Manganese‐iron relationship in soybean grown in calcareous soils 1

Although a positive response to iron (Fe) is, usually, expected in calcareous soils; this has not been always the case; and in some instances a depressing effect has been observed. An induced micronutrient imbalance is suspected. This experiment was designed to study the effect of Fe fertilizer on the plant micronutrients. Twenty three highly calcareous soils (18–46% calcium carbonate equivalent; pH 7.7–8.4; and a wide range of extractable Fe) from southern Iran were used in an eight‐week greenhouse experiment to study the effect of Fe fertilizers on soybean [Glycine max (L.) Merr.] growth and chemical composition. The statistical design was a 23 × 3 factorial arranged in a completely randomized block with three replications. Treatments consisted of 23 soils and three levels of applied Fe (0, 10, and 20 mg Fe/kg as FeEDDHA). Uniform doses of nitrogen (N), phosphorus (P), copper (Cu), manganese (Mn), and zinc (Zn) were applied to all pots. Dry matter (DM) and micronutrients concentrations and uptakes of plant tops were determined and used as the plant responses. Application of Fe either had no significant effect on DM or even decreased it. The plant concentration and uptake of Fe increased significantly in all soils. The concentrations and uptakes of Cu and Zn did not change but those of Mn decreased significantly. The negative effect of Fe application was, therefore, attributed to the interference of Fe with Mn nutrition. The mechanism involved appears to be the restriction in Mn translocation from soil to root and/or from root to the plant tops.     

Iron‐stress response of inoculated and non‐inoculated roots of an iron inefficient soybean cultivar in a split‐root system

The objective of this study was to establish whether the iron‐stress responses observed in T203 soybean (Fe‐inefficient) with active nodules are products of the nodules or of the entire root system. A split‐root system was used in which half the roots of each plant were inoculated and actively fixing nitrogen and the other half were not. Soybean cultivar T203 is normally Fe‐inefficient and does not exhibit the Fe‐stress responses, however an iron‐stress response did occur during active N₂ fixation in earlier studies. This implies that the active nodules influenced the plant's ability to respond to Fe‐deficiency stress. In this study, the Fe‐stress response (H⁺ and reductant release) observed in T203 soybean was limited to the inoculated side of the split‐root system. The severe Fe chlorosis which developed in these plants was overcome in a manner similar to Fe‐efficient cultivars undergoing normal Fe‐stress response and the T203 plants completely regreened. Exudation of H⁺ ions was similar in both the presence and absence of Fe, and was generally limited to inoculated roots. Reductant release was nearly nonexistent from the non‐inoculated roots and was greater for the Fe‐stressed (‐Fe) plants than for non‐stressed (+Fe) plants. Thus, the response observed, which alleviated Fe chlorosis, appeared to be associated with N₂ fixation of the active nodules.     

Evaluation of agronomic effectiveness of phosphate rocks for aluminum‐tolerant soybean cultivar

Abstract

The effect of liming on the agronomic effectiveness of three phosphate rocks (PRs) Pesca and Huila from Colombia and Sechura from Peru as compared with TSP was evaluated in a greenhouse experiment for an Al‐tolerant soybean cultivar grown on an acid Ultisol. On both unlimed (pH 4.4) and limed (pH 5.0) soils, the agronomic effectiveness of P sources in terms of increasing seed yield followed the order of TSP > Sechura PR > Huila PR > Pesca PR > check, an order similar to that of solubility of P sources. Liming slightly decreased the effectiveness of Pesca PR, whereas liming had no effect on Huila PR. A significant increase in agronomic effectiveness was observed upon liming for Sechura PR and TSP. Soil‐available P as extracted by the Pi method was closely related to the amount of N fixed by soybean crop that, in turn, was related to the soybean seed yield. Values of relative agronomic effectiveness (RAE) of PRs with respect to TSP were calculated by assuming the check = 0% and TSP = 100%. On unlimed soil, the RAE values of PRs were: Pesca PR = 31%, Huila PR = 42%, Sechura PR = 84%. On the limed soil, the RAE values were: Pesca PR = 8%, Huila PR = 24%, Sechura PR = 66%. It can be concluded that the use of PR with respect to that of TSP for soybean crop is more favorable in the unlimed soil than in the limed soil, provided that the soybean plant is relatively Al‐tolerant.     

Nitric acid‐ and o‐phenanthroline‐extractable iron for diagnosis of iron chlorosis in citrus lemon trees

Abstract

Plant analysis for total iron (Fe) is frequency used for diagnosis of Fe‐deficiency chlorosis. However, chlorotic plants frequency contained similar or higher amount of total Fe than the healthy green plants. The objectives of this study were to (i) determine if Fe chlorosis in citrus lemon can be diagnosed by total or active Fe and can be related to the degree of chlorosis, and (ii) determine the optimum extraction time and ratio of extracting solution to plant sample for extracting the active Fe. Leaf samples of different degrees of Fe chlorosis were sampled from different citrus lemon trees from three different sites. Total Fe was extracted with nitric acid (HNO₃) and active Fe with o‐phenanthroline from lemon leaves. An extraction time of 20 and 45 hours and the ratios of the extractor to the sample of 5:l, 10:1, and 20:1 were investigated. The results indicated that an extraction time of 20 hours is enough for extracting the active Fe from citrus lemon leaves by o‐phenanthroline. The amount extracted by all ratios (5:1, 10:1, and 20:1) were detectable and at the same time similarly and consistency showed the differences in degrees of chlorosis in all plant samples. Total Fe content was always higher in moderately and severely chlorotic leaves compared to the green leaves and was not related to the degree of chlorosis. Therefore, total Fe cannot be used as a criteria to differentiate between the Fe‐deficient and non‐deficient plants. On the other hand, active Fe tended to decrease with the increase in the degree of chlorosis. The ratio of active to total Fe was calculated and was found to be closely correlated with the degree of chlorosis. This clearly illustrates the failure of plant analysis for total Fe and the effectiveness of active Fe and/or the ratio of active to total Fe for diagnosing Fe chlorosis.     

Differential expression of iron deficiency‐induced genes in barley genotypes with differing manganese efficiency

The expression of two barley genes, Ids1 and Ids2, that were induced specifically by iron (Fe) deficiency stress in solution culture, was examined in two barley genotypes differing in manganese (Mn) efficiency. Plants were grown in a calcareous soil supplied with two levels of Mn (15 and 100 mg/kg soil). Ids1 was expressed at equal levels in the roots of both genotypes, and this expression was not affected by Mn supply. These results suggest that the expression of Ids1 probably does not contribute to Mn efficiency. A contrasting result was obtained for Ids2, which was expressed at a higher level in the roots of the Mn‐inefficient genotype than in the Mn‐efficient genotype. However, the expression levels also were not affected by Mn supply. The differential expression of Ids2 may indicate that this gene plays a role both in the Fe deficiency response and in the Mn efficiency mechanism. An interesting observation made on the time course of expression of the two genes. Initially, both genes had low expression in two week old plants and then much higher expression in three week old plants. The timing of this increase probably relates to the exhaustion of the seed Fe reserves. Therefore, our results indicate a need to consider the effect of seed nutrient content in research on the molecular basis for micronutrient acquisition.     

A greenhouse technique for screening Trifolium seedlings for iron‐deficiency chlorosis 1

Susceptible Trifolium plants often exhibit symptoms of iron (Fe)‐deficiency chlorosis when grown on high pH, calcareous soils. A greenhouse method was developed to screen seedlings for Fe‐deficiency chlorosis. ‘Yuchi’ arrowleaf (T. vesiculosum Savi.) and ‘Dixie’ crimson (I. incarnatum L.) clover seedlings were grown in “Super Cell”; Cone‐tainers in six calcareous Texas soils differing in Fe and selected other chemical characteristics. At the fourth trifoliolate leaf stage, chlorosis was induced by saturating the soil for a minimum of 2 weeks. The soils differed in their capacity to induce chlorosis in both clovers. Yuchi was more susceptible than Dixie, showing a higher percentage of chlorosis in five of the six soils. The results indicate that this screening method would be a useful tool for studying Fe‐deficiency chlorosis in Trifolium spp.     

Reduction of structural iron in selected iron‐bearing minerals by soybean root exudates grown in an in vitro geoponic system

Research on the reduction of iron (Fe) by plant‐root exudates has been conducted using hydroponic solutions containing Fe salts or chelates. These solutions, however, fail to reflect the true soil environment because plants derive their majority requirement from the solid Fe(III) sources. An in vitro Geoponic system (IVGS) is developed to study the reduction of Fe‐bearing clay minerals, i.e., Upton and SWa‐1 (smectite), and Si‐containing amorphous Fe oxide by soybean‐root exudates. Surface sterilized soybean seeds, [Glycine max (L.) Men.] cv. Williams (marginally susceptible to Fe chlorosis), were germinated in presterilized glass culture tubes containing semi‐solid agar media (sucrose free) and Fe minerals. These tubes were placed in an incubator programmed for a white‐fluorescent light cycle for 16 h and temperature setting of 25±2°C. After 15 d of plant growth, the system was analyzed for Fe²⁺ and total Fe. The amount of structural Fe reduction was 0.012, 0.095 and 0.182 mmol/g for Upton, SWa‐1, and Si‐containing amorphous Fe oxide samples, respectively. The reduction of structural Fe in the Fe containing minerals was likely caused by phenolic root exudates which oxidized to diquinones.     

Effect of potassium salts on alleviation of lime‐induced chlorosis in soybean 1

Studies were conducted to determine the efficacy of K salts in alleviating lime‐induced chlorosis. Greenhouse studies using a Gibbon silt loam [fine‐silty, mixed (calcareous), mesic Typic Haplaquoll] and a 1: 1 mixture of Gibbon soil and washed sand were conducted with KCl, KNO₃, K₂SO₄, K₂HPO₄, or KHCO₃ applied at rates of 0, 250, and 500 mg K/kg soil. An FeEDDHA treatment was included for comparison. Similar studies were conducted at two field sites known to produce lime‐induced chlorosis. Potassium salts were applied at 0, 20, and 40 g K/m of row. In the greenhouse, plants treated with KCl, KNO₃, and K₂SO₄ on Gibbon soil were less chlorotic than controls or plants treated with K₂HPO₄, or KHCO₃. No K treatment totally alleviated chlorosis except FeEDDHA. Chlorophyll correlated positively with chlorosis rating. No relationship was found between leaf Fe uptake and chlorosis. Plants grown in soil/sand exhibited no chlorosis and had lower Fe uptake than plants grown in Gibbon soil. Thus chlorosis was not due strictly to low soil‐Fe availability or inadequate Fe uptake. Bicarbonate in the soil solutions of both growth media treated with KCl was lower than controls which may explain the reduced chlorosis associated with this treatment.

One field site showed positive effects of K treatments on chlorosis rating, chlorophyll concentration, and seed yield. No treatment was as effective as FeEDDHA in influencing plant growth or yield. Total leaf Fe concentration was unrelated to leaf chlorophyll concentration. Inorganic cation/anion ratios in the plant were from 4.4–8.4 which could cause net H⁺ efflux by the plant and alkalinization of plant tissues. One possibility is that H⁺ efflux solubilizes P in the rhizosphere, which after uptake could immobilize Fe in the plant. Application of KCl, KNO₃, and K₂SO₄ generally lowered HCO₃ content of the upper 15 cm of both soils. High bicarbonate could increase rhizosphere P availability and increase immobilization of Fe in the plant.     

Evaluation of Nutrient Release in Salt‐Saturated Soils

Abstract

The effects of irrigating with saline water on native soil fertility and nutrient relationships are not well understood. In a laboratory experiment, we determined the extent of indigenous nutrient [calcium (Ca), magnesium (Mg), potassium (K), manganese (Mn), and zinc (Zn)] release in salt-saturated soils. Soils were saturated with 0, 75, and 150 mmolc L^?1 sodium chloride (NaCl) solution and incubated for 1, 5, 10, and 15 days. The saturation extracts were analyzed for pH, ECe, and water‐soluble Ca, Mg, K, Mn, and Zn, and the remainder soil samples were analyzed for exchangeable forms of these elements. In a subexperiment, three soil types (masa, red‐yellow, and andosol) were saturated individually either with 100 mmolc L^?1 of NaCl, sodium nitrate (NaNO₃), or sodium sulfate (Na₂SO₄) salt. These salts were also compared for nutrient release. Soils treated with NaCl released higher amounts of water‐soluble than exchangeable nutrients. Except for Zn, the average concentrations of these nutrients in the soil solution increased significantly with time of incubation, but concentrations of the exchangeable forms varied inversely with time of incubation. The masa soil exhibited the highest concentrations of Ca and Mg, whereas K was highest in andosol. The extract from soils treated with NaCl contained greater amounts of soluble cations, whereas soils treated with Na₂SO₄ produced the lowest concentration of these elements irrespective of the type of soil used.     

Response of soybean to foliar‐applied boron and magnesium and soil‐applied boron 1

Annual plants may partition carbon (C) preferentially to reproductive structures slowing root elongation and subsequent nutrient uptake. Although foliar applications of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) supplement uptake by roots, soybean [Glycine max (L.) Merr.] yield increases have not been found in most studies. Experiments were designed to determine if foliar applications of boron (B), magnesium (Mg), or B+Mg would increase soybean yield and if soybean would respond to B applied to the soil several weeks prior to planting. Foliar B or Mg applied separately four times during reproductive growth did not affect soybean yield. However, four foliar applications of B+Mg increased soybean yield 12% at Mt. Vernon and 4% at Columbia over a three‐year period. Two foliar applications of B+Mg during the late reproductive stages increased soybean yield 8% over a two‐year period. The yield increase from foliar B+Mg treatment resulted from an increased number of pods on the main stem (18%) and branches (44%). A 2.8 kg/ha B application to soil eight weeks prior to planting increased soybean yield 11% during the first year and 13% the second year but had no effect on soybean yield by the third year after application. When results from the first two years were combined, 2.8 kg/ha B applied to soil increased the number of pods per branch by 17% and the number of branch pods per plant by 39%. Foliar applications of B+Mg increased soybean yield in four of six site‐years in the three‐year experiments at two locations.     

Behavior of iron‐supplying materials in incubated calcareous soils 1

Two Fe chlorosis‐inducing calcareous soils were incubated for up to 5 months, at room temperature and field capacity, with Fe‐EDDHA, Fe‐DTPA, FeSO₄, an amino acid chelate “Fe‐Metalosate”;, an oxide “Micronized‐Iron”;, and a precipitated Fe‐S compound “Iron‐Sul”;. Other treatments included DTPA chelate alone, elemental S and H₂SO₄ at comparable rates. Both water‐soluble, and DTPA‐extractable Fe fractions were measured periodically from each sample. All water‐soluble sources decreased with time. Soluble Fe was highest after Fe‐EDDHA addition but was not detectable after “Fe‐Metalosate”; and FeSO₄. Acidification to neutralize CaCO₃ significantly increased DTPA‐extractable Fe, which remained high with increasing incubation time. “Micronized‐Iron”; and S had only a slight effect on DTPA‐ extractable Fe. Though Fe‐EDDHA is the most efficient Fe material, pelleted acidified Fe sources, i.e., “Iron‐Sul”;, may be more economical for some crops in the long term.     

Root and rhizosphere responses of iron‐efficient or ‐inefficient apple genotypes to solution pH

Solution culture with four pH levels was employed in this experiment to evaluate root and rhizosphere responses of Malus xiaojinensis [iron (Fe)‐efficient species] and M. baccata (Fe‐inefficient species) in order to pursue some of their physiological mechanism for Fe absorption. The results showed that M. xiaojinensis had a higher fresh weight per seedling than M. baccata at any of the solution pH levels tested and the differences were significant between the two species with increasing of the solution pH levels, particularly at the pH of 7.4 or 8.4. The reducing abilities of root exudates for the two species under test were decreased with increasing of the solution pH from 5.4 to 8.4, in which the reducing abilities for M. xiaojinensis were always more than two times higher than those for M baccata. The significant decrease of the reducing ability was found only at pH of 8.4 for M. xiaojinensis or at both 7.4 and 8.4 for M. baccata, respectively. Malus xiaojinensis had significantly higher respiration rates than M. baccata at the higher solution pH levels. Both rhizosphere pH and rhizosphere redox potential were influenced by the solution pH levels remarkably in distances of 0–4 mm to root surface or in distances of 5–10 mm along the root from the root tip, respectively. Genotypic differences in these two parameters were clearly showed at the solution pH of 7.4, in which rhizosphere pH of M xiaojinensis was clearly lower than that of M. baccata, while the rhizosphere redox potential of the former was much higher than that of the latter.     

Root responses of sterile‐grown onion plants to iron deficiency 1

Onion (Allium sativum) plants grown without iron (Fe) in sterile nutrient solutions readily developed chlorosis symptoms. Iron deficiency in the sterile‐grown plants stimulated the rates of root extracellular reduction of Fe³⁺, copper (Cu²⁺), manganese (Mn⁴⁺), and other artificial electron acceptors. While rapid reduction occurred with the synthetic chelate Fe³⁺HEDTA, no short‐term reduction occurred with the fungal siderophore Fe³⁺ferrioxamine B (FeFOB). In addition to the increased rate of extracellular electron transfer at the root surfaces, the Fe‐deficient plants showed greater rates of Fe uptake and translocation than the onion plants grown with Fe. The rates of uptake and translocation of Fe were sharply higher for the Fe‐deficient plants supplied with FeHEDTA than for similar plants supplied with FeFOB. Inhibition by BPDS of the Fe uptake by the Fe‐deficient onion plants further supported the importance of Fe³⁺ chelate reduction for the uptake of Fe into the roots. Rates of Fe uptake and translocation by Fe‐deficient onion plants supplied with ⁵⁵FeFOB were identical to the rates of uptake of ferrated [14C]‐FOD; a result that gives evidence of the uptake and translocation of the intact ferrated siderophore, presumably by a mechanism not involving prior extracellular Fe³⁺ reduction. Differences in the rates of transport of other micronutrients into the roots of the Fe‐deficient onion plants were evident by the significantly higher Zn and Mn levels in the shoots of the Fe‐deficient onion.     

Response to iron‐deficiency stress of pear and quince genotypes 1

Roots of iron (Fe)‐efficient dicots react to Fe‐deficiency stress by strongly enhancing the ferric (Fe³⁺)‐reductase system and by lowering the rhizo‐sphere pH. In this study, we tested whether such adaptation mechanisms characterize pear and quince genotypes known to have differential tolerance to calcareous and alkaline soils. Two trials were performed using micropagated plants of three quince rootstocks (BA29, CTS212, and MC), three Pyrus communis rootstocks (OHxF51 and two selections obtained at the Bologna University: A28 and B21) and of two pear cultivars (Abbé Fétel and Bartlett, own‐rooted). In the first trial, plants were grown in a nutrient solution with [Fe(+)] and without [Fe(‐)] Fe for 50 days. Their root Fe‐reducing capacity was determined colorimetrically using ferrozine and FeEDTA, and Fe uptake of Fe(+) plants was estimated. In the second trial, the rhizosphere pH of plants grown in an alkaline soil was measured by a micro‐electrode. With the only exception of pears OHxF51 and A28, whose Fe‐reduction rates were similar in Fe(+) and Fe(‐) plants, the Fe‐deficiency stress resulted in a significant decrease in Fe reduction. Among the Fe(‐) plants, the two pear cultivars, OHxF51 and A28, had a higher Fe‐reducing capacity than the quince rootstocks and the cv. Abb6 F. When plants were pre‐treated with Fe, reduction rate was highest in the P. communis rootstocks, intermediate in the own‐rooted cultivars, and lowest in the quinces. Root Fe‐reducing capacity of Fe(+) plants proved to be linearly and positively correlated with Fe uptake and root proton release. Rhizosphere pH was highest in quince MC, intermediate in the other two quinces and in the cv. Abbe F., and lowest in the pear rootstocks and in the cv. Bartlett. Our results indicate that roots of pear and quinces do not increase their ability to reduce the Fe under Fe‐deficiency stress. The genotypical differential tolerance to Fe chlorosis likely reflects differences in the standard reductase system and in the capacity of lowering the pH at the soil/root interface. The determination of the root Fe‐reducing capacity is a promising screening technique for selecting pear root‐stocks efficient in taking up Fe.     

An evaluation of MES (2(N‐Morpholino)ethanesulfonic acid) and amberlite IRC‐50 as pH buffers for nutrient solution studies ∗

All buffering agents used to stabilize pH in hydroponic research have disadvantages. Inorganic buffers are absorbed and may become phytotoxic. Solid carbonate salts temporarily mitigate decreasing pH but provide almost no protection against increasing pH, and they alter nutrient absorption. Exchange resins are more effective, but we find that they remove magnesium and manganese from solution. We have tested 2(N‐Morpholino)ethanesulfonic acid (MES) as a buffering agent at concentrations of 1 and 10 mol m^‐3 (1 and 10 mM) with beans, corn, lettuce, tomatoes, and wheat. MES appears to be biologically inert and does not interact significantly with other solution ions. Relative growth rates among controls and MES treatments were nearly identical for each species during the trial period. The pH was stabilized by 1 mol m^‐3 MES. This buffer warrants further consideration in nutrient research.     

Long‐Term Integrated Nutrient Management for Rice‐Based Cropping Pattern: Effect on Growth,Yield, Nutrient Uptake,Nutrient Balance Sheet,and Soil Fertility

Abstract

A 7‐year‐long field trial was conducted on integrated nutrient management for a dry season rice (Boro)–green manure (GM)–wet season rice (T. Aman) cropping system at the Bangladesh Rice Research Institute Farm, Gazipur during 1993–1999. Five packages of inorganic fertilizers, cow dung (CD), and GM dhaincha (Sesbania aculeata) were evaluated for immediate and residual effect on crop productivity, nutrient uptake, soil‐nutrient balance sheet, and soil‐fertility status. Plant height, active tiller production, and grain and straw yields were significantly increased as a result of the application of inorganic fertilizer and organic manure. Usually, the soil‐test‐based (STB) fertilizer doses for a high‐yield goal produced the highest grain yield of 6.39 t ha^?1 (average of 7 years) in Boro rice. Application of CD at the rate of 5 t ha^?1 (oven‐dry basis) once a year at the time of Boro transplanting supplemented 50% of the fertilizer nutrients other than nitrogen (N) in the subsequent crop of the cropping pattern. A positive effect of GM on the yield of T. Aman rice was observed. Following GM, the application of reduced doses of phosphorus (P), potassium (K), sulfur (S), and zinc (Zn) to the second crop (T. Aman) did not reduce yield, indicating the beneficial residual effect of fertilizer applied to the first crop (Boro rice) of the cropping pattern. The comparable yield of T. Aman was also observed with reduced fertilizer dose in CD‐treated plots. The total P, K, and S uptake (kg/ha/yr) in the unfertilized plot under an irrigated rice system gradually decreased over the years. The partial nutrient balance in the unfertilized plot (T₁) was negative for all the nutrients. In the fertilized plots, there was an apparent positive balance of P, S, and Zn but a negative balance of N and K. This study showed that the addition of organic manure (CD, dhaincha) gave more positive balances. In the T_4c treatment at 0–15 cm, the application of chemical fertilizers along with the organic manures increased soil organic carbon by (C) 0.71%. The highest concentration of total N was observed with T_4c followed by T_4d and T_4b, where CD was applied in Boro season and dhaincha GM was incorporated in T. Aman season. The sixfold increase in soil‐available P in T_4b‐, T_4c‐, T_4a‐treated plots was due to the addition of CD. Dhaincha GM with the combination of chemical fertilizer helps to mobilize soil‐available P by 3 to 6 ppm. The highest amount of soil‐available S was found in T_4c‐ and T_4a‐treated plots. It was 2.5 times higher than that of the initial soil. The application of CD and dhaincha GM along with chemical fertilizers not only increased organic C, total N, available P, and available S but also increased exchangeable K, available Zn, available iron (Fe), and available manganese (Mn) in soil.     

Modified procedures for commercial adaptation of root iron‐reducing capacity as a screening technique

Abstract

Genotypic evaluation is critical to development of soybean [Glycine max (L.) Merr.] cultivars with genetic resistance to Fe‐deficiency chlorosis. Root Fe³⁺ reducing activity is correlated with genotypic resistance to Fe chlorosis measured in field nurseries, and thus may be a reliable method for identifying chlorosis‐resistat genotypes. However, to develop methods useful for large‐scale screening, several modifications of the previously published procedure for measuring root Fe³⁺ reducing activity were investigated. Several hydroponic experiments were conducted to test proposed modifications. It was determined that: (a) different genotypes may be grown together in the same nutrient solution without affecting Fe³⁺ reduction, (b) genotype separation is maximized by growth in CaCO₃ buffered solution (37.5 mg L^?1), (c) a labor‐intensive elongation step can be eliminated, and (d) denotype evaluation can be accomplished without introducing Fe into the hydroponic solutions. These refinements to the procedure should allow its adaptation and use in soybean breeding programs.     

Evaluating iron‐impregnated paper strips for assessing available soil phosphorus

Abstract

Iron (Fe)‐impregnated filter paper strips (Pi) have been proposed as a method for measuring available soil phosphorus (P). A well‐defined Pi method has not yet been developed and Pi strips are often prepared with different filter papers and procedures. A study aimed at arriving at a consistent Pi method is thus needed. Four types of Pi strips, prepared with the two most widely used papers, Whatman No. 50 and 541, following a procedure that incorporates improvements both proposed in the literature and made in our laboratory, were evaluated for P extraction capacity and error. Two of the best strips, which are significantly different in P extraction capacity, along with the Mehlich 1 (0.05M HCl and 0.0125M H₂SO₄) and the Olsen method (0.5M NaHCO₃, pH 8.5) were further evaluated in a greenhouse experiment involving eight soils planted with corn (Zea mays L.). Results indicated that strips prepared with both Whatman No. 50 and 541 were appropriate for P extractions as long as strips were washed with deionized water after treatment with ammonium hydroxide (NH₄OH). At room temperatures the strips probably contain both hydrous Fe hydroxides and oxides in both crystalline and amorphous forms. Pi P was well correlated with Olsen P and P uptake in all soils, indicating that Pi is generally applicable in diverse soils. No obvious advantage was found for the Pi with respect to the Olsen method. Both the Pi and the Olsen method were better extractants with respect to the Mehlich 1, which was ineffective for extracting P in calcareous soils. Extractable P by Mehlich 1, Olsen, and Pi all correlated highly with accumulated plant available P estimated by eight sequential crops in the greenhouse. However, none of the methods could account for all the variation in plant P removal.     

Foliar Symptomology and Tissue Concentrations of Nutrient‐Deficient Vegetative Strawflower Plants

Abstract

Elemental deficiencies of nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, copper, zinc, or boron (N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, or B) were induced in plants of Florabella Pink strawflower [Bracteantha bracteata (Vent.) A. A. Anderberg]. Rooted stem cuttings were planted in 4.87‐L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested for tissue analyses as well as dry weights when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Deficiency symptoms for all treatments were observed within 7 weeks. The most dramatic expression of foliar symptoms occurred with N (chlorotic lower foliage leading to necrotic margins on the mature leaves), Ca (black necrotic spots on the tips of the young leaves), S (uniform chlorosis of young leaves and recently mature leaves), B (thick, leathery, and deformed young leaves), Fe (uniform yellowish‐green chlorosis on the young leaves), and Zn (brownish‐gray necrosis on the tips of the mature leaves). At the initial stage, only Fe‐deficient plants weighed less than the control, whereas K‐, Ca‐, and Mg‐deficient plants had greater dry weights than plants receiving the complete modified Hoagland's solution (control plants). Dry weights of plants treated with solutions not containing N, P, Ca, S, Cu, or Mn were significantly lower when compared with the control plants under an advanced deficiency. Foliar‐tissue concentration data will assist plant‐tissue analysis laboratories in establishing foliar symptom standards for growers.     

Effect of different nitrogen‐forms and iron‐chelates on the development of stinging nettle

The development of stinging nettle (Urtica dioica L.) grown on culture solution containing with either ammonium or nitrate ions, or urea, was investigated under iron deficiency conditions, and with added FeEDTA or FeCto. Both seed‐cultured and vegetatively‐cultured stinging nettle plants produced normally developed green shoots when nitrate and 4 μM FeEDTA or FeCto were supplied. Stinging nettle plants were able to utilize Fe‐citrate, Fe‐ascorbate, and Fe‐malate effectively at the same concentration as well. When K3Fe(CN)6 was supplied, which is impermeable to the plasmalemma, and therefore is used to measure the reductive capacity of the roots, stinging nettle plants became chlorotic because the complex was stable at the pH of the culture solution. Urea did not induce chlorosis but inhibited growth. The plants died when ammonium was supplied as a sole N source. Applying bicarbonate and ammonium together prevented the plants from dying, but the plants became chlorotic. Total exclusion of iron from the culture solution resulted in iron‐deficiency stress reactions as has been described for other dicotyledonous plants (Strategy II).