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Foliar fertilization is not a new concept. Historically foliar fertilizers have been around since 1844. About this time in France foliar fertilizers with Iron sulfate was successfully used to correct plant chlorosis. Some studies actually showed that foliar fertilizer’s use was widely practiced, and many people knew about foliar fertilizers, and how to apply them. The qualities of foliar fertilizers of foliar fertilizers are still not known in many places around the world, whereas in other places, graduate agriculturists and agricultural scientists even contest their existence. Scientists have had many discussions about plant feeding by the leaf, and specially about the absorption by the leaf. It is true that foliar fertilizer’s efficiency has already been proved in practice long before science was able to give a clear explanation of the mechanisms of foliar fertilization.
There are many reasons foliar fertilizers are better than basic soil fertilizers, for example in case of soil deficiency in nutrients due to their total absence or trace elements being bound because of unfavorable soil conditions.(Alexander pg. 5). Stress situations during growing stages can be effectively overcome with foliar fertilization. This is an important factor because stress influences growth, and also overall yield of our crops. Foliar fertilization is more economic than root fertilization due to the higher degree of applied nutrients used and taken up by the leaf. This usually is approximately 85% compared to a mere 10%, 30% max and in exceptional cases’ 50% by the roots.(Fergoni,M pg231-233) This of course makes the nutrients more available to the plants. It seems strange that even though there are all these advantages foliar fertilization it is still met with skepticism. There are many reasons for this though. In these days nobody doubts that foliar fertilizers are capable of quickly and cheaply overcoming deficiency symptoms. Many specialists however admit the yield guaranteeing effect of foliar fertilization, but argue its increase on actual yield on not particularly deficient soils is still often contested.(Alexander pg. 6) This skepticism also results out of very different foliar fertilizers affects which are a result of foliar fertilizers general directions for use. Foliar fertilizers often require a special application according to local particularities such as cultivated variety, climate, location, stage of plant growth, the timing of application, and many other circumstances.
So now we know a brief history of foliar fertilizers and why they are economically beneficial in plant growth. We also have looked at the conditions that can determine their actual effectiveness. But, we know nothing about how the plant actually takes in the nutrients and uses them. In the next paragraphs I will give a brief explanation of the physiology of a plant and its uptake of foliar fertilizers.
The actual mechanism of plants taking up foliar fertilizers is a very difficult one to explain and for me it is even harder to comprehend. It is to be hoped that I will understand more on the subject after Biology 215. However I will try to explain in two steps.
1. Aqueous solutions Are absorbed or excreted not through the entire cuticle but through punctiform areas, the location that coincides with the position of the ectoteichodes that project radially into the wall. This at least means that a preferred area of permeation for aqueous solutions exists in the cuticle above an ectoteichode.
2. If these structures serve to excrete aqueous solutions from the leaf, as has been demonstrated, then they will also be suitable for the reverse process, for example absorption into the leaf. This has also been demonstrated with the aid of radiolabbelled materials.( Radioactive materials were actually put into a foliar concentration and after intake by the plant they could see the actual mechanisms of foliar fertilization.) When the dissolved substance , i.e. HgCL2 , have penetrated the cuticle on their way in, they are not diffused in all directions but in the tubular cavity systems of the ectoeichodes as far as the plasmalemma, where the active transport process into the cytoplasm is completed.
In all, the theoretical capability of leaves to absorb materials, e.g. of foliar feeding, exist, although the intensity of absorption is limited because of the relative barrier represented by the cuticle: it is not possible, as trials have shown( Zu Frage pg. 63-68) solely to feed plants by the leaves and to bring them to full development and adequate fruit formation. Compared with the uptake of nutrient salts through the roots, however, foliar fertilization is doubtless a much more speedy way of supplying microelements in particular. It can although be used to satisfy acute needs, with lower concentrations of microelements.( Alexander pg. 23)
Now that we have an idea of how foliar fertilizers actually work we need to know how and when to actually apply them. There are crucial stages of growth in each plants life. Some need to be sprayed when they are young, and some fruit trees need to be sprayed after harvest. In Alexander s book I found a very useful chart on a numerous number of crops grown throughout the world.(Alexder pg. 49-55.) Please note these following charts.
So we know when to apply these foliar fertilizers, but how should we actually apply them in order for maximum efficiency. One important criterion of the effectiveness of nutrient sprays is the rate at which the foliar applied nutrients are absorbed by the leaves and translocated throughout the plant. The uptake of the nutrients is farther effected by the number of factors which many are still not known to this day. Some of these factors include temperature, light, wind, humidity, photoperiod, the concentration of the spray, wetting agent, pH of foliar spray, cuticle wax on plant, age of leaf, surface moisture of leaf, the growth stage and many other factors. These factors lead lead to a great variability in the uptake of foliar uptake of nutrients and therefore are responsible in part for the variable response of foliar fertilizers. The effect of any of these factors varies with the soil and environmental conditions, some are related, thereby making the yield response to foliar fertilization both variable and complex in nature. Out of all the factors that effect foliar sprays efficiency the most important is the timing of the spray and this depends directly on the individual plants.
Foliar fertilizer application allows a combination of operations, namely applications that contain both pesticides and fertilizers. (Alexander pg 45.) Where repeated spraying are normally done because of the pest problem, the disadvantage of application costs for foliar fertilization is reduced. From the point of view of optimum yield, foliar fertilization, should be performed when the plant s requirements are high and the nutrient uptake through the plant roots is restricted. The restriction may be due to either plant or soil limitations. It will not be possible to combine foliar fertilization with pesticide spraying agents in order to save costs. Many farmers then switch to a regular application of foliar fertilizers together with the plant protection agent.
Foliar fertilization presume that sufficient foliage has developed for the major part of the nutrients in an application of foliar fertilizer to be in fact absorbed by the leaves a certain stage of development must therefore have been completed during which the plants can be nourished only by the roots, before there is any point in foliar fertilization.
If in certain crops and for certain crops and for certain nutrients foliar application should be done at an early growth stage, it is therefore necessary to reach a compromise between early application and allowing the crop to attain a leaf large enough for the absorption of large amounts of nutrients. With wheat and barley, for instance, copper should be applied not much later than the end of tilling, so that the plants have an adequate supply of copper to pollen formation and development. (Alexander pg.47)
All crops are characterized by growth stages needing a particular supply of all or of certain nutrients to reach their optimum yields. Plant demand is generally at its maximum during the period of exponential growth.(Alexander pg. 47) During these critical stages leaves can absorb a large amount of nutrients by the leaves. There are also times when the nutrient uptake from the soil is handicapped to such a point that there is no guarantee that all the parts of the plants will receive an adequate supply of nutrients. A good example is dry weather, even foliar fertilization is no longer able to exercise favorable influence on the yield. On the other hand, during short times of dry weather foliar fertilization may be the only measure particularly in critical growth stages that can assure the full yield.
If a period that the plant has difficulty absorbing nutrients by the leaves coincides with a period the plant has a high demand for nutrients, there will be significant loss to yield. The farmer will not be unable to notice this before it’s too late. In the next tables’ recommendations for optimum timing of foliar nutrient sprays for specific crops these are drawn from Alexander s book. The recommended timing of foliar sprays generally reflects the growth stages of the single crops where the demand for specific nutrients is crucial.
In conclusion foliar fertilizers can be a great benefit to increasing yield to crops, but they must be applied at the correct time. Every plant has a different growth stage that foliar fertilization is most beneficial. As well as the time of plant many environmental conditions must also be perfect also for maximum efficiency. Knowing these facts about the yield increasing effects of foliar fertilization we can say there is no doubt it has a definite place in agriculture and horticulture and we will probably see its use more in the future.
Foliar Fertilization Developments in Plant and Soil Sciences
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