Soil Zn Application Research Articles

Relevance for food sciences of quantitative spatially resolved element profile investigations in wheat ( Triticum aestivum ) grain

Bulk element concentrations of whole grain and element spatial distributions at the tissue level were investigated in wheat (Triticum aestivum) grain grown in Zn-enriched soil. Inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry were used for bulk analysis, whereas micro-proton-induced X-ray emission was used to resolve the two-dimensional localization of the elements. Soil Zn application did not significantly affect the grain yield, but did significantly increase the grain Ca, Fe and Zn concentrations, and decrease the grain Na, P and Mo concentrations; bulk Mg, S, K, Mn, Cu, Cd and Pb concentrations remained unchanged. These changes observed in bulk element concentrations are the reflection of tissue-specific variations within the grain, revealing that Zn application to soil can lead to considerable alterations in the element distributions within the grain, which might ultimately influence the quality of the milling fractions. Spatially resolved investigations into the partitioning of the element concentrations identified the tissues with the highest element concentrations, which is of utmost importance for accurate prediction of element losses during the grain milling and polishing processes.

Effect of tire rubber ash and zinc sulfate on yield and grain zinc and cadmium concentrations of different zinc-deficiency tolerance wheat cultivars under field conditions

The aims of these field experiments were to investigate the effectiveness of soil application of rubber tire ash in comparison with soil and foliar applications of zinc (Zn) sulfate to increase Zn and decrease cadmium (Cd) concentrations in wheat grain. A two-year field experiment was conducted during the 2007–2008 and 2007–2008 growing seasons at Isfahan research field, Iran. Ten different Zn-efficiency bread wheat cultivars (Triticum aestivum L.) commonly cultivated in different parts of Iran were subjected to no Zn fertilizer addition (control), soil application of 40kgha−1 ZnSO4, soil application of 100 (for the first year) and 250 (for the second year) kgha−1 waste rubber tire ash, foliar application of Zn at the mid tillering stage, and foliar application of Zn at the early anthesis stage. In the foliar application, ZnSO4 was sprayed at a rate of 0.66kg Zn/ha. Foliar spray of zinc sulfate at early anthesis, in general, had no significant effect on the yield and grain Cd while significantly increased grain Zn concentrations of most cultivars. On average, the foliar Zn treatment at the mid tillering stage (0.66kg Zn/ha), decreased the mean grain Cd concentration from 0.032mgkg−1 in the control treatment to 0.024mgkg−1. While the grain Zn concentrations of some cultivars increased with soil application of Zn sulfate, they were not affected or even decreased in other cultivars. For most studied wheat cultivars, pre-planting application of rubber tire ash in soil resulted in a significant decrease of grain Cd concentrations. The results show that the effectiveness of soil and foliar application of Zn on yield and grain Zn and Cd concentrations greatly depends on the cultivar. The currently recommended rates of soil applications of Zn to ameliorate Zn deficiency are sufficient to increase grain Zn and decrease grain Cd concentrations in some wheat cultivars, while they do not in the others. In this study, soil application of 250kg rubber tire ash/ha and foliar spray of 0.66kg Zn/ha at tillering stage were the most effective treatments to ameliorate Zn deficiency and to increase Zn and decrease Cd concentration in grains of most wheat cultivars.

AMELIORATION OF ZINC DEFICIENCY OF CORN IN CALCAREOUS SOILS OF THAILAND: ZINC SOURCES AND APPLICATION METHODS

A variety of zinc (Zn) fertilizer sources are applied with varied responses on calcareous soils in Thailand. Seed treatment is an alternative method to deliver Zn to corn and alleviate Zn deficiency. To address this Zn delivery methods we conducted greenhouse studies on corn grown in three calcareous soils of Thailand to three Zn fertilizer sources [zinc sulfate (ZnSO4), Zn-ethylenediaminetetraacetic acid (EDTA) and Zn citrate]. We also evaluated effectiveness of soaking corn seed in three concentrations of ZnSO4 (0.4, 0.8 and 1.6%) prior to planting compared to soil applied methods. Applications of zinc increased the growth, dry matter yield and zinc uptake of corn with few differences observed among the types of fertilizers. Seed soaking with ZnSO4 solution also increased Zn uptake, growth rate and yield comparable to soil-applied Zn. Seed soaking prior to planting is an effective and efficient method to supply Zn to corn grown in Zn deficient calcareous soils of Thailand.

Different increases in maize and wheat grain zinc concentrations caused by soil and foliar applications of zinc in Loess Plateau, China

Zinc (Zn) is an essential mineral nutrient for plant and human growth, and dietary Zn deficiency is a worldwide nutritional problem. Using different Zn fertilizer application methods, this study determines the potential of increasing the Zn concentrations of maize and wheat grain to improve the nutritional status of local residents. Field trials were conducted in the Loess Plateau for two growing seasons to investigate the effects of different Zn fertilizer application methods on the grain Zn concentrations of maize and wheat as well as the grain Zn recovery, yield, and iron (Fe) status of grains under rain-fed conditions. Soil and foliar Zn application did not significantly affect the biomass and grain yield of maize and wheat, suggesting that local soils are not Zn deficient. However, foliar Zn application significantly improved the grain Zn concentration of maize by 27% and 37% and of wheat by 28% and 89% during the first and second growing seasons, respectively. The maize grain Fe concentrations during both growing seasons were also enhanced by foliar Zn application. The foliar application of Zn realized higher grain Zn recoveries of 35.2‰ and 42.9‰ in maize as well as 26.4‰ and 32.3‰ in wheat during the first and second growing seasons, respectively, compared with the soil Zn application with a maximum grain Zn recovery of 1.7‰. Hence, in the Loess Plateau in China, foliar Zn application is an economical method of improving the grain Zn concentration in maize and wheat and increasing grain Fe concentration in maize.

Zinc priming promotes seed germination and seedling vigor of rice

AbstractThe present study evaluated effects of seed zinc (Zn) priming at concentrations from 0 to 25 mM ZnSO4 on seedling vigor and viability in rice (Oryza sativa L.). Zinc priming substantially increased Zn concentration in the husk, but not in brown rice. The movement of primed Zn from the husk into the inner layers of rice seed during germination was suggested by Zn concentration declining in the husk coinciding with the increase in brown rice over time (r = –0.62; p < 1%), which did not happen in unprimed seed. Zinc priming significantly enhanced seedling growth and development up to 5 mM. Germination rate, root number, and dry weight were much higher than in unprimed seed, but higher Zn concentrations (10 and 25 mM) depressed seedling vigor. Priming rice seed with 2.5 mM Zn also improved the germination rate of rice in a Zn‐deficient soil, with or without soil Zn application. The results confirm that priming rice seed with Zn can improve germination and seedling vigor and for the first time show how Zn requirement of germinating rice seed and seedlings can be met by the prime Zn accumulated in the husk.

Biofortification and estimated human bioavailability of zinc in wheat grains as influenced by methods of zinc application

Agronomic biofortification of Zn requires an effective Zn application method and efficient Zn utilization by the crops. Various Zn application methods were compared for Zn biofortification in grains of wheat grown in a calcareous soil under glasshouse conditions. Wheat (cv. Shafaq-2006) was treated with different Zn applications to soil (0, 4.5 or 9 mg Zn kg−1), seed (100 mL of either 0 or 6.75 % Zn w/v sprayed on 1 kg seed) and foliage (distilled-water-sprayed control, 1 mL of 0.05 % Zn w/v at jointing, 2 × 1 mL of 0.50 % Zn w/v at heading or combined jointing and heading sprays) in all possible combinations. Mineral (Zn, Ca and Fe) bioavailability to humans was estimated based on phytate-to-mineral molar ratios. Zinc bioavailability was also quantitatively estimated using trivariate model of Zn absorption. Soil Zn application increased grain yield (29 %), whole-grain Zn concentration (95 %) and whole-grain estimated Zn bioavailability (74 %). Foliar Zn application at heading also increased Zn bioavailability, but progressively less so with incremental soil Zn rates. Soil Zn application increased grain concentration and bioavailability of Ca, but decreased them for Fe. High soil Zn application increased estimated Zn bioavailability to humans. Also, medium soil Zn rate may be combined with foliar Zn sprays at heading where high soil Zn application is not feasible because of economic or environmental reasons.

Biofortification of rice grain with zinc through zinc fertilization in different countries

Increasing zinc (Zn) concentration of rice seed has potential benefits for human nutrition and health. Enhanced levels of Zn in grain also contributes greatly to crop production through better germination and seedling vigor of rice plants grown on soils with limited Zn supply. This study evaluated the effect of soil and/or foliar Zn fertilizer application on grain yield and grain Zn concentration of rice grown in 17 field trials conducted in 2008 to 2010 in China, India, Lao PDR, Thailand and Turkey on soils ranging in pH from 4.8 to 8.8 and DTPA- extractable Zn from 0.5 to 6.5 mg kg−1. Zinc fertilization had little effect on rice grain yield with the exception of increases of up to 10 % in some locations in China and India. As an average of all trials, Zn application increased grain yield by about 5 %. Grain Zn concentrations were, however, more effectively increased by Zn fertilization, especially with foliar Zn applications. On average, Zn concentration in brown rice (whole caryopsis with husk removed) was increased by 25 % and 32 % by foliar and foliar + soil Zn applications, respectively, and only 2.4 % by soil Zn application. The Zn concentration of un-husked rice (whole grain with husk), which was increased by 66 % by foliar Zn, showed a close association with the Zn in brown and white rice, indicating a possible penetration of Zn from the husk into the inner layers of the rice endosperm. Increase in grain Zn concentration by foliar Zn spray was significantly affected by the timing of the foliar application. More distinct increases in grain Zn by foliar Zn application were achieved when Zn was applied after flowering time, e.g., at early milk plus dough stages. Foliar Zn spray offers a practical and useful means for an effective biofortification of rice grain with Zn. This practice consistently and significantly contributed to increases in grain Zn of rice irrespective of cultivars, environmental conditions and management practices in 5 different countries.

Influence of zinc supply on the phytotoxicity of cadmium in maize (Zea mays L.) grown on cadmium-contaminated soil

Zinc and cadmium have been found to interact with each other differently under different conditions. The zinc supply may enhance or offset the phytotoxicity of Cd. Therefore, in a pot experiment, a sandy loam soil (Typic Ustipsamments) was treated with cadmium at rates of 0, 10, 20 and 40 mg kg−1 and with zinc at rates of 0 and 20 mg kg−1 soil to assess their effect on dry matter yield and the concentrations of Cd and micronutrients. There was a significant decrease in dry matter yield due to the phytotoxic effect of Cd. The dry matter yield was not affected by the application of zinc at any rate of Cd application. The concentration and uptake of Cd in the crop increased gradually at increasing rates of cadmium application. The increase in cadmium concentration was greater in the presence of zinc than in its absence. This suggests that the effect of soilapplied Zn is reflected in the enhancement of the Cd content in plants. Thus, zinc application cannot offset the toxic effect of Cd. The relationship of Cd with Zn and Fe was synergistic at all rates of Cd application, whereas Mn and Cu exhibited an antagonistic relationship.

Effect of soil and foliar zinc application on zinc concentration and bioavailability in wheat grain grown on potentially zinc-deficient soil

Three field experiments were conducted to determine the effect of soil Zn, foliar Zn, and soil N application on Zn and phytic acid concentrations in wheat grain grown on potentially Zn-deficient soil. Results showed significant genotypic variation in grain Zn concentrations among fifteen wheat cultivars commonly grown in northwest China. Soil Zn application had mixed effects, increasing grain Zn concentrations of some cultivars by as much as 21%, but reducing grain Zn concentrations of other cultivars by as much as 14%. In comparison, foliar Zn application increased grain Zn concentrations by 26 to 115%. Grain Zn concentrations were 14% larger in the combined (foliar Zn + soil Zn) treatment compared to the foliar Zn treatment, but the added cost of soil Zn application may not be economically justifiable. Wheat grain phytic acid concentrations and phytic acid: Zn molar ratios were less in the foliar Zn and (foliar Zn + soil Zn) treatments compared to the soil Zn and the unfertilized treatments. This indicated that foliar Zn increased Zn bioavailability. Best results were obtained when foliar Zn was applied at early grain filling. Overall, these findings indicate that foliar Zn application to Zn-efficient cultivars could reduce human Zn deficiency in regions with potentially Zn-deficient soil.

Zinc biofortification of wheat through fertilizer applications in different locations of China

Zinc (Zn) deficiency caused by inadequate dietary intake is a global nutritional problem in human populations, especially in developing countries. Biofortification of wheat and other staple foods with Zn is, therefore, an important challenge and a high-priority research task. In this study, one field experiment was conducted to examine the effects of soil and foliar Zn application with or without foliar urea application on Zn nutrition in whole grain and flour of wheat, and on flour processing traits. A second field experiment was conducted at four locations in China to evaluate the adaptability of foliar Zn and/or urea application on the enrichment of grain with Zn in wheat. The results showed that foliar Zn application was much more effective than soil Zn application in enrichment of wheat grain with Zn. Compared with no foliar Zn application, foliar 0.4% ZnSO 4·7H 2O application resulted in best effect on grain Zn, with 58% increase in whole grain Zn, 76% increase in wheat flour Zn, and up to 50% decrease in the molar ratio of phytic acid to Zn in flour. Foliar Zn application had little effect on flour processing traits including protein concentration, peak viscosity, and dough development time. The second experiment showed that foliar Zn application had reliable adaptability in biofortification of wheat with Zn, while had no yield penalty in regional scale. The results suggest that foliar Zn application represents an effective approach to provide more dietary Zn from wheat-derived products to humans.

Biofortification and Localization of Zinc in Wheat Grain

Zinc (Zn) deficiency associated with low dietary intake is a well-documented public health problem, resulting in serious health and socioeconomic problems. Field experiments were conducted with wheat to test the role of both soil and foliar application of ZnSO4 in Zn concentration of whole grain and grain fractions (e.g., bran, embryo and endosperm) in 3 locations. Foliar application of ZnSO4 was realized at different growth stages (e.g., stem elongation, boot, milk, dough stages) to study the effect of timing of foliar Zn application on grain Zn concentration. The rate of foliar Zn application at each growth stage was 4 kg of ZnSO4·7H2O ha(-1). Laser ablation (LA)-ICP-MS was used to follow the localization of Zn within grain. Soil Zn application at a rate of 50 kg of ZnSO4·7H2O ha(-1) was effective in increasing grain Zn concentration in the Zn-deficient location, but not in the locations without soil Zn deficiency. In all locations, foliar application of Zn significantly increased Zn concentration in whole grain and in each grain fraction, particularly in the case of high soil N fertilization. In Zn-deficient location, grain Zn concentration increased from 11 mg kg(-1) to 22 mg kg(-1) with foliar Zn application and to 27 mg kg(-1) with a combined application of ZnSO4 to soil and foliar. In locations without soil Zn deficiency, combination of high N application with two times foliar Zn application (e.g., at the booting and milk stages) increased grain Zn concentration, on average, from 28 mg kg(-1) to 58 mg kg(-1). Both ICP-OES and LA-ICP-MS data showed that the increase in Zn concentration of whole grain and grain fractions was pronounced when Zn was sprayed at the late growth stage (e.g., milk and dough). LA-ICP-MS data also indicated that Zn was transported into endosperm through the crease phloem. To our knowledge, this is the first study to show that the timing of foliar Zn application is of great importance in increasing grain Zn in wheat, especially in the endosperm part that is the predominant grain fraction consumed in many countries. Providing a large pool of Zn in vegetative tissues during the grain filling (e.g., via foliar Zn spray) is an important practice to increase grain Zn and contribute to human nutrition.

Short communication. Response of chickpea (Cicer arietinum L.) to soil zinc application

The response of chickpea (Cicer arietinum) to Zn nutrition was studied in pot experiments under natural conditions using four acid soils of northwest Spain during 2007 and 2008. Five concentrations of Zn (0, 1, 2, 4 and 8 mg Zn/pot) were added to the pots as Zn chelate. Chickpea responded to the soil Zn applications and there were highly significant differences between soils. At maturity plants fertilized with Zn had greater total dry matter production mainly due to increments in pods weight. The lowest yield (2.65 g/plant) was obtained from 0 mg Zn/pot, while the highest yield (3.52 g/plant) was recorded at 4 mg Zn/pot. The increased yields in Zn applied plants was the result of increased number of pods per plant. Furthermore, this yield component was closely correlated with the seed yield.

Zinc Nutrition in ‘Nagpur’ Mandarin on Haplustert

ABSTRACT Zinc (Zn) deficiency is the most prevalent nutritional disorder in citrus orchards world over. The management strategy of Zn deficiency today is still governed by the efficacy of two conventionally used methods of Zn supply to plants via soil or foliar fertilization. A field experiment with 12-yr-old ‘Nagpur’ mandarin (Citrus reticulata Blanco) orchard was, therefore, carried out during 2004–07 comparing soil application versus foliar application of Zn, each at three levels viz., 100, 200, and 300 g tree−1 with constant doses of N (600 g tree−1), P (200 g tree−1), K (300 g tree−1), and Fe(60 g tree−1) on Haplustert soil type with reference to response on flowering intensity, fruit set, tree volume, fruit yield, changes in soil fertility/leaf nutrient status, fruit quality, and transformation of native soil Zn fractions. Soil application of Zn at all the three levels, produced significantly higher increase in tree volume over foliar application on equivalent rates viz., T1 (2.53 m3) vs. T4 (2.06 m3) and T2(4.30 m3) vs. T5 (2.23 m3). The yield-determining parameters like flowering and fruit set intensity (no. m−1 shoot length) were, respectively, much higher with soil applied (135.74 and 21.90) than foliar applied Zn (31.20 and 11.6). These observations set the favorable conditions required for yield response, e.g., all the three treatments involving soil application of Zn, T1 (32.1 kg tree−1), T2 (52.6 kg tree−1), and T3 (51.8 kg tree−1) were correspondingly superior over T4 (22.5 kg tree−1), T5 (34.3 kg tree−1), and T6 (42.1 kg tree−1) as foliar application treatments. All the three major fruit quality parameters (juice, acidity, and TSS) were likewise more influenced by soil application than foliar application of Zn. Improvements in soil Zn fractions (mg kg−1) viz., exchangeable Zn (0.25–0.60), complex-Zn (2.71 to 4.86), organically bound Zn (0.86 to 2.0), and Zn-bound to carbonates and acid soluble minerals (2.56–4.96) were observed in response to Zn fertilization with treatments T1–T3. On the other hand, foliar applied Zn treatments (T4–T6) produced no such changes in any of the soil Zn fractions.

Vegetative and Reproductive Responses of Apple Trees to Zinc Fertilization under Conditions of Acid Coarse-Textured Soil

ABSTRACT The aim of this study was to examine response of apple (Malus domestica Borkh.) trees to zinc (Zn) fertilization under conditions of acid coarse-textured soil with low 1M hydrochloric acid (HCl)-soluble Zn level. The experiment was carried out during 2004-2005 at a commercial orchard in Central Poland on mature ‘Jonagold’ apple trees/M.26 EMLA, planted at a spacing of 4 × 2.5 m. The trees were sprayed with Zn: (i) prebloom, at the stage of silver tip, and tight cluster at a rate of 140 and 100 g ha− 1, respectively, (ii) postbloom, at the stage of petal fall, and 2 weeks later at a rate of 80 g ha− 1 in each spray treatment, and (iii) postharvest, 4–5 weeks before the natural leaf fall at a rate of 500 g ha− 1. Other trees were supplied with Zn to soil at a rate of 3 kg ha− 1. In all the studied treatments, Zn was used as ethylenediaminetetraacetic acid (EDTA). Trees unsupplied with Zn served as the control. Tree vigor, fruit set, yield and fruit quality at harvest (mean fruit weight, firmness, color, russeting, soluble solids concentration, and acidity) were not influenced by Zn fertilization. Postharvest Zn sprays slightly damaged leaf tissues but did not cause defoliation. Soil Zn application raised Zn concentrations in flowers, and leaves 28, 56, and 84 days after petal fall. Pre- and postbloom Zn sprays increased Zn status in flowers and leaves 28 days after flowering, respectively. The obtained results indicate that Zn fertilization of ‘Jonagold’ apple trees with Zn status in mid-summer leaves and flowers of 17 mg kg− 1 and 27 mg kg− 1, respectively, is not successful in improving vigor and tree yield.

Effect of split application of zinc on yield of rice (Oryza sativa L.) in an inceptisol

Rice is mostly transplanted under puddled low land soil conditions in India, where Zinc (Zn) deficiency is a common problem. The objective of this study was to find out the efficacy of split application of Zn on growth and yield of rice in an inceptisol. The split application of Zn as ZnSO4 · 7H2O performed better than its single basal application, while the split application of Zn-EDTA did not show any significant difference on yield and yield components of rice over its single basal application. Zn-EDTA was found to be better for growth and yield of rice among the two sources of Zn. The soil application of Zn at 1.0 kg ha−1 as Zn-EDTA (T7) recorded highest grain yield of 5.42 t ha−1, filled grain percentage of 90.2%, 1000-grain weight of 25.41 g and number of panicles m−2 of 452. The Zn content of grain and straw were found to be maximum in the treatment T7 i.e. 38.19 and 18.27 mg kg−1, respectively. Linear regression studies indicated that grain yield of rice is significantly influenced by Zn content of grain, Zn content of straw and DTPA extractable Zn content of soil at the level of 95.96, 96.74 and 95.57%, respectively.

THE EFFECT OF TRANSPORTER GENES ON ZINC STRESS IN APPLE (MALUS × DOMESTICA BORKH.)

Zinc deficiencies are commonly encountered on apple and are associated with poor tree growth, yields and fruit quality. Corrective foliar sprays and/or soil applications of Zn are only partially effective and may elevate Zn in the soil to levels of regulatory concern. The goal of this work is to elucidate the feasibility of increasing the uptake and transport of Zn to the aboveground parts by constitutively overexpressing Zn transporter genes in 'M.26' apple rootstock. Clones containing the coding regions of Zn transporter genes ZNT1 or ZIP4 were ligated along with a dual 35S promoter into a pBIN+ARS plasmid vector. Agrobacterium-mediated transformation was used to introduce the gene construct into in vitro apple explants of 'M.26' rootstock. The ability of three transgenic lines, T4 (ZNT1), T5 (Vector Control), T6 (ZIP4) and untransformed 'M.26', to absorb Zn were evaluated in a greenhouse, using diethylenetriamine pentaacetic acid (DTPA) chelator-buffered nutrient solutions containing low (2 μM) or optimal (24 μM) Zn concentrations. Plants grown under the low Zn level showed Zn deficiency symptoms and had reduced growth. The over-expression of ZIP4 and ZNT1 transporter genes in 'M.26' apple rootstock had very limited and no effect on the plants' Zn nutritional status, respectively. The over-expression of ZIP4, but not the ZNT1 transporter gene, consistently increased the concentration of Ca and Cu in all roots and aboveground tissues, thus indicating enhanced uptake and transport of these elements. The fact that ZIP4 was expressed to a greater extent than ZNT1, corroborates the increased tissue nutrient concentrations of the T6 (ZIP4) line.

Zinc Application Effects on Yield and Seed Oil Content of Sunflower Grown on a Saline Calcareous Soil

ABSTRACT Two field experiments (2000–2001 and 2001–2002) were conducted at two nearby fields in the Qanavat region of Qom province, central Iran, to investigate the effects of zinc (Zn) fertilization on production of sunflower. The experiment was conducted in a randomized complete block design with six treatments in three replicates. Treatments were: Zn0 (non-Zn fertilized), Zn10, Zn20, Zn30, and Zn60 (soil application of 10, 20, 30, and 60 kg Zn ha−1, respectively), and ZnSpray (foliar spraying of 0.5 kg Zn ha−1 using ZnSO4). Seeds of sunflower (Helianthus annuus cv. ‘Record’) were planted on June 20, 2000 and June 15, 2001. At harvest, shoot and seed yields as well as concentration of Zn, iron (Fe), manganese (Mn), sodium (Na), and chloride (Cl) in leaves of sunflower were determined. Addition of 20 kg Zn ha−1 significantly increased seed production and shoot dry-matter yield of sunflower, while other Zn treatments had no significant effect on shoot dry-matter yield, or decreased it. The thousand-seed weight was the yield component most affected by Zn fertilization, while plant height and head diameter did not change. The maximum content of seed oil was achieved under the Zn10 treatment, then decreased at higher rates of soil-applied Zn such that oil content of seed under the Zn30 and Zn60, treatments was significantly lower than that of the control. Seed oil content was unaffected by foliar spraying of Zn. The concentration of Zn in sunflower leaves was increased with an increase in soil-added Zn of from 0 to 60 kg Zn ha−1. The highest leaf concentrations of Zn (162 and 175 mg kg−1 day matter (DM) in the first and second year, respectively) were achieved by foliar application of ZnSO4. Leaf concentration of Fe was significantly increased in the Zn20 treatment compared with the control but decreased at the higher rates of soil-added ZnSO4. Soil addition of different levels of ZnSO4 decreased concentration of Na and Cl in leaves. The lowest concentration of Na and Cl in leaves was observed under Zn20. The results of this study suggest that soil application of a suitable amount of Zn has a positive effect on both quantitative and qualitative yield of sunflower in saline, calcareous soils.

An evaluation of foliar nitrogen and zinc applications to macadamia

The efficiency and effectiveness of foliar nitrogen (N) applications as urea to macadamia leaves were investigated in field experiments at Alstonville, New South Wales. The first experiment (August 2000) evaluated the effect of 1–8% urea solutions on the evidence of leaf burn. A 2% urea solution produced negligible leaf burn (1% leaves with lesions) whereas the incidence of leaf burn increased with urea concentration; 20% of leaves were affected with an 8% urea solution. In the following month, a second experiment was conducted using a 2% urea solution that was painted onto both sides of leaves to measure N uptake efficiency. The urea was enriched with the stable isotope 15N, which allows a direct measure of urea uptake, a common method for tracing plant N uptake. Leaves were sampled after 3 and 6 days, and cellulose acetate was then applied to remove urea adhering to the surface of leaves. Leaves adjacent to urea-treated leaves were also sampled to account for any transport out of treated leaves. The experiment was repeated in September 2001. In 2000, a mean of 31% of the urea was absorbed by the mature leaves and this increased the N content by 2.2%. In 2001, a mean of 38% of the urea was absorbed by the mature leaves and this increased N content by 1.9%. Leaves from part of a large mature macadamia tree were stripped to provide an estimate of leaf biomass. From this, the increase in leaf N uptake for a mature orchard was calculated to be 3.98 kg/ha in 2000 and 4.57 kg/ha in 2001. The efficiency of application and hence leaf N uptake from a commercial spray would be expected to be lower than that of the present study. Commercial foliar urea applications are unlikely to meet the N requirements of a productive macadamia orchard. In a separate study, the efficiency of zinc (Zn) fertiliser as soil (5–20 g Zn/m2 canopy ground area) and foliar applications were examined at a mature commercial orchard near Alstonville on a Ferrosol soil. In August 2001, a 2% solution of zinc sulfate heptahydrate was thoroughly applied to the canopy of trees using a backpack misting machine and mature leaves were sampled 4 weeks later. Non-sprayed control trees were also sampled. Cellulose acetate was applied to sampled leaves to remove foliar-applied Zn adhering to the surface of leaves. The leaf Zn concentrations were increased (P<0.05) from 11 to 52 mg/kg 4 weeks after foliar Zn application. Sprayed leaf Zn concentrations were stable 18 weeks later, and flush leaves that emerged after spray application had similar (P>0.05) Zn concentrations to control leaves 12 months later indicating that little if any remobilisation of Zn had occurred over these periods. Soil Zn application had no effect (P>0.05) on leaf Zn concentrations 1 and 2 years after application. The effectiveness of a commercial foliar Zn application was evaluated in September 2001 using a low set orchard sprayer and a 1% Zn solution. After 4 weeks, leaf Zn concentrations were increased from 12 to 26 mg/kg. Foliar Zn applications can be recommended to increase leaf Zn concentrations in macadamias despite evidence in the literature for only 1% uptake efficiency.

Micronutrient Constraints to Crop Production in Soils with Mediterranean-type Characteristics: A Review

Mediterranean-type soils generally have free CaCO3, high pH, and low organic matter. Consequently, nutrient disorders in these soils are the most important limiting factor to crop production, second only to moisture stress. Major problems are deficiencies of nitrogen and phosphorus; however, recent research has revealed that micronutrient problems are also hampering crop production. Unlike major nutrient deficiencies, micronutrient problems are highly genotype-specific and location-specific. Zinc (Zn) deficiency is the most widespread problem, because of factors like alkaline soil pH, calcareousness, low organic matter, exposed subsoils, Zn-free fertilizers, and/or flooding-induced electro-chemical changes. Now zinc sulfate is commonly used in rice, wheat, barley, potato, citrus, deciduous fruits, and many other crops. Soil-applied Zn has a relatively long residual effect. Efforts are also underway to develop crop varieties for higher Zn efficiency. Iron (Fe) chlorosis, the second most important micronutrient disorder, is induced by high soil in calcareous soils; high moisture and cold temperature accentuate it. Legumes, citrus, and deciduous fruits are more susceptible. Soil fertilization for iron is problematic; therefore, foliar feeding or breeding for tolerance remains the practical solutions. Boron (B) is a nonmetal micronutrient. While B deficiency has not been observed widely, research in the recent past has revealed this to be a widespread problem in crops like cotton, rapeseed, wheat, peanut, sorghum, and rice. The deficiency can be corrected by its soil application or by foliar feeding. As the concentration range between B deficiency and toxicity is exceptionally narrow, both are field-scale problems in the Mediterranean-type soils. Unlike B deficiency, B toxicity diagnosis is not simple, because of its accumulation in sub soils and resemblance of the symptoms with leaf fungal diseases. Also, B toxicity cannot be ameliorated for all practical purposes. Thus, breeding for B tolerance remains the only option. Luckily, many landraces of barley and wheat are quite tolerant to B toxicity. Deficiencies of manganese (Mn) and copper (Cu) are not a perceived problem, and availability of molybdenum (Mo) and chloride (Cl) is high in Mediterranean-type soils. Soil micronutrient deficiencies not only reduce crop productivity, but low Zn and Fe plant food is also adversely affecting human health and well-being. Though fertilizer use for micronutrients is highly cost-effective, actual use remains rather limited to a few specific crops in various countries. Thus, micronutrient problems are likely to be accentuated because of increased pressure on soil resources.

Zinc responses of dry beans in Manitoba

Close to 80% of dry beans in western Canada are grown in southern Manitoba. A need was identified to develop soil-testing criteria based on local conditions as well as derive an optimum fertilizer rate to alleviate Zn deficiency. Two experiments with a number of dry bean (Phaseolus vulgaris L.) cultivars were carried out between 2000 and 2002 at a number of locations in Manitoba. Each experiment included two trials per year. The first experiment consisted of two foliar application rates of Zn (0 and 0.33 kg ha-1) as main plots and five rates of broadcast and incorporated soil Zn (0, 2.8, 5.6, 8.4 and 11.2 kg Zn ha-1) as sub-plots. The second experiment also included two rates of foliar Zn (0 and 0.33 kg Zn ha-1) as the main plots; however, sub-plots included a control and four Zn products that were broadcast and incorporated at a rate of 5.6 kg Zn ha-1. Soil DTPA-extractable Zn levels varied from 0.38 to 1.14 mg Zn kg-1 soil. Soil Zn applications resulted in a significant increase of Zn in plant tissue levels at 1/10 bloom growth stage, however, actual levels varied, thus, suggesting that a plant tissue critical level will have to be derived separately for each cultivar. Significant seed yield responses were obtained only when DTPA-Zn levels were equal to, or less than, 0.5 mg Zn kg-1. Optimum yields at responsive sites were obtained with 5 kg Zn ha-1 broadcast and incorporated. All products used (Zn mono- and heptasulphate or oxysulphate) performed equally well, except in one case when ZnSO4.H2O exhibited superior performance. Foliar application of a sulphonic acid based Zn product was not always as effective as soil applied Zn products. Key words: Dry bean, Phaseolus vulgaris L., DTPA extraction, foliar, soil, Zn products