Cadmium Phytoextraction Efficiency of Arum (Colocasia antiquorum), Radish (Raphanus sativus L.) and Water Spinach (Ipomoea aquatica) Grown in Hydroponics

Selection of a phytoextraction plant with high Cd accumulation potential based on compatibility with mechanized cultivation practice and local environmental conditions may provide more benefits than selection based mainly on high Cd tolerance plants. In this hydroponics study, the potential of Cd accumulation by three plant species; arum (Colocasia antiquorum), radish (Raphanus sativus L.) and water spinach (Ipomoea aquatica) were investigated. Arum (Colocasia antiquorum L.) plants were grown for 60 days in a nutrient solution with 0, 10 or 50 μM Cd, while radish and water spinach plants grew only 12 days in 0, 1.5, 2.5, 5 or 10 μM Cd. Growth of radish and water spinach plants decreased under all Cd treatments (1.5 to 10 μM), while arum growth decreased only at 50 μM Cd. At 10 μM Cd treatment, the growth of arum was similar to the control treatment indicating higher tolerance of arum for Cd than radish and water spinach. Cadmium concentrations in different plant parts of all plant species increased significantly with Cd application in the nutrient solution. Arum and water spinach retained greater proportions of Cd in their roots, while in radish, Cd concentration in leaves was higher than in other plant parts. Cadmium concentrations in arum increased from 158 to 1,060 in the dead leaves, 37 to 280 in the normal leaves, 108 to 715 in the stems, 42 to 290 in the bulbs and 1,195 to 3,840 mg kg^?1 in the roots, when the Cd level in the solution was raised from 10 μM Cd to 50 μM Cd. Arum accumulated (dry weight?×?concentration) 25 mg plant^?1 at 10 μM, while the corresponding values for radish and water spinach were 0.23 and 0.44 mg plant^?1, respectively. With no growth retardation at Cd concentrations as high as 166 mg kg^?1 measured in entire plant (including root) of arum at 10 μM Cd in the nutrient solution, arum could be a potential Cd accumulator plant species and could be used for phytoremediation.     

Root and Leaf Ferric Chelate Reductase Activity in Pond Apple and Soursop

Abstract

Root and leaf ferric chelate reductase (FCR) activity in Annona glabra L. (pond apple), native to subtropical wetland habitats and Annona muricata L. (soursop), native to nonwetland tropical habitats, was determined under iron (Fe)-sufficient and Fe-deficient conditions. One-year-old seedlings of each species were grown with 2, 22.5, or 45 µM Fe in a nutrient solution. The degree of tolerance of Fe deficiency was evaluated by determining root and leaf FCR activity, leaf chlorophyll index, Fe concentration in recently mature leaves, and plant growth. Root FCR activity was generally lower in soursop than in pond apple. Eighty days after plants were put in nutrient solutions, leaf FCR activity of each species was lower in plants grown with low Fe concentrations (2 µM) than in plants grown with high (22.5 or 45 µM) Fe concentrations in the nutrient solution. Leaves of pond apple grown without Fe became chlorotic within 6 weeks. The Fe level in the nutrient solution had no effect on fresh and dry weights of soursop. Lack of Fe decreased the leaf chlorophyll index and Fe concentration in recently matured leaves less in soursop than in pond apple. The rapid development of leaf chlorosis in low Fe conditions and low root and leaf FCR activities of pond apple are probably related to its native origin in wetland areas, where there is sufficient soluble Fe for adequate plant growth and development. The higher leaf FCR activity and slower growth rate of soursop compared to pond apple may explain why soursop did not exhibit leaf chlorosis even under low Fe conditions.     

Does the Sulfur Assimilation Pathway Play a Role in the Response to Fe Deficiency in Maize (Zea mays L.) Plants?

Abstract

The finding that the methionine is the sole precursor of the mugineic acid family phytosiderophores induced us to evaluate whether sulfur assimilation pathway has a role in plant response to Fe deficiency. Maize plants were grown for 10 days in nutrient solution (NS) containing 80 µM Fe in the presence (+S) or absence (?S) of sulfate. After removing the root extraplasmatic iron pool, half of the plants of each treatment (+S and ?S) were transferred to a new Fe deficient NS (0.1 µM final Fe concentration) (?Fe). The remaining plants of each pre‐culture condition (+S and ?S) were transferred to a new NS containing 80 µM Fe (+Fe). Leaves were collected 4 and 24 hours from the beginning of Fe deprivation period and used for chemical analysis and enzyme assays. Results showed that iron content in the leaves was lower in plants grown in S‐deficiency than in those grown in the presence of the macro‐nutrient. Iron deprivation produced an increase in the level of SH compounds in both nutritive conditions (+S and ?S). These observations are suggestive of some relationship between S nutrition and Fe uptake. For this reason, we next investigated the influence of Fe availability on S metabolism through the evaluation of changes in ATPs and OASs activity, the first and the last enzyme of S assimilation pathway respectively. Results showed that S‐starvation increased the activity of both enzymes, but this effect disappeared in plants upon Fe deficiency suggesting that S metabolism is sensitive to Fe availability. Taken together these evidences suggest that S metabolism is sensitive to soil Fe‐availability for plant nutrition and support the hypothesis of S involvement in plant response to Fe deprivation.     

The Effect of Cadmium Toxicity and Silicon Supplementation on the Activity of Antioxidative Enzymes and the Concentration of Zinc and Iron in Hydroponically Grown Cucumber

Two cucumber cultivars (Cucumis sativus L.) exposed to three cadmium (Cd) concentrations (0, 1, and 5 μM) were supplemented or un-supplemented with silicon (Si) (1 mM). Exposure to 1 μM Cd had no effect on shoot and root dry mass, whereas exposure to 5 μM Cd significantly reduced plant growth. Addition of Si stimulated the growth of Cd-treated cucumber. Exposure to 5 μM Cd significantly increased shoot Cd concentration and decreased iron (Fe) and zinc (Zn) concentration. Plants supplied with Si had lower Cd and higher Zn and Fe compared with unsupplied plants. Exposure to Cd resulted in a higher production of malondialdehyde (MDA). Si nutrition partly ameliorated lipid peroxidation induced by Cd toxicity. Activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and catalase (CAT) decreased, whereas ascorbate peroxidase (APX) activity increased in response to 5 μM Cd. Induction of APX activity might play an important role in the response of cucumber to Cd toxicity.     

STUDY OF THE INTERACTIONS BETWEEN IODINE AND MINERAL NUTRIENTS IN LETTUCE PLANTS

Iodine is vital to human health, and iodine bio-fortification programs help improve the human intake through plant consumption. Essential processes in plants that can be altered by iodine bio-fortification include the nutritional state of plants. The main objective of this work was to determine whether mineral nutrient concentrations were affected by the application of different forms (iodide [I^?] vs. iodate [IO₃ ^?]) and dosages (0, 20, 40, and 80 μM) of iodine, to ascertain the influence of this trace element in Lactuca sativa var. longifolia plants. The application of 80 μM of I^? significantly reduced the nutrients nitrogen (N), phosphorus (P), and potassium (K) to below the optimal ranges established for this crop. The IO₃ ^? treatments represented optimal maintenance of the nutritional state for most of the nutrients and even an improvement of nutrients as important as magnesium (Mg) and iron (Fe).     

Nutrient uptake and use efficiencies in Medicago ciliaris under salinity

Salt-induced responses of Medicago ciliaris was studied under controlled conditions. Twenty-two-day old seedlings were cultivated for one month in a nutrient medium added or not with 75 mM sodium chloride (NaCl). Our results showed that this species is relatively salt-tolerant since the whole biomass production of salt-treated plants was affected a little (?30%) as compared to the control. The slight salt effect was mainly nutritional and concerned both macro potassium, calcium and magnesium (K, Ca, and Mg) and micro-nutrients iron (Fe). K and Fe uptake efficiencies were more affected than those of Ca and Mg. Nevertheless, M. ciliaris was able to counterbalance this impact by increasing both K and Fe use efficiencies. The enhancement of K use efficiency could be due in part to the plant aptitude to accumulate sodium (Na⁺) ions within its shoot tissues and to use them for osmotic adjustment. This “includer” behavior allowed M. ciliaris to maintain an adequate water status under saline conditions.     

EFFECT OF LONG-TERM SEWAGE SLUDGE APPLICATION ON THE DISTRIBUTION OF NUTRIENTS IN MAIZE (ZEA MAYS L.)

The distribution of the nutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) in maize (Zea mays L.) was studied in a long-term sewage sludge field application in an acid coarse sandy soil at Bordeaux, France. Sewage sludge had been applied since 1974 at 100 t (dry weight) ha^?1 per 2 years (SS 100) in plots cultivated annually with maize. Treatment with farmyard manure (FYM) at 10 t (dry weight) ha^?1 per year and mineral fertilization served as control. Five plants per treatment were investigated at six different growth stages. The plants were separated into their different organs and the distribution of nutrients was determined in up to 12 different plant parts. Sludge application did not significantly influence the nutrient partitioning in maize, but improved slightly the plants' nutrient status compared with the FYM treatment. Grain yield was similar for both treatments. The values for N, P, K, Ca, Mg and Fe content in sludge-treated plants were in the recommended range for optimal growth. Thus, sewage sludge would be a valuable source for maize nutrition even after long-term application, if the critically high copper (Cu) and zinc (Zn) concentrations, previously reported in these sludge-amended plants, could be avoided by the use of sludge low in these elements.     

ROOT FERRIC CHELATE REDUCTASE IS REGULATED BY IRON AND COPPER IN STRAWBERRY PLANTS

In the present experiment, we studied the interaction between copper (Cu) and iron (Fe) in strawberry plants grown in nutrient solutions containing different concentrations of Fe. Plants grown in the absence of iron (Fe0) had the characteristic symptoms of Fe deficiency, with smaller chlorotic leaves, less biomass, acidification of the nutrient solution, and roots that were smaller and less ramified, while no symptoms of Fe deficiency were observed in plants grown with Fe. A greater amount of Cu was found in roots of chlorotic plants than in those grown with Fe, while plants grown with 20 μM of Fe (Fe20) in the nutrient solution had a greater amount of Fe compared with plants from the other treatments. Chlorotic plants (Fe0) and plants grown with the greatest level of Fe (Fe20) had a greater root ferric chelate reductase (FC-R; EC 1.16.1.17) activity compared with the other treatments with 5 or 10 μM Fe in the nutrient solution. The same pattern was obtained for relative FC-R mRNA concentration and for the sum of Fe and Cu contents in shoots (leaves plus crowns). The DNA obtained from amplification of the FC-R mRNA was cloned and several of the inserts analysed by single strand confirmation polymorphism (SSCP). Although there were different SSCP patterns in the Fe20 treatment, all the inserts that were sequenced were very similar, excluding the hypothesis of more than one FC-R mRNA species being present. The results suggest that Cu as well as Fe is involved in FC-R expression and activity, although the mechanism involved in this regulation is unknown so far. Both small contents of Fe and Cu in plants led to an over-expression of the FC-R gene and enhanced FC-R activity in strawberry roots.     

Enhancement of maize plant growth with inoculation of phosphate-solubilizing bacteria and biochar amendment in soil

Maize plant has an absolute requirement of nutrients (N, P, and K) for growth and development. The microbial application can facilitate in addressing limited access to chemical fertilizer concern. Moreover, biochar and phosphorus-solubilizing bacterial (PSB) community can contribute together in nutrient availability. Both have the P-supply potential to the soil, but their interaction has been tested less under semiarid climatic conditions. The purpose of the study was to evaluate the potential of biochemically tested promising PSB strains and biochar for maize plant growth and nutritional status in plant and soil. Therefore, two isolated PSB strains from maize rhizosphere were biochemically tested in vitro and identified by 16S rDNA gene analysis. The experiment was conducted in the greenhouse where the plant growth and nutrient availability to the plants were observed. In this regard, all the treatments such as PSB strain-inoculated plants, biochar-treated plants, and a combination of PSBs + biochar-treated plants were destructively sampled on day 45 (D₄₅) and day 65 (D₆₅) of sowing with four replications at each time. PSB inoculation, biochar incorporation, and their combinations have positive effects on maize plant height and nutrient concentration on D₄₅ and D₆₅. In particular, plants treated with sawdust biochar + Lysinibacillus fusiformis strain 31MZR inoculation increased N (32.8%), P (72.5%), and K (42.1%) against control on D₆₅. Besides that, only L. fusiformis strain 31MZR inoculation enhanced N (23.1%) and P (61.5%) than control which shows the significant interaction of PSB and biochar in nutrient uptake. PSB and biochar have the potential to be used as a promising amendment in improving plant growth and nutrient absorption besides the conventional approaches.     

The Influence of Cadmium Toxicity on Some Physiological Parameters as Affected by Iron in Rice (Oryza Sativa L.) Plant

The effects of interaction between cadmium chloride (CdCl₂) and iron (Fe)- ethylenediaminetetraacetic acid (EDTA) were studied in rice plant. The seedlings of rice were treated with 0, 50, and 100 μM CdCl₂ supplemented with 5, 10 and 20 ppm Fe as Fe-EDTA for 30 days. Plants were grown under controlled condition. In all the plants treated with CdCl_2, growth parameters [relative leaf growth rate (RLGR), specific leaf area (SLA), and leaf water content area (LWCA)], soluble, and unsoluble sugars contents decreased. Addition of Fe-EDTA moderated cadmium effects. Under CdCl₂ stress without Fe, malondialdehyde (MDA) content, proline content, catalase (CAT) and peroxidase (POD) activity increased, however, in solutions containing both CdCl₂ and Fe-EDTA, MDA content, proline content and activities of antioxidant enzymes decreased. In 50 μM CdCl₂, total protein content increased but in 100 μM decreased. With increasing Fe in solutions containing CdCl₂, protein content decreased. The results indicated that with increasing Fe-EDTA in CdCl₂ treated plants, the effects of toxicity of Cd decreased.     

Oxidative stress response in spinach plants induced by cadmium

In this work we studied the effect of cadmium (Cd) (25 μM), in spinach plants (Spinacea oleracea) growing in nutrient solution, for 1, 2 and 7 days. Spinach growing in the contaminated solution showed a decrease in biomass, chlorophyll content and an increase in malondialdehyde (MDA) content, showing that photosynthetic apparatus was affected and lipid peroxidation occurred. The main defence mechanisms against the induced oxidative stress were the activation of catalase, glutathione reductase and guaiacol peroxidase. Glutathione reductase activity suggests that glutathione is involved in the response against Cd toxicity. The uptake of zinc (Zn), potassium (K), iron (Fe) and copper (Cu) was affected, mainly at the higher exposition times. Spinach leaves showed no signs of toxicity and looked healthy although containing up to 35 mg kg^?1 dry weight (DW) of Cd. This can present a food security issue as there is no visible indication of the high amounts of Cd in the edible parts of the plant.     

Changes in nutritional homeostasis of Poncirus trifoliata and Ceratonia siliqua as a response to different iron levels in nutrient solution

Abstract

Iron (Fe) deficiency is a nutritional disorder in plants. Poncirus trifoliata is susceptible to Fe deficiency, but symptoms of Fe deficiency are rare in Ceratonia siliqua, a slow-growing species. Specimens of the two species were grown in nutrient solutions containing three Fe concentrations: without Fe (0?µM), 1?µM Fe, and either 10?µM Fe (for Ceratonia) or 40?µM Fe (for P. trifoliata). Growth, the degree of chlorosis, the plant mineral composition, and the activity of the root ferric chelate-reductase (FCR) were assessed. Ceratonia plants exposed to 1?µM Fe were efficient at using Fe in the synthesis of chlorophyll. The activity of FCR was enhanced in the total absence of Fe. In Poncirus a low activity of the FCR was observed in plants with no Fe. The balance between micronutrients in the Ceratonia roots was not affected with 1?µM Fe compared with the higher Fe concentration treatments.     

Effects of different organic materials on forage yield and nutrient uptake of silage maize (Zea mays L.)

The use of organic materials as a source of nutrients on agricultural lands ameliorates soil physical properties as well as being an environmentally friendly way of disposing of their wastes. This study was conducted to determine effects of three organic materials (poultry litter, cattle manure, leonardite) on yield and nutrient uptake of silage maize. Poultry litter and cattle manure were applied based on phosphorus (P) or nitrogen (N) requirements of the crop whereas leonardite was applied only one dose (500 kg ha^?1) and also combined with three inorganic fertilizer doses (100%, 75%, 50% of recommended inorganic fertilizer dose). According to the results, the highest green herbage yield and nutrient uptake values were observed in LEO-100 whereas N-based treatments significantly decreased yield and nutrient uptake of silage maize. The use of organic materials as a combination with inorganic fertilizer in silage maize cultivation is highly beneficial for sustainable forage production.     

Effects of exogenously applied salicylic acid on the induction of multiple stress tolerance and mineral nutrition in maize (Zea mays L.)

Abstract

It has been proposed that salicylic acid (SA) acts as an endogenous signal molecule responsible for inducing environmental stress tolerance in plants. In this study, the effects of seed soaked (1.0 mM for 24 h) and soil incorporated (0.1 mM and 0.5 mM) salicylic acid (SA) supply on growth and mineral concentrations of maize (Zea mays L., Hamidiye F₁) grown under either salt, boron toxicity or drought-stressed conditions were investigated. Exogenously applied SA either with seed soaked (SS) or soil incorporated (SI) increased plant growth significantly in all the stresses conditions. Salicylic acid inhibited Na and Cl accumulation in saline conditions, and 0.5 mM of soil incorporated SA decreased B significantly in boron toxicity treatment. Except in drought condition, SA treatments stimulated N accumulation in plants. And P, K, Mg and Mn concentrations of SA received plants were increased in the stress conditions. These results suggest that SA regulates the response of plants to the environmental stresses and could be used as a plant growth regulator to improve plant growth and stimulate mineral nutrient concentrations under stress conditions.     

Nitrogen,Potassium, and Nitrate Concentrations of Lettuce Grown in a Substrate with KNO3-Enriched Zeolite

Zeolite minerals improve the efficiency of nutrient use by plants by helping to regulate the release of nitrogen and nitrate accumulation in tissues. The main objectives of this research were to evaluate effects of the addition of zeolite enriched with potassium nitrate (KNO₃) on the nitrate (NO₃-N) and potassium (K) levels of lettuce shoot. Treatments arranged in a completely randomized block design with three replications comprised two types of the natural zeolite: concentrated zeolite, zeolite + KNO₃, and a control grown in substrate fertilized with a nutrient solution without zeolite supply. Four levels of enriched zeolite were tested (20, 40, 80, and 160 g per pot). Nitrogen, K, and NO₃-N data were evaluated and response equations were fitted. The results indicated that zeolite enriched with KNO₃ released the macronutrients N and K to lettuce plants. The concentrations of total N, total K, and NO₃-N increased with zeolite levels, and there was a positive correlation between total N and NO₃-N forms. To keep levels of NO₃-N^? in shoots within the safe limit for human consumption, based upon the regression equation for NO₃-N the recommended dose of KNO₃-enriched zeolite should be up to 78 g per plant.     

Sodium Chloride Effects on Water and Nutrient Uptake Efficiency in Sarcocornia fruticosa Containerized Production

The ability to produce native plants well adapted to the saline conditions without the production of nutrient-rich runoff will be a boon to nurseries hoping to reduce their environmental contamination impact and water use while at the same time producing quality plants to be used in the restoration of saline lands. Sarcocornia fruticosa plants were grown for 8 weeks in plastic containers with a source of sphagnum peat moss and perlite (80:20 v/v) to evaluate the effect of two salinity levels (2.0 (low-salinity treatment) and 7.5 dS m^?1 (high-salinity treatment)) on plant growth, nutrient concentration in leachate and water and nutrient uptake efficiency and their losses. Leachate was collected to determine the runoff volume and composition, which included nitrate-nitrogen (NO₃^–N), phosphate-phosphorus (PO₄^3–P) and potassium (K⁺) concentrations. Plant dry weight (DW) and nutrient content were determined in plants at the beginning and at the end of the experiment to establish the nutrient balance. Increasing salinity levels of irrigation water did not reduce either the plant DW or the water-use efficiency (WUE), but increased the volume of leachate per plant. The nutrient concentrations in leachates without significant differences between salt treatments exceeded the thresholds established by environmental guidelines, leading to a great risk of pollution. Based on nutrient balance, the irrigation with a higher salinity level reduced the plant nutrient uptake efficiency (10%, 18% and 12% for nitrogen (N), phosphorus (P) and potassium (K), respectively) and increased the nutrient losses (6% N, 7% P and 8% K), resulting in the recommendation to grow this species with the low salinity level based on the highest nutrient-use efficiency and the lowest levels of nutrient losses.     

Plant density and nitrogen effects on growth dynamics,light interception and yield of maize

Maize (Zea mays L.) growth and yield are most sensitive to variations in plant density and nitrogen (N) in north-western Pakistan. This study was conducted on the Agricultural Research Farm of NWFP (North West Frontier Province) Agricultural University, Peshawar, from 2002–2004 to establish an accurate plant density and N management system aimed at high yield of maize. The 2 × 3 × 6 factorial experiment was designed having two plant densities (P1 = 60,000 and P2 = 100,000 plants ha^?1) and three nitrogen rates (N1 = 60, N2 = 120 and N3 = 180 kg N ha^?1) applied to the main plots, while six split application for N in different proportions were applied to subplots at different growth stages of maize in two equal (S1), three equal (S2), three unequal (S3), four equal (S4), five equal (S5) and five unequal splits (S6) at sowing and with 1st, 2nd, 3rd and 4th irrigation at two-week intervals. Growth rate and yield increased with elevated dose and number of N split applications. Improved endurance to high stands allowed maize to intercept and use solar radiation more efficiently, contributing to the remarkable increase in the crop growth rate and yield.     

Nitrogen fertilization does not affect micronutrient uptake in grain maize (Zea mays L.)

Abstract

Due to continuous single nitrogen fertilization, we hypothesized a built-up deficiency of micronutrients in crops that would limit plant growth and crop quality. In 2-year field experiments using urea-N fertilized grain maize (Zea mays L.), hybrid KWS 2376 at 0, 120 and 240 kg N ha^?1 crop uptake of Zn, Mn, Cu and Fe was studied at DC 32, DC 61 and in the grain harvested. Micronutrient contents at DC 32 stage – 1st node (aboveground phytomass) and DC 61 – flowering (ear leaf) were all at levels indicative of adequate micronutrient supply to the crop. At both sampling occasions the Fe:Zn and Fe:Mn ratios were adequate implying that Fe did not inhibit the uptake of Zn and Mn. The application of nitrogen increased the Fe content at the 1st sampling in both years; in the second year the same was also the case for the Zn content. Nitrogen nutrition increased the contents of Mn and Fe at the 2nd sampling only in year 2; in the other treatments no changes were observed in the micronutrient contents. Micronutrient correlations in the grain were discovered between Zn and Mn contents and between Fe and Mn contents. In the second year the highest N-rate significantly increased the Fe and Zn content of the grain compared with the lower rates of nitrogen fertilization. Grain yields were not affected by the rate of nitrogen and ranged between 13.65 and 14.34 t ha^?1 (1st year) and between 13.68 and 14.18 t ha^?1 (2nd year). Nitrogen fertilization did not reduce the content of micronutrients in the plant or grain of maize. It is evident that the continuous single use of N fertilization so far has not resulted in a micronutrient deficiency of the plants limiting the nutrient density of the grain or reducing its quality.     

Organic Acid Metabolism in Roots of Various Grapevine (Vitis) Rootstocks Submitted to Iron Deficiency and Bicarbonate Nutrition

Abstract

The effects of Fe limitation and bicarbonate addition to the nutrient medium on the organic acid metabolism were investigated in the root tips of various grapevine genotypes. Cuttings of two limestone‐tolerant and two limestone‐susceptible Vitis genotypes were grown for four weeks in nutrient solutions containing 10 or 0.5 µM Fe. The effect of bicarbonate addition (5 mM) was studied for two of these genotypes. Compared to 10 µM, Fe limitation (0.5 µM) significantly increased citrate concentration in root tips after 2 weeks, and malate concentration after 4 weeks. When Fe limitation and bicarbonate addition were combined, citrate and malate concentrations were significantly increased after 2 weeks. Fe limitation or addition of 5 mM bicarbonate had a larger effect on citrate than on malate concentrations. Addition of 5 mM bicarbonate discriminated more clearly tolerant and susceptible genotypes than Fe limitation. High malate and citrate concentrations in the roots were associated to high PEPC activities. These results confirm that root organic acid metabolism is involved in grapevine response to Fe deficiency stress. If verified on a larger range of genotypes, a procedure using bicarbonate effect on root tip citrate concentration could be proposed to screen limestone‐tolerant Vitis rootstocks.     

Soybean Growth on Calcareous Soil as Affected by Three Iron Sources

Abstract

Iron (Fe) chlorosis is a common symptom in many soybean (Glycine max L. Merr.) producing areas throughout the United States. On the Blackland soils found in northeast Texas, Fe chlorosis occasionally appears during vegetative growth, but often abates by the time plants flower. However, it is not clear whether preplant additions of Fe will enhance soybean growth or yield on this soil or whether different sources of Fe give different responses. In a greenhouse study, soil from a pH 8.4 Houston Black clay (fine, smectitic, thermic Udic Haplusterts), with a DTPA‐extractable concentration of 11.7 mg Fe kg^?1, was treated with FeSO₄ (0, 3, 10, 30, and 100 ppm Fe), sodium ferric diethylenetriamine pentaacetate (FeDTPA) (0, 0.3, 1.0, 3, and 10 ppm Fe) or sodium ferric ethylenediamine‐di (o‐hydroxyphenylacetate) (FeEDDHA) (0, 0.3, 1.0, 3, and 10 ppm Fe). Pot size was 19 L and soil dry mass was 10 kg. Soybean (cv. Hutcheson) seed were planted in November 2000 and seedlings were thinned to three per pot at the first true leaf stage. The third uppermost fully expanded leaf of each plant was harvested at growth stage R3 for nutrient analysis. Between 20 and 100 days after planting, six nondestructive leaf chlorophyll readings were obtained from the third uppermost fully expanded leaf. Entire plants were harvested at R6 (mid podfill) for nutrient and biomass yield determination. Leaf blade Fe concentration ranged from 79 to 87 mg kg^?1 in the untreated check plants to a high of 109 mg kg^?1 for the 10 ppm FeDTPA‐Fe treatment, all of which were greater than the acknowledged critical level of 60 mg kg^?1. No visible Fe‐deficiency symptoms appeared during the study. Chlorophyll (SPAD 502) values during the R3 to R5 growth stages were greater for all of the FeSO₄ treatments than for the 0 ppm treatment. The 10 ppm FeDTPA‐Fe treatment and the 3 ppm FeEDDHA‐Fe treatment exhibited higher leaf chlorophyll readings than the untreated checks during the R3 to R5 growth stage. The average seed yield from the 12 Fe fertilized treatments at growth stage R6 was only 12% greater (not significant) than the untreated check. Total biomass (root plus shoot) was not affected by the treatments. There was no evidence that the higher rates of Fe caused reduced growth. Overall, our results do not suggest that soil‐applied Fe will consistently stimulate soybean growth or yield on this soil, at least when DTPA‐extractable soil Fe is at 12 mg kg^?1 or higher. However, because of the trends for increased seed yield in some of the Fe treatments, field studies using soil‐ and/or foliar‐applied Fe are warranted.