Miracle-Gro 3002510 Shake 'N Feed Tomato, Fruits and Vegetables Continuous Release Plant Food Plus Calcium
- Contains natural ingredients to feed microbes in the soil
- Specially formulated with micronutrients to help plants grow strong and produce more fruits and vegetables versus unfed plants
- Feeds up to 3 months
- Calcium helps form stronger cell walls, producing better quality and longer-lasting fruits and vegetables. Plus, it helps prevent disorders in edible crops commonly associated with calcium deficiency.
- For use in ground and in containers
- Now contains natural ingredients that helps feed and nourish above and below soil, for even better quality and longer lasting fruits and vegetables versus unfed plants
SOIL ELEMENTS ESSENTIAL FOR PLANTS
Summary.
- 1. Criteria of essentiality.
- 2. Absorption of nutritive elements by plants.
- 3. Classification of nutritional elements.
- 4. Conclusions.
SUMMARY
Current knowledge about plant organisms makes it possible to ensure that almost all of them are composed of only three fundamental elements, which are C, H and O. Plants obtain both carbon and oxygen directly from the air by photosynthesis, while the Hydrogen comes directly or indirectly from soil water. Plants, however, are incapable of living solely on air and water, requiring chemical elements that, generally, are provided at the expense of mineral substances in the soil. It is interesting to note that these elements, which plants obtain from the soil, are the ones that commonly limit the development of crops. Plant growth, except for exceptional circumstances, such as drought, low temperatures, abnormal soils or diseases,
1. ESSENTIAL CRITERIA
These essential criteria were established by Arnon and Stout in 1939 and are listed below:
- 1. An element cannot be considered essential unless its absence makes it impossible to complete the vegetative or reproductive stages of its life cycle.
- 2. The deficiency must be specific to the item in question, and can only be avoided or corrected by providing it.
- 3. The element must be directly involved in the nutrition of the plant, regardless of its possible effects on the correction of unfavorable chemical or microbiological conditions of the external environment.
Although these criteria have been accepted as valid and fully applied to all living things, some researchers consider that the second criterion is not totally correct. For example, molybdenum is required for N fixation by bacteria of the genus Azotobacter sp . However, in some species of this genus molybdenum can be substituted for vanadium. Another example is sodium, which is not considered essential for all plants, but its presence has been shown in practice to increase yield in many crops. Therefore, from an economic point of view, sodium should be considered an essential element.
2. ABSORPTION OF NUTRITIVE ELEMENTS BY PLANTS
Only a small part of each nutrient present in the soil is available to plants (2%). The rest (98%) appears in forms not assimilated by plants, that is, it is firmly linked to the mineral fraction and organic matter, being inaccessible as long as it is not affected by the decomposition processes. These occur slowly, over long periods, and the nutrients are released gradually.
Plants absorb the nutrients contained in the air and in the soil through the leaves and roots. CO 2 , a source of carbon and oxygen, is absorbed through the stomata of the leaves, while the other nutrients are generally absorbed from the dissolution of the soil through the roots .
Plants absorb nutrients through the numerous root hairs that young roots have, which are continually renewed, since they have a life of a few days. These root hairs secrete acidic substances that help to solubilize difficultly soluble compounds, such as phosphates and carbonates. In this solubilization action the CO 2 produced by the respiration of the roots also intervenes .
The nutritive elements that plants absorb from the soil come from rocks (except in the case of N, which comes from the air), which slowly degrades into soluble compounds. These compounds dissociate in soil water into positive ions (cations) and negative ions (anions), and in these forms they are assimilated by plants (photo 1). The ions can be free in the soil solution or can be adsorbed by the colloidal particles of the same. The anions and a small part of the cations are contained in the soil solution, while most of the cations are adsorbed on the colloidal complex. The ions adsorbed by the colloidal particles can be absorbed directly by the roots or, more frequently, pass first into the soil solution, from where they are absorbed by the roots. When an ion passes from solution to the plant, another ion passes from the complex to solution, in order to maintain a proper ion concentration.
In general, the amount of macronutrients that plants need to absorb in order to develop their life cycle is significantly higher than that of micronutrients. In this way, it is explained the fact that the absorption of macroelements by crops can represent a significant amount compared to the reserves of said elements contained in the soil. This shows the need to add manures and fertilizers to most agricultural soils (photo 2).
The proportion of macronutrients extracted by the harvests can represent practically all of the stocks in the soil, while in the extraction of micronutrients from the soil, these quantities never represent such a high proportion of the total but, in general, only represent a small percentage of the total amount existing in a soil. This means that, with few exceptions, deficiencies should not appear in terms of crop nutrition, and yet this is not the case. It must be taken into account that, due to their characteristics, microelements generally have low mobility derived from conditioning factors, which is why they are not easily assimilated by plants. This, together with the influence of cultivation techniques and the characteristics of the cultivated species,
There are numerous factors inherent to the environment (soil and climate) that influence the greater or lesser degree of absorption of nutrients. These factors include the following:
1. Soil texture.
Soils with fine textures have a greater external surface, so the agents that alter their structure have a greater possibility of action: 1g of colloidal clay presents an external surface 1,000 times greater than that presented by the same amount of coarse sand.
2. Soil pH .
For certain pH values, some assimilable elements are transformed into their non-assimilable forms, due to the fact that they become part of the insoluble compounds. For example, iron in a basic medium results in an insoluble hydroxide. On other occasions volatile compounds are produced, which are lost as they escape into the atmosphere; such is the case of ammonium fertilizers, which in basic soils produce ammonia, part of which is lost to the atmosphere when the fertilizer is added to the soil surface.
3. Interactions between ions.
On some occasions there are interactions between two ions, which make it difficult or easier to absorb one of them. Antagonism occurs when one of the ions tends to inhibit the absorption of the other, especially when the concentration of one of them increases. This is the case, for example, of potassium-magnesium antagonism, where the higher concentration of potassium causes a deficient assimilation of magnesium. Synergism occurs when one of the ions favors the absorption of the other, as occurs, for example, with nitrogen and potassium.
4. Climate.
The factors that most influence absorption are temperature and humidity. As the temperature increases, the absorption increases, due to a greater biochemical activity, until it reaches an optimum level, above which it progressively decreases until it stops. At low temperatures, the opposite occurs since biochemical activity is hampered and solubility in the soil decreases. Similarly, it happens that as humidity increases there is an increase in the absorption of nutrients.
3. CLASSIFICATION OF NUTRITIVE ELEMENTS
Currently it is admitted that higher plants can contain up to 60 elements, of which 16 of them (C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, B, Mo, Cu, Zn and Cl) are considered essential for their normal development while another 4 (Na, Si, Co and V) are considered only essential for some of them (figure 1). All these elements perform very important functions in plants, and when they are present in insufficient quantities, serious alterations can occur and their growth can be significantly reduced.
Of the 16 essential elements, the first 3 are supplied mainly by air and water, while the remaining 13 are supplied by the soil. These nutritive elements supplied by the soil can be classified into macro- and microelements, depending on whether the plants need to absorb relatively large or small amounts of them. As macroelements, N, P, K, Ca, Mg and S should be highlighted and as microelements, trace elements or trace elements essential for plants are Fe, Mn, B, Mo, Cu, Zn, and Cl.
MACRONUTRIENTS: Primary elements (N, P and K) and secondary (Ca, Mg and S).
Macronutrients are the necessary elements in relatively abundant quantities to ensure the growth and survival of plants. The presence of a sufficient quantity of nutritive elements in the soil does not by itself guarantee the correct nutrition of the plants, since these elements must be found in molecular forms that allow their assimilation by the vegetation. In short, it can be said that a sufficient quantity and adequate availability are essential for the correct development of the vegetation.
Within these, it is possible to distinguish between primary elements (N, P and K) and secondary elements (Ca, Mg and S).
1. Primary elements.
In most crops, the needs of the plants are higher than the existing reserves in assimilable form of the elements in the soil, so it is necessary to make contributions through the use of compost and fertilizing substances. The primary elements are considered to be N, P, and K.
- Nitrogen (N) .
The processes of combining N with another element are called nitrogen fixation and are carried out, in nature, thanks to the action of certain microorganisms and the electrical discharges that take place in the atmosphere. However, the amount of fixed N is usually small compared to what plants could use. About 99% of the combined N in the soil is contained in organic matter. Organic N, included in large and complex molecules, would be inaccessible to higher plants if it were not previously released by microorganisms. Microbial activity gradually breaks down complex organic materials into simple inorganic ions, which can be used by plants. How quickly crops would potentially be able to use N, it usually exceeds the speed with which it is released. Consequently, the amount of N available in the soil is usually relatively very small.
- Phosphorus (P) .
Unlike N, which can be incorporated into soils through biochemical fixation by microorganisms, P does not have such microbial support since it comes only from the decomposition of the bedrock that takes place during the weathering process. The amount of total P in the soil, expressed as P 2 O 5 , rarely exceeds 0.50% and can be classified as inorganic and organic. Inorganic P is supplied by the weathering of minerals such as apatite Ca 5 (PO 4 ) 3F and to a lesser extent it can be part of the silicate chain where it replaces silicon, or found in newly formed minerals. Organic P is of great importance for soil fertility because certain organic compounds are an indirect source of soluble forms. Humus and other types of non-humid organic matter are the main source of organic P in the soil.
- Potassium (K).
K is, perhaps, the mineral element that is found in the highest proportion in plants and is relatively frequent in rocks. Regardless of the K that is added as a component of various fertilizers, the K present in soils comes from the disintegration and decomposition of rocks that contain potassium minerals. Along with this mineral K should be included that from the decomposition of plant and animal remains. Unlike P, K is found in relatively large amounts in most soils. In general, its content as K 2Or it ranges from 0.20-3.30% and depends on the texture. In sodium soils, it varies between 2.50-6.70%. The clayey fraction is the one with the highest K content, so clay and silty-clayey soils are richer than silty-sandy and sandy soils, also taking into account that the variation in K content is influenced by the intensity of losses due to crop extraction, leaching and erosion.
2. Secondary elements.
The amounts of these elements present in the soil usually cover the needs of the crops, so, in general, it is not necessary to make contributions of any kind to the soil. This group of elements includes Ca, Mg and S.
- Calcium (Ca).
The Ca present in the soil, apart from being added as fertilizer or amendment, comes from rocks and minerals in the soil, and its total content can vary widely. In soils considered non-limestone it ranges between 0.10 and 0.20%, while in limestone it can reach up to 25%. In general, it can be said that Ca comes from the weathering of minerals. These materials are so common that most soils contain enough Ca to cover much of the plant's needs.
- Magnesium (Mg).
Mg is a chemically very active element, but it does not appear by itself as a free element in nature, but is distributed in mineral form. According to various estimates, its average content in the earth's crust can be around 2.30% while in the ground it is close to 0.50%.
MICRONUTRIENTS
They are called micronutrients, those essential elements for plants to complete their life cycle, even if the necessary amounts of them are very small. The total content of micronutrients in the soil is a function of the starting material and the edaphological processes. Those elements whose total concentration in the soil is normally less than 1000 mg / kg are called trace elements. Within this group we can include micronutrients (Cu, Mn and Zn), essential for plants and animals in low concentration, but which can become toxic when reaching certain levels. The exception among them is in Fe, which is a micronutrient but not strictly a trace element.
- Iron (Fe).
Despite its abundance in soils and rocks, it is one of the most deficient micronutrients. Fe is the fourth most abundant element in the continental crust after O, Si and Al, constituting around 15% by weight of the earth's crust. It is, by far, the most abundant microelement in soils, either as a mineral constituent or in the form of oxides and hydroxides. However, in soils with horizons enriched in organic matter, Fe appears mainly in the form of chelates. Its content in temperate soils usually varies between 1 and 5%. In isolated cases, values close to 10% can be found. In the soil, the Fe content fluctuates in the range of 0.20 to 5%, in an order of magnitude similar to that of the underlying rock.
- Copper (Cu).
Cu is one of the most important essential elements for both plants and animals; however, excessive amounts of it can produce toxic effects. Among the different types of igneous rocks, Cu prevails in the basalts. In sedimentary rocks it is more abundant in shales. In general, its abundance in basaltic rocks is higher than in granitic ones, and very low in carbonate rocks.
-Manganese (Mn) .
The Mn present in soils is mainly caused by the decomposition of ferromagnesic rocks. It is a microelement similar to Fe, both in its chemistry and in its geology and very abundant in the lithosphere. In rocks, the Mn content varies between 350 and 2000 mg / kg. The content in the soil shows considerable variations, but normally fluctuates between 20 and 800 mg / kg. However, and as in the case of Fe, these total contents cannot be considered as an indication of its availability to plants since there are many factors that affect its absorption.
- Zinc (Zn).
Zn is a widely distributed element that is found in small but sufficient amounts in most soils and plants. The amount of Zn that can be found in a soil depends directly on the nature of the bedrock. There is, however, an important aspect that needs to be highlighted in relation to the useful Zn in soils and that is that the superficial part of many of them, which corresponds to the upper horizons, always contains more Zn than the lower horizons. It is believed that this fact is due, on the one hand, to the fact that plant residues, upon being deposited on the surface of the soil, provide after their decomposition, a certain amount of the element; on the other hand, Zn does not present a downward migration in the profile, as occurs with other elements,
4. CONCLUSIONS
Water and dissolved nutrients, which are normally absorbed by the roots, can also be absorbed by the leaves. Foliar applications are effective especially when the plant needs some nutrients immediately, such as: Fe, Zn, Mn, Cu and Mo. When the soil contains an excessive amount of essential elements in a form assimilable by plants, normal development of these can be seriously affected. In general, there are usually no problems in this regard with macroelements, but there may be problems with some microelements, where there is a narrow margin between optimal and toxic levels.







