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NPK's of Plant Growth

                                                by Robert L. Ellsworth, Ph.D.

There are several responses in plants to the essential minerals required for them to complete the “life cycle”. It is always beneficial to review the reactions to each of the minerals, especially those which we can express great control. The three most prevalent are the “major” nutrients: Nitrogen, Phosphorous, and Potassium. These are the liquid (N) pepper (P) and salt (K) of the “broth” essential for all plant metabolism functions.

NITROGEN,  the cornerstone for tissue analysis, is a major nutrient that is integral in plants and all life as part of the DNA molecule. It ranks as the sixth most abundant element in all matter of the the universe, and ranks as the first most abundant element in the Earth’s atmosphere, representing 75% by weight, and 78% by volume.

Nitrogen is taken into the plant mostly from the soil by the root, and primarily in the nitrate form (NO3), or ammonia (NH4).  It is used by plants to synthesize amino acids, and subsequently proteins, some of which enter into the chlorophyll. Thus, Nitrogen expresses a great controlling factor over the energy supply within the plant. It represents 16% to 18% of the total protein within the plant body.

Nitrogen deficiency symptoms would include yellowing of the leaves due to lack of chlorophyll, especially in older tissue. Under more severe deficiency, the growth rate slows dramatically and may form short “rosette” type growth in the new tissue before ultimate plant death. Nitrogen deficient plants will show drought symptoms earlier than will healthy plants. The combination of these symptoms results in decreased yields and ultimate death to plant tissue.

On the other hand, excess Nitrogen can have results that are just as disastrous as deficiency.  Under extreme conditions, the plant may grow so rapidly that it will die prematurely. This is illustrated in some areas by the use of excess liquid Nitrogen applied to crops to desiccate the plant for “early” harvest. By proper handling and supply of Nitrogen, one can control the time of harvest within limits of 10 to 30 days (depending on the species). Remember, excess Nitrogen during plant maturity slows the processes involved in “fruit set”. This, in turn, will delay harvest. By careful manipulation of Nitrogen in the plant, maturity can be hastened and quality improved.

PHOSPHOROUS, is the most important mineral element we will discuss. It is not found free in nature, except in a few meteorites. It does occur abundantly in compounds that are widely distributed in rocks, minerals, plants, and animals. It ranks twelfth in abundance among the elements in the Earth’s crust, representing 0.1%.

Phosphorous is essential for all life as it is an integral element of nucleic acids (DNA and RNA), and is essential in the plant cell division process. Phosphorous is essential for proper growth, as growth occurs by cell division and then enlargement. During rapid growth, the plant will usually show Phosphorous deficiency as this is the time of peak demand, not only for cell division, but for the second primary use of phosphorous, the ATP cycle.

Briefly, the Adenosine Tri-Phosphate (ATP) cycle is the primary energy storage and movement mechanism utilized by plants. It is a complicated chemical process.  The chlorophyll captures the energy from the sun and transfers it into the ATP cycle. A crude description involves a three step process to “recharge the battery”, so to speak. The first step involves a molecule of protein bearing one molecule of Phosphorous (ATPH). As energy is captured from the sun within the chlorophyll, it is transferred and stored onto the base molecule (ATPH) by adding one more molecule of Phosphorous. This stores a large quantity of energy, forming Adenosine Di-Phosphate (ADP).  When this step is complete, a third molecule of Phosphorous is added, turning the base energy carrier into (ATP).  This is then transferred to the plant to supply energy for respiration.

When the Phosphorous supply is limited, the energy captured and transferred is limited, slowing growth and maturity of the crop. The more ATP formed during the day, the longer the plant will respire after sundown. Deficiency symptoms include reddening of the plant tissue as sugars accumulate. This accumulation occurs due to lack of energy to drive the movement mechanism. Cell division is limited by the lack of Phosphorous, and subsequent plant growth and maturity can be significantly delayed or affected.

POTASSIUM is the seventh most abundant element in the Earth’s crust, making up 2.6% of its total mass. It is a unique element in that it does not become part of any molecule in the plant, but seems to be found only as an independent element. It is absorbed by plants more than any other element, except for Nitrogen, and in some cases, Calcium. The primary function of Potassium appears to be movement of all materials through the plant body. Whenever and wherever materials are moving in the Xylem and Phloem, there is Potassium present. Thus, Potassium is present with all processes within the plant involving metabolism.

With a shortage of Potassium, plants grow slower, and any of the following deficiencies may occur: Plants become more susceptible to insect and disease. Sugars accumulate at the point of manufacture. Stalks and stems become weaker, roots grow slower. Nitrogen may accumulate at the roots or other locations of uptake. Less chlorophyll will be produced and will be less functional. Regulation of nutrient uptake by the roots from the soil will become skewed. Calcium may flow out of the plant faster than it is taken in. Subsequent to these problems, all aspects of growth and production are greatly decreased. The results are adversely affected fruiting, flavor fails to develop, size is reduced, and “shelf life” decreases. Decreased stem strength makes harvest more difficult and the harvest quality is decreased dramatically because of insufficient sugar and Calcium.

From this brief coverage, one can visualize the consequence of having inadequate Potassium. Unfortunately, most Western states have copious quantities of Potassium present, though in a condition that plants have difficulty absorbing. It becomes necessary, therefore, to alter a condition or status of the soil Potassium to allow easier uptake by the plant. One approach to this is to increase application of Potassium to the soil. Frequently, when this is undertaken, much of the material applied reacts in the soil with the other elements, and becomes unavailable, or only slowly available to the plant root. A second approach is to alter the condition of the organic portion of the soil by application of ViTech’s ViBasic twice a year. This will stimulate the biological activity of the soil and allow more of the Potassium found in the body of previous crops to become available to the following crop.  Utilization of ViBasic in this manner will also improve the availability of all the other elements as well.


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