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.     

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.     

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.     

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     

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.     

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.     

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.     

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.     

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.     

Nitrogen Assimilatory Enzymes and Amino Acid Content in Inoculated Foliar Fertilized Pea Plants Grown at Reduced Molybdenum Concentration

ABSTRACT

A possibility to improve nitrogen assimilation in nitrogen fixing Molybdenum (Mo) deficient pea plants was shown. The influence of foliar supplied nutrients in addition to root nutrition resulted in reducing the unfavorable effects of inorganic nitrogen on nodule function and Mo deficiency on the nitrogen assimilatory enzymes. Inoculated pea plants were grown on liquid nutrient solution both with and without Mo. The following variants were tested: Mo supplied plants with root nutrition (F1 + Mo); Mo supplied plants with root and foliar nutrition (F2 + Mo); Mo deficient plants with root nutrition (F1 ? Mo); and Mo deficient plants with root and foliar nutrition (F2 ? Mo). Foliar application of nutrients had a positive effect on the glutamine synthetase and glutamate synthase enzyme activities in the roots and nodules of Mo deficient plants. It was found that the foliar fertilization reduced the inhibitory effect of Mo shortage on the aspartate/asparagine content in the pea shoots.     

Nutrient availability and response of sago palm (Metroxylon sago Rottb.) to controlled release N fertilizer on coastal lowland peat in the tropics

Sago palms (Metroxylon sagu Rottb.) growing on peat soils were found to grow more slowly and to show a lower production than palms growing on mineral soils. This difference was related to the physical and chemical constraints of peat soils, which include low bulk density, high acidity, and low N, P, K, Ca, Zn, and Cu levels. In coastal lowland peat soils, the distance from the sea has been found to be an important determinant of soil elemental composition. We predicted that a sufficient supply of N at the rosette stage would improve sago palm growth and that the availability of N in soil to which controlled release N fertilizer was applied might be higher than that in soil treated with soluble fertilizer. To investigate the changes in the nutrient composition of peat soils at various distances from the sea and the effect on sago palm growth, we studied sago palm areas in Indonesia and Malaysia. To observe the influence of N on the growth performance, we also conducted a fertilizer experiment on coastal lowland peat soil in Indonesia. Distance from the sea had no significant effect on the cation concentration in the soil solution (with the exception of Mg) or on the levels of soil-exchangeable cations. No significant differences were observed between the concentrations of exchangeable cations in surface peat soils and those in mature leaves. However, the concentrations of K, Na, and Ca in mature leaves increased significantly with their concentrations in the soil solution. This finding implies that the concentrations of cations in sago palm leaves depend directly on the concentrations of cations in the soil solution. No significant effect of N fertilizers on plant height and leaf formation was observed. N fertilizers applied twice a year did not affect appreciably the foliar concentration of N determined in December 1998 (5 months after the initial application) and December 1999. In June 2000, we detected a significantly higher concentration of N (p < 0.01) in young leaves of the palms treated with LP-100 or urea than in control leaves. However, no significant difference was detected between the LP-100 and urea treatments in the concentration of N in both mature and young leaves. This finding indicated that the concentration of N in sago palm leaves increased with the level of soil-applied N, regardless of whether N was applied as controlled release fertilizer or in the soluble form. We anticipate that a significant difference in the effects of these N fertilizers may occur during the next rainy season, when there should be a considerable loss of soluble N.     

Morphophysiological and Grain Yield Responses to Foliar and Soil Application of Boric Acid on Soybean

ABSTRACT

Boric acid (H₃BO₃) fertilization as source of boron (B) is a common practice in modern agriculture, aims to correct the deficiency of this micronutrient in the Cerrado soils, and ensure the maintenance of plant metabolism for the proper crops’ development. Therefore, the aim of this work was to evaluate the effects of H₃BO₃ fertilization on soil and leaves during the soybean development. The experimental design was completely randomized with six replicates. The treatments were obtained in a 3 × 2 factorial scheme, fertilization with H₃BO₃ for three doses of B in the soil: 0 (control); 0.62 and 3.4 kg ha^?1 and two foliar supplementation conditions: absence and presence. The best results for the variables length, dry mass and leaf area of soybean plants occurred with B applied to soil at doses 0 and 3.4 kg ha^?1 in the absence of foliar supplementation. B content in the plants gradually increased with the micronutrient supply via soil and in leaves. Physiological apparatus of the plants was more efficient in the absence of foliar supplementation, independently of the fertilization with doses in the soil. The grain mass was up to 57% higher in the control treatment. Fertilization with H₃BO₃ in the soil and foliar did not improve the morphophysiological traits and the production of soybeans grown in greenhouse using clayey soil with initial B content of 0.30 mg dm^?3.     

Comparing Two Extraction Methods to Evaluate the Composition of Substrate Solution of a Burnt Rice Husk Substrate Used for Carnation Crops

Substrates have been increasingly used in recent years for carnation crops. Burnt rice husk (BRH) is widely available and used as a substrate in Colombia. The present work aims to compare the effects of two aqueous extraction methods on the chemical contents. Saturated and 1:1 (v/v) extractions were performed in three replications. Ionic forms of the macronutrients (NO₃^?, NH₄⁺, PO₄H₂^?, K⁺, Ca²⁺, Mg²⁺, and SO₄^2?, in meq L^?1), micronutrients (Fe, Mn, Zn, Cu, and B, in mg L^?1), Cl^?, CO₃ H^? in meq L^?1, electrical conductivity in dS m^?1, and pH were analyzed. Except for NH₄⁺, Cl^?, and B the determination coefficient R² was greater than 95 percent. Average values and standard errors of data have been used to define suitable intervals for 1:1 extractions. Proposed intervals for 1:1 extracts are consistent with the saturated extract and therefore are a good tool to optimize the management of fertigation in those crops.     

Effects of Sodium on Potassium Nutrition in Three Tropical Root Crop Species

The potassium (K) nutrition and high K requirement of tropical root crops may be affected by their sodium (Na) status, as has been observed in a number of plant species. Solution culture was used to study the effects of K and Na supplies in tannia [Xanthosoma sagittifolium (L.) Schott.], sweet potato [Ipomoea batatas (L.) Lam.] and taro [Colocasia esculenta (L.) Schott]. At low K supply, Na ameliorated symptoms of K deficiency and increased growth in tannia, and to a lesser extent in sweet potato, but not in taro. None of the species responded to Na at adequate K supply. Differences in response to Na were attributed to differences in Na translocation to plant tops. At maximum Na supply, the Na concentration in index leaves averaged 1.82% in tannia, 0.205% in sweet potato, and 0.0067% in taro. An increase in the supply of Na resulted in a shift in the critical K concentration for deficiency (i.e., 90% of maximum yield) in index leaves from 2.9% to 1.2% in tannia, and from 4.8% to 2.5% in sweet potato. The critical K concentration in taro was 3.3%, irrespective of Na supply. To overcome the problem in tannia and sweet potato of determining the critical concentration relevant to a leaf sample of unknown K status, a relationship was established for each species relating the critical K concentration to the concentration of Na in the index leaves.     

Foliar Application of Manganese Increases Seed Yield and Improves Seed Quality of Cotton Grown on Calcareous Soils

Cotton (Gossypium hirsutum L.) is often grown on calcareous soils where manganese (Mn) deficiency is quite common. Despite the fact that Mn deficiency can limit cotton productivity the effect of foliar application of Mn was not determined. A field study was conducted to determine if foliar Mn applications during anthesis affects the growth and yield of cotton. Manganese increased the chlorophyll content by up to 17% compared with the control treatment with no difference between the two rates of Mn. Moreover, Mn increased the seed yield by an average of 30%, the number of bolls per plant by 31%, the number of bolls per square meter by 31% and boll retention by 37% compared with the control, but it did not affect the mean boll weight and the quality of the fibers. Foliar application of Mn increased seed germination by an average of 14% and increased seed vigor (AA) by an average of 28% compared with the control treatment. The results obtained here suggest that foliar Mn application can improve the lint and seed yield and also the seed quality of cotton grown for seed production on calcareous soils.     

Use of Treated Wastewater as Fertilization and Irrigation Amendment in Pot-grown Processing Tomatoes

ABSTRACT

Plants of tomato cultivar ‘TITANO M’ were grown under glasshouse conditions, in plastic pots filled with the upper (Ap, Soil A) and the underlying horizons (Bt, Soil B) of an Alfisol from central Greece in a randomized complete block design. Four treatments were utilized: no fertilization and irrigation with distilled water (C), irrigation with wastewater without fertilization (W), complete fertilization (110 kg N ha^?1, 150 kg P₂O₅ ha^?1, 150 kg K₂O ha^?1) and irrigation with distilled water (CF), complete fertilization and irrigation with wastewater (WF) each replicated four times. The results showed that wastewater significantly increased electrical conductivity (EC), exchangeable sodium percentage (ESP), exchangeable magnesium (Mg), and extractable zinc (Zn). A three-fold increase of above ground biomass (AGB) compared to C treatment was recorded in Soil A. Photosynthates allocation to AGB and water use efficiency (WUE) were promoted by effluent application. Wastewater could be a water source for agriculture under water limited conditions substituting partially for inorganic fertilization.