Molybdenum Requirements of Dry Bean with and without Liming

Molybdenum (Mo) is an essential micronutrient for crop plants, and its deficiency has been reported in many parts of the world. Two greenhouse experiments were conducted with the objective to determine Mo requirements of dry bean (Phaseolus vulgaris L.) grown on a Brazilian Oxisol with and without liming. The Mo treatments were 0, 5, 10, 15, and 20 mg kg^?1. In one experiment dolomitic lime was added at the rate of 2.5 g per kg of soil before the application of Mo treatments and incubated 5 weeks before sowing. In other experiments, Mo treatments were same as the lime-added experiment but no lime was added. Most of the growth, yield, and yield components were significantly increased with the addition of Mo in both the experiment. Growth, yield, and yield components were increased in a quadratic fashion when Mo was applied in the range of 0 to 20 mg kg^?1. Maximum shoot dry weight was obtained with the addition of 17 mg Mo kg^?1 in the experiment with Mo rates without lime and 9.69 mg Mo kg^?1 in the experiment of Mo rates with lime application. Maximum seed yield was obtained with the application of 10.48 mg Mo kg^?1 in the experiment that did not receive lime along with Mo treatments and 10.28 mg Mo kg^?1 in the experiment that received lime along with Mo treatments. Similarly, the maximum number of pods per plant was obtained with the addition of 9.33 mg Mo kg^?1 in the experiment that did not receive lime and 8.83 mg Mo kg^?1 in the experiment that did receive lime. Maximum root length was obtained with the addition of 12.38 Mo kg^?1 in the experiment that did not receive lime and 9.75 mg Mo kg^?1 in the experiment that received lime. Maximum root dry weight was obtained with the addition of 11.67 mg Mo kg^?1 in the experiment that did not receive lime and 9.28 mg Mo in the experiment that received lime. Soil properties determined after harvest of dry bean plants were not influenced significantly with the addition of Mo in the Oxisol under investigation.     

Effect of High‐Molybdenum Compost on Soils and the Growth of Lettuce and Barley

A pot experiment evaluated the growth of lettuce (Lactuca sativa L.) and barley (Hordeum vulgar) and accumulation of molybdenum (Mo) in plants and soils following amendments of Mo compost (1.0 g kg^?1) to a Truro sandy loam. The treatments consisted of 0 (control), 12.5, 25, and 50% Mo compost by volume. The Mo compost did not affect dry‐matter yield (DMY) up to 25% compost, but DMY decreased at the 50% compost treatment. The 50% compost treatments increased the soil pH an average of 0.5 units and increased the nitric acid (HNO₃)–extractable Mo to 150 mg kg^?1 and diethylenetriaminepentaacetic acid (DTPA)–extractable Mo to 100 mg kg^?1 in the growth medium; the same treatment increased tissue Mo concentration to 569 and 478 mg kg^?1 in the lettuce and barley, respectively. Plants grown in the 25% compost produced about 55 mg kg^?1 of total Mo in the growth medium; this resulted in tissue Mo concentration of 348 mg kg^?1 in lettuce and 274 mg kg^?1 in barley without any phytotoxicity. Our results suggested that 55 mg Mo kg^?1 soil would be an appropriate limit for Mo loading of soil developed from compost additions, a value which is presently greater than the Canadian Council for Ministers of the Environment (CCME) Guidelines for the use of type B compost in Canada.     

Effect of pH of ammonium oxalate extracting solutions on prediction of plant available molybdenum in soil

Abstract

Molybdenum (Mo) is an essential element of plants and animals and is of concern from human nutrition and environmental standpoints. Rational applications to soil of Mo in fertilizers, sewage sludges, or other soil amendments requires information of the concentrations of Mo in soils and plants. Two greenhouse experiments were conducted at Lexington, Kentucky, using surface samples of 12 soils (11 soil types) derived from diverse parent materials in Kentucky with soil pH ranging from 5.18 to 7.46. Molybdenum (Na₂MoO₄.2H₂O) was added at rates equivalent to 0, 0.3, and 0.6 mg Mo kg^‐1 soil. Tobacco (Nicotiana tabacum L., cv. Ky14) and soybean [Glycine max. (L.) Merrill cv. McCall] were grown to provide plant Mo data for Mo soil test correlations and comparisons. The primary purpose of these investigations was to determine the effect of pH of NH₄‐oxalate extractant solution on the relationship of soil Mo and Mo uptake by tobacco and soybeans, and to evaluate the automated KI‐H₂O₂ procedure for use in determining Mo in soil extracting solutions. The mean dry weight and Mo concentration of tobacco and soybean were increased by applications of Mo fertilizer to soil in the greenhouse. Dry matter of tobacco was increased 11 to 25% and concentration of Mo from 40 to 82% by each increment of added Mo fertilizer. The results of this study suggest that many soils in Kentucky are not meeting the requirements for Mo sufficiency for tobacco and soybean plants. The average amount of soil Mo extracted by NH₄‐oxalate decreased with increasing pH of extractant. Regression estimates for the relationship of Mo uptake by tobacco or soybean and extractable soil Mo show that the slope and the coefficients of determination increased with pH of NH₄‐oxalate solution from pH 3.3 to 6.0 and then decreased again at pH 6.4. The greatest amounts of variation in Mo uptake by plants (67% and 20%, respectively, for tobacco and soybean) were accounted for by the soil Mo data at pH 6.0. Soil Mo values for the NH₄‐oxalate extractant (pH 6.0) were related to values for anion exchange resin extractant (r² = 0.61**), but not soil pH. However, values for anion exchange resin were more closely related to Mo uptake by tobacco (r² = 0.86**) and soybean (r² = 0.60**) than were values for NH₄‐oxalate (r² = 0.65** and r² = 0.27**, respectively). Results of this study indicate that the automated KI‐H₂O₂ method used previously in analysis for plant Mo can be used to analyze Mo in soil extracts. Other instrumentation such as GFAAS and ICP may be effective in the analysis of extracts obtained by the NH₄‐oxalate (pH 6.0) or by anion exchange resin procedures when the Mo concentration of extracts falls within the detection limits of the instrument.     

Effect of Zinc Humate on Growth of Soybean and Wheat in Zinc‐Deficient Calcareous Soil

Abstract

Humic acids have many benefits for plant growth and development, and these effects may be maximized if these materials are combined with micronutrient applications. In the present study, pot experiments were conducted to evaluate the effects of zinc (Zn) humate and ZnSO₄ on growth of wheat and soybean in a severely Zn‐deficient calcareous soil (DTPA‐Zn: 0.10 mg kg^?1 soil). Plants were grown for 24 (wheat) and 28 days (soybean) with 0 or 5 mg kg^?1 of Zn as either ZnSO₄ or Zn humate. Zinc humate used in the experiments was obtained from Humintech GmbH, Germany, and contained 5% of Zn. When Zn was not supplied, plants rapidly developed visible symptoms of Zn deficiency (e.g., chlorosis and brown patches on young leaves in soybean and necrotic patches on middle‐aged leaves in wheat). Adding Zn humate eliminated Zn‐deficiency symptoms and enhanced dry matter production by 50% in soybean and 120% in wheat. Zinc‐humate and ZnSO₄ were similarly effective in increasing dry matter production in wheat; but Zn humate increased soybean dry matter more than ZnSO₄. When Zn was not supplied, Zn concentrations were 6 mg kg^?1 for wheat and 8 mg kg^?1 for soybean. Application of Zn humate and ZnSO₄ increased shoot Zn concentration of plants to 36 and 34 mg kg^?1 in wheat and to 13 and 18 mg kg^?1 in soybean, respectively. The results indicate that soybean and wheat plants can efficiently utilize Zn chelated to humic acid in calcareous soils, and this utilization is comparable to the utilization of Zn from ZnSO₄. Under Zn‐deficient soil conditions, plant growth and yield can be maximized by the combined positive effects of Zn and humic acids.     

Determination of molybdenum in soil test extracts with potassium iodide plus hydrogen peroxide reaction

Abstract

The potassium iodide and hydrogen peroxide reaction (KI+H₂O₂) is catalyzed by molybdate. Our objective was to use this reaction to determine molybdenum (Mo) in Mehlich 1 (1:10) soil test extracts. A 350‐nm wavelength and 10‐minute reaction time were selected for the determination and absorbance was linear for 0.0 to 0.15 mg L^‐1 Mo. Ten samples of a LEd‐Iturama soil were extracted with Mehlich 1 and Mo determined. These extracts were also mixed and Mo determined on 10 aliquots of the mixture. Molybdenum concentration in the soil had a coefficient of variation (CV) of 23.5%, whereas that for the mixture was 3.95%. The low CV for the mixture indicates good precision for this method. The higher CV for the individual extracts indicates that most of the variation comes from the extraction phase of individual samples. To show the practical utility of the method, Mo maximum adsorption capacities (MoMAC) of 16 soils, primarily Oxisols, from Minas Gerais, Brazil were determined. The MoMAC varied from 0.15 to 2.02 mg g^‐1 and there were good correlations between MoMAC and soil clay content as well as between MoMAC and soil organic carbon content. From our experience, use of the KI+H₂O₂ reaction is a practical method of determining Mo in Mehlich 1 soil test extracts.     

Effect of Enhanced Nickel Levels on Wheat Plant Growth and Physiology under Salt Stress

A pot experiment was conducted to study the response of wheat to concurrent stresses of salinity and nickel (Ni)-toxicity. Soil was spiked with Ni (0, 20 and 40 mg kg^?1) combined with two levels of salinity (control and 10 dS m^?1) using Ni(ii) nitrate hexahydrate (Ni(NO₃)₂.6H₂O) and sodium chloride (NaCl), respectively, in a completely randomized design with four replicates. Plants were harvested at the tailoring stage and the results showed that wheat growth was positively affected by Ni at 20 mg kg^?1, and negatively at 40 mg kg^?1 concentration both in control and at 10 dS m^?1. Ni (20 mg kg^?1) had a nonsignificant positive effect on tissue potassium (K⁺) and a significant negative effect on Na⁺ concentration. Moreover, Ni translocation from root to shoot and accumulation decreased by increasing the levels of Ni in both control and salinity treatments. It can be concluded that Ni at 20 mg kg^?1 increased wheat growth by alleviating salinity stress; however, at 40 mg kg^?1 it aggravated the plant stress and decreased the plant growth.     

Comparison of Various Analysis Methods for Determination of Iron Chlorosis in Apple Trees

Abstract

The objective of this study was to compare iron (Fe) concentrations (mg kg^?1) of the leaves measured by different methods and to determine the most suitable method to be used in evaluation of iron chlorosis in apple trees. For this purpose, green and chlorotic leaves were collected from 76 apple orchards in 1998 and 1999. Iron concentrations (mg kg^?1) of dried leaf samples were measured with 4 different methods, 1 N HCl (Method 1), 0.1 N HCl (Method 2), 0.005 M DTPA (Method 3), and 1.5% o-phenanthroline (Method 4). Total Fe concentrations (mg kg^?1) of dried leaf samples were also analyzed. Total chlorophyll and peroxidase enzyme activity in fresh leaf samples were measured. The total chlorophyll, peroxidase enzyme activity, Fe concentrations (mg kg^?1) determined by Method 1, Method 3, Method 4, and total Fe concentrations (mg kg^?1) of green leaves were higher than those of chlorotic leaves. On the other hand, no significant difference was found between Fe concentrations (mg kg^?1) of green and chlorotic leaves, measured with Method 2. Significant relationship observed amongst chlorophyll concentrations, peroxidase enzyme activity, and Fe concentrations (mg kg^?1) of samples suggests that 1 N HCl method was the most suitable method amongst the methods used in this study for apple trees.     

Digestion of plant tissue for analysis by ICP emission spectroscopy

Abstract

A method of digesting plant tissue samples for multi‐element analysis by inductively‐coupled plasma (ICP) emission spectroscopy was developed which does not require the use of HclO₄. A substitute oxidant, H₂O₂, eliminated the hazards associated with hot, concentrated HClO₄. Optimal conditions for pre‐digestion and digestion were investigated.

The procedure adopted consists of a pre‐digestion in concentrated HNO₃ from room temperature to 60°C in 30 min followed by digestion at 90°C for 90 min with the addition of 30% H₂O₂ Analysis of NBS standard tissue samples by the proposed method gave results in good agreement with analysis following digestion in HNO₃,‐HClO₄ and with certified values, except for Fe.     

In Situ Heavy Metal Accumulation in Lettuce Growing Near a Former Mining Waste Disposal Area: Implications for Agricultural Management

Mining wastes may pose risk nearby urban and agricultural areas. We investigated a lettuce crop land close to a former capped mine tailing in order to determinate the metal uptake by crops. Soil plot sampling design within the crop area and two transects along the tailing were performed. In addition, lettuces (root and leaves) were analyzed after transplant and harvest. The results showed a pH of around 7–8 for all the soil samples. Total metal concentrations were as follows: 190–510 mg kg^?1 Pb, 13–21 mg kg^?1 Cu, and 210–910 mg kg^?1 Zn. Diethylene triamine pentaacetic acid-extractable Pb was around 18% of the total Pb in some samples. Transects along the base and on the plateau of the tailing showed high metal concentrations of Pb (up to 5,800 mg kg^?1) and Zn (up to 4,500 mg kg^?1), indicating that capping layer had been eroded. Lettuce leaves showed Pb concentrations within standard for human health (<0.3 mg kg^?1 in fresh weight). For essential micronutrients such as Cu and Zn, leaves had optimal content (10–28 mg kg^?1 Cu, 60–85 mg kg^?1 Zn). A continued monitoring in metal uptake is needed in crop lands close to mining wastes in order to prevent risks in food safety. Capped tailings must be monitored and rehabilitation works performed from time to time.     

Ameliorative Effects of Potassium Phosphate on Salt‐Stressed Pepper and Cucumber

Abstract

Bell pepper (Capsicum annuum cv. Urfa Isoto) and cucumber (Cucumis sativus cv. Beith Alpha F1) were grown in pots containing field soil to investigate the effects of supplementary potassium phosphate applied to the root zone of salt‐stressed plants. Treatments were (1) control: soil alone (C); (2) salt treatment: C plus 3.5 g NaCl kg^?1 soil (C + S); and (3) supplementary potassium phosphate: C + S plus supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil (C + S + KP). Plants grown in saline treatment produced less dry matter, fruit yield, and chlorophyll than those in the control. Supplementary 136 or 272 mg KH₂PO₄ kg^?1 soil resulted in increases in dry matter, fruit yield, and chlorophyll concentrations compared to salt‐stressed (C + S) treatment. Membrane permeability in leaf cells (as assessed by electrolyte leakage from leaves) was impaired by NaCl application. Supplementary KH₂PO₄ reduced electrolyte leakage especially at the higher rate. Sodium (Na) concentration in plant tissues increased in leaves and roots in the NaCl treatment. Concentrations of potassium (K) and Phosphorus (P) in leaves were lowered in salt treatment and almost fully restored by supplementary KH₂PO₄ at 272 mg kg^?1 soil. These results clearly show that supplementary KH₂PO₄ can partly mitigate the adverse effects of high salinity on both fruit yield and whole plant biomass in pepper and cucumber plants.     

施磷对麦/玉/豆套作体系土壤磷素变化的影响

小麦/玉米/大豆带状套作是四川省丘陵低山区主要旱地作物生产体系,了解该体系磷养分变化对优化磷肥管理和促进可持续生产有重要意义。本研究通过连续3年(2011—2013年)田间定位试验,设置P0、P1、P2、P3和P4共5个磷(P2O5)水平(玉米带分别为0 kg·hm-2、37.5 kg·hm-2、75 kg·hm-2、112.5 kg·hm-2、150 kg·hm-2,小麦-大豆带分别为0 kg·hm-2、45 kg·hm-2、90 kg·hm-2、135 kg·hm-2、180 kg·hm-2),探讨该体系中土壤全磷、速效磷、水溶性磷的变化规律和速效磷的年际变化。结果表明:在麦/玉/豆套作体系中施磷165 kg(P2O5)·hm-2(玉米带75 kg·hm-2,小麦-大豆带90 kg·hm-2),可以满足体系作物对磷的需求,基本达到磷的表观平衡,维持土壤速效磷含量在20 mg·kg-1左右。3年后5个磷水平下体系耕层土壤(0~20 cm)全磷变化量分别为-0.024 g·kg-1·a-1、-0.016 g·kg-1·a-1、0.016 g·kg-1·a-1、0.11 g·kg-1·a-1、0.15 g·kg-1·a-1,速效磷变化量依次为-1.2 mg·kg-1·a-1、-0.9 mg·kg-1·a-1、0.2 mg·kg-1·a-1、2.0 mg·kg-1·a-1和2.7 mg·kg-1·a-1。通过线性平台函数的模拟,该体系中玉米、小麦、大豆产量的土壤速效磷临界值分别为16.5 mg·kg-1、12.6 mg·kg-1和8.8 mg·kg-1。当土壤全磷含量低于0.55 g·kg-1时,土壤全磷每增加0.1 g·kg-1,土壤速效磷增加1.70 mg·kg-1;当土壤全磷大于0.55 g·kg-1,全磷每增加0.1 g·kg-1,土壤速效磷增加6.49 mg·kg-1。当土壤速效磷含量在40 mg·kg-1以下时,速效磷每增加1 mg·kg-1,水溶性磷增加0.017 mg·kg-1。综上,在麦/玉/豆体系磷肥管理中应该维持土壤全磷含量低于0.55 g·kg-1,同时速效磷含量在20 mg·kg-1左右,这样既可以保证作物产量和系统生产力又不会产生较大的环境威胁。     

Impact of Boron Deficiency on Changes in Biochemical Attributes,Yield, and Seed Reserves in Chickpea

To determine the effect of boron (B) deficiency on biomass, reproductive yield, metabolism, and alterations in seed reserves of chickpea (Cicer arietinum L.) cv. ‘13.G‐256,’ plants were grown in refined sand until maturity at deficient (0.033 mg L^?1) and adequate (0.33 mg L^?1) B, supplied as boric acid (H₃BO₃). Boron‐deficient plants exhibited visible deficiency symptoms in addition to reduced number of pods and seeds, resulting in lowered biomass and economic yield. Boron deficiency lowered the concentration of B in leaves and seeds, photosynthetic pigments (leaves), Hill reaction activity, starch (in leaves and seeds), and proteins and protein N (in seeds), whereas phenols, sugars (in leaves and seeds), and nonprotein N (in seeds) were elevated. Specific activity of peroxidase (POX) increased in leaves and pod wall and decreased in seeds, while activity of acid phosphate and ribonuclease were stimulated in leaves, seeds, and pod wall in B‐deficient chickpea.     

Investigation of Aluminum‐Tolerant Species in Acid Soils of South China

Abstract

The low‐hilly regions in South China are mainly covered with Ultisols and Alfisols with a pH of 4.5–6.0. The major factor limiting crop performance is soluble aluminum (Al) in acid soils, resulting in phytotoxicity in susceptible species. An investigation in Jiangxi and Zhejiang provinces in South China showed that many plants including some native plants and cultivated crops (total of 27 species) could grow well in acid soils of these areas. The Al‐accumulating capacity in leaves varied greatly from species to species. Camellia oleifera Abel accumulated more than 13,500 mg kg^?1 Al in old leaves; Camellia sinensis (L.) O. Kuntze, Fagopyrum esculentum Moench, and Dicranopteris pedata (Houtt.) Nakaike accumulated more than 1000 mg kg^?1 Al in leaves; and Oryza sativa L., Eucalyptus globulus Labill., Citrus reticulata Blanco, and Brassica chinensis L. accumulated less than 200 mg kg^?1 Al in leaves. This investigation provides an important basis for further exploring Al accumulation and resistant mechanisms in plants.     

Trace metals in the soils of Water Conservation Area of Florida Everglades: Considerations for ecosystem restoration

Purpose

Inorganic contaminants present a major challenge for the restoration of aquatic ecosystems. The objectives of this study were to determine the extent of trace metal contamination and investigate the influence of different plant communities on trace metal accumulation in the soils of the Florida Everglades.

Materials and methods

Soil samples (n?=?117) were collected from 0 to 10-cm depth using a stainless steel coring device from sites with three dominant plant communities—cattail, sawgrass, and slough—of Water Conservation Area-2A (43,281 ha) of Florida Everglades.

Results and discussion

The mean pH in soils collected from three plant communities was 6.75–6.82, whereas electrical conductivity was slightly greater in the sawgrass (0.69 dS m^?1) than cattail (0.58 dS m^?1) and slough (0.40 dS m^?1). Mean reduction–oxidation potential was greatest in cattail (?113 mV) than sawgrass (?85.3 mV) and slough (?48.3 mV) soils. Among 11 trace metals (As, B, Co, Cr, Cu, Mn, Mo, Na, Ni, Pb, Zn) found in soil samples, Na had the greatest contents and was greater in cattail (2070 mg kg^?1) and sawgrass (1735 mg kg^?1) than slough (1297 mg kg^?1). Four trace metals (B, Cu, Mo, Ni) were significantly greater in cattail than sawgrass and slough. Whereas, Mn was significantly lower in cattail (31 mg kg^?1) than both sawgrass (84 mg kg^?1) and slough (51 mg kg^?1). Cattail also had significantly lower Cr (1.97 mg kg^?1) and Pb (10 mg kg^?1) than sawgrass (Cr 2.5 mg kg^?1; Pb 20.8 mg kg^?1). As (<6.9 mg kg^?1), Co (<1.3 mg kg^?1), and Zn (<17.2 mg kg^?1) were not significantly different among soils collected from three plant community-dominant sites. Contents of Cd and Se were below the method detection limits (Cd 0.01 mg L^?1; Se 0.2 mg L^?1) and are not reported.

Conclusions

None of the trace metals in the soils exceeded the US Environmental Protection Agency sediment toxicity thresholds. Results from this study provided baseline concentrations of trace metals, which can be used to measure the success of restoration efforts in Florida Everglades.

     

Versatile Flow Injection System for Spectrophotometric Determination of Silicon in Agronomic Samples

Abstract

A versatile flow injection system for spectrophotometric determination of silicon (Si) in agronomic samples is proposed. For plant and slag analysis (1.0–10.0 mg L^?1 Si), the method involves monitoring the yellowish molybdosilicic acid at 410 nm. Soil, fertilizer, water, and sugarcane juice analysis (0.5–5.0 mg L^?1 Si) were accomplished by adding a reducing agent, and the molybdenum blue compound that formed was monitored at 735 nm. Flexibility of the method allows determination in a variety of matrices involving a wide range of concentrations. Beer's law is followed up to 20.0 mg L^?1 Si (r<0.9997; n=6) for analysis at 410 nm and up to 10.0 mg L^?1 Si (r<0.9998; n=6) at 735 nm. For the yellow‐color and blue‐color methods, the detection limits were estimated as 0.5 and 0.1 mg L^?1 Si. Measurement frequency for both methods is approximately 75 h^?1 using 48 mg of ammonium heptamolybdate, 80 mg of oxalic acid, and 24 mg of ascorbic acid per determination. Results are precise (r.s.d.>0.1%, n=10) and in agreement with inductively coupled plasma–optical emission spectroscopy (ICP‐OES). Statistical differences between data sets were not confirmed after applying the Student's ttest at the 95% confidence level (t_exp=0.195>t_tab=2.57) related to n=6.     

Comparison of Seven SO4-S Extraction Methods for Analysis by Turbidimetry or ICP Spectrometry

Soil sulfur (S) analyses for fertilizer recommendations in the northern Great Plains often do not reflect crop S requirements. Seven SO₄-S extraction methods with S determination by either turbidometry or inductively coupled plasma emission spectroscopy including Ca(H₂PO₄)₂ and KH₂PO₄ (both containing 500 ug/l P), 0.25 M KCl (40 ºC) and 0.25 M KCl (room temperature), H₂O, DTPA, and Mehlich 3 extractants. Three horizon depths of three soils from a previous field study were used for these comparisons. Average standard deviations for turbidometric determinations were 4.3 times greater than ICP determinations. With turbidometry, S values were H₂O > KH₂PO₄ > Ca(H₂PO₄)₂ > KCl (40 ºC) = KCl, while with ICP, the values were Mehlich 3 > KCl (40 ºC) = KCl > DTPA (diethylenetriaminepentaacetic acid) > KH₂PO₄ > H₂O > Ca(H₂PO₄)₂. Extraction with KCl at room temperature with ICP determination appears to show promise, but further method evaluation is necessary before it can be recommended as a SO₄-S test method.     

Soil Carbon and Nitrogen Fractions of a Grassland in Central Missouri,USA

Quantification of soil carbon (C) and nitrogen (N) fractions in grasslands is vital for estimating C sequestration and climate change studies. We quantified background soil total carbon (TOC) status, recalcitrant carbon (RC), acid hydrolysable labile carbon (AHC), hot- and cold-water extractable carbon (HWC and CWC, respectively) fractions in the grassland in this study. Soil C fractions were as follows: TOC (11,633 to 15,525 mg C kg^?1); RC (11,500 to 15,357 mg C kg^?1); AHC (132 to 168 mg C kg^?1); HWC (57 to 70 mg C kg^?1); and CWC (27 to 33 mg C kg^?1). Labile C fractions contributed at most 1.2% to total C. Concentrations of total N ranged from 1072 to 1230 g N kg^?1. Recalcitrant C contributed higher amounts (>90%) to total C, indicating the incorporation of C into the stable C fraction. Carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes were not significantly correlated with total C.     

Comparison of Two Soil Phosphorus Analytical Methods in Croatia

Abstract

The purpose of this article was to compare soil phosphorus (P) extraction by sodium bicarbonate solution (Olsen P) and by ammonium lactate (AL P) and to create a model for prediction of Olsen P using ordinary soil‐fertility control data. The soils data used in this study included Olsen P, pH_KCl, pH_H2O, organic matter, AL P, and AL K. Soil pH_KCl ranged from 3.5 to 8, organic matter up to 5%, AL K up to 400 mg kg^?1, and AL P up to 200 mg kg^?1. Olsen P and AL P were significantly correlated, and the difference between them was influenced by soil pH. Regression models included all soil data grouped by soil pH range, which significantly decreased the difference between predicted and measured Olsen P. The validation of the model was conducted on new data sets from field fertilization trials. The results show that Olsen P can be related to AL P and used for fertilizer recommendations instead of AL P.     

Validation and Recalibration of a Soil Test for Mineralizable Nitrogen

Abstract

A soil test for mineralizable soil N had been calibrated for winter wheat in the Willamette Valley of western Oregon. Seventy‐eight percent of the variation in spring N uptake by unfertilized wheat was explained by N mineralized from mid‐winter soil samples incubated anaerobically for 7 days at 40°C. Mineralizable N (Nmin) ranged from 10 to 30 mg N kg^?1 and was used to predict N fertilizer needs. Recommended rates of N were correlated (R²=0.87) with maximum economic rates of N fertilizer. Subsequent farmer adoption of no‐till sowing and a high frequency of soil tests>30 mg N kg^?1 prompted reevaluation of the soil test. Four N fertilizer rates [0, 56, G, and G+56 kg N ha^?1] were compared in 12 m×150 m farmer‐managed plots. Grower's N rates (G) ranged from 90 to 180 kg N ha^?1 and were based on N_min and NH₄‐N plus NO₃‐N soil tests. Averaged across ten no‐till and five conventionally tilled sites, grain yield and crop N uptake were maximized at the recommended rate of N. Results demonstrate that N fertilizer needs for winter wheat can be predicted over a wide range of mineralizable soil N (10 to 75 mg N kg^?1) and that the same soil test calibration can be used for conventionally sown and direct‐seeded winter wheat.     

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.