboratory work, seven extraction times were studied and compared for repeatability and biological accuracy, using 150 samples of soils and covering a wide range of properties. The results showed dissimilar quantities of extractable P, according to the nature of soils and the period of extraction time. On average of all soils, values of extractable P ranged from a 2.4 mg kg^?1 and 26.7 mg kg^?1 in 0.25‐h and 16‐h extraction times, respectively. Relative to the repeatability aspects, the results reveal a tendency of increasing results with the decrease of the period of extraction, showing coefficient variation (CV) values ranging from 5% (16 h) to 14% (0.25 h). All the extraction periods tested for the CAERM presented highly significant values of r (0.824–0.943) between extractable P and each of the three biological parameters: relative yield of ryegrass, P content, and P uptake. Considering the three biological parameters simultaneously, the best results were obtained for extraction periods of 8 h, 2 h, and 4 h. Based on the results, and considering both practical and accuracy aspects, it is conclude that 2 h of extraction is a valid alternative to the 16‐h standard extraction period for the CAERM methodology.     

Critical Limit of Extractable Phosphorous in a Gleysol for Rice Production in the Senegal River Valley of West Africa

Abstract

Soil‐test correlation and calibration, a useful tool for fertilizer recommendations, has been little used in West Africa. Soils from a long‐term fertility experiment have been used to study the relationship between rice yields and soil extractable phosphorus (P) with Bray 1 and Olsen methods. The Cate and Nelson graphical method was used for critical limits of soil P determination. The critical limits of soil extractable P at 95% relative grain yield were 9 mg P for the Bray 1P and 17 mg P kg^?1 for Olsen P. The Olsen P was more correlated (r=0.63) with rice grain yields than Bray P (r=0.50), but a strong correlation (r=0.92) was also observed between the values of the two methods. Results indicate that at levels less than these critical levels of extractable P, P fertilizers should be applied to increase rice yields.     

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

Abstract

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

Evaluation of Agro Services International Soil Test Method for Phosphorus and Potassium

Soil testing is widely adopted as an essential diagnostic tool for identifying soil nutrient factors that limit sustained crop production. A systematic approach for rapid soil testing and fertilizer recommendation has been introduced and widely used in China by Agro Services International (ASI), USA. To verify the usefulness and reliability of the ASI method in soil testing and fertilizer recommendation in comparison with other commonly used traditional soil testing methods, 294 soil samples from major agricultural regions and soil types in China with a wide range of soil pH, from 5.1 to 8.9, were taken and analyzed for available phosphorus (P) and potassium (K) by the ASI multielement extraction solution and selected traditional methods, Olsen extractant for P, ammonium acetate (NH₄OAc) extractant for K, and multielement extractant Mehlich 3 for P and K. Also, 46 soils were selected from northern China regions for a greenhouse trial with sorghum seedlings to determine if the soil testing values correlate well with plant response. Results indicated that the amount of soil P extracted by the ASI method (ASI P) was correlated to both soil extractable P tested by the Olsen extractant (Olsen P) and Mehlich 3 extractant (Mehlich 3 P). The correlation coefficient of ASI P with Mehlich 3 P (R² = 0.86) was greater than that of ASI P with Olsen P (R² = 0.74) across all selected soils. A good correlation was also found between the exchangeable K from the ASI method with the traditional ammonium acetate method (R² = 0.81) and the Mehlich 3 method (R² = 0.85). The results from the greenhouse trial showed that the extractable P and exchangeable K by the ASI multielement extraction solution could be used to represent the fertility status of soil P and K for the selected soils. Regression analysis indicated that the relative dry-matter yield of the sorghum plants can be predicted with either ASI P and ASI K values with the correlation coefficients (R²) values of 0.78 and 0.72 respectively and could be a good measure for soil testing and fertilizer recommendation in the selected soils and regions in China.     

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.     

诊断油菜缺硼的土壤硼素临界范围

Relationships between seed yields of oilseed rape(Brassica napus L.) and extractable boron concen-trations in three soil layers(A,P and W) were investigated through ten experiments on three types of soils(Alluvic Entisols,Udic Ferrisols and Sagnic Anthrosols) in northern,Western and middle Zhejing Province.Among several mathematical models used to described the relationships,the polynomial equation,y=a bx cx^2 dx^3,where y is the yield of oilseed rape seed and x the extractable boron concentration in P layer of soil,was the best one.The critical range of the concentrations corresponding to 90% of the maximum oilseed rape yield was 0.40-0.52 mg kg^-1,The extractable boron concentration of the P layers of the soils was the most stable,The critical range determined was verified through the production practices of oilseed rape in Zhejiang and Anhui provinces.     

土壤环境质量指导值与标准研究Ⅳ.保护人体健康的土壤苯并[a]芘的临界浓度

：基于人体健康风险评估制定土壤环境质量指导值或标准是当前国际上广泛采用的方法.本文全面调研了国际上保护人体健康的土壤苯并[a]芘（B[a]P）的各类临界浓度,初步确定了量化土壤中B[a]P暴露剂量的暴露场景和暴露参数,率先提出了制定我国土壤中保护人体健康的B[a]P临界浓度的方法体系,这种方法可用来制定持久性有机污染物的土壤临界浓度.考虑了口腔摄入、皮肤接触、呼吸摄入和取食污染蔬菜摄入四个主要暴露途径,探讨了B[a]P的致癌风险水平为10-5或10-6时,农业用地、居住用地和工业用地方式下土壤中B[a]P的临界浓度,同时制定了保护地下水的土壤B[a]P的临界浓度.     

Factors Affecting Mehlich III Soil Test Methodology for Extractable P

Agronomic and environmental testing laboratories in Texas and elsewhere have adopted Mehlich III (M3) as their official soil test phosphorus (P) methodology. However, M3-P data could be skewed due to non-homogenous soil samples or failure to follow standard protocol which could influence recommendations or restrictions. Twelve agricultural soils with a wide range of properties were collected from across Texas. Exhaustive efforts via multiple methods were made to prepare homogeneous representative soil samples. The standard M3 protocol selected was a 2 g weighed soil sample placed in a 148 ml disposable plastic cup, using a 1:10 soil:M3 solution ratio, shaken on a 200 rpm orbital shaker with a 2.5 cm throw for exactly 5 min, and filtered through Whatman No. 2 filter paper. The standard protocol was compared with nine different protocol variations with variables including soil weighing versus scooping, scooping repeatability of different technicians, soil sample weight, shaking type, speed and time, different filter papers, and varying soil:extractant ratios. Extent of soil pulverization on M3-P results was also evaluated. Tests were performed in four replications for all protocols to assess effects on M3-extractable soil P. Percent recovery of soil during grinding had no effect on M3-extractable P. Little difference in M3-extractable P was observed between scooping and weighing of 2 g soil samples. Shaker type had no effect on extractable P in soils with low clay contents, however, increasing shaking speed and using an orbital shaker resulted in higher extractable P, especially in clayey soils. Both Whatman No. 1 and 2 filter papers were found suitable for M3-P analyses. Different soil:extractant ratios resulted in a highly significant influence on the amount of M3-P extracted. However, when ratios were maintained between 1:9 and 1:11, few differences in extractable P were observed. Using sample weights below 3 g did not significantly alter precision or accuracy of results. However, technician variation in scooping of 2 or 5 g soil samples resulted in significant differences in M3-P.     

采用健康风险评价模型研究场地土壤有机污染物环境标准取值的区域差异及其影响因素

前人研究及国外已有标准表明,一些有机污染物的土壤环境标准的区域差异显著。我国的土壤环境标准正在酝酿之中,研究土壤环境标准的区域差异及其影响因素十分必要。本文选择了取自我国不同地区的13种典型土壤,以萘为例,应用RBCA模型估算了非致癌危害商为1的目标风险水平下,土壤环境中污染物的最高限值,并对取值区域差异的影响因素进行了探讨。结果表明,不同地区土壤中萘的最高限值差异显著,住宅用地萘的最高限值范围为370～1 400 mg·kg^-1,工业用地限值范围为610～4 100 mg·kg^-1。不同地区土壤中萘的最高限值差异最高可达3.8～6.7倍。土壤质地和有机质含量是影响最高限值取值的两种主要因素。随着土壤质地粘粒含量的增加,最高限值取值增加,达到一定程度后保持不变或略有降低;随着有机质含量的增加,最高限值取值呈增大趋势,但也有某些情况下,有机质含量增加到一定程度后最高限值趋于稳定。该结果预示了某些有机污染物的土壤环境标准取值受区域变异的影响较大,在标准制修订过程中对此需适当加以考虑。     

Effects of plant residues and environmental factors on phosphorus availability in soils

Abstract

Phosphorus availability is a major nutritional problem in several northern Idaho soils. Traditionally, fertilizers containing P have been applied to improve availability in soils; however, organic materials added to soils have the ability to provide large quantities of labile P via mineralization processes and to reduce sorption of P. Using this concept, plant residues applied to soils would increase P availability for future plant needs. This research evaluated the effect of plant residue, incorporated into a Northern Idaho soil, on P availability under controlled laboratory conditions. Alfalfa (Medicago sativa), pea (Pisum sativum) and wheat (Triticum aestivum) plant residues were incorporated into soil collected from the Ap horizon of a Latahco silt loam (fine‐silty, mixed, frigid Argiaquic Xeric Argialboll) at rates of 0, 1, 5 and 10% (w/w). The soils were incubated at soil water potentials of ‐0.05, ‐0.15 and ‐0.40 MPa, and temperatures of 10, 20 and 30°C over a 20 week period. Soils were sampled at 2, 4, 8, 12, 16 and 20 weeks for determination of NaOAc extractable P. Data were analyzed by SAS‐GLM and Omega squared (ω²) values were used to identify the impact of each main effect and interaction. A significant 4‐factor interaction of plant residue x amendment rate x water potential x incubation time, four 3‐factor interactions, six 2‐factor interactions and four main effects were observed at each of the three incubation temperatures. Since all interactions and main effects significantly affected P availability, ω² values were used to assess their relative importance. Amendment rate was the most important factor and plant residue material was the second most important factor observed affecting extractable P levels. In general, NaOAc extractable P increased with increasing amendment rates and incubation time‐period. Increasing incubation temperature and soil water potential also positively affected the extracted P level. The greatest amount of P was mineralized from alfalfa residue material while the smallest amount was released from wheat residue. Pea residue contributed an intermediate quantity of extractable P. This study demonstrated that residues applied to northern Idaho soils have the ability to enhance P availability in addition to providing a usable N source.     

Effect of incubation and microbial inhibition at field moisture capacity on changes in DTPA‐extractable Fe,Zn, and Cu in soils of varying pH

Abstract

To determine the effect of incubation on DTPA‐extractable Fe, Zn, and Cu in soils with a wide pH range (4.2 ‐ 9.4) and to determine the nature of this effect, soils were incubated at field moisture capacity for 1 week with and without a sterilant (toluene). After incubation these soils as well as their air‐dry counterparts were analyzed for DTPA‐extractable Fe, Zn, and Cu.

Incubated soils were significantly lower in DTPA‐extractable Fe, Zn, and Cu than air‐dry soils over all soil pH values tested but there was no significant difference in mean values for incubated soils due to the addition of toluene. The results suggest that, upon incubation at field moisture capacity, the decrease in DTPA‐extractable Fe, Zn, and Cu observed was noa‐microbial in nature.     

Effects of different lime application rates and time on some chemical properties of an acid soil in Ghana

Abstract. Finely ground calcium carbonate was applied at six rates (0–7.0 t/ha) to samples from four depths of an acid tropical soil (Oxisol). The mixtures were kept moist and maintained at 18 °C for a period of 30 days. There was a significant increase (> 28%) in soil pH at all the sampling depths. Extractable P also increased significantly (> 90%). Significant positive correlations between pH, extractable P and liming rate were obtained ( r > 0.9, P = 0.01). The effect of time was significant only on the 10th day after liming, when soil pH had stabilized. Exchangeable Al was completely eliminated on the 5th day after liming, when most of the soil samples had pH values > 5.0. The results clearly indicate that liming, as a management practice, could be used to alleviate or prevent acidification of Oxisols like the soil studied.