Extractability of available boron and its sequential fractionation in alkaline calcareous soils of India

The evaluation of different extractants for boron (B) estimation and the study of different boron pools is of utmost importance for the effective use of native and soil applied B. For evaluation of different extractants in diverse soils, twenty-one soil samples varying in soil properties were analyzed to estimate chemical pools of B and available B by using extractants (NH₄OAc, AB-DTPA, hot and cold CaCl₂, tartaric acid, HCl, mannitol, and hot water soluble). Available B extracted by the most commonly used method (HWS-B) was significantly and positively correlated with that extracted by other reagents (r = 0.772** to 0.905**) and the maximum value was observed with HCC-B (r = 0.917**) followed by Mann-B (0.905**). The amount of B in readily soluble, specifically adsorbed, oxide bound, organically bound and residual mineral fraction varied from 0.17 to 2.71, 0.14 to 1.77, 0.31 to 5.88, 0.56 to 7.42 and 0.17 to 2.71% of total B in soils, respectively. Thus, HCC and Mann methods can be used as extracting reagent of B in alkaline calcareous soils instead of HWS.     

Methods of assessing boron availability to kiwifruit plants growing on high boron soils

Abstract

Five soil boron (B) extraction methods were evaluated for their ability to predict available B to kiwifruit plants in soils with high B concentration. The methods were hot water soluble (Hws‐B), 0.05M mannitol in 0.01M calcium chloride (CaCl₂ extractable (Man‐B), 0.05M hydrochloride acid (HCl) soluble (HC1‐B), resin extractable (Resin‐B), and saturation extract (Sat‐B). The amounts of B recovered by the first four methods investigated were strongly correlated with each other, the highest correlation obtained being between Hws‐B and HC1‐B. Plant B was highly correlated to the B recovered by the first four extractants and poorly correlated to the B determined by the saturation method. Soil B concentrations corresponding with B toxicity in kiwifruit are 0.51, 0.80, 0.18, and 2.0 μg‐g^‐1 soil for Hws‐B, Man‐B, HC1‐B, and Res‐B, respectively. The coefficients of determination in some cases were improved when in the regression equations, soil pH and clay content were included.     

Extraction of soil boron for predicting its availability to plants

Abstract

Field and greenhouse studies were conducted in Prince Edward Island (P.E.I.) on soybean (Glycine max (L.) Merr.), red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.), and rutabaga (Brassica napobrassica, Mill). Plant B concentrations were compared to soil B extracted by hot water, 0.05M HCl, 1.5M CH₃COOH, and 0.01M CaCl₂. The r values for extractable soil B versus plant B were: hot water (0.67), 0.05M HCl (0.82), 1.5M CH₃COOH (0.78), and hot 0.01M CaCl₂(0.61). Results of soil B from the 0.05M HCl extracts were generally found to give the best correlation and linear regression among the four extractants tested for predicting the B availability to plants. Overall, the 0.05M HCl proved to be the best extractant and is recommended for predicting the available B status of acid soils. The probability of error with 0.05M HCl is less since it is shaken for a fixed period of time as opposed to subjective error which could be introduced in monitoring the boiling time using hot water. Since HCl is the cheapest among the chemical extractants used it would be most suited for determining soil B in countries with poor economic resources.     

Fractionation and colorimetric determination of boron in soils

We attempted to modify and evaluate existing sequential fractionation schemes for B involving the use of chemicals, which subsequently do not interfere with the measurement of B by colorimetry. Also evaluated was the contribution of various soil B fractions to the amount of B extracted by hot CaCl₂, CaCl₂‐mannitol, salicylic acid, ammonium acetate, HCl, and tartaric acid. For this purpose, 17 soils with diverse properties were used. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl₂, 0.05 M KH₂PO₄, 0.175 M NH4‐oxalate (pH 3.25), 0.5 M NaOH, and HF + H₂SO₄ + HClO₄. The procedure of elimination of color from extracts of oxide bound, organically bound, and residual B fractions was also evolved. Relationships of individual B fractions with physicochemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme. The relationships of different B fractions with extractable B in soils suggest that hot CaCl₂ and salicylic acid may be better extractants for available B in soils.     

Appraisal of Some Soil Tests for Zinc Availability to Late‐Sown Wheat Grown in Mollisols

Abstract

Five soil extractants, namely, 0.005 M diethylene triamine pentaacetic acid (DTPA) (pH 7.3), 0.005 M DTPA+1 M ammonium bicarbonate (pH 7.6), Mehlich 3, 0.01 M ethylene diamine tetraacetic acid (EDTA)+0.05 M ammonium carbonate (pH 8.6), and 1 M magnesium chloride (MgCl₂) (pH 6.0), were evaluated to predict the response of wheat to zinc (Zn) application in Mollisols. These extractants could be arranged in the following decreasing order of their Zn extracting power: Mehlich 3>0.005 M DTPA+1 M ammonium bicarbonate>0.01 M EDTA+0.05 M ammonium carbonate>0.005 M DTPA>1 M MgCl₂. The critical limits of Zn in soil, below which the yield response to late sown wheat (var. UP‐2338) to Zn application could be expected, were 0.57 mg 0.005 M DTPA (pH 7.3) extractable and 1.72 mg Mehlich 3–extractable Zn kg^?1 soil. The critical limit of Zn in whole shoot at 60 days after emergence was found to be 26.1 mg Zn kg^?1 plant tissue. The DTPA and Mehlich 3–extractable soil Zn also correlated significantly and positively with Zn concentration in whole shoot at 60 days after emergence and total Zn uptake by wheat at harvest.     

Evaluation of Extractants and Quantity–Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

Accurate estimation of the available potassium (K⁺) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K⁺, determined by ammonium acetate (NH₄OAc), might not be the best predictor of the soil K⁺ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K⁺ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K⁺. The following methods extracted increasingly higher average amounts of soil K⁺: 0.025 M H₂SO₄ (45 mg K⁺ kg^?1), 1 M NaCl (92 mg K⁺ kg^?1), 0.01 M CaCl₂ (104 mg K⁺ kg^?1), 0.1 M BaCl₂ (126 mg K⁺ kg^?1), and 1 M NH₄OAc (312 mg K⁺ kg^?1). Potassium extracted by 0.01 M CaCl₂, 1 M NaCl, 0.1 M BaCl₂, and 0.025 M H₂SO₄ showed higher correlation with K⁺ uptake by the crop (P < 0.01) than did NH₄OAc (P < 0.05), which is used to extract K⁺ in the soils of the studied area. There were significant correlations among exchangeable K⁺ adsorbed on the planar surfaces of soils (labile K⁺) and K⁺ plant uptake and K⁺ extracted by all extractants. It would appear that both 0.01 M CaCl₂ and 1 M NaCl extractants and labile K⁺ may provide the most useful prediction of K⁺ uptake by plants in these calcareous soils containing micaceous minerals.     

Availability of extractable boron in some acid soils,west Bengal,India

Abstract

A relatively small range between deficiency and toxic limits of boron (B) necessitates precise evaluation of the availability of extractable boron before applying B in deficient soils. Keeping this in view, laboratory and greenhouse experiments were conducted to assess the availability of native B in soils. For this purpose, 25 acid soils with diverse properties and varying hot water extractable B content, were selected from lateritic and alluvial tracts of Southern West Bengal. A greenhouse pot experiment with four rates of B (0, 0.5, 1.0, and 2.0 mg kg^‐1) was conducted in completely randomized design to study the response of soybean (Glycine max L.) to native and applied B in all 25 soils. The suitability of nine extractants for determining available soil B was assessed by correlating the amount of extractable B in untreated soils with Bray's percent yield, uptake, and tissue B concentration of soybean plants. Optimization of salicylic acid concentration is described and the advantages of this extractant are discussed. The interference of amethyst color (produced by iron and salicylic acid) with the colorimetric estimation of B is studied. Hot CaCl₂ was found to be the most suitable extractant for the determination of available B in these soils, followed by hot water, salicylic acid, and ammonium acetate. However, salicylic acid appeared to be the most efficient extractant for routine soil analysis for available B, where a large number of samples are analyzed. The critical values in respect to sufficiency of extractable B for soybean plants were 0.51 for hot water, 0.61 for hot CaCl₂, 0.27 for ammonium acetate and 0.45 mg kg^‐1 for salicylic acid. The critical B concentration in soybean plants was 18 mg kg^‐1 on dry weight basis. Multiple regression equations relating soil properties to native soil B extracted by various extractante were developed. It was observed that organic carbon and clay contributed positively to B extracted by hot water, hot CaCl₂, and ammonium acetate, while salicylic acid extractable B showed positive relationships with cation exchange capacity (CEC) and clay. The CEC and Fe₂O₃ were found to have positive influence on tartaric acid extractable B. Implications of the influences of soil properties on the extractable B content of soils are discussed.     

Effect of lime and organic matter application on the availability of added boron in acidic alluvial soils

Abstract

A laboratory incubation experiment was conducted to study the influence of organic matter and lime application on the recovery of added boron (B) by four different extractants (hot‐CaCl₂, mannitol‐CaCl₂, tartaric acid, and ammonium acetate) in two B‐deficient acid alluvial soils. Soils were brought to four relatively constant pHs and three organic matter levels before application of B. Recovery percentages of 23.9 to 60.9 of added B by the four extractants indicate a soil fixation of B. This is more so in fine‐than in coarse‐textured soils. Both liming (from pH 4.8 to 6.8) below neutrality and organic matter application increased such recovery of added B in all the extractable forms, the effect being more pronounced in fine‐than in coarse‐textured soils. A positive interaction between liming and organic matter particularly at the latter's higher level was observed. Complexation of added B and coating of the surfaces of Fe‐and Al‐oxides by soluble organic compounds are suggested as the possible reasons for such increased recovery of added B in soils.     

Estimation of Plant‐Available Nitrogen in Soils using Rapid Chemical and Biological Methods

The relationships between potential laboratory indices for plant‐available nitrogen (N) and the plant N uptake in a pot experiment with ryegrass were assessed for 13 mineral soils and 2 peat soils. The methods included aerobic soil incubation, soil incubation in a bioreactor, hot potassium chloride (KCl)–extractable mineral N, 0.01 M calcium chloride (CaCl₂)–extractable N, and N loss at heating. The indices for total plant‐available N accounted for 63–93% of the variance in N uptake in a statistical analysis with all soils (n = 15) and 27–89% for the mineral soils (n = 13). Most indices were not a direct quantitative measure of the plant N uptake. The N mineralization indices accounted for 57–86% of the variance in N mineralization for all soils and 5–50% for the mineral soils. Hot KCl‐extractable mineral N and 0.01 M CaCl₂–extractable N were the most promising rapid indices for plant‐available N.     

Combination of Different Extractants to Assess Binding Forms of Some Elements in Soil Profiles

Abstract

Three different chemical extractants were evaluated as to their extraction efficiency for copper (Cu), zinc (Zn), lead (Pb), aluminium (Al), iron (Fe), chromium (Cr), manganese (Mn), potassium (K), magnesium (Mg), and calcium (Ca) on forest soil profiles from the Romanian Carpathians. The extractants were hot 14 M nitric acid (HNO₃), 0.05 M hydrochloric acid (HCl), and 0.1 M sodium pyrophosphate. By comparing amounts extracted by 0.05 M HCl and 0.1 M sodium pyrophosphate relative to that dissolved by hot 14 M HNO₃, some conclusions were drawn concerning the chemical forms of the metals in the extractable pool. The amount released by 0.05 M HCl was generally less than 10% of the HNO₃‐extractable fraction but showed considerable variation among the elements studied. The relative amount extracted by pyrophosphate increased with organic‐matter content of the soils for Cu, Zn, Pb, Al, Fe, and Cr; stayed more or less constant for Mn, K, and Mg; and decreased for Ca. These findings are discussed with respect to the different binding forms of the metals in the soil and the processes affecting their mobility. From the present results, the metals were ranked as follows with respect to their ability to form organic complexes in natural soils: Cu>Cr, Pb>Ca>Al>Fe, Zn, Mn, K>Mg. However, the use of cold dilute HCl as a fractionation step may be questionable in cases of soils with a high content of substances possessing large neutralization capacity for protons.     

Evaluation of Soil Tests for Plant‐available Mercury in a Soil–Crop Rotation System

A reliable soil test is needed for estimating mercury (Hg) availability to crop plants. In this study, four extraction procedures including 0.1 M hydrochloric acid (HCl), 1 M ammonium acetate (NH₄OAc) (pH 7.0), 0.005 M diethylenetriaminepentaacetic acid (DTPA), and 0.1 M calcium chloride (CaCl₂) (pH5.0) were compared for their adequacy in predicting soil Hg availability to crop plants of a rice–cabbage–radish rotation system. The amounts of Hg extracted by each of the four procedures increased with increasing equilibrium time. The optimal time required for extraction of soil Hg was approximately 30 min, though it varied slightly among the four extractants. The amounts of Hg extracted decreased with increasing soil/solution ratio, and a soil/solution ratio of 1:5 appeared to be adequate for soil Hg availability tests. The amounts of Hg extracted increased in the order of NH₄OAc < CaCl₂ < DTPA < HCl in silty loam soil (SLS) soil, and the order was NH₄OAc < CaCl₂ ≈ DTPA < HCl in yellowish red soil (YRS) soil. Significant positive correlations among the four extractants were obtained in SLS soil. In contrast, the correlations were poor in YRS soil, especially for HCl. There were significant correlations between concentrations of Hg in edible tissue of three plants and the amounts of soil Hg extractable to the four extractants for soil–rice system and soil–radish system, but not for soil–Chinese cabbage system. The 0.1M HCl extraction overall provided the best estimation of soil‐available Hg and could be used to predict phytoavailability of Hg in soil–crop systems.     

A procedure for the determination of soluble boron in soils ranging widely in boron concentrations,sodicity, and pH.

Abstract

Soils in southern Australia within the Mediterranean‐type climate zone vary widely in boron concentrations, from potentially deficient to toxic for plant growth. A general method is needed for the determination of boron in soils ranging from acidic to alkaline, with wide ranges of clay content and sodicity.

The amounts of boron extracted were compared following boiling in 0.01M CaCl₂ in test tubes in temperature‐controlled programmable digestion blocks, or in Erienmeyer flasks on hot plates under different analytical conditions. Comparisons were also made between CaCl₂, hot water, and mannitol extractable boron. All analyses of boron were made by inductively coupled plasma spectrometry (ICPS).

The extraction of boron was dependent on extraction time and temperature of the heating block. Addition of 20 ml of 0.01M CaCl₂ to 10g of soil in 250 ml test tubes fitted with air condensers and placed in a pre‐heated temperature‐controlled digestion block set at 140°C and boiled for 30 minutes. This method was found to be a suitable extractant of boron in soils with a wide range of sodicity, pH and extractable boron (from concentrations potentially deficient to toxic for plant growth).     

Evaluation of Chemical Extractants for the Determination of Available Potassium

Abstract

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. This research was carried out to determine the potassium (K) available to corn (Zea mays) in 15 soils from the Hamedan province in the west of Iran. The treatments included two K levels [0 and 200 mg K kg^?1 as potassium sulfate (K₂So₄)] and 15 soils in a factorial experiment in a randomized block design with three replications. The results indicated that K application increased yield, K concentration, and K uptake of corn. According to the mechanism of the extraction, these extractants can be classified into four groups. The first group of extractants, acidic extractants, includes 0.02 M strontium chloride (SrCl₂)+0.05 M citric acid, 0.1 M hydrochloric acid (HCl), and Mehlich 1. The second group includes 0.1 M barium chloride (BaCl₂), 0.01 M calcium chloride (CaCl₂), and 1 M sodium acetate (NaOAc). The third group includes 1 M ammonium acetate (NH₄OAc), ammonium bicarbonate–diethylenetriamine tetraacetic acid (AB‐DTPA), and finally distilled water. The results showed that correlation between extractants in each groups were significantly high. Correlation studies showed that NH₄OAc and AB‐DTPA cannot be used as available K extractants. The correlation of other extractants with relative yield, plant response, and K uptake were significantly high. Therefore, these extracting solutions can be used as available K extractants.

Potassium critical levels by extractants were also determined using the method by Cate and Nelson (1971) Cate, R. B. and Nelson, L. A. 1971. A simple statistical procedure for partitioning soil test correlation into two classes. Soil Science Society of America Proceeding, 35: 658–660. [Crossref], [Web of Science ®] , [Google Scholar]. Potassium critical levels for 90% relative yield were 29, 27, 82, 84, 45, 145, and 272 mg kg^?1 for 0.002 M SrCl₂, distilled water, 0.02 M SrCl₂+0.05 M citric acid, 0.1 M HCl, Mehlich 1, 1 M NaOAC, and 0.1 M BaCl₂, respectively.     

Evaluation of Universal Extractants for Determination of Some Macronutrients from Soil

Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. The objective of this work was to find out the most suitable universal extractant for determination of available phosphorus (P) and nitrate (NO₃-) and exchangeable potassium (K), calcium (Ca), and magnesium (Mg) from soils using 0.01 M calcium chloride (CaCl₂), 0.01 M barium chloride (BaCl₂), 0.1 M BaCl₂, 0.02 M strontium chloride (SrCl₂), Mehlich 3, and ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) extractants. Composite surface soil samples (0–20 cm) were collected from the Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa, and Humbo Districts), and Dire Dawa Administrative Council by purposive sampling. The experiment was carried out in a completely randomized design (CRD) with three replications. Results indicated that the greatest correlations were found between Mehlich 3 and Olsen method and also between 0.02 M SrCl₂ and Olsen method for available P. The amount of NO₃^– extracted by 0.02 M SrCl₂ was significantly correlated to the amount determined by 0.5 M potassium sulfate (K₂SO₄). The amounts of exchangeable K, Ca, and Mg determined by ammonium acetate (NH₄OAc) method were significantly correlated to the amount determined by universal extractants tested. In general, both 0.02 M SrCl₂ and Mehlich 3 can serve as universal extractants for the macronutrients considered in this study with the former being more economical when NO₃^– is included.     

Extractable Concentrations of Cobalt from Serpentine Soils with Several Single‐Extraction Procedures

In this study, we selected three soil pedons on the shoulder, backslope, and footslope along a serpentine toposequence to measure cobalt (Co) extractability using six single‐extraction procedures. These extraction procedures are distilled water, 0.11 M acetic acid in the first step of the BCR sequential extraction (BCR1), 1 M ammonium acetate (NH₄OAc; pH 7.0), 0.01 M calcium chloride (CaCl₂), diethylenetriamine pentaacetic acid (DTPA), and 0.1 M hydrochloric acid (HCl). Although the Co concentrations in the water extracts of the study soils ranged from 0.15 to 0.93 mg kg^?1, those with HCl extraction can be up to 22.1 mg kg^?1. The extractable Co concentrations in the study soils demonstrate that the extraction capacity is in the order HCl > DTPA > CaCl₂ ? NH₄OAc > BCR1 > H₂O. The percentages of extractable Co after applying the six single‐extraction procedures reveal that Co mobility is greatest in the soils on the backslope, moderate on the footslope, and least mobile on the shoulder.     

Plant availability of boron in acid soils as assessed by different extractants

Estimation of available‐boron (B) status through conventional methods in B‐deficient acidic Inceptisols and Entisols is often hampered because of their very low B content. In the present study, the extractability of available B by different extractants was tested in relation to soil properties. Plant availability of B was assessed with mustard (Brassica campestris L.) and wheat (Triticum aestivum L.) in pot experiments. Twelve soils with varying characteristics were extracted for available B with hot water (HW), hot CaCl₂ (HCC), KH₂PO₄ (PDP), tartaric acid (TA), and mannitol‐CaCl₂ (MCC). Mustard (cv. B‐9) and wheat (cv. PBW‐343) were grown with four levels of B (0, 0.25, 0.50, and 1.0 mg [kg soil]^–1). Dry‐matter accumulation and B concentrations were determined at pre‐flowering and full‐maturity stages for mustard and at panicle‐initiation and maturity stages for wheat. The extraction of B from the soils ranked HCC > HW > PDP > TA > MCC. The higher extractability with HW and HCC was likely due to higher temperature and that of PDP because of its phosphorus content, which facilitated the desorption of B. The low B extraction with MCC resulted from the poor mannitol‐B complex formation in acidic soils. The application of B increased dry‐matter accumulation, plant B concentration, and uptake at all B levels and growth stages in both crops with the responses being more pronounced during the early developmental stage. Based on linear correlations, Mallow's Cp statistics, and principal‐component analyses, HCC and HW were the best extractants for estimating available B in the acidic experimental soils.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Comparison of a hot water and cold 0.01 M Cacl2 extraction procedures for the determination of boron in soil

Abstract

In 100 different soils, hot (100C) water extractable boron was determined and the results were compared with boron data after extraction of the same soil samples with cold (20C) 0.01 M CaCl₂. Since the boron concentrations in cold soil extracts are too low for direct determination, the extracted boron was converted into BF4‐ and subsequently extracted with a liquid anion exchanger, Aliquat 336, into xylene, and measured by ICP‐AES. A linear relation with R² = 0.74 was found between the two tested procedures. It is, therefore, concluded that with a cold 0.01 M CaCl₂ extraction equally valuable soil boron values can be obtained as with the more difficult to standardize hot water extraction procedure.     

Comparison of mehlich 3, mehlich 1, ammonium bicarbonate‐DTPA, 1.0M ammonium acetate,and 0.2M ammonium chloride for extraction of calcium,magnesium, phosphorus,and potassium for a wide range of soils

Abstract

Extractants employed for routine soil analysis vary from one laboratory to another. Lack of a universal soil extractant is a serious limitation for interpretation of analytical results from various laboratories on nutritional status of a given soil. This limitation can be overcome by developing functional relationships for concentrations of a given nutrient extractable by various extradants. In this study, extractability of Ca, Mg, P, and K in a wide range of soils (0–15 cm) from citrus groves in Florida representing 21 soil series, with varying cultural operations, were compared using Mehlich 3 (M3), Mehlich 1 (M1), ammonium acetate (NH₄AOc), pH = 7.0 (AA), 0.2M ammonium chloride (NH₄Cl), and ammonium bicarbonate‐DTPA (AB‐DTPA) extractants. Soil pH (0.01M CaCl₂) varied from 3.57 to 7.28. The concentrations of Ca or Mg extractable by M3, M1, AA, and NH₄Cl were strongly correlated with soil pH (r² = 0.381–0.482). Weak but significant correlations were also found between AB‐DTPA extractable Ca or Mg and soil pH (r² = 0.235–0.278). Soil pH relationships with extractable K were rather weak (r² = < 0.131) for M1 and NH₄Cl but non‐significant for M3, AB‐DTPA, and AA. Concentrations of Ca, Mg, and K extractable by M3 were significantly correlated with those by either M1, AA, or NH₄Cl extractants. Mehlich 3‐P was significantly correlated with P extractable by M1 extractant only. Mehlich 3 versus AB‐DTPA relationship was strong for K (r² = 0.964), weaker for Mg and P (r² = 0.180–0.319), and non‐significant for Ca. With the increasing emphasis on possible use of M3 as an universal soil extractant, data from this study support the hypothesis that M3 can be adapted as a suitable extractant for routine soil analysis.     

Diagnosing boron deficiency in rapeseed and mustard by plant analysis and soil testing

Abstract

Boron (B) deficiency is a widespread nutritional disorder in crop plants, including rapeseed and mustard. However, plant analysis and soil testing diagnostic criteria for B are inadequately reported in the literature. Therefore, greenhouse and incubation studies were carried out using a B‐deficient alkaline calcareous soil (hot water extractable B, 0.11 mg/kg) of Pakistan to determine the internal and soil test B requirement of rapeseed and mustard. Boron fertilization substantially enhanced the growth of both species; the maximum increase in grain yield was 43% for rapeseed and 36% for mustard over the yield of respective control plants. Fertilizer requirement for near‐maximum (95%) grain yield was 0.7 mg B/kg for rapeseed and 0.9 mg B/kg for mustard. Critical plant tissue B concentration in rapeseed was 32 mg/kg in whole shoots and 38 mg/kg in most recently matured leaves. However, internal B requirement of mustard was relatively greater: i.e. 41 mg/kg in whole shoots and 49 mg/kg in leaves. The three soil tests studied, hot water, hydrochloric acid (HCl), and mannitol, were almost equally effective in determining soil B status. Because of simplicity and low cost, however, the HCl method appears superior than the other two for routine B analysis. Critical soil B levels (mg/kg) for rapeseed were: hot water, 0.5; HCl, 0.45; and mannitol, 0.4. Similar to internal B requirements, soil test critical B levels (mg/kg) were also greater for mustard, i.e. hot water, 0.6; HCl, 0.55; and mannitol, 0.48.