[0:00]Hi, in this video lecture, we will tackle about soil plant relationship. For the outline of topics, we will try to to discuss the following: the essential elements in soil and their forms, the profile distribution of elements, the roles of essential elements in plant nutrition, the biochemical classification of nutrients, the availability of nutrients, mechanism of nutrient update, relationship between soil nutrient supply and plant growth, the LRP or the linear response plateau model, the law of minimum or Liebeg's law of minimum, the Mic equation, the nitrogen, phosphorus, potassium and sulfur economy of soils, and the cause of decline in soil fertility.
[1:04]Let's begin with a discussion on the essential elements in soils and their forms.
[1:13]For the essential nutrient elements, we have two classifications. The first classification is the macro elements, and the other one is what we call the micro elements. So for the macro elements, we have the following in the soil. We have the nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. And these are the forms of the elements that are available for plant use. For nitrogen, we have ammonium and nitrate. For phosphorus, we have dihydrogen phosphate ion and hydrogen phosphate ion. For potassium, we have K+ or potassium ion, for calcium we have calcium ion, for magnesium, we have magnesium ion, and for sulfur we have sulfate. So, if you can notice, the available forms of nutrients for plant use are all in ionic form. It's either a cat ion or an an ion.
[2:34]Now, for the micro elements, these are the forms that are available for plant use. For iron, we have iron 2+ or ferrous. For manganese, we have MN2+ or manganese ion. For boron, we have the boric acid or the hydrogen borate. For zinc, we have zinc 2+. For copper, we have Cu2+. For chlorine, we have Cl-.
[3:07]For molybdenum, we have the molybdate. For nickel, we have Ni2+. And for cobalt, we have CO2+.
[3:23]So for the sources of nutrient elements, the essential nutrient elements can be derived from the following: from organic matter, minerals, air, and from water. For the CHO or the carbon, hydrogen and oxygen, these nutrients can be derived from air and water. For example, carbon can be derived from carbon dioxide, hydrogen can be derived from water, and oxygen can be derived from oxygen gas and water. Now, let us discuss some of. Now, let us discuss the sources of some essential elements. Let's begin with nitrogen. The air partly supply nitrogen. In fact, the air in the Earth's atmosphere is made up of approximately 78% nitrogen. The nitrogen from the air can go to the soil through biological nitrogen fixation, and when lightning converts it to nitrate.
[4:29]The enormous energy of lightning breaks nitrogen molecules and enables their atoms to combine with oxygen in the air forming nitrogen oxides. These nitrogen oxides dissolve in rain, forming nitrates that are carried to the Earth. Now, the major source of nitrogen is what we call the organic matter. The organic matter contains about 5% nitrogen. Most minerals in the soil do not contain nitrogen.
[5:12]Now, let's discuss the source of phosphorus, sources of phosphorus. Phosphorus is released from soil organic matter. About 1% phosphorus comes from organic matter. They are bound in phytin, for examples, in the hulls of seeds. For example, in the hulls of seeds, from phospholipids, such as eggs, meats, fish, cereal grains and oil seeds, and nucleic acids of vegetables.
[5:46]The major inorganic source of phosphorus in the soil are the acid-soluble phosphorus, the calcium phosphate, the aluminum phosphate, and the iron phosphate.
[6:02]For potassium, potassium is found in minerals like feldspars and micas. In the soil, 90% of potassium found in these kinds of minerals.
[6:19]It can also be found fixed inside of clay minerals. About 9% of soil K is fixed, or are fixed inside clay minerals. And 1% on the soil exchange sites, and 0.1% can be found in the soil solution.
[6:45]For sulfur, sulfur is contained in organic matter, about 1% sulfur. It can also be present in minerals, such as gypsum and pyrite. And when released into the soil, they are in the forms of hydrogen sulfide, iron sulfide, and sulfate.
[7:09]There are other nutrient elements present in the organic matter at very low concentrations. And most comes from the weathering of minerals, such as calcium. Calcium is found in hornblende, plagioclase, dolomite, and calcite. For magnesium, magnesium occurs in hornblende, dolomite, and biotite. Now, for the micronutrients derived from various minerals, we have iron. Iron is among the most abundant of micronutrients. Iron can be found in limonite, hematite, goethite, and other minerals. We also have chlorine.
[7:57]Chlorine is also contained in minerals and may also be supplied from the salt sprays from oceans and irrigation water. So that's all for the sources of nutrient elements. Now, let's go to the roles of essential elements in plant nutrition. There are 18 essential elements in plant nutrition. And this table summarizes the 18, and their role in plant growth and development. For carbon, carbon is the constituent of carbohydrates, and this element is also necessary for photosynthesis. Hydrogen maintains osmotic balance, and it is important in numerous biochemical reaction happening in plants. And it also, it is also necessary for photosynthesis. Oxygen is also a constituent of carbohydrates and necessary for respiration. Nitrogen, nitrogen is a constituent of proteins, chlorophyll and nucleic acids. Now let's go to phosphorus, potassium and calcium. Phosphorus is the constituent of many proteins, coenzymes, nucleic acids and metabolic substrates. It is also important for energy metabolism.
[9:23]Potassium, it is involved in photosynthesis, carbohydrate translocation and protein synthesis. On the other hand, calcium is a component of cell wall. It plays a role in the structure and permeability of plant membranes.
[9:45]Magnesium, it is an enzyme activator and it is also a component of chlorophyll. Sulfur is a component of plant proteins. Boron is important in sugar translocation and carbohydrate metabolism. Chlorine is involved in oxygen production in photosynthesis, and copper is a catalyst for respiration and a component of various enzymes. For iron, manganese and molybdenum. Iron is involved in chlorophyll synthesis and enzyme for electron transfer. Manganese, it is involved in the control of several oxidation-reduction systems in photosynthesis. Molybdenum, it is involved in nitrogen fixation and transforming nitrate to ammonium. Nickel, nickel is necessary for proper functioning of the enzyme, urease, and found to be necessary in seed germination. We also have zinc and cobalt. Zinc is involved with enzyme systems that regulate various metabolic activities, and last but not the least, is the cobalt that is necessary for nitrogen fixation. So that's for the 18 essential nutrient elements for plant growth and development. Now, let's take a look on the profile distribution of nutrients. Now, the suit of mechanisms that shape the vertical distribution of soil nutrients can be grouped in at least four major processes. And these are the four.
[11:41]We have the weathering, the atmospheric deposition, leaching, and biological cycling. Now, the first two, the weathering and the atmospheric deposition, affect the depth at which nutrient input occur. While the last two, the leaching and the biological cycling, influence the vertical transport of nutrients in opposite ways. Now, I have here an illustration that can help you picture out what's happening in the soil profile when it comes to the distribution of nutrients. Now, acting in isolation, leaching moves nutrients downward and may increase nutrient concentrations with depth. As you can see in this figure, the arrows indicate water inputs and outputs and vertical water fluxes at different, different depths. Now, decreasing vertical water flow with depth depletes nutrients from the top soil and accumulates them in deeper soil layers, producing a peak at the maximum rooting depth. So that's what happens in when there is leaching. Now, another illustration is this. In contrast, biological cycling generally moves nutrients upwards because some proportion of the nutrients absorbed by the plants are transported above ground, and then recycled to the soil surface by litter fall and through fall. Plant cycling should therefore produce nutrient distributions that are shallower for decreased with depth.
[14:09]Now, as you can see in this figure, arrows indicate nutrient uptake, transport, and above ground cycling via litter fall and through fall. Plant cycling tends to accumulate nutrients in the top soil and deplete them in the root zone. Below the rooting depth, there is an increase of nutrient concentrations because there is no depletion. So that's for the profile distribution of nutrients. Now, let's take a look on the biochemical classification of nutrients. Now, this table shows you the classification of plant nutrients according to biochemical behavior and physiological function.
[15:11]Now, the first group, it includes the major constituents of organic plant material. The carbon, hydrogen, oxygen, nitrogen and sulfur. So, these elements are constituents of amino acids, proteins, enzymes, and nucleic acids, the building blocks of life. The assimilation of all these nutrients by plants is closely linked with oxidation reduction reactions.
[15:48]Now, for the second group, the phosphorus, boron, and silicon, constitute the second group of elements with close similarities in biochemical behavior.
[16:04]Also, we are taken up from the soil solution as inorganic anions or acids, and occur in this form, plant cells are about by hydroxyl groups of sugars to form phosphate, borate, and silicic acid esters. Now, for the third group, it is made up of potassium, sodium, calcium, magnesium, manganese, and chlorine. All of which are taken up from the soil solution in the form of their ions. In plant cells, they are also present in ionic form where they have non-specific functions. For example, they are involved in establishing electro potentials. Now, last but not the least, the fourth group, this group includes the cations which are associated which are associated with diffusible or infusible anions. Example, calcium, oxalate, or with the carboxylic groups of pectin and cells. We also have magnesium that can be found very strongly by coordinate and covalent bonds. As occurs in the chlorophyll molecule. Now, the ability of magnesium, calcium and manganese to form keylates means that these elements closely resemble those of the fourth group. The iron, copper, zinc and molybdenum, which are predominantly present in plants in chelated form. This is an important function of this latter elements. that is to to facilitate electron transport by valent change.
[18:13]So that would be the first part of this video lecture. I'll see you again on the second part. Thank you.
[21:22]This is the all pH scale, including the availability of those essential elements for plant growth. So, the shaded area with color gray indicates the availability of those nutrients to the plants in different pH levels. For example, nitrogen is becomes limiting when the soil pH is 5 uh lower than 5.5 and another example is that iron is becoming limiting starting pH greater than 7. So that that is how you can use this pH scale um soil pH relationship with nutrient availability.
[23:09]This is a table showing the rates of root interception, mass flow, and diffusion in ion transport to corn roots.
