(IPPM) in Vegetables - Vegetableipmasia.org

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Resource Manual on IPPM in Rice World Education Philippines, Inc. These facts, coupled with the significant cost farmers devote to nitrogen fertilizers, are enough reasons why farmers need to learn how to better manage their nitrogen inputs. 2. Phosphorus a. Adenosine di-Phosphate (ADP) & Adenosine Tri-Phosphate ATP: The Shortterm Storage of Energy Phosphorus (P) is one of the major nutrients that farmers apply when they buy inorganic fertilizers. It plays several important roles. Notably, it is important in the construction of the genetic material, DNA. Hence, DNA is found in important concentrations in seeds. Also, phosphorus is associated with the short-term storage of energy captured from the sun. b. ADP & ATP: “Rechargeable Batteries” in the Plant Phosphorus acts as the energy transfer agent. As such, it works by being attached (or unattached) to a small, but very important molecule. The ADP molecule has two phosphates attached (di meaning two) to it, while the ATP molecule has three phosphates. Attaching the third phosphate atom to ADP to make ATP requires (and thereby stores) energy. Similarly, when the ATP molecule has phosphorus molecule broken off, it gives up energy that can be used by the plant. In other words, ADP is like a battery with the charge gone out, and ATP is like a charged battery. The energy-charged ATP molecule can and does go everywhere inside the plant, from the smallest root to the tip of the flower, to the inside of the grains. Every cell in the plant uses the ATP molecule to give up energy so that the cell can do its work. In fact, ATP is found, not only in every plant, but also in every animal on earth. It is the common currency of energy transfer for all life on earth, from the smallest bacteria to the largest whale or the tallest tree. c. Behavior in the Soil The amount of phosphorus found in surface soils ranges from about 200 kg/ha in sandy soils, to about 2,000 kg/ha in soils derived from rocky subsoils. Chemical weathering results in solubilization of orthophosphate (H 2 PO 4 - ) and pH 7.2. This is the form in which phosphate is available to the plant, and usually accounts for not more than 1% of the total phosphorus in the soil in any location. This is because the release of orthophosphate (either through solubilization or by application of phosphate fertilizers) is followed by precipitation (the forming of insoluble solids from chemicals in solution). Phosphorus goes out of solution in the form of iron and aluminum phosphates in acid soils, and calcium phosphates in basic soils. These reactions result in low orthophosphate concentrations at pH levels above or below about pH 6.5. Another source of phosphorus is from organic matter. Total organic phosphorus accounts for usually between 3050% of total soil phosphorus, and the microbial pool (total amount of living and dead microbes) represents the majority of the actively cycling pool of phosphorus. 22
Resource Manual on IPPM in Rice World Education Philippines, Inc. d. Not Enough P Seeds contain a large amount of phosphorus, so a deficiency in P might be seen in the small seeds of plants. Phosphorus also stimulates root growth. This can be observed by putting a small source of phosphorus in the soil near the plant roots and then digging down to examine the roots in the area of the phosphorus. The roots in such areas should be longer, stronger and with many fine root hairs. Unlike nitrogen, phosphorus is not readily absorbed by the roots, so P can be overwhelmed by too much N. P is very rapidly bound by several factors in the soil, so any free phosphorus absorbed by the plant must come from very close by the roots. One problem with P is that it is not very soluble (able to be broken into small molecules and to move through the soil and water). Phosphorus is more soluble in a soil that has a good amount of oxygen (aerobic conditions). One benefit from the solubility problem is that it takes a very long time to leach P from the soil. Hence, farmers that add phosphorus every season may have built up much more than they need. e. Factors Affecting P Movement The atomic symbol P is used to refer to phosphorus. However, this is just a convention to simplify the text, just like N is used to refer to nitrogen in forms such as nitrate or ammonium. Similarly, P can be found in several forms, both inorganic and organic. The form in which phosphorus is made available to living organisms is most commonly found as orthophosphates (H 2 PO - 4 at pH7.2). The pH of a soil affects not only the form, but also the mobility (movement) of orthophosphate. If the soil is near neutral (pH 6.5-6.8) then orthophosphate is optimally available to plant roots. Highly acidic or basic soils have almost no orthophosphate available to the plant, except that which is released from decaying organic matter. The amount of total phosphorus found in a surface soil can vary greatly, ranging from about 200 kg/ha, in very sandy soils, to about 2,000 kg/ha in soils derived from basic rocks. However, very little orthophosphate is present in the soil solution at any one time, usually
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