Leaching foliar

Mechanism The processes by which aluminum is mobilized in acidic soils with low base saturations by additions of acidic anions are based on accepted concepts of ion exchange processes (Reuss and Johnson 1986), and have been validated by results from the Integrated Forest Study (D.W. Johnson, personal communication). The mechanisms of aluminum-caused dysfunction of physiological or biochemical processes of red spruce are not known. Research has not yet clearly identified the mechanisms by which acid deposition and ozone reduce the capacity of red spruce to assimilate carbon. Likewise, mechanistic research on acidic deposition-caused foliar leaching, foliar injury, and reduced cold tolerance is continuing. 

When a forest system is subjected to acid deposition, the foliar canopy can initially provide some neutralizing capacity. If the quantity of acid components is too high, this limited neutralizing capacity is overcome. As the acid components reach the forest floor, the soil composition determines their impact. The soil composition may have sufficient buffering capacity to neutralize the acid components. However, alteration of soil pH can result in mobilization or leaching of important minerals in the soil. In some instances, trace metals such as Ca or Mg may be removed from the soil, altering the A1 tolerance for trees. 

Several facts have emerged from our studies with 2,7-DCDD and 2,3,7,8-TCDD. They are not biosynthesized by condensation of chloro-phenols in soils, and they are not photoproducts of 2,4-dichlorophenol. They do not leach into the soil profile and consequently pose no threat to groundwater, and they are not taken up by plants from minute residues likely to occur in soils. Photodecomposition is insignificant on dry soil surfaces but is probably important in water. Dichlorodibenzo-p-dioxin is lost by volatilization, but TCDD is probably involatile. These compounds are not translocated within the plant from foliar application, and they are degraded in the soil. 

Rea AW, Lindberg SE, Keeler GJ. 2001. Dry deposition and foliar leaching of mercury and selected trace elements in deciduous forest throughfall. Atmos Environ 35 1352-2310. 

Atmospheric dry and wet deposition contribute significantly to the metal fluxes in forest soils (Lindberg et al. 1982). An assessment of dry deposition and foliar leaching of mercury and selected trace metals based on washed foliar and surrogate surfaces has been recently presented by Rea et al. (2000). In another set of investigations. 

Wood, T. and Bormann, F. H. (1975) Increases in foliar leaching caused by acidification of an artificial mist. Ambio 4 169-171. 

Early application of nitrogen to winter barley often encourages foliar diseases. The nitrogen should be apphed to the seedbed with late-sown spring crops (other than on sands), whereas with the early-sown crop it should be spUt to avoid leaching. 

Sulfur and/or nitrogen derived pollutants alone or in combination with oxidants affect red spruce through the mechanism of increased leaching of foliar nutrients. ... 

Responsiveness The concentration of soil solution aluminum is related to sulfate and nitrate inputs from atmospheric deposition (Johnson, D. et al. 1988, Joslin and Wolfe 1988, Reuss and Johnson 1986). Experiments with seedlings have documented reductions in plant biomass, root elongation, and levels of calcium, magnesium, and phosphorous in roots and shoots as a function of increased aluminum concentration (Joslin and Wolfe 1988, Thornton et al. 1987, Taylor et al. 1986, Hutchinson et al. 1986,). The ratio of aluminum to calcium in wood is higher at high deposition sites than at low deposition sites (Bondietti et al. 1989). Acidic mist treatments produced visible foliar injury in proportion to treatment acidity and sulfate concentration relative to nitrate. Calcium and magnesium were leached from red spruce foliage... 

Hypotheses related to soil-mediated factors and winter injury have stronger support than those related to carbon dynamics and foliar leaching research to test these two hypotheses is ongoing and will address some of the uncertainties. 

Table 2 Fluxes of leached cations as a percentage of the foliar nutrient pools...

The amounts of nutrient losses by foliar leaching are of crucial interest with regard to i) induction of or contribution to mineral im-balances/deficiencies of the foliage and ii) scaling-up from laboratory experiments to relevant field situations. Direct measurements of leaching fluxes under forest canopies are not possible and the interpretation of throughfall analysis needs several assumptions. On... 

FLOCKIGER, W., S. LBGNARDI, AND S. ERAUN. 1988. Air pollution effects on foliar leaching. In ... 

PAOlfm, E., R. GELUNI, AND E. BARBOLANI. 1989. Effects of acid fog and detergents on foliar leaching of cations. Water Air Soil Pollut. 45, 49-61. 

Formulation and initial placement influence the susceptibility of organophosphorus insecticides to transport in surface runoff, as well as their degradation by abiotic and microbial processes. Formulation affects the kinetics of insecticide release into soil water and overland flow, as well as sorption to soil solids and plant surfaces. Spray adjuvants affect initial placement by influencing the amount of insecticide depositing on foliar and soil surfaces. Initial placement determines the relative importance of such processes as volatilization, photolysis, biodegradation, and leaching out of the zone of interaction with overland flow. 

Activator adjuvants are often added to spray mixtures of foliage-applied herbicides to enhance the level of weed control. Such adjuvants increase herbicidal activity by increasing cuticle retention, penetration, absorption, and possibly translocation. Activator adjuvants include surfactants, wetting agents, penetrants, and oils. Oils used as additives have been found to influence wetting properties, evaporation, leaching, and foliar uptake and translocation of herbicides while surfactants increase their solubility, spreading, and penetration. " ... 

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