Agenda - Planning Commission - 03/02/1999

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is a salt made up of a lattice of anions and cations, just as ordinary table salt is made up of a grand lattice of connected sodium cations and chloride anions. When salt as sodium chloride dry granules is poured into water, the sodium and chloride ions separate. When they separate, they carry electrical charges and are called the sbdium ion and the chloride ion. When a cation enters a root, another cation must exit. This is very important, as we will see. When nitrogen enters a root as a nitrate anion, a bicarbonate anion from carbonic acid exits. The bicarbonate ion is the second most imPortant compound in nature, next to water, because it &ives the absorption process. When a'bicarbouate ion exits into the rhizosphere, the pH increases. When urea is used in fertilizers as the nitrogen source, the pH in the rhizosphem could increase by 2 or more pH units. The chemistry behind this is complex, but here I present only the · conclusion, because a common problem with trees in some high pH soils is chlorosis. There is no easy field method for measuring the pH of the one-imllimeter-wide rhizosphere. The rhizosphere. could be pH 8, and the bulk soil would measure pH 6. As pH increases, the availability of elements such. as iron and manganese decreases. In soils, it is one thing to have an element present and another to have it in ionic form available to the Plant. As pH increases, iron and manganese form molecules that precipitate in water rather than ionize. If they are not available as ions, they will nO~.. be absorbed. And, if they are not absorbed, several enzymes es- sential for chlorophyll formation and photosynthesis will not form. When the energy flow from the top of the pump is blocked, the. bottom does not get enough energy for growth and defense. The pathogens invade, and [he tree'declines. This scenario does not mean that every time you use urea, trees will decline from . ' chlorosis. But the use of urea could be a contributing factor where trees with genetic codes for growth on low pH soils are planted in high pH soils. If fertilization is a desired treatment, then·a fertilizer with nitrogen in a ~0ositively charged form, such as an ammonium ion, would help to reduce the rhizosphere pH. When the ammonium ion enters the root, a proton of positive charge will exit. The protons in rhizosphere water ~vill bring about more acidic conditions, so there is a way out. In summary, fertilizers can be very beneficial for health and' survival of trees planted outside their forest homes. How beneficial will depend greatly on an understanding of many of the points mentioned here and of some basic chemistry. Primary Causes of Diseases . . . . . It is often very difficult for people to recognize the impoxtance of small organisms in small places doing big things..Blame for the death ora tree is often placed on big things that can be seen or felt. Most pathogens are opportunistic weaklings waiting for a defense system to decrease. Many small disrupting events often lead to the decrease in a defense system. Then after the tree has been weakened, the final agent comes along'and gets the full blame for the cause. A perfect eXample is the canker on honey locust. Flush pn-ning is usually the real cause. Pumps and Food Trees are oscillating pumps. When the pump begins to wobble, some parts will begin to weaken. When they weaken to the point where some other agent causes a part to break, the pump will stop. It is very difficult to determine where problems start in an oscillating pump. Symptoms may be in the bottom, but the cause may have been in the top. Or, it could bo the other way around. I go back to two points that may be part of the answer:. exudates and the self-thinning nde of ecology. All living things 28 THE PERMACULTURE ACTIVIST,//40 require food and water for growth. Leaves and photosynthesis provide the energy at the top of the pump. The non-woody roots and the rhizosphere provide the elements and water at the bottom. Photosynthesis will not work without water and elements, and the absorption processes will not work without an energy source. Trees became trees growing in groups in forests where the self-thinning rule had strong survival value. Not only did exudates provide quick energy for the rhizosphere organisms, but the carbon in the wood that fell to the ground also p{ovided a long- lasting energy source for a succession of organisms. Reports from some countries indicate an abundanc& of soluble nitrogen compounds in runoff water and even in ground water. This is a strong indication that the carbon-nitrogen ratio has disrupted in the soil. It is well established from studies of tho physiology of fungal parasitism that the degree of parasitism is often determined by the carbon-nitrogen ratio. It is probably similar for other organisms: · The organisms in tho rlfizosphere and Surrounding softs have many different ways to weather rocks and to get nitrogen and other elements essential for their growth. What they cannot get in~ the soil is a sufficient energy source. Yes, some small animals die and provide carbon, and some microorganisms can get energy by chemosynthesis, but the requirements for carbon are much greater than what could be supplied by those sources alone. Carbon must Come from the top of the pump. When the energy source from the top begins to decrease, the rhizosphere organisms will begin to starve. -The oscillating pump model soon takes on the form of a circle, because now it could be said that the top did not work ' efficiently because the bottom bad a problem first, and this court be so.' My point is that the energy problem does play a key role in declines. If a single tree is already very low in energy reserves, it cannot contribute much to the rhizosphere even if the genetic codes nde that eX~_~d~tes should increase as a tree begins to decline. Soon we Will be facedwith the Chicken or egg problem. I believe there is a way to decrease the potential starvation problem. In forests, moro wood should be left on the ground, and in cities, more composted wood and leaves should be added in correct quantifies to the soil about the base of trees. Incorrect treatments of pruning, watering, planting, and ferOlizing should be corrected, because they often start the pumps to wobble. If these simple adjustments can be made, rhizosphere starvation will decrease and our trees will lead healthier and longer lives. Author'S Note Much of the information here has 6omo from several books I foundvery helpful in preparing for this article. 1. Foster R.C, A. D. Rovira, and T.W. Cock. 1983. Ultrastructure ofthe Root-Soil Interface. The American Phytopathologicld Society, St. Paul, Minnesota. 2. Kilham Ken. 1994. $oilEcology, Cambridge Univ. Press. 3. Wild, Alan; 1994. Soils and the Environment: An introduction, Cambridge University. Press.A Am sn; O the a.ther of umero boo 'o, bioPSy and pruning, and was formerly chief scientist for the U.S. Forest. 'Service. He travels and teaches thrOughout the U.S~ and inter- nationally. Through his consuItancy, Shigo & Trees, he offers 16 educcm'onal paclcages. He can be contacted thrOugh the Worm ' Vfule Web at www. chesco, cond~treeman/SHIGO/rhi~o, html or at PO Box 769, Durham, New Hampshire 03824 USA. This article first appeared in Tree Care Industry, VoL VII, No. 10, October, 1996, and is published here by permission of the author.