The stability of iron chelates in calcareous soils

The stability of Fe-EDTA and Fe-CDTA was investigated in order to evaluate their effectiveness under calcareous soil conditions. To accomplish this evaluation the reaction rate of fixation, K, the adsorption coefficient, K_d, and the retardation factor, S, of the iron chelate were determined through column experiments at pH 7.8 and two ionic strengths, I, of CaCl₂. The results indicated that iron in Fe-EDTA was more fixed than in Fe-CDTA. The fixation increased by increasing the ionic strength. Also it increased linearly with increasing CaCO₃ content of the soil. The values of retardation factor, S, showed that this parameter depended more on the surface area of the soil than on I or CaCO₃ content. The product KS depends on CaCO₃ content, surface area of the soil, ionic strength and chelating agent used. It can be taken as an index for the efficiency of the iron chelate under different conditions. Fe-EDTA was more adsorbed than Fe-CDTA, the adsorption increased with increasing ionic strength and surface area of the soil.     

Predicting the incidence of iron chlorosis in calcareous soils of southern Spain

Abstract

Iron chlorosis is a serious crop production problem in many calcareous soils of Southern Spain. The objective of this study was to determine which indigenous soil properties (i.e., those which are essentially permanent) were related to Fe chlorosis. Experiments, using two chickpea (Cicer ariethinum L.) cultivars and a sunflower (Helianthus annuuus L.) cultivar, were carried out in a growth chamber with 25 calcareous soils representing widespread Xerofluvents, Xerorthents, Xerochrepts, Haploxeralfs, Rodoxeralfs, Chromoxererts, and Pelloxererts of Southern Spain. The average chlorophyll contents for the three cultivars were significantly correlated with several properties of the carbonate and Fe oxide phases, such as calcium carbonate equivalent (r = 0.69***), “active lime”; (r = 0.58**), acid NH₄‐oxalate extractable Fe (r = 0.68***), Tiron‐extractable Fe (r = 0.61**), and DTPA‐extractable Fe (r = 0.55**). The present and other studies indicate that the soil property most consistently related to Fe chlorosis is acid NH₄‐oxalate extractable Fe (Feo). The Feo critical level separating soils with a high probability from those with a low probability of responding to Fe fertilization was 0.63 g/kg soil, a value similar to those found in other studies. This further supports the use of Feo as a key property to predicting the appearance of Fe chlorosis.     

Micronutrient deficiencies in rainfed calcareous soils of Pakistan. I. Iron chlorosis in the peanut plant

Abstract

Peanut (Arachis hypogaea L.) is susceptible to iron (Fe) chlorosis, however, plant analysis diagnostic criteria are lacking for determining the intensity of chlorosis in this crop. As total Fe content is a misleading index of Fe nutritional status of plants, determination of physiologically active Fe fraction (Fe²⁺) is suggested for the purpose. In a nutrient indexing survey of the chlorosis‐affected peanut crop grown in the rainfed Potohar plateau of Pakistan, o‐phenanthroline extractable Fe²⁺ concentration in plants decreased with increasing severity of chlorosis and thus proved an effective technique for determining the intensity of Fe chlorosis. Green plants contained 40.1 to 67.3 mg Fe²⁺/kg, mildly chlorotic 32.1 to 40.0 mg Fe²⁺/kg, moderately chlorotic 28.0 to 32.0 mg Fe²⁺/kg, and severely chlorotic <28.0 mg Fe²⁺/kg. The minimum Fe²⁺ requirement in green plants was estimated to be 40 mg/kg on dry weight basis. In rainfed field experiments on a calcareous Typic Hapludalfs soil, foliar sprays of 1% solution of sequestrene (NaFeEDDHA) proved superior to the foliar sprays of 0.5% FeSO₄.7H₂O in correcting Fe chlorosis in two cultivars of peanut. Maximum increase in pod yield with sequestrene was 42% in cv. BARD‐92 and 27% in cv. BARD‐699 over the respective control yields. Ferrous concentration in plants increased with both the Fe sources, however, a substantial increase was recorded only with sequestrene. As peanut is a low‐input high‐risk rainfed crop, correction of Fe chlorosis by using sequestrene may not be economically feasible. Thus, development and/or screening of peanut varieties tolerant to Fe chlorosis is suggested by employing Fe²⁺ analysis technique.     

Iron chlorosis and the iron status of soils

Abstract

The iron status of soils and its relation to iron uptake and iron‐chlorosis is discussed. In many soils, the soluble iron level is so low that rather than having to screen against iron uptake, plants are likely limited in their iron uptake by diffusion. The relationship between the plant root‐soil‐iron environment and the plant's ability to alter this environment is related to the development of iron‐chlorosis.     

花生缺铁黄化的敏感时期及耐低铁品种的筛选指标

采用盆栽试验,系统研究了石灰性土壤上16个花生品种在各个生育时期新叶的黄化度、叶绿素值、活性铁含量的差异及其动态变化。结果表明,缺铁胁迫下花生耐低铁和铁敏感品种间叶片的黄化程度存在着显著差异,大多数铁敏感品种在出苗后50～65 d时黄化度最高。供试16个品种顶部新展开叶片的叶绿素值（SPAD值）和活性铁含量在整个生育期的变幅分别为4.5～34.6和8.0～36.3 mg/kg, FW,随生长时间的延长两者均呈高―低―高的动态变化趋势。在生长前期,耐低铁品种新叶的叶绿素值和活性铁含量均显著高于铁敏感品种;开花期是花生对缺铁胁迫最为敏感的时期,此阶段黄化现象最严重、各品种新叶的叶绿素值和活性铁含量最低。相关分析表明,在生长前期叶绿素值与黄化度、活性铁及荚果产量之间均呈极显著的相关关系。新叶叶绿素值可作为花生耐低铁品种筛选的一可靠指标。     

铁肥根系输液矫正果树缺铁失绿症机理

邻二氮杂啡铁示踪结果表明 ,铁肥根系输液处理时铁以二价态由根被动吸收 ,并运输到根、茎、和叶的主脉内。运输部位都是靠近形成层的木质部 ,运输速度每小时可达数十厘米。室内营养液培养的八棱海棠苗用59Fe示踪结果表明 ,断根中分配的59Fe为 18.1% ,叶中分配的59Fe占 70 .9% ;断 1、2、3条根的植株59Fe在叶中的分配比例分别为 57.9%、63.6 %、68.0 %。     

Timing and rate of iron chelate application to correct chlorosis of peanut

The timing and rate of application of iron (Fe) chelates (seques‐trene 138 Fe) to correct Fe chlorosis of peanut grown on calcareous soils was studied for three seasons (1985–87) in seven experiments. It was found that the biological yield of peanut increased up to the highest rate of chelate used (8 g/m²). However, under the existing prices of the chelate and peanuts, application is financially untenable above 4 g/m². The time of chelate application should not be at sowing, but after the crop becomes chlorotic. Even though the yield differences between early application at branching, 25 to 30 days after emergence, and an application at anthesis, 45 to 50 days after emergence, was small, the trend in yield and size of nuts favored the earlier application. Therefore, it is recommended that the application of the Fe chelate be at the early stages of plant development, particularly in cases of severe chlorosis.     

小麦与花生间作改善花生铁营养的效应研究

采用砂-土联合培养根箱试验装置,模拟田间试验研究石灰性土壤小麦与花生间作改善花生Fe营养的效应结果表明,石灰性土壤高pH和高CaCO3是导致花生缺Fe黄化的主要原因。叶片已发生黄化的花生与小麦间作可明显改善花生缺Fe症状,间作16d后花生根际土壤有效铁含量、花生新叶叶绿素和活性Fe含量均显著提高。小麦与花生间作对改善花生Fe营养的效应可能与缺Fe小麦根分泌的Fe载体对土壤中Fe活化有关。     

不同铁制剂与施用方法对矫正花生缺铁黄化症的效果

研究了在盆栽和田间小区试验条件下,叶面和土壤施用铁肥以及土施酸化肥料对纠正花生缺铁黄化症的作用效果。在盆栽条件下,叶面喷施黄腐酸铁(FeFA)、土施硫酸亚铁及酸化肥料都可以提高花生新叶中活性铁以及叶绿素含量,促进花生植株的生长;在田间小区栽培条件下,叶面喷施FeFA可以提高花生的叶绿素含量,尿素与FeFA结合使用的作用效果大于单喷FeFA。土施硫酸亚铁在花生生长前期提高了花生叶绿素含量,后期作用不明显。叶面喷施与土施铁肥都可以增加花生产量,土施铁肥的作用效果不如叶面喷施效果明显,酸化肥料对提高花生叶绿素含量及产量没有明显效果。     

Characterization of commercial iron chelates and their behavior in an alkaline and calcareous soil

Iron deficiency is a common problem for many plants grown in alkaline and calcareous soils. To correct this problem, iron is supplied to plants as chelates. Several iron chelates are sold under diverse trademarks with different characteristics. This work evaluated 18 commercial products containing the most representative chelated iron sources used in agricultural practice in Spain when the study was done, namely the ferric chelates of EDDHA, EDDHMA, EDDCHA, EDDHSA, EDTA, and DTPA. The chelates were comprehensively characterized and quantitated by several techniques, including several chromatographic methods. Iron and chelate dynamics in soil were also studied in a model alkaline and calcareous soil. Results indicate that, in this model soil, among the different iron compounds studied only FeEDDHA and analogues have the capacity to maintain soluble iron in soil solution over time. These results are in agreement with general experience under field conditions. Furthermore, among the different ortho-ortho isomers of FeEDDHA's, FeEDDHSA and FeEDDCHA showed greater capacity than FeEDDHA and FeEDDHMA to maintain the chelated iron in soil solution over time.     

Effect of iron oxide on phosphate sorption by calcite and calcareous soils

Pure calcite (AR grade CaCO₃) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (x_m) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg^?1 as the amount of coating increased from 0.00 to 16.0 g Fe₂O₃, kg^?1 CaCO₃. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.     

Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybean

The application of synthetic chelates is the most efficient remedy for correcting iron (Fe) chlorosis. However, chelates are usually expensive and nondegradable products. Recently, new degradable chelates have been proposed for their use as Fe fertilizers. Also, Fe complexes cheaper than synthetic chelates and derived from natural products are also used to correct Fe deficiencies. Fifteen products, including five different synthetic chelates (Fe‐EDDS, Fe‐IDHA, and three Fe‐EDTA formulations) and ten natural complexes (humates, lignosulfonates, amino acids, glycoproteins, polyamines, citrate, and gluconate), have been compared when applied at low concentration to soybean (Glycine max L.) chlorotic plants grown in hydroponics under controlled conditions. In the first experiment, Fe compounds were applied to the nutrient solution, while in the second trial, Fe was foliar‐supplied. Dry matter, Fe concentration in shoots and roots, and SPAD values were used to evaluate the effectiveness of the Fe in the different products. In the nutrient‐solution experiment, synthetic chelates provided better plant growth, Fe concentration, and SPAD values than complexes. Among the Fe complexes, transferrin generally provided good plant responses, similar to those obtained with synthetic chelates. After foliar application, the highest regreening was observed for plants treated with synthetic chelates and amino acid complexes, but the translocation to roots only occurred for Fe lignosulfonate. Fe‐EDDS and Fe‐EDTA performed in a similar way when applied in nutrient solution or as foliar sprays.     

Sulfuric acid effects on iron and phosphorus availability in two calcareous soils

An attempt was made to study the effects of sulfuric acid additions to iron (Fe)‐ and phosphorus (P)‐deficient calcareous soils. Several greenhouse experiments were conducted with sorghum (Sorghum bicolor L.) grown in two calcareous soils. Addition of sulfuric acid to soils increased soil acidity, salinity, DTPA‐extractable Fe, available P (NaHCO₃‐extractable), and crop yield. The change in soil pH is the primary cause of increased nutrient availability and thus crop yield. Leaching after acid application is highly beneficial in decreasing salinity during germination and seedling stages and therefore has a direct impact on the yield. The beneficial effects of acid carried over for at least two greenhouse cropping seasons (approximately 4.5 months).     

Effects of phosphate carriers,iron, and indoleacetic acid on iron nutrition and productivity of peanut on a calcareous soil

Results of a field experiment designed to assess the effects of phosphate carriers, iron (Fe), and indoleacetic acid (IAA) on the Fe nutrition of peanut grown on a calcareous soil showed that single superphosphate (SSP) was more effective than diammonium phosphate (DAP) in improving Fe nutrition and chlorophyll synthesis. Increased phosphorus (P) and Fe contents of chlorotic leaves showing symptoms of Fe deficiency suggested that Fe, despite absorption and uptake, was subjected to inactivation, and that the Fe content per se was not the cause of the observed chlorosis. Better amelioration of chlorosis with the SSP treatment as compared with DAP indicated a role of sulphur (S) in preventing inactivation of Fe, possibly caused by excessive P accumulation. A foliar spray of Fe‐EDDHA corrected the chlorosis, but a ferric citrate foliar treatment did not. This further suggested that the mobility of Fe was impaired in chlorotic plants. An IAA foliar spray only also tended to improve Fe nutrition. Significant increase in peanut productivity was observed following improvement in Fe nutrition both with soil and foliar treatments.     

Mechanisms of exogenous nitric oxide and 24-epibrassinolide alleviating chlorosis of peanut plants under iron deficiency

Iron(Fe) is a crucial transition metal for all living organisms including plants; however, Fe deficiency frequently occurs in plant because only a small portion of Fe is bioavailable in soil in recent years. To cope with Fe deficiency, plants have evolved a wide range of adaptive responses from changes in morphology to altered physiology. To understand the role of nitric oxide(NO) and 24-epibrassinolide(EBR) in alleviating chlorosis induced by Fe deficiency in peanut(Arachis hypogaea L.) plants, we determined the concentration of chlorophylls, the activation, uptake, and translocation of Fe, the activities of key enzymes, such as ferric-chelate reductase(FCR),proton-translocating adenosine triphosphatase(H~+-ATPase), and antioxidant enzymes, and the accumulation of reactive oxygen species(ROS) and malondialdehyde(MDA) of peanut plants under Fe sufficiency(100 μmol L~(-1)ethylenediaminetetraacetic acid(EDTA)-Fe) and Fe deficiency(0 μmol L~(-1)EDTA-Fe). We also investigated the production of NO in peanut plants subjected to Fe deficiency with foliar application of sodium nitroprusside(SNP), a donor of NO, and/or EBR. The results showed that Fe deficiency resulted in severe chlorosis and oxidative stress, significantly decreased the concentration of chlorophylls and active Fe, and significantly increased NO production. Foliar application of NO and/or EBR increased the activity of antioxidant enzymes, superoxide dismutase,peroxidase, and catalase, and decreased the ROS and MDA concentrations, thus enhancing the resistance of plants to oxidative stress.Application of NO also significantly increased Fe translocation from the roots to the shoots and enhanced the transfer of Fe from the cell wall fraction to the cell organelle and soluble fractions. Consequently, the concentrations of available Fe and chlorophylls in the leaves were elevated. Furthermore, the activities of H~+-ATPase and FCR were enhanced in the Fe-deficient plants. Simultaneously,there was a significant increase in NO production, especially in the plants that received NO, regardless of Fe supply. These suggest that NO or EBR, and, especially, their combination are effective in alleviating plant chlorosis induced by Fe deficiency.     

Co-situs application of controlled-release fertilizers to alleviate iron chlorosis of paddy rice grown in calcareous soil

Abstract

Co-situs is the placement with one application of a sufficient amount of controlled-release fertilizer for an entire growing season at any site, together with seeds or seedlings, without causing fertilizer salt injury. An experiment was conducted to find an efficient method for ameliorating Fe deficiency in two rice cultivars (cv. Tsukinohikari and cv. Sasanishiki) grown in a calcareous soil (pH 9.2, CaCO₃ 384 g kg^?1), which was poor in organic matter (0.1 g kg^?1) and available Fe (3.0 μg g^?1 soil). The field treatments consisted of co-situs application of the following fertilizers: 1) controlled-release NPK fertilizer (CRF-NPK) containing no micronutrients; 2) controlled-release NPK fertilizer containing micronutrients (CRF-M1); and 3) controlled-release NPK fertilizer containing micronutrients (CRF-M2). The main difference between CRF-M1 and CRF-M2 was that the former had larger granules than the latter. All the fertilizers were placed in contact with the roots of rice seedlings at transplanting time. Plants in the CRF-M1 and CRF-M2 treatments had similar lengths, number of stems, leaf age, and leaf color (SPAR value) during the cultivation period. By contrast, plants from the CRF-NPK treatments grew poorly, showed severe chlorosis symptoms of Fe deficiency, and all died on 30 DAT. Plants of both cultivars accumulated more macroand micronutrients with the CRF-M2 treatment than with the CRF-M1 treatment. The grain yield of cv. Tsukinohikari was 0.0, 1,910, and 2,160 kg ha^?1 for the CRF-NPK, CRF-M1, and CRF-M2 treatments, respectively, and 0.0, 2,490, and 2,860 kg ha^?1 for the same treatments for cv. Nihonbare. Chlorosis due to iron deficiency was successfully ameliorated and world-average grain yields were obtained with the co-sites application of both controlled-release fertilizers.     

Correction of iron chlorosis in peanut (arachis hypogea shulamit) by ammonium sulfate and nitrification inhibitor

Peanut (Arachis hypogea cv. Shulamit) grown on very high calcium carbonate (CaCO₃) content soils is showing iron (Fe) chlorosis symptoms. Supplying the plant with ammonium sulphate ((NH₄)₂SO₄) in the presence of nitrapyrin (N‐Serv) for preventing nitrification reduced Fe chlorosis. Nitrate (NO^‐ ₃) developed in the soil with time, even with nitrapyrin present. When ammonium (NH⁺ ₄) was even less than 20% of the total mineral N in the soil, no Fe‐stress could be observed, suggesting that the NH⁺ ₄ uptake by the plant and the consequence of hydrogen (H⁺) efflux occurs from the root to the rhizosphere, resulting in a decrease of redox potential near the root, and solubilizing enough Fe near the root to overcome the chlorosis.     

Distribution of iron oxides forms on a transect of calcareous soils,north-west of Iran

The iron oxides fractions of four major physiographic units obtained from a transect of calcareous materials were studied to assess the effects of key pedogenic processes and local hydrology conditions as well as physiographic units in controlling iron oxides forms in the north-west of Iran. Samples from different horizons belonging to six pedons were selected and analyzed for soil physicochemical properties, clay minerals, and Fe oxides forms (Fe_d, Fe_o, Fe_p). In general, the soils indicated some variation in the concentration of iron oxides that could be related to rate of weathering, pedogenic accumulations, geomorphologic conditions (as results of different in physiographic units), wet and dry cycle, and organic matter. A wide relative variation in mean values of Fe_d (6.4–9.9 g kg^?1), Fe_o (2.9–4 g kg^?1), and Fe_p (0.68–1.3 g kg^?1) was observed among physiographic units. On the plateau unit, the presence of the most stable geomorphologic conditions and high rate in situ weathering (reflected in clay content), coupled with minor deposition of sediment suggest that the soils have more dynamic conditions than other units, reflecting in the greatest amount Fe_d and the lowest Fe_o/Fe_d ratio. Fe_d content of the soils containing less clay content (15–25%) was significantly different from those with greater clay content (25–35%).     

A study on the improvement iron nutrition of peanut intercropping with maize on nitrogen fixation at early stages of growth of peanut on a calcareous soil

Abstract

A glasshouse study employing a split-root technique was conducted to investigate the influence of intercropping with maize (Zea mays L.) in a calcareous soil on N₂ fixation by peanut (Arachis hypogaea L.) at early stages of growth. In this intercropping system, competitive interactions between maize and peanut for N and improvement of Fe uptake were likely to be important factors affecting N₂ fixation of peanut. The experiment was comprised of three treatments which included treatment I: peanut monocropping; treatment II: maize/peanut intercropping (the major and the minor compartments with low N, 50 mg kg^?1); treatment III: maize/peanut intercropping (the major compartment with low N, 50 mg kg^?1 and the minor compartment with high, N 200 mg kg^?1). The minor compartment of treatment III was fertilized with 200 mg kg^?1 N for reducing or eliminating the competition of N coming from intercropping maize. Intercropping with maize corrected Fe chlorosis of peanut by significantly increasing plant Fe concentration and uptake. Compared with the monocropping treatment, iron uptake increased from intercropping treatment II and III by 22 and 24% per plant, 30 and 29% shoots, 38 and 60% nodules. Iron uptake by the root nodules was especially enhanced in the intercropping system. In contrast, intercropping with maize had little effect on NO₃ ^?1-N concentrations in the soil rhizosphere of peanut or on N concentrations and uptake by peanut compared with plants in monoculture. The results indicate that the improvement in Fe nutrition was an important factor promoting N₂ fixation by peanut in the intercropping system at the flowering stage of peanut growth, and that competition for N by intercropped maize had little effect on N₂ fixation by peanut under the experimental conditions.     

Determining phosphorus needs for cabbage grown on calcareous soils

Cabbage (Brassica olearacea var. capitata L.) yield differences from added P were highly significant up to the predicted response level of 0.4 mg 1 . The increases in yield were basically due to larger head sizes. No statistical differences were found after the soil P levels were adjusted above 0.4 ppm, as determined by P isotherms constructed from initial soil samples. Slight differences occurred between years, but likely were due to cultivar growth differences. Data show that the isotherm predicted level fits rather closely the P requirements for cabbage as related to crop yields. Since extraction methods measure only the intensity factor of P, these methods could lead to incorrect P fertilization recommendations. The absorption of P is progressively reduced as the temperature goes down.