| Water, Soil and Trees
Arborist and Landscape managers are very concerned about the effects urban water supplies may have on plant appearance and growth. Urban waters come from deep wells, rivers and man made lakes.
Water Quality In context of landscape irrigation, water quality refers to the presents and concentration of total salts as well as several specific ions (chlorine, sodium, and boron) bicarbonate, pH, trace elements and nutrients ( nitrogen, phosphorus, and potassium ). Municipal water supplies using injected chlorine and water softeners, has a higher level of chlorine and sodium. Water quality may vary throughout the year, water is usually better during the rainy season than during the periods of summer and fall droughts.
Total Salts Water that contains heavy ions or salts are toxic to plants. Salinity is most important measure of water quality for landscape plants. It is expressed as total dissolved solids and electrical conductivity. When water is applied to soils, some of the salts, notably sodium, chloride, and boron accumulate in the soil creating plant toxicity. The degree of the problem depends on the sensitivity of the plant to salts and the accumulated concentration in the soil. Salt toxicity is expressed as stunting of growth, yellowing of foliage, burning of the edge of the leaves and defoliation. Ion toxicity is difficult to distinguish specific symptoms from each other. Ion toxicity through foliar absorption occurs at much lower concentrations than soil absorption. Toxic symptoms of specific ions are difficult to distinguish, as some plants have a high tolerance, as others are highly sensitive. There is little information is available on plant sensitivity to specific ions and one must rely on experience and observation. (See Essential Nutrients)
Bicarbonate Hill Country soils typically have high bicarbonate levels which, can cause iron chlorosis (See Iron Chlorosis) and also affect plants through its influence on pH (See Soil pH) and interaction with sodium. Water, high in bicarbonate, carbonate, calcium, or magnesium, or a combination of these elements, can cause white precipitate of foliage under irrigation and can cause harm not only to the equipment, but create residual problems in the soil as well as water absorption.
Heavy Metals Are rarely present in water in sufficient quantities to be directly toxic to plants. Most metals, however, become tied up in the soils and their concentrations increase over time. It is this accumulation of these elements which become toxic to plants. This is where biological and microbial activity become essential.
Soils Urban Natural conditions create forest soils, whereas, urban soils lack the natural characteristics that benefit trees. Urban soils rarely have an organic layer. They may be compacted, crusted, have poor water absorption, elevated pH, asphalt hardscape (parking lots) and, surface barriers (buildings). All these factors harm "soil life" .... root growth and tree health. (See Soil of Life)
Trees, Soil, Boilogical and Microbal Life The loss or reduction of organic matter decreases biological and microbial activity, hampers soil structure development and interrupts element cycling. (See Cation Exchange) Soil compaction is often caused by construction, foot or vehicular traffic, and recovery from structural damage can take a long time. Urban soils may be contaminated with construction debris, such as asphalt, concrete, plaster, paper, paint etc. and other waste materials. These conditions for trees range from unfavorable to antagonistic. To best describe the micro eco-system or rhizophere under a tree, it is like a piece of thick fresh baked bread, spongy soft and porous. All the capillaries contain all the gasses,nutrients, and moisture for the health of the tree and roots. Compact or flatten this rhizophere like a tortilla and the nutrients, water,oxygen and elements are present but no longer available to the tree roots which can in turn forfeit the overall tree health.
Trees blend with, rather than grow on, the soil. Fallen leaves and twigs accumulate as a distinctive organic layer on top of, and incorporates into, soil. The chemical makeup of organic matter brings about species, and these effects positively impact growth, vitality, disease resistance, and longevity. Trees and soils are so ecologically interdependent. (See Trees are Vital) (See Bio-Stimulants)
Trees are living systems driven by energy for their metabolism growth, reproduction and resistance to disease. Trees must obtain sufficient oxygen, water, essential elements and nutrients from the soil to meet their energy requirement. Organic, and nutrient rich soils contribute to biological and microbial activity, particularly mycorrhizal which are essential to tree health. (See Nitrogen Article)
Mycorrhizae are nonwoody roots and nonpathogenic fungi that form a symbiotic relationship. The fungi enhances water absorption and essential nutrients for the tree, and in turn the fungi receives food in the form of sugars and starch. Damage this eco-system and the health of the tree is in serious danger. (See Mycorrhizal Management)
When nature can not provide all the needs for trees, and return the balance into the soils then in is up to the arborist to help rebuild the soils with humus, microbial and biological activity, nutrients, vitamins and micro nutrients that will restore and maintain the health of the soil and trees. Diseases attack weak faltering victims, whereas healthy trees are generally free of disorders and their immune systems can better fend off disease. (See Fertilizing Trees & Shrubs)
We must encourage growth without destroying balance;
We must preserve balance without impairing growth.
W. R. Dixon
To exist as a nation, to prosper as a state, and live as a people, we must have trees.