Suitable vegetable oils include all liquid vegetable oils. Preferably, the vegetable oils are refined so as to remove gums and excess acidity to 10 ensure that the liquid emulsion composition is stable, liquid and sprayable. A typical embodiment are methyl esters of canola oil, where the major component is methyl oleate.
A typical embodiment is a C Guerbet alcohol. For example, zinc could be incorporated into a formulation according to the invention as zinc chloride or zinc sulphate 5 water-soluble salts. Other examples of suitable essential elements include manganese chloride tetrahydrate, magnesium chloride, calcium chloride, boric acid, and boric acid diethanolamine adduct. When formulating with water soluble salts of essential elements, those with high solubility are preferred such as the chlorides, nitrates, sulphates or carbonates.
Other issues, such as 10 incompatibility between different ingredients, redox reactions and formation of insoluble salts, need to be taken into account when preparing compositions according to the invention, particularly when formulating with more than one essential element.
The essential elements may also be present in an oil soluble form such as an oil soluble salt or chelate. Examples of an oil soluble salts are zinc 2-ethylhexanoate and copper abietate. There are different ways of reporting the quantity of essential elements in foliar nutrient products.
The compositions in Table 1 of Example 1 show the proportion of ingredients input so a calculation is required to determine the amount of essential element in each composition. For example, a greater weight of the boric acid-diethanolamine adduct would be used than if boric acid is used to provide an equivalent amount of the essential element 25 boron.
Preferably, the amount of essential elements used in the composition is in the range of from 0. In certain embodiments, where the essential element is in an oil-soluble form, then the essential element can simply be dissolved into the oil to form an oil solution.
The emulsion may be of any form including a micro-emulsion or a coarse emulsion depending on the particular salt or chelate and the surfactant used. In certain embodiments, where more than one essential element is used and at least one essential element is in an oil-soluble form and at least one essential element is in a 5 water-soluble form, then the formulation according to the invention may be an emulsion comprising the oil-soluble essential element in the oil phase and the water soluble essential element in the water phase.
In the embodiments, where a surfactant is used to prepare an emulsion, the surfactant's role will be multi-faceted. It will enable the oil and essential elements to form a homogeneous 10 liquid. It will also allow the formulation to be dispersible into water for spray application and may help the spray application to adhere to and spread across foliar surfaces and to promote foliar uptake.
In the embodiments where an oil-soluble essential element is dissolved in oil, it may be desired to also add a surfactant to act as a dispersing agent and potentially help the spray 15 application to adhere to and spread across foliar surfaces and to promote foliar uptake.
Preferably, the amount of surfactant used in the composition is in the range of from 0. Some surfactants may be responsible for undesirable side-effects when applying foliar nutrients to certain crops. For example, some surfactants may increase the risk of crop phytotoxicity, foaming, driftable fines and toxicity to non-target organisms such as insects and aquatic life and as such there may be a need for foliar nutrient products containing low 15 levels of total surfactants.
In certain embodiments, it is preferable for the liquid foliar nutrient composition to contain a low level of surfactant. For example, such liquid foliar nutrient compositions may comprise an amount in the range of from 0. The composition may contain other surfactants to assist with application of the composition. Preferably, the ratio of total surfactants both the high molecular weight polymeric surfactants and the surfactants to assist with application in the composition to oil is less than , more preferably less than , and most preferably less than Preferably, the composition may include other additives such as acidifiers and coupling agents which may be desirable to help the form of the composition.
Examples of acidifiers include lactic acid, propionic acid and citric acid. Compositions according to the invention may comprise components which provide some of the major elements normally provided to such plants. Whilst these major elements are 5 not the focus of this invention, one or more of them may be present in compositions according to the invention, either deliberately or as a natural consequence of the choice of ingredients. For example, the urea, nitrogen containing surfactants and ammonium acetate coupling agents will also provide some nitrogen supplementation.
Other major elements which may be included are phosphorous, potassium and sulphur. For example, if the 10 essential element is provided as a sulphate or phosphate salt then the plant will also receive some sulphur or phosphorous. Nitrogen supplementation can also be achieved by adding amino acid solution to the composition. Compositions according to the invention increase the uptake of the essential elements by the crop after foliar application.
Further, the increase obtained by specifically formulating 15 the essential elements with oil in a composition according to the invention is significantly more than that obtained by simply adding individual oil-based adjuvants to the tank mix.
Zn, Ca, Mg, Si, Se and 25 mixtures thereof; and b administering the composition to the crop. As per current common practice, the method may further comprise adding organic matter or combinations of N, P, K or S to the crop. Example 1 In this example, various formulations according to the invention were prepared. All the formulations presented in Table 1 are stable homogeneous liquids which can be easily dispersed into water for spray application.
Formulations A, B, C, D, H, I, J and K are micro-emulsion formulations where an aqueous solution containing essential element s in salt form is emulsified with an oil using 15 surfactants. Formulation G is a stable coarse emulsion prepared using polymeric surfactants with a ratio of total surfactants to oil of Formulations E and F are oil solutions where the zinc has been dissolved in the oil as an oil-soluble salt. Formulation L was prepared using polymeric surfactants with a ratio of total surfactants to oil of Formulation I contains a boric acid - diethanolamine adduct containing approximately 25 Methodology and Results 5 Table 2 shows the treatment list and results for the field experiment.
The results reported are an average of four replicates plot size 2 x 20m. Analysis was of the youngest emerged blade 14 days after treatment for Zn 10 content of the foliage and for zinc content of the grain at harvest. This was exhibited in both the foliage and in the grain. The individual adjuvants appeared to enhance the uptake of zinc cf Treatment 3 , but not as significantly as the 25 formulations according to the invention where zinc was co-formulated with the oil and surfactants.
In particular, VCC Example 4 In this example, formulations according to the invention were tested to determine foliar 5 uptake of boron into the foliage and developing fruit. Hence, the main challenge of foliar sprays is to apply the optimum nutrient dose which corrects or prevents nutrient deficiency without causing leaf scorch. Foliar uptake rates are not only controlled by the resistance of the leaf surface but also by the nutrient concentration on the leaf.
The solute concentrations in foliar sprays are in most cases initially not in equilibrium with the humidity of atmosphere. As a consequence, spray solutions will evaporate until this equilibrium is reached.
It has been shown that the equilibrium concentrations of foliar-applied solutes present on the leaf surface depend on both the ambient relative humidity RH and the hygroscopicity of the solute Fernandez and Eichert, The degree of hygroscopicity of a solute can be defined by the RH above which the salt dissolves in the water absorbed from the atmosphere. The pathways by which foliar-applied solutes penetrate leaf surface have been a matter of debate for a long time.
They were believed to be specific structures in the cuticle designed for foliar uptake of hydrophilic solutes such as nutrient salts Franke, , ; Schumacher and Lambertz, This concept was later revoked Schonherr, ; Schonherr and Bukovac, but still circulates in textbooks and reviews.
While some research groups regarded the role of stomata as negligible Schonherr and Bukovac, and thus focused on the cuticle e. It is now established that these two pathways, stomata and the cuticle, act in parallel, but their relative importance will depend on the properties of the foliar-applied solute Eichert and Fernandez, Relative humidity not only regulates the concentration of applied nutrients on the leaf surface as described above but also affects the permeability of the leaf surface by modifying the aperture of stomata and the hydration state of the cuticle.
However, the functional relationship between RH and leaf permeability is still not fully understood Fernandez and Eichert, The increased theoretical knowledge on the principles of foliar penetration has some implications for the practical use of foliar application of mineral nutrients on fruit trees. Since many plant species, such as fruit trees, lack stomata on the upper leaf side, maximum uptake rates of foliar-applied nutrients can only be achieved if the lower leaf sides are sprayed as well.
Furthermore, knowledge on the deliquescence properties of the applied salts may enable us to more accurately control the uptake rate and recovery of foliar-applied nutrients. Salts with a low DRH such as calcium chloride CaCl 2 tend to remain in solution and can thus be efficiently absorbed by leaves even if RH is low, leading to high uptake efficiency or recovery.
If on the other hand, fast absorption has to be avoided to reduce the risk of leaf scorch, salts with a high DRH can be selected. Nitrogen, for example, is often sprayed in comparably high concentrations, and the resulting high N doses on the leaf surface would induce scorch if absorbed in too high rates. Therefore, foliar N application compounds with rather high DRH values, such as urea, should be selected when the environmental conditions such as RH and temperature permit Eichert and Fernandez, Calcium and N are the most important and commonly used elements applied through foliar applications in tree fruit, including apple.
Fisher reported that trees receiving three foliar urea applications had a similar yield as those with a similar amount of N applied to the soil.
In that report, leaf minerals other than N also were affected by both amount and method of urea application Forshey, The effectiveness of spring-applied foliar urea sprays for fruit trees is controversial. Some researchers have reported that foliar urea applied in the spring is equally or more effective than soil N applications in improving fruit set and subsequent fruit size and yield Blasberg, ; Fisher and Cook, Others have found that the effects of this practice are largely confined to the sprayed leaves and do not affect fruiting or the N status of the entire tree Forshey, Sanchez et al.
Structural N may be more difficult to remobilize than N that accumulates in leaves later in the season Khemira et al. The orchard was irrigated using a sprinkler system.
Experimental N treatments started in The rate in the ground application was similar to the lowest rate that is commonly applied to young apple trees in the Pacific northwestern United States. At each application time during , trees were sprayed to the drip point with urea dissolved in water, at one of the following rates: 3. Spray3 caused minor leaf burning in At each spray time during and , the foliar treatments were: 1.
Spray3 treatment was at the maximum rate beyond which leaves would be injured. In , the foliar applications were made on 1 July, 1 Aug. In and , foliar applications started at full bloom 5 May and 3 May and continued once per month until September total of five sprays each year.
In the ground treatment, urea was applied to the soil in a 2-ft radius around the tree trunk at the rate of To establish the one rate ground-applied urea treatment, two ground applications of The experimental design was a randomized-complete-block split-plot design, with three rootstocks as main plots, four N treatments as subplots, and five blocks.
Within each block, a single tree was used for each rootstock-nitrogen combination. Each treatment was protected with at least two guard trees. Trunk cross-sectional area TCA was calculated from trunk diameter 6 inches above the bud union in late February in — Yield was recorded and yield efficiency was calculated as kilograms per square centimeter of TCA. Thirty-four fruit from each tree were picked randomly at commercial harvest 17 Oct.
Fruit were divided into two groups, weighed, and placed in perforated polyethylene bags. Fruit from one bag were tested for various quality attributes at harvest and fruit of the other bag were used for poststorage analyses.
Fruit firmness was measured on three peeled sides of each fruit by a penetrometer Facchini, Alfonsine, Italy. Fruit were then cut equatorially. One wedge from the calyx-end half of every fruit was juiced and the soluble solids concentration SSC was measured. The stem-end half of the fruit at harvest was dipped in iodine solution containing potassium iodide and iodine crystals dissolved in water and the starch degradation pattern SDP for each fruit at harvest was recorded.
Leaves were washed, dried, ground, and analyzed for N by the micro-Kjeldahl method Schuman et al. Analyses of variance were conducted by SAS version 9. Soil conditions, tree training, and cultural practices, other than Ca treatments, were similar to those described earlier for urea experiment. Two formulations of commercial foliar Ca fertilizers were sprayed at different frequencies during Treatments were as follows: 1 untreated control; 2 chelated calcium 5x, CaCl 2 3x where chelated calcium was applied five times, beginning with the early petal fall stage and continued during growing season, and CaCl 2 at 0.
In each treatment containing chelated calcium, 1. Fruit yield and quality attributes were measured as described earlier for urea applications. There was no interaction between rootstocks and N treatments for any parameter measured and thus, results over the three rootstocks were pooled and only results for the N treatments are reported here.
Trunk cross-sectional areas of all trees were similar before treatment in Table 1. In and 1 and 2 years after the beginning of N treatments, respectively , trees in the ground treatment had higher TCA than other treatments Table 1. In , differences in TCA among treatments were not significant Table 1.
Yield per tree and yield efficiency in the ground treatment were significantly greater than those with foliar N sprays Table 1. Fruit from trees with ground and Spray3 treatments were heavier larger than those of Spray1 and Spray2 treatments because both ground and Spray3 had similar levels of leaf N, and these levels tended to be greater than those of Spray1 and Spray2 in Table 2.
With the exception of the higher fruit weight in Spray3 treatment, the effects of various N sprays on growth, yield, and most fruit quality attributes were not different from each other. The total N application from to in the ground treatment was also slightly higher than that of the highest foliar application Spray3.
Ground-applied N in this experiment was at a low to medium rate that commercial growers apply to new orchards in the Pacific Northwest. Nevertheless, the portion of untaken N by the trees in the ground treatment was greater than the amount absorbed through the foliar applications, leading to a greater leaf N concentration in Table 2 , which resulted in greater tree growth, yield, and fruit size. In this experiment, the highest foliar treatment per application time Spray3 was We had less number of foliar sprays during growing season than in or We noticed very minor leaf burning along the tip of the leaves in Spray3 treatment.
Thus, if we had sprayed enough N to supply the same amount of N that we did with the ground application, this would have caused phytotoxicity in the trees.
Although maximum production of high-quality fruit is the goal of any apple grower, extremely high production often results in lower fruit quality Fallahi et al. It is noteworthy that in this experiment, ground N application increased fruit size, in spite of the yield increase compared with Spray1 and Spray2 treatments Table 1. Thus, ground N application, even at as low of a rate as used in this experiment, is more effective in early canopy establishment and production than repeated spray applications of N throughout the growing season.
Leaf N concentrations from all N treatments were similar in Table 2. In , however, leaf N increased with an increase in the total amount of N application because N treatments had more time to show their effects. Fruit color was unaffected by N applications data not shown. Fruit from all treatments, including those of ground treatment, had color ratings greater than 3. None of these treatments resulted in an excessively high leaf N and thus did not affect the fruit skin color adversely.
Ground application of N decreased fruit firmness both at harvest and after storage, as compared with low foliar application, perhaps due to the larger fruit size in this treatment Table 1. Leaves from trees with the ground treatment had lower percent dry weights than those from all foliar treatments in and lower than those from the Spray1 and Spray2 treatments in Table 2.
Trees receiving ground N application had significantly lower leaf K but higher leaf Ca than those receiving foliar treatments in both and Table 2. Fruit flesh of trees sprayed with CaCl 2 had lower N concentration than untreated control Table 3 and the reason for this warrants further study. Applications of Ca in both formulations and all frequencies increased flesh Ca concentrations as compared with untreated control. There was no significant difference in the Ca concentration of peels among different treatments.
With the exception of the chelated calcium 4x, CaCl 2 3x treatment, all the other Ca treatments tended to increase flesh and peel B concentrations, although differences were not significant Table 3. Five applications of chelated calcium plus CaCl 2 resulted in higher leaf Ca than other treatments. Fruit from all Ca treatments had lower sunburn, which is very beneficial to apple growers. There was no difference between the untreated controls and any of the Ca treatments on quality attributes and yield factors at harvest.
The fact that Ca application tended to increase flesh Ca and reduce flesh N concentrations indicates that Ca application could increase fruit quality after storage, even though these differences could not be seen at harvest time.
A better understanding of the cuticle uptake mechanism is essential to achieve efficient foliar nutrient uptake in tree fruit. Relative humidity plays an important role in the foliar nutrient uptake and this field deserves further study. In addition to the routine applications of micronutrients, N and Ca can be foliary applied to improve fruit quality. However, a ground application of N is required as the N requirements of an apple tree may not solely be fulfilled through foliar N applications.
It appears that application of Ca in the form of CaCl 2 could be as effective as the application of more expensive forms of Ca compounds but this area also deserves further investigation.
Blasberg, C. Chaplin, M. Eichert, T. In: P. Marschner ed. Academic Press, Oxford, UK.
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