Acute SO 2 effects on vegetation are less likely because large point sources comply with ambient air quality standards and emission limits. The remaining concern is for direct effects of SO 2 , which might occur from exposure to intermittent, subacute dosages. Limited data exist for assessing chronic effects because experimental exposure regimes used in most effect studies on soybean [ Glycine max. (L.) Merr.] are from field and laboratory exposure regimes consisting of SO 2 , NO 2 , and O 3 dosages with a high degree of uncertainty. Chronic exposure of ‘Essex’ soybean to 0.06 µ L L −1 (0.06 ppm) O 3 for 8 h d −1 , 5 d wK +−1 , for 18 wk in the greenhouse caused a 34% reduction in yield compared to charcoal‐filtered air. Sulfur dioxide in combination with O 3 and NO 2 caused no additional reduction in yield, but lower dosages of SO 2 increased yields compared to the O 3 treatment, apparently by retarding O 3 ‐induced premature senescence. Emissions from a power plant had no adverse effect on yield on the cultivar Essex during a 3‐yr field study (1981–1983).

AbstractAn air pollution exclusion system was designed, tested, and operated at four field sites during four growing seasons near the Tennessee Valley Authority Widows Creek Steam Plant to measure the effect of emissions from the coal‐fired power plant on soybean [Glycine max (L.) Merr., cv. Essex] production. Soybean plants were exposed to background levels of ambient air pollutants. When the plume from the power plant was at ground level the air pollution exclusion system was activated and passed charcoal‐filtered air through the plant canopy of the control plots, thereby reducing SO2 concentration to 10 to 20% of ambient level. The maximum 3‐h average SO2 concentration ranged from 1935 to 9944 µg/m3 (from 1972–1975) and from 502 to 1478 µg/m3 (from 1977–1979). Soybean plants were also grown in charcoal‐filtered and unfiltered air in greenhouse chambers for 4 yr (1972–1975) near the Widows Creek Steam Plant and for 3 yr (1977–1979) at a remote site 70 km from the power plant. Soybean yield was significantly reduced by 27% in greenhouse chambers with unfiltered air compared with chambers with charcoal‐filtered air near the power plant. Emissions from the power plant significantly reduced soybean yield by 12% for only 1 out of 4 yr in the field tests. An estimated 6.4% of the total leaf area in the ambient air + SO2 plots showed chlorosis after an exposure to a maximum 1‐h average SO2 concentration of 1663 µg/m3. At the remote location, soybean yield averaged 25% less in unfiltered air than in filtered air, indicating that air pollutants other than power plant emissions were affecting soybean yield at both sites.

An investigation was undertaken to determine the cause of fishkills in a trout-rearing facility that uses water from Raven Fork Creek in western North Carolina. The kills followed rain events during which the (H/sup +/) of the creek increased as much as 50 fold and Al concentrations increased as much as 7 fold. Analyses showed that the soils had a very large capacity to buffer atmospheric inputs of H/sup +/. Precipitation chemistry was dominated by the anions of strong mineral acids. Throughfall and soil solution chemistry was dominated by weak acids and contained large amounts of soluble Al. Laboratory leaching experiments with simulated acidic precipitation and field lysimeter studies showed that the acidity and aluminum contents of the soil solution were independent of the acidity of precipitation and that the chemistry of hydrologic flow was determined by the soil horizons through which the precipitation had moved any contribution by acidic deposition was small or undetectable. It appears that the internal generation of hydrogen ions in the forest-soil system was the principal cause of large increases in (H/sup +/) and (Al+++) during storm events.

The Tennessee Valley Authority conducted studies to measure the amount of sulfur (S) that is transferred from the atmosphere to agro-ecosystems and to determine the S-supplying capacity of soils in the Tennessee Valley. Three techniques were tested for determining the fractional contribution of the soil and the atmosphere to the total S content in field-grown plants. Soybeans, cotton, and fescue were grown in equal quantities of the same soil with a low sulfur content at three field locations and in a greenhouse with charcoal-filtered air. Technique III, which provided a direct method for calculating the amount of plant S that was derived from the soil at any location, proved to be satisfactory for measuring the amount of atmospheric S accumulated by plants. Cotton grown 4 and 3 km from coal-fired power plants accumulated 125 and 240 mg S per 100 g, but fescue accumulated only 65 and 58 mg S per 100 g at the same locations. Cotton grown near the power plants produced significantly more biomass than that grown at a location remote to sources of SO2. The S-supplying capacity of selected soils was evaluated by measuring the rate of S accumulation by fescue grown in a greenhouse withmore » charcoal-filtered air. The rate of S mineralization in soil collected from a depth of 0 to 30 cm at five sites was about 1 mg per kilogram of soil during the 27 weeks of plant growth.« less

AbstractThree greenhouse pot experiments with corn (Zea mays L.) were conducted to study effects of multiple rates of applied N, P, and K on growth and yield—nutrient concentration trends. Harvests were made each 4 or 6 days from 15 to 56 days after plant emergence. Growth and plant nutrient concentrations and uptake increased with rate of each applied nutrient at adequate levels of other nutrients. Applied N also increased both P concentrations and uptake in young corn plants. Yield response to applied K resulted only in dilution of N and P concentrations at even the earliest harvest. Concentrations of all nutrients were soon diluted to lower levels with increase in dry matter and/or age of plants, so that comparative results varied with time of harvest. Growth rates increased with adequacy of nutrient supply and more favorable growth conditions; they declined greatly soon after depletion of applied N. The limited soil volume in pot experiments, rate of growth, and time of harvest all greatly influence the effects of one nutrient on plant concentrations of other nutrients.

AbstractAccumulation of NO3‐N in plants is important in regard to plant N nutritional status, in the formation of NO2‐N toxic to animals and people consuming the plants, and as a producer of lethal gas in silos. This paper describes relationships between NO3‐N and total N concentrations in plants grown in several greenhouse pot experiments, as affected largely by response to applied N and by continuing growth. Corn (Zea mays L.) was grown in soil with 200 to 800 mg of N/pot and in nutrient solutions with 2 to 16 ppm of N. Both crops were harvested at 4‐day intervals. Spinach (Spinacea oleracea L.) and mustard (Brassica pervirdis L.) were grown in soil with several rates of N, P, and K, and tall fescue (Festuca arundinacea Shreb.) with 1.0 and 2.0 g of N/pot.These experiments conducted on N‐deficient soils resulted in marked yield response and higher concentrations of total N and NO3‐N with increase in rates of applied N. Concentrations decreased with age, dry matter accumulation, and depletion of N. Total N was higher in leaves than in stems, but the reverse was true for NO3‐N. Concentrations of NO3‐N started to increase in various crops above minimum total N values of 1.5 to 4.5%, which were highest for leaves, intermediate for leaves + stems, and lowest for stems or petioles. Below these minimum total N values, NO3‐N remained near zero (< 0.1%). Discontinuous regression models appear most satisfactory to fit the entire range of the relationships between total and NO3‐N. It was concluded that NO3‐N concentrations in plants are negligible if the total N was < 1.5% to 4.5%, depending largely on plant part composition, plant species, and N source.

AbstractHybrid corn (Zea mays L.) was sampled each week on field plots of soil testing adequate in P and K at Muscle Shoals, Alabama, in 1972, to relate plant analyses results to growth and maturity. Treatments of N compared were no N, 28 kg/ha at planting + 84 kg/ha topdressed at tasseling, 56 kg/ha at planting, and 112 kg/ha at planting. Plots of cumulative yields vs nutrient concentrations were used to evaluate the results.Corn yields increased markedly with amount of applied N, but single and split applications of N resulted in similar yields. Concentrations of N in the top leaves, ears, and entire topgrowth also increased at each harvest date with amount of applied N. Applied N also resulted in higher concentrations of P, Ca, and Mg, but lower K concentrations in the top leaves at most sampling dates. At each rate of applied N, concentrations of N in leaves, ears, and entire tops decreased with maturity. Concentrations of P remained about the same; Ca and Mg first decreased and then increased to maturity, whereas the opposite trends resulted for K concentrations. These opposite trends in results from this experiment and from other studies illustrate the strong reciprocal relationship between concentrations of K and Ca + Mg in plants. Nutrient concentration trends with increasing yields and age of plant are influenced in general by amounts of available nutrients and various growth‐limiting factors.

AbstractYields and concentrations of N and P were studied in young corn (Zea mays L.) plants as a basis for correct interpretation of plant analysis results. The corn was grown on soils deficient in these nutrients in several greenhouse pot experiments comparing rate, source, and placement of N or P. Results from such pot experiments were satisfactory for establishing minimum and critical nutrient concentrations in corn if various growth‐limiting factors were properly corrected. These included age of plant, application rates of one or more deficient nutrients, and adequacy of other yield‐limiting factors, including liming and other nutrients.The minimum concentrations of total N or of P in corn forage appear to be rather constant for a given age of plant and can be more accurately estimated than critical concentrations can. The results suggest the estimation of critical values from the minimum concentrations.C‐type curves resulting from plots of dry matter yield vs nutrient concentration could be explained largely by dilution resulting from growth response to application of a second deficient nutrient.

AbstractThe total concentration of inorganic cations (K+, Na+, Ca2+, Mg2+) exceeds the total concentration of inorganic anions (NO3‐, H2PO4‐, SO42‐, Cl‐) in most plant tissue, and the difference between the two is an estimate of the organic anion concentration. Previous investigations have shown that vegetative growth of barley with high fertilization rates was regulated to some extent by the organic anion concentration. In this study, 16 plant species were grown in the greenhouse to test the consistency of this relation with different ion accumulation patterns. The inorganic anion content of the plant tissue was varied by applying either SO42‐ or Cl‐ to the soil. All Cl‐treated plants had a higher inorganic anion concentration than the SO4‐treated plants. The organic anion concentration in 10 of the plant species was lower in the Cl‐treated plants. The lower yield of each plant species was associated with the plants that had the higher total inorganic anion concentration. The results of this study, with one possible exception, are consistent with the concept that reducing the organic anion concentration in plants reduces growth.

AbstractThe uptake rates of Rb and Ca, applied alone or together, by excised barley and plantain roots were compared. The barley roots absorbed Rb at a faster rate than Ca, whereas the reverse was true for plantain roots. The presence of Ca increased the rate of Rb uptake by barley roots, but the presence of Rb had very little effect upon the Ca uptake. The uptake rate of either ion by plantain was reduced by the presence of the other ion.Calculations indicate that the depressing effect of one ion on the uptake of the other by plantain was due predominantly to ionic competition when the ions were present in the concentration range of 10‐2N, but factors in addition to competition were responsible in the concentration range of 10‐4N. The significance of the differences in response of the two species is discussed.

The transport of ions from a bathing solution to top of a plant has been described as a passive (7, 8, 18, 19, 22, 23, 28) and active (2, 3, 17, 26, 27) process. Brouwer (3) states that at least 70 to 85 % of ions appearing in tops of plants go through an active process, i.e., owing to a mechanism controlled or started by metabolism lands into transpiration stream. On other hand, Epstein (7) concludes that the cells of roots, as well as shoots, derive their ions from solution in 'outer' of root tissue. He defined outer as space to which inorganic ions have free and reversible access by diffusion. The purpose of this study was to investigate these suggested concepts of ion passage from outside solutions to top of plant, and to formalize observations with equations consistent with available data. The technique is kinetic analysis of ion uptake from solutions of radioactive rubidium ranging in concentration from 10-5 to 10-2 molar, in presence and absence of inhibitors.

AbstractA kinetic analysis was made of P absorption at steady state by excised roots of millet, barley, and alfalfa. Short‐time absorption studies indicated that the rate of P absorption is greater for millet than barley and greater for barley than alfalfa. The specific reaction rate constants for the metabolic turnover of the two carriers of P are of the same order of magnitude for the three plant species. They are approximately 1 × 10‐2 moles of P per mole of combined carrier per second. The apparent dissociation constant for carrier “a” is approximately 9 × 10‐4 for all three plant species, but the value for carrier “b” varies from 3 × 10‐6 for millet and alfalfa to 8 × 10‐6 for barley. The major difference between species is in concentration of carrier. These values are 2 × 10‐7, 3 × 10‐8, and 1 × 10‐8 moles per g. of millet, barley, and alfalfa roots, respectively.

Steady-state analysis was applied to the absorption of cations by excised barley roots. The results indicate that ions are adsorbed and absorbed by specific ion-binding compounds of the root. Only negligible amounts of the cations tested were adsorbed nonspecifically. The intercept of the uptake time curves equals the amount of cation adsorbed to the specific binding compound. The concentration of these ion-binding compounds was the order of magnitude of 2 me. per 100 g. of dry barley roots for Na, K, and Rb and 4 me. for Sr. The specific reaction-rate constants for both sites of ion uptake for each of the cations appeared to be the same order of magnitude. This was approximately 1 × 10-3 moles of cation per mole of combined site per second for Na, K, and Rb and 6 × 10-5 moles per mole of combined site per second for Sr.

Techniques used in making an experimental measurement of a step-by-step uptake of nutrients by plants are reported. Metal pans, divided in half, were filled with soil and covered by a collodion membrane. By fitting the halves of the pan together, plants were grown between the two membranes without actual soil-root contact. This technique made possible the growing of plant roots in a soil-free condition and enabled the measurement of the suites of cations at each of the following stages of nutrient uptake, (a) the non-adsorbed stage, (b) the adsorbed stage, (c) the absorbed stage in which the cations were absorbed into the roots, and (d) the suite of cations that were translocated to the above ground portions of the plant. Aliquots of electrodialyzed Sharkey and Ruston soils saturated to give 65% Ca and 3% K saturation of the exchange complex, and either 3, 6, 12, or 18% Mg saturation were prepared. Soybean plants were grown for a period of 4 weeks at which time the living plants were removed and the measurement of nutrient uptake at each of the various stages was carried out. Increasing the percentage of Mg in either soil resulted in an increase in the percentage of Mg and a corresponding decrease in the percentage of Ca and K in the suite of cations at each stage of nutrient uptake. Ca dominated the suite of adsorbed cations on plant roots grown in the Ruston soil, while K dominated the suite of adsorbed cations on plant roots grown in the Sharkey soil. The Sharkey soil produced plants with Ca percentages of less than one-fourth of those grown on the Ruston soil despite the fact that with equal percentages of Ca saturation (65%) the Sharkey clay offered about 10 times the quantity of exchangeable Ca to the plant roots. A Mg saturation of 9% of the Ruston soil produced plants with equal Mg contents (0.30%) as did the Sharkey clay with 3% Mg saturation. The exchange properties of the plant root and the metabolic effects of the plant favored a greater movement of K than Mg or Ca from the root surface into the roots and tops of plants.