Foliar Iron Fertilization: A Critical Review

Application of foliar iron (Fe) sprays is a common means of correcting Fe deficiency of agricultural crops. However, variable plant responses to iron sprays, ranging from no effect to defoliation, have often been described in the Fe-fertilization literature. Knowledge is still limited concerning the mechanisms of penetration of a leaf-applied, Fe-containing solution and the role of Fe in the leaf. The complex and multi-disciplinary character of the factors determining the effects of Fe sprays hinder the development of suitable foliar fertilization strategies, applicable under variable local conditions and for different plant types. This review describes some key factors involved on the process of penetration of a leaf-applied, Fe-containing solution before briefly analyzing the available foliar Fe-fertilization literature. Iron chemistry, leaf penetration, and plant-nutrition principles will be merged with the aim of clarifying the constraints, opportunities, and future perspectives of foliar Fe sprays to cure plant Fe deficiency.     

Leaf Potassium Accumulation in Olive Plants Related to Nutritional K Status,Leaf Age,and Foliar Application of Potassium Salts

Four separate experiments were carried out in greenhouse conditions from spring of 2001 to summer of 2003. The aim of this research was to study the effect of factors such as leaf age, salt type and concentration, number of foliar applications, and the nutritional status on the efficiency of foliar applications of potassium (K) in olive plants. In all experiments, mist-rooted ‘Picual’ olive plants growing in 2 L pots containing perlite were fertigated with a complete nutrient solution containing 0.05 mM or 2.5 mM potassium chloride (KCl). In one experiment, plants received two foliar applications with five concentrations of KCl (0%, 2%, 4%, 6%, or 8%) at 63 and 84 days after transplanting. Foliar KCl applications at 2% or 4% increased shoot lengths and the K content of plants fertigated with 0.05 mM KCl (poor K nourished), while foliar KCl application did not have any influence on the growth or K content of plants fertigated with 2.5 mM KCl (normal K nourished). When the number of foliar applications was increased, the results showed that two foliar applications were enough to increase leaf K concentration in olive plants above the sufficiency level. Leaf age could influence the efficiency of foliar K application. Leaf K concentration were higher in young leaves than in mature ones. All K-salts studied as foliar sprays [KCl, potassium sulfate (K₂SO₄), potassium nitrate (KNO₃), potassium carbonate (K₂CO₃), and potassium phosphate (KH₂PO₄)] were effective in increasing leaf K concentration. The results obtained in the present study indicate that foliar applications of K effectively increase K content in K-deficient olive plants, and that foliar applications might be more effective on young leaves. Two foliar applications of 4% KCl or the equivalent for other salts are enough to increase leaf K concentration.     

Influence of Foliar and Ground Fertilization on Yield,Fruit Quality,and Soil,Leaf, and Fruit Mineral Nutrients in Apple

ABSTRACT

The effectiveness of nitrogen (N)+ zinc (Zn) soil and foliar fertilizer applications on growth, yield, and quality of apple (Malus domestic Borkh ‘Golden Delicious’) fruit was studied in the Zanjan province, Iran. There were eight treatments 1) control (no fertilizer), 2) soil applied N, 3) soil applied Zn, 4) soil applied N+Zn, 5) foliar applied N, 6) foliar applied Zn, 7) foliar applied N+Zn and 8) combined soil and foliar applied N+Zn. The N source was urea [CO(NH₂)₂, 46% N] applied at 276 N tree^{? 1} yr^?1 and the Zn source was zinc sulfate (ZnSO₄,7H₂0, 23% Zn) applied at 110 g Zn tree^{? 1} yr^{? 1}. The soil treatments of N and Zn, were applied every two weeks during June through August (total of 6 times/year) in a 1 m radius around the tree trunk (drip line of trees). The foliar solutions of N (10 g l^{? 1} urea) and Zn [8 g l^{? 1} zinc sulfate (ZnSO₄)] were sprayed at the rate of 10 L tree^{? 1} every two weeks at the same times as described for soil applications. The highest yield (49 kg tree^{? 1}), and the heaviest fruits (202 g) were obtained in the soil and foliar combination of N+Zn treatment. The lowest yield (35 kg tree^{? 1}), and the smallest fruits (175 g) were recorded in the control. Nitrogen, and to a lesser extent Zn, foliar application resulted in decreasing fruit quality (caused russeting, and lower soluble solid), but increasing N leaf and fruit concentrations (2.4% DW and 563 mg kg^{? 1}, respectively). There were significant differences among yield and leaf mineral nutrient concentration in different treatments. But there was no significant difference between fruit mineral nutrient concentration (except N). Ratio of N/calcium (Ca), potassium (K)/Ca, and [magnesium (Mg)+K]/Ca in fruits were found suitable for fruit quality prediction. Combining the zinc sulfate with urea in the foliar applications increased the concentration of Zn from 0.7 to 1.5 mg per kg of apple tissue. Leaf N concentration varied during growth season. Foliar applied nutrient can be more efficient than soil applied, but a combination of soil and foliar applications is recommended for apple tree nutrient management.     

Development of Standard Concentrations of Foliar Nutrients for Saskatoon

Soil and foliar samples were collected from saskatoon orchards in Saskatchewan, Manitoba, and Alberta, Canada from 1997 to 1999 and analyzed for macro- and micronutrient content. Foliar samples were collected twice a month from the end of May until September in 1997 to examine the pattern of change in foliar nutrient concentrations throughout the season and to determine the most stable time period for foliar sampling. This period was determined to be from the last week in July until mid-August. Nutrient concentrations of foliar samples collected during this period from 1997 to 1999 were summarized according to the mean, median, minimum, and maximum values. Mean foliar nutrient concentrations were as follows: 2.48% nitrogen (N), 0.18% phosphorus (P), 1.15% potassium (K), 0.15% sulfur (S), 1.52% calcium (Ca), 0.50% magnesium (Mg), 6.9 ppm copper (Cu), 106 ppm iron (Fe), 124 ppm manganese (Mn), 16 ppm zinc (Zn), and 27 ppm boron (B). A number of significant positive correlations were found between soil and foliar levels of a nutrient, with the majority of these correlations occurring for the nutrients Cu, P, and Mn. Another study conducted during 2001–2002 examined differences in the foliar nutrient concentrations of the saskatoon cultivars ‘Smoky’ and ‘Thiessen’ sampled from nine orchards in Saskatchewan. Foliar concentrations of N, K, S, Ca, Mg, Cu, Mn, Zn, and B were significantly higher in ‘Smoky’ than in ‘Thiessen,’ whereas foliar K content was higher in ‘Thiessen’ than in ‘Smoky’.     

Boron Foliar Application in Nutrition and Yield of Beet and Tomato

The objective of this work was to evaluate the effect of the application of boron (B) by foliar spraying for the yield of beet (Beta vulgaris L.) and tomato (Solanum lycopersicum L.) crops. An experiment for each crop was done in a greenhouse at the São Paulo State University (UNESP), Jaboticabal campus, in Brazil. The experiments evaluated the B concentrations of 0, 0.085, 0.170, 0.255, and 0.340 g L^?1; applied in the 20, 35, and 50 days after the transplant (DAT) of beet cv. ‘Tall Top Early Wonder’, and in the 20, 40, and 60 DAT for the tomato cv. ‘Raisa N’. The plants were cultivated in pots with washed sand with 5 dm³ for the beet crop and 10 dm³ for the tomato crop. The beet and tomato crops were harvested 58 and 154 DAT, respectively. The leaves and fruits numbers; the foliar area; the dry matter of leaves, bark and roots; the fresh and dry matter of the fruits and the tuberous root; the dry matter of the total plant and the B foliar content were evaluated. The total dry matter of beet and tomato the plant were influenced by the concentration of the foliar B spray. The highest yield of the tuberous root and the total plant dry matter of beet occurred with B foliar concentration of 0.065 g L^?1 and it was associated with the B foliar content of 26 mg kg^?1. The highest yield of fruit and total plant dry matter of tomato occurred with the B foliar spraying of 0.340 g L^?1 and it was associated with the B foliar content of 72 mg kg^?1.     

Influence of Foliar Iron Fertilization Rate on the Breakage Susceptibility of Wheat Seeds

The objectives were to determine the effect of different levels of foliar iron fertilization on the some physical properties and breakage susceptibility of wheat seed. Foliar iron treatments were combinations of three fertilization rates [0 (control), 1.2 and 2 L ha^?1, Fusin] at three replications. The harvested seeds were then subjected to impact energies of 0.1 and 0.2 J, at moisture contents of 8.5, 15, 20 and 25% (w.b.), using an impact test apparatus. Results indicated that the values of the seed physical properties increased with increasing iron rate. Iron fertilizer rate, moisture content and the interaction between two variables significantly influenced breakage susceptibility of wheat seeds at the 1% probability level (P < 0.01). Resistance to the breakage of wheat seeds increased following a polynomial relationship with increase in the foliar iron rate. Increasing the rate of foliar iron from 0 to 2 L ha^?1 caused a significant decrease in the mean values of damage by a factor of 1.8 from 66.188 to 36.688%. As the moisture content of the seeds increased from 8.5 to 25%, the amount of the percentage breakage of seeds decreased, as a polynomial. The maximum rate of decrease in the damage to seeds, with increasing moisture content, was obtained at higher iron fertilizer rates.     

Mobility of Iron and Manganese within Two Citrus Genotypes after Foliar Applications of Iron Sulfate and Manganese Sulfate

Seedlings of sour orange (Citrus aurantium L.) and Carrizo citrange (C. sinensis L. cv. Washington navel x Poncirus trifoliata)] were grown in plastic pots containing a sand: perlite mixture and watered with a modified Hoagland No 2 nutrient solution throughout the experiment. Three-months-old plants were divided in three groups and sprayed with 0.018 M iron sulfate (FeSO₄ ^.7H₂O), 0.018 M manganese sulfate (MnSO₄ ^.H₂O), or deionized water. Two months later, plants were harvested and divided into top leaves that grown after the treatments, basal leaves that existed prior to the treatments, stems that partially came in contact with the spray, and roots. The manganese (Mn) spray resulted in a significant increase of Mn concentrations in top leaves, basal leaves, stems and roots of sour orange, and in top leaves, basal leaves, and stems of Carrizo citrange. The iron (Fe) spray significantly increased the concentrations of Fe in the stems and basal leaves of both genotypes. For both genotypes, transport of Mn from basal (sprayed) leaves to top (unsprayed) ones was found. However, the results of this experiment did not give any evidence neither for Mn translocation from sprayed tissues to roots nor for Fe transport from sprayed tissues to unsprayed ones (top leaves, roots). Mn and Fe were found to be relatively mobile and strictly immobile nutrients, respectively, within citrus plants after their foliar application as sulfate salts.     

Foliar fertilization of nickel affects growth,yield component and micronutrient status of barley (Hordeum vulgare L.) grown on low nickel soil

Foliar application of nickel (Ni) has higher use efficiencies and is preferred over soil application in view of its very low requirement. Pot experiments were conducted during winter season of 2012-2013 and repeated during 2013-2014. Treatments consisted of twelve Ni levels applied as nickel sulphate (NiSO4.7H₂O) spray (T₁-Ni_0%, T₂-Ni_0.05%, T₃-Ni_0.1%, T₄-Ni_0.2%, T₅-Ni_0.3%, T₆-Ni_0.4%, T₇-Ni_0.5%, T₈-Ni_0.6%, T₉-Ni_0.7%, T₁₀-Ni_0.8%, T₁₁-Ni_0.9%,and T₁₂-Ni_1.0%,) with recommended doses of fertilizers (RDF) applied in all pots. The result showed that growth and yield attributes viz. plant height, leaf greenness index, number of tillers, number of ears pot^-1, number of grains ear^-1, straw yield, grain yield and weight of 1000 grains of barley was the maximum with three foliar application of 0.2% of NiSO4.7H₂O (T₄-Ni_0.2%) at 20, 40, and 60 days after sowing (DAS) during both the years. The concentration of Fe, Mn and Zn in grain increased significantly up to T₄-Ni_0.2% and after this level, a significant decline was recorded during both the years. As regards to the concentration of Ni is concerned, it increased significantly both in grain and straw with increasing levels of Ni spray and the maximum concentration was at T₁₂-Ni_1.0%, during both the years. The uptake of Fe, Mn, Cu and Zn in grain of barley increased significantly during both the years up to T₄-Ni_0.2%,thereafter, it declined significantly with successive increase in dose of Ni spray. Thus 0.2% foliar spray of NiSO4.7H₂O significantly increased growth, yield and Fe, Cu, Mn, Zn (micronutrients) status in barley.     

Foliar and Radicular Absorption of Boron by Beetroot and Tomato Plants

The isotopic technique was employed to study boron (B) mobility in tomato and beetroot plants under protected cultivation conditions. An experiment was conducted in which both species grew in 10-dm³ vases filled with coconut fiber, under hydroponic conditions. The plants were subjected to four different treatments: (1) no B in the substratum and no foliar fertilization; (2) no B in the substratum, with foliar ¹⁰B fertilization; (3) B in the substratum, with foliar ¹⁰B fertilization; and (4) ¹⁰B in the substratum and no foliar fertilization. The biological growth variables and total B and ¹⁰B contents in the plant parts grown after the application of the nutrient were evaluated. For increasing B content in young tissues, the foliar application of this element was not as efficient as application via root system, indicating low mobility of B in the tissues of both beetroot and tomato plants.     

Crop Nutrients Review and the Impact of Fertilizer on the Plantation in Malaysia: A Mini Review

ABSTRACT

Improving the production of crops is always a concern in the plantation sector since higher production leads to the economic growth of a country. For developing countries, including Malaysia, one of their incomes is crop production. Focusing on crop nutrients supply using fertilizers to increase the production of the crops is better than expanding the plantation areas. The limited knowledge regarding the appropriate nutrients supply and the relation between the nutrients in Malaysia has caused the yield of the crops not meet expectations. Thus, sharing knowledge about the nutrient requirements and the nutrient availability toward the uptake rate of the plants are required. Hence, this work reviews the nutrient supply, the effect of each nutrient on the crop, and the nutrient availability in Malaysia’s plantation. A better understanding of the nutrient requirement to sustain crop health helps to improve the quality of the crop, its yield, and soil performance for future agriculture work. Moreover, this work also discusses the impact of fertilizer on the plantation and different types of fertilizer. Additionally, their nutrient release patterns will be discussed, along with the pros and cons of these existing fertilizers.

Abbreviations: ATP: Adenosine Triphosphate; SRF: Slow-release fertilizers; CRF: Controlled release fertilizer; SCU: Sulfur-coated urea fertilizer; PCU: Polymer-coated urea fertilizer; SRB: Slow release blending fertilizer; NUE: Nitrogen-use efficiency; AV: Ammonia volatilization; CRNF: Controlled release nitrogen fertilizer     

叶面喷施硒肥对小麦籽粒及面粉硒含量的影响

为了探明叶面喷施硒肥对小麦籽粒及制粉各粉路硒含量的影响,本研究选用4个小麦品种,在拔节和抽穗期分2次喷施0.017%亚硒酸钠叶面肥,并对成熟期籽粒进行制粉,分析各粉路的总硒、无机硒和有机硒含量。结果表明,叶面喷硒对小麦籽粒和面粉的总硒、有机硒和无机硒含量的影响存在品种间差异。喷施硒肥后,4个小麦品种籽粒的总硒含量提高了26.4~35.8倍,但小麦籽粒产量无显著变化。皮磨粉、心磨粉、统粉、小麸和大麸5种粉路中,小麸的总硒含量最高,其次为大麸,皮磨粉、心磨粉和统粉的总硒含量较低。与硬质小麦相比,软质小麦出粉率低,面粉的总硒量损失较多。经制粉,对照和喷硒样本的总硒积累量分别损失52.97%~69.28%和36.73%~44.51%。对照样本中,各粉路的有机硒含量略高于无机硒含量;而喷硒处理样品中,除宁麦20的小麸外,各粉路的有机硒含量均略低于无机硒含量。本研究揭示了制粉粉路硒分布规律,这对于富硒小麦的加工利用具有重要的指导作用。     

Effects of Foliar Spray of K on Mint,Radish, Parsley and Coriander Plants in Aquaponic System

An aquaponic system was designed to investigate the effects of foliar applications of potassium (K) on mint, radish, parsley, and coriander growth and physiological characteristics. Plants were sprayed with 100 mL pot^?1 of 0.5 g L^?1 potassium sulfate (K₂SO₄) twice a week. Fresh and dry masses of shoot in all species were higher in K-treated plants. Potassium concentration increased with K spray in the shoots of all species. K-sprayed parsley accumulated a greater amount of Fe and chlorophyll in shoots. Values of SPAD index in all species decreased significantly in untreated plants. The highest Quantum Photosynthetic Yield (F_v/F_m) values were observed in coriander plants treated with K, which was attributed to higher SPAD value in these plants. Potassium application had a negative effect on sodium (Na) and positive effect on magnesium (Mg), manganese (Mn), and zinc (Zn) concentrations in plants. These results indicated that foliar spray of K can effectively alleviate nutrient deficiencies in leafy and root vegetables grown in aquaponics.     

抗蒸腾型叶面肥对造林树种蒸腾速率的影响

黄土半干旱地区是林业生态工程建设退耕还林的重点地区。由于该区降水相对不足且潜在蒸散力大等特殊气候条件,蒸腾作用会造成植物水分大量丢失,从而引起水分亏缺和脱水的伤害,使人工造林遇到极大的困难。此时叶面喷施抗蒸腾叶面肥不仅能提供植物生长所需养分,而且还能抑制植物蒸腾作用,提高植物水势,减少植物水分的蒸发量,一定程度上提高植物生存能力。本试验以黄土高原干旱半干旱地区造林中主要采用的生态经济型树种文冠果(Xanthoceras sorbifolia Bunge)、紫穗槐(Amorpha fruticosa)、火炬树(Rhus typhina)为研究对象,以自制的两种抗蒸腾叶面肥及市场上已推广施用的叶面肥肥效为主要依据,运用正交试验探讨自制肥料在降低植物蒸腾作用方面的效果。研究结果证明,自制叶面肥C+紫穗槐或文冠果+稀释800~1200倍+土壤含水量为12%~22%时,对降低植物蒸腾速率效果最为明显。     

叶面喷施外源多胺提高夏玉米灌浆前期抗涝性

为缓解玉米涝渍胁迫危害,该研究在夏玉米灌浆前期设置3、5、7、9 d的测坑淹水试验,分析淹水及淹水后叶面喷施外源多胺对夏玉米叶片可溶性糖、根系活力、地上部干物质、内源亚精胺、籽粒质量动态变化和产量的影响。结果表明:淹水后与CK相比,淹水5、7、9 d叶片可溶性糖含量下降,地上部干物质质量均显著减少,淹水3、7、9 d百粒质量增加,5 d减少,籽粒质量、穗行数、行粒数、产量均显著降低。叶面喷施外源多胺后,相同淹水天数处理间比较,淹水5、7、9 d叶片可溶性糖含量增加、根系活力增强,淹水7、9 d叶片内源亚精胺含量增加,淹水5 d百粒质量显著增加,淹水3、5 d植株行粒数分别增加8.24%和7.41%,产量分别提高7.92%、5.85%(P0.05)。因此,夏玉米灌浆前期遭遇淹水后5 d内叶面喷施外源多胺,能够提高其抗涝性,减少产量损失。     

抗蒸腾型叶面肥对植物叶水势影响的研究

2009年6月于北京鹫峰国家森林公园,采用PSYPRO露点水势仪连续4个月测定分析了黄土高原干旱半干旱地区主要造林树种叶水势与其他因素(肥料、树种、喷施浓度、土壤含水量等)之间的影响作用。本试验以黄土高原干旱半干旱地区造林中主要采用的生态经济型树种山杏(Prunus sibirica)、杨树(Populus)、核桃(Juglans regia)为研究对象,以自制的抗蒸腾叶面肥、市场上已推广施用的叶面肥以及清水对照为主要依据,运用正交试验探讨自制肥料在提高植物叶水势值方面的效果,比较各树种在不同土壤含水量和喷施浓度处理下叶水势的日变化进程趋势和波幅。研究结果表明:清水处理条件下山杏和杨树叶水势全天波幅能维持在较低的范围内(分别为1.12Mpa和1.19Mpa),有高水势延迟脱水的抗旱机理表现,而核桃在清水处理条件下的叶水势日波动幅度最大,全天波幅高达1.59Mpa,显示出低水势忍耐脱水的耐旱机理,即其叶组织抗脱水能力较强。最终研究结果证明山杏或核桃、自制叶面肥A、稀释800~1 200倍、土壤含水量为12%~22%时对提高植物叶水势值效果最为明显。     

Response of Pinus radiata D. Don to Boron Fertilization in a Glasshouse Study

Limited information is available on the effect of slow-release boron (B) fertilizer on Pinus radiata growth and physiological properties and soil microbiological activities. A 7-month-long pot experiment was carried out under glasshouse conditions to investigate the response of Pinus radiata to different rates (0.0222, 0.0446, 0.089, and 0.178 mg B g^?1 soil), equivalent to 0, 4, 8 16, and 32 kg B ha^?1 of ulexite, a slow-release B fertilizer. Hot 0.02 M calcium chloride (CaCl₂)–extractable soil B, soil dehydrogenase activity, plant B concentration, growth, and photosynthesis were measured at the time of harvest. The B concentrations in the soil and plant organs (needles, stem, and roots) significantly increased with increasing rates of B fertilizer. The optimum B fertilizer rates of 4–8 kg B ha^?1 produced the greatest plant growth and net photosynthetic rate. However, the B rates of 16 and 32 kg B ha^?1 significantly reduced net photosynthetic rate, and the rate of 32 kg B ha^?1 significantly reduced stem diameter growth when compared to the optimum B rates. Soil dehydrogenase activity, an indicator of soil microbiological activities, was significantly reduced by B application at the rates of 16 and 32 kg ha^?1. This study confirms the narrow range between B deficiency and toxicity in a tree crop and stresses the need for selection of the optimum rate of B fertilizer application.     

宿根蔗后期叶面追肥对甘蔗品质和某些生理特性的影响

宿根蔗生长后期叶面喷施KH2PO4和石灰水,能有效地提高甘蔗蔗糖分,降低蔗汁还原糖分,以KH2PO4效果较好。KH2PO4和石灰水处理使甘蔗叶片的酸性转化酶活性降低,Mg2+－ATP酶和Ca2+－ATP酶活性则明显提高。KH2PO4处理明显降低了甘蔗叶片水溶性蛋白质含量,而提高了中性转化酶活性。石灰水处理提高叶片水溶性蛋白质和类胡萝卜素含量,而使水分含量和过氧化物酶、多酚氧化酶活性降低。     

PHOSPHORUS UPTAKE AND USE EFFICIENCY IN FIELD CROPS

Phosphorus (P) is required by crop plants for many physiological and biochemical functions. Knowledge of phosphorus uptake and its use by crop plants is essential for adequate management of this essential nutrient. A field experiment was conducted during four consecutive years to determine P uptake and use efficiency by upland rice, dry bean, corn and soybean grown in rotation on a Brazilian Oxisol. Plant samples were taken at different growth stages during the growth cycle of each crop for phosphorus analysis. Phosphorus concentration (content per unit dry matter) significantly decreased in a quadratic fashion with the advancement of plant age in four crop species. Phosphorus concentration was higher in legumes compared to cereals. Phosphorus uptake in shoot, however, significantly increased in an exponential quadratic fashion with the advancement of plant age of crop species. At harvest, P uptake was higher in grain compared to shoot, indicating importance of this element in improving crop yields. Phosphorus use efficiency (grain or straw yield per unit P uptake) was higher in cereals compared to legumes. The P use efficiency for grain production was 465 kg kg^?1 for upland rice, 492 kg kg^?1 for corn, 229 kg kg^?1 for dry bean and 280 kg kg^?1 for soybean. The higher P use efficiency in cereals was associated with higher yield of cereals compared to legume species.     

Nutrient disorders of Dianthus ‘Bouquet Purple’

‘Bouquet Purple’ pinks (Dianthus sp.) were grown in silica-sand culture to induce and photograph symptoms of nutritional disorders. Plants received a complete modified Hoagland's all-nitrate (NO₃) solution. Nutrient-deficient treatments were induced with a complete nutrient formula minus one of the nutrients, and a boron (B)-toxicity treatment was induced by increasing B 10-fold in the complete nutrient formula. Plants were monitored daily to document sequential series of symptoms as they developed. Typical symptomology of nutrient disorders and corresponding tissue concentrations were determined. All treatments exhibited deficiency symptomology. Disorders for nitrogen (N), iron (Fe), calcium (Ca), and sulfur (S) were the first to manifest in pinks. Unique symptomology was observed for plants grown under potassium- (K), B-, copper- (Cu), and molybdenum- (Mo) deficient conditions, which supported the need for a species-specific approach when characterizing nutrient disorders of floriculture crops.     

The Contribution of Foliar Exposure to Boron Toxicity

Boron toxicity is commonly considered in terms of plant B uptake and accumulation. This work tested the hypothesis that foliar exposure of water with high B content leads to more severe toxicity reactions in plants as compared to exposure to high B simply through the soil solution. Growth and B uptake were studied in corn, tomatoes, onions, celery and radish where B laden water was applied with and without a component of foliar contact. Increased visual symptoms of B toxicity and decreased yields were found in plants with foliar applied B for all of the crops, while associated increased B tissue concentrations were not measured. The results imply that the relative toxicity of B entering through the leaves is greater than that of B entering via roots. Biomass reduction due to B was found to be a function of neither absolute B accumulation nor relative B mobility in the plant.