MITIGATION EFFECTS OF SILICON ON TOMATO PLANTS BEARING FRUIT GROWN AT HIGH BORON LEVELS

Interactive effects of silicon (Si) and high boron (B) on growth and yield of tomato (Lycopercison esculentum cv. ‘191 F1’) plants were studied. Treatments were: 1) control (B1), normal nutrient solution including 0.5 mg L^?1 B (boron), 2) B1 +Si treatment: 0.5 mg L^?1 boron plus 2 mM Si, 3) B2 treatment: 3.5 mg L^?1 B, 4) B2 +Si treatment: 3.5 mg L^?1 B plus 2 mM Si, 5) B3 treatment: 6.5 mg L^?1 B, and 6) B3 +Si: 6.5 mg L^?1 B plus 2 mM Si. High B reduced dry matter, fruit yield and chlorophyll (Chl) in tomato plants compared to the control treatment, but increased the proline accumulation. Supplementary Si overcame the deleterious effects of high B on plant dry matter, fruit yield and chlorophyll concentrations. High B treatments increased the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7) and polyphenol oxidase (PPO; EC 1.10.3.1). However, supplementary Si in the nutrient solution containing high B reduced SOD and PPO activities in leaves, but POD activity remained unchanged. These data suggest that excess B-induced oxidative stress and alterations in the antioxidant enzymes. Boron (B) concentrations increased in leaves and roots in the elevated B treatment as compared to the control treatment. Concentrations of calcium (Ca) and potassium (K) were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplementing the nutrient solution containing high B with 2 mM Si increased both nutrients in the leaves. These results indicate that supplementary Si can mitigate the adverse effects of high B on fruit yield and whole plant biomass in tomato plants.     

Chronic effects of low ph and elevated aluminum on survival,maturation, spawning and embryo-larval development of the fathead minnow in soft water

Fathead minnows (Pimephales promelas) were exposed to a range of pH and A1 concentrations in soft water (8 mg Ca L^?1) to determine effect levels at various life stages. The tested pH levels ranged from 8.0 through 5.2 and inorganic monomeric Al from 15 through 60 μg L^?1. Reproductive processes including spawning, embryogenesis and early larval survival were more sensitive to acid stress than were juvenile growth and survival. Juvenile survival was significantly reduced at pH 5.2 + 60 μg Al L^?1 (P <0.05). Spawning success was reduced at pH 6.0 and 5.5 (P <0.10) and failed completely at pH 5.2, regardless of Al concentration. An apparant beneficial effect of added Al was observed during spawning at pH 7.5 + 35 μg Al L^?1, but this effect was not significantly greater than at pH 7.5 + 15 μg Al L^?1. A significant (P <0.05) decrease in larval survival occurred at pH 6.0 + 15 μg Al L^?1 and lower compared to the survival at pH 7.5 + 15 μg Al L^?1. Aluminum at 30 μg L^?1 provided protection resulting in short term increased embryo-larval survival at pH 5.5. The effect of parental exposure on progeny survival was assessed by an interchange of embryos from the spawning treatment to all tested exposure conditions. When reared at pH 8.0 + 15 μg Al L^?1 through 6.0 + 15 μg Al L^?1 or at pH 5.5 + 30 μg Al L^?1, parental exposure did not significantly influence progeny survival. However, survival was significantly reduced among progeny from brood fish reared at pH 5.5 + 15 μg Al L^?1 as compared to those spawned at pH 6.0 + 15 μg Al L^?1 and above, or at pH 5.5 + 30 μg Al L^?1 (P <0.05). Juvenile or 14 d larval growth effects were not detected under any exposure condition (P >0.05). Ultimately, fathead minnow young-of-the-year recruitment and production potential can be expected to diminish when environmental pH falls to 6.0, and to fail completely at 5.5 and lower.     

EFFECT OF ZINC ON CADMIUM TOXICITY IN WINTER WHEAT

This nutrient solution experiment investigated the effects of zinc (Zn) and cadmium (Cd) on winter wheat growth and enzymatic activity. Twelve nutrient solution treatments were prepared of four zinc levels (0, 0.5, 5 and 50 mg L^?1) and three cadmium levels (0, 5 and 50 mg L^?1). Cadmium concentrations ≥5 mg L^?1 decreased plant growth, superoxide dismutase activity, and leaf and stem zinc concentrations, but increased plant cadmium concentrations, proline content, and peroxidase and catalase activities. Root activity and zinc concentration were highest in the 5 mg L^?1 treatment and lowest in the 50 mg L^?1 treatment. Zinc concentrations ≥5 mg L^?1 inhibited plant growth, but increased proline content and cadmium concentration in stems and leaves. Low levels of zinc (0.5 mg L^?1) increased cadmium-induced toxicity in wheat plants but high levels of zinc (50 mg L^?1) reduced. In conclusion, these results indicated that the addition of zinc alleviated cadmium toxicity if the zinc/cadmium ratio was >10/1. Additional study needs to be done to quantify zinc content before zinc is supplied to alleviate cadmium toxicity.     

EFFECT OF FOLIAR SPRAY OF SOLUBLE SILICIC ACID ON GROWTH AND YIELD PARAMETERS OF WETLAND RICE IN HILLY AND COASTAL ZONE SOILS OF KARNATAKA,SOUTH INDIA

Field experiments were conducted to evaluate the effect of foliar spray of soluble silicic acid on growth and yield parameters of wetland rice. The results revealed a significant effect on achieving higher grain and straw yield with foliar silicic acid over control. Foliar spray of silicic acid at 2 and 4 ml L^?1 increased the grain and straw yield and application of 8 ml L^?1 decreased the yield. Foliar spray of silicic acid at 4 ml L^?1 along with half dose of recommended pesticide effectively increased the yields over all other treatments. The content and uptake of silicon in grain and straw was recorded higher with the foliar spray of silicic acid over control. This investigation concludes that application of silicic acid at 4 ml L^?1 along with half dose of recommended pesticide as foliar spray increased the grain and straw yield, besides Si content and its uptake over control.     

IMPACT OF VERMICOMPOST AND NITROGEN-PHOSPHORUS- POTASSIUM APPLICATION ON BIOMASS PARTITIONING,NUTRIENT UPTAKE AND PRODUCTIVITY OF ARECANUT

A long-term field experiment (1998 to 2010) investigated the effects of vermicompost (VC) and chemical fertilizers (CF) application alone or in combination on biomass partitioning, nutrient uptake and productivity of arecanut. Trunk biomass (kg palm^?1) was significantly higher with integrated treatments (40.8–43.0) than control (23.9). Biomass partitioning to kernel varied between 4.6% in control to 7.7% in CF 100 and 200% nitrogen (N)- phosphorus (P)- potassium (K). The leaf P and K content varied significantly among treatments. The N immobilized in trunk (g palm^?1) was significantly higher in integrated treatments (119-127) than in control (93). Phosphorus and K uptake by trunk followed same trend. The leaf K uptake and total K removed were found significant. The nutrition treatments registered significantly higher kernel yield (2508–3176 kg ha^?1) than control (1721 kg ha^?1). The increased yield of arecanut from chemical fertilizers (73–85%) was more pronounced when compared to VC (48–59%) and integrated treatments (46–63%) over control.     

CALIBRATION OF SUGARCANE RESPONSE TO CALCIUM SILICATE ON FLORIDA HISTOSOLS

Silicon is considered a beneficial nutrient for sugarcane (Saccharum spp.) and yield responses to Si applications on Florida organic soils have been well documented. Growers need calibrated Si recommendations to be able to make cost-effective decisions regarding Si applications. The objective of this study was to develop a soil-test Si calibration based on yield responses to Ca silicate on Everglades Histosols. Twelve paired commercial field comparisons and three small-plot tests of Ca silicate application were conducted. Strong responses in t cane ha^?1 and t sucrose ha^?1 were determined with acetic acid-extractable soil Si <15 g m^?3, with some response to approximately 25 g m^?3. Recommendations were developed over this range with a maximum Ca silicate rate of 6.7 t ha^?1. Optimum leaf Si concentration was determined to be ≥ 6.0 g kg^?1, with 0.95 and 0.80 relative yield at 5.0 and 2.5 g kg^?1, respectively.     

Silicon and salicylic acid in the physiology and yield of cotton

Silicon (Si) and salicylic acid (SA) foliar applications can benefit cotton yield especially if there is stress during cultivation. The objective of this study was to evaluate the foliar application of Si and SA on the photosynthetic variables and cotton yield. The experimental design used was randomized complete block, constituted by Si foliar application in potassium and sodium balanced silicate form (0 and 3.6?g L^?1 of Si) and SA (0 and 210?mg L^?1). The treatments were applied in three leaf sprays during the reproductive stage that coincided with water stress in tillage. Therefore, the Si foliar application associated with SA favors the physiological variables, increasing the photosynthesis, stomatal conductance and water use efficiency reflecting on the increase of cotton yield.     

Effect of Silicon on Growth, Physiology, and Cadmium Translocation of Tobacco (Nicotiana tabacum L.) in Cadmium-Contaminated Soil

Silicon(Si) offers beneficial effect on plants under cadmium(Cd) stress such as promoting plant growth and increasing resistance to heavy metal toxicity. In this study, a pot experiment was performed to study the role of Si in alleviating Cd toxicity in tobacco(Nicotiana tabacum L.) plants on a yellow soil taken from Guiyang, China. Nine treatments consisting of three concentrations of Cd(0, 1, and 5 mg kg~(-1)) together with three Si levels(0, 1, and 4 g kg~(-1)) were established. Plant growth parameters, Cd concentration,and the malondialdehyde(MDA), chlorophyll, and carotenoid contents were determined 100 d after transplanting of tobacco seedlings.Application of exogenous Si enhanced the growth of tobacco plants under Cd stress. When 5 mg kg~(-1) Cd was added, Si addition at 1 and 4 g kg~(-1) increased root, stem, and leaf biomass by 26.1%–43.3%, 33.7%–43.8%, and 50.8%–69.9%, respectively, compared to Si addition at 0 g kg~(-1). With Si application, the transfer factor of Cd in tobacco from root to shoot under both 1 and 5 mg kg~(-1) Cd treatments decreased by 21%. The MDA contents in the Si-treated tobacco plants declined by 5.5%–17.1% compared to those in the non-Si-treated plants, indicating a higher Cd tolerance. Silicon application also increased the chlorophyll and carotenoid contents by 33.9%–41% and 25.8%–47.3% compared to the Cd only treatments. Therefore, it could be concluded that Si application can alleviate Cd toxicity to tobacco by decreasing Cd partitioning in the shoots and MDA levels and by increasing chlorophyll and carotenoid contents, thereby contributing to lowering the potential health risks of Cd contamination.     

Nitrogen Source and Concentration Affect Growth and Performance of Bedding-Plant Impatiens

ABSTRACT

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the United States, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. The objective was to determine the N concentration and the nitrate (NO₃ ^??N):ammonium (NH₄ ⁺?N) ratio of N source that optimized bedding-plant impatiens growth and flower development. Four N concentrations (3.5, 7, 10.5, and 14 mmol N · L^?1) were used in factorial combination with four ratios of NO₃ ^??N:NH₄ ⁺?N (4:0, 3:1, 1:1, and 1:3). Application of treatments was made for 30 d. Then for 10 d only deionized water was applied to reduce salt buildup. Substrate pH was lowest (4.9) with the NH₄ ⁺?N source and electrical conductivity (EC) highest, but never > 2.4 dS m^?1. Nitrogen concentration and N source displayed an interaction for most growth parameters. Shoot fresh and dry weights and flower bud number were maximized at the 1:3 NO₃ ^??N:NH₄ ⁺?N ratio with a N concentration of 10.5 mmol L^?1. However, plant diameter, leaf number, and leaf chlorophyll content responded quadratically to N form ratio, with the 1:1 ratio optimum at a concentration of 10.5 mmol N· L^?1.     

Vegetative Growth,Yield and Leaf Mineral Composition in Strawberry (Fragaria × Ananassa DUCH. CV. Pajaro) as Influenced using Nickel Sulfate and Urea Sprays

In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L^?1 and urea 0 and 2 g L^?1 concentrations. Results indicated that nickel (Ni; 300 mg L^?1) plus urea (2 g L^?1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L^?1and urea (2 g L^?1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L^?1 without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L^?1 without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L^?1 along with urea at 2 g L^?1 were the best treatments.     

CALIBRATION OF SOIL AND PLANT SILICON ANALYSIS FOR RICE PRODUCTION*

Calibration of field crop response to nutrient availability is the bases for making a fertilizer recommendation from soil and tissue analyses. The purpose of this study was to evaluate and summarize results from a series of experiments on silicon (Si) fertilization of rice in the Everglades Agriculture Area. Twenty-eight rice field experiments were conducted from 1992 through 1996. The experiments consisted of 2 to 5 rates of calcium silicate applied to soils (Histosols) of varying Si soil-test values. Soil samples were taken before planting and analyzed for acetic acid (0.5 mol L^?1) extractable Si. Straw samples were collected at harvest and analyzed for total Si. Grain yield was determined. The “critical” levels for Si in the soil (point below which response to Si fertilizer is expected) calculated by the Cate & Nelson procedure was 19 mg Si L^?1 soil. The amount of silicon to correct Si deficiency in the soil and to obtain optimum rice yield was 1500, 1120 and 0 kg ha^?1 for low (<6 mg L^?1), medium (6 to 24 mg L^?1), and high (>24 mg L^?1) level of soil Si, respectively. Silicon in the straw was classified as high when Si concentration was >34 g kg^?1, medium when in between 17 and 34, and low when <17 g kg^?1 (3.4 and 1.7%, respectively).

     

EFFECTIVENESS OF DIFFERENT FOLIAR IRON APPLICATIONS TO CONTROL IRON CHLOROSIS IN ORANGE TREES GROWN ON A CALCAREOUS SOIL

The effectiveness on controlling Fe chlorosis in orange trees grown on calcareous soils was tested. The treatments were Fe(II) sulfate (500 mg Fe L^?1), sulfuric acid (0.5 mM H₂SO₄), Fe(III)-chelate (Hampiron 654 GS, 120 mg Fe L^?1) and distilled water as a control. A non-ionic wetting agent was used in all treatments. The use of frequent foliar sprays alleviated Fe chlorosis in orange trees. Sprays of Fe(II) sulfate increased the concentrations of chlorophyll, Fe and zinc in leaves and improved fruit size and quality compared to fruits of control trees. Sprays of Fe(III)-chelate also increased leaf chlorophyll and Fe concentrations and improved fruit quality, but did not increase fruit size. Sprays of sulfuric acid alone slightly increased leaf chlorophyll and Fe concentrations, without improving fruit size and quality. These results suggest that foliar sprays with Fe could help to avoid yield and quality losses caused by Fe chlorosis in citrus orchards. Furthermore, these treatments could be done with relatively cheap materials such as solutions containing Fe(II) sulfate.     

ACCUMULATION OF SILICON IN CYNODON DACTYLON X C. TRANSVAALENSIS AND POA TRIVIALIS USED AS AN OVERSEED GRASS

Calcium silicate has been used to supply silicon (Si) as a plant nutrient for enhancing crop production and the suppression of turf diseases. Research was initiated to determine the effect of calcium silicate on silicon uptake, turf quality, and its residual activity in providing plant available Si in two turfgrass systems. During 2005 and 2006, calcium silicate (CaSi, 12% Si) was applied as a topdressing at eight rates ranging from 0 to 342 kg m^?2 to a ‘Tifdwarf’ (Cynodon dactylon × C. transvaalensis Burtt Davy) green in the spring and to the same plots overseeded with ‘Wintergreen’ rough bluegrass (Poa trivialis L.) in the fall. At initiation of the study, dolomitic limestone and magnesium sulfate (MgSO₄) was applied to equilibrate calcium across all treatments based on the highest rate of CaSi. Every 28 days, treatments were rated for turf quality and then harvested to determine Si accumulation. One month after applying CaSi in 2005, Si concentration in the leaf tissue of Tifdwarf had increased linearly with increasing rates. This response continued through the months of May, June, July, August, and October with a 9%, 21%, 40%, 22% and 21% increase in Si concentration in the leaf tissue between the control and the 342 kg m^?2 rate, respectively. Although the rate response remained, there was an overall drop in average percent Si accumulation in leaf tissue across the treatments beginning three months after the first application. Similar responses were noted with the overseeded rough bluegrass with a 46%, 85%, 69%, 111% and 58% increase in Si concentration in the leaf tissue between the control and the 342 kg m^?2 rate, respectively. In contrast to the bermudagrass, over the five month period following application, the residual activity of Si in rough bluegrass remained high, suggesting that rough bluegrass might be a better Si accumulator in comparison to Tifdwarf bermudagrass. The second run of the experiment (2006–2007) and the residual trial had the same response with Si concentration in the leaf tissue increasing as the amount of CaSi applied increased. Although turfgrass quality was not well correlated to CaSi rate for Tifdwarf bermudagrass, there was an increase in quality ratings for rough bluegrass from December 2005 to April 2006.     

Silicon Leaf Fertilization Promotes Biofortification and Increases Dry Matter,Ascorbate Content,and Decreases Post-Harvest Leaf Water Loss of Chard and Kale

This study aimed to evaluate the effects of silicon (Si) leaf fertilization in different concentrations and sources on the production and quality of chard and kale. We carried out two experiments with chard and kale under a completely randomized design with four replicates in a 2 × 4 factorial scheme and two sources of silicon: potassium silicate and stabilized sodium potassium silicate with four concentrations of Si: 0.00; 0.84; 1.68 and 2.52 g L^?1. We performed three leaf sprays every 10 days. The chard and kale were harvested at 48 and 54 days after transplanting the seedlings, respectively. Silicon leaf fertilization is important for leafy vegetables like chard and kale because it increases the content and the accumulation of Si and the growth and production of the vegetables. It also improved growth, productivity, and quality. The Silicon leaf fertilization of 2.52 g L^?1 in the form of potassium silicate was the most notable.     

Optimum Nutrient Level on Growth,Flowering, and Rhizome Production in Curcuma

ABSTRACT

This study investigated the effect of liquid fertilizer treatments on growth, flowering, leaf mineral content, and rhizome production during forcing of Curcuma alismatifolia ‘Chiang Mai Pink’ and C. thorelii ‘Chiang Mai Snow’. Plants were irrigated with 200 mL of 1.3 g L^?1 of 15 nitrogen (N) -7 phosphorus (P) -14 potassium (K) water soluble fertilizer at 0, 1.3, 2.7, 4.0, 5.3, or 6.6 g L^?1 weekly. Days to flower, flower stem length, and leaf length were recorded, the mineral contents in leaves were analyzed, and the number of rhizomes with tuberous roots were recorded at harvest. Flowering of the first inflorescence in both C. alismatifolia ‘Chiang Mai Pink’ and C. thorelii ‘Chiang Mai Snow’ was significantly delayed when plants received 6.6 g L^?1 fertilizer as compared to the control plants. The number of rhizomes with more than 4 tuberous roots was highest when plants received 2.7 g L^?1 fertilizer. No medium-sized rhizomes with more than seven tuberous roots were produced when ‘Chiang Mai Pink’ plants received 0, 4.0, 5.3, and 6.6 g L^?1 fertilizer. Based on the production of rhizomes with four to six tuberous roots, optimum concentration of 15N -7P -14K water soluble fertilizer is 2.7 g L^?1 for C. alismatifolia ‘Chiang Mai Pink’ and 1.3 to 4.0 g L^?1 for C. thorelii ‘Chiang Mai Snow’. Although high boron content occurred only in the outer part of the second leaf when fertilizer concentrations were increased, leaf-margin burn (LMB) symptoms were not observed in both species and this could not be related to the production of rhizomes.     

Effects of soil pH and salt on N2O production in adjacent forest and grassland soils in central Alberta, Canada

Purpose

The effects of soil pH manipulation and KCl addition on N₂O production in adjacent forest and grassland soils in central Alberta were studied in a 16-day laboratory incubation experiment.

Materials and methods

The soils were subjected to four pH and two salt treatments: CK (control)—no addition of acid or alkali solution (pH 4.50 and 4.48 for the forest and grassland soils, respectively; same below); HCl—addition of HCl solution to lower soil pH (3.95 and 3.75); L-KOH and H-KOH—addition of 6 mL of 0.2 (5.36 and 5.57) and 0.4 (6.41 and 6.72)?mol?L^?1 KOH solution, respectively, to increase soil pH to two different levels. In order to differentiate between the effect of a change in pH and of changed salt concentrations on N₂O production, 6 mL of 0.2 (L-KCl) (4.56 and 4.41) or 0.4 mol?L^?1 (H-KCl) (4.59 and 4.42) KCl solutions were also applied as treatments to create two levels of salt application rates.

Results and discussion

Increasing pH promoted gross nitrification and cumulative N₂O production in both soils, particularly in the forest soil. However, cumulative N₂O production decreased in the forest soil but increased in the grassland soil when pH decreased. Cumulative N₂O production in the grassland soil was 36 times higher in the L-KCl treatment (1,442 μg?N?kg^?1) than in the CK (40 μg?N?kg^?1), whereas the H-KCl treatment reduced cumulative N₂O production. In contrast, in the forest soil, both KCl treatments reduced cumulative N₂O production.

Conclusions

(1) The most important factor to increase N₂O production in this study was increasing soil pH, suggesting that careful soil pH management could be used as a tool to control soil N₂O production; (2) salt effect was also involved in affecting N₂O production.     

Effect of applying calcium chloride and three milk supplements to poinsettia ‘Prestige Red’

Some poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) cultivars are susceptible to bract calcium (Ca) deficiency in developing bracts. In this study, we evaluated the efficacy of foliar uptake of Ca from milk-based products plus calcium chloride (CaCl₂) as a potential Ca source. Weekly foliar applications of 237 mL L^?1 whole milk, 80 mL L^?1 powdered milk, 30 mL L^?1 condensed milk, 0.94 g L^?1 CaCl₂, or distilled water (used as a control) were applied to runoff of ‘Prestige Red’ for four weeks. The four largest bracts with petioles on three different inflorescences and three leaves with petioles below the transitional leaf per inflorescence were collected per pot. None of the treatments affected bract or leaf Ca concentration. Powdered milk treatments resulted in a higher concentration of zinc (Zn) in bracts and aluminum (Al) in bracts and leaves. White residue remained on the bracts and leaves after treatment with powdered milk, which would reduce marketability.     

Avoidance of low pH and elevated Al concentrations by Brook Charr (Salvelinus fontinalis) Alevins in laboratory tests

Laboratory studies were conducted to test the ability of brook charr (Salvelinus fontinalis) alevins, the earliest free-swimming life stage of the species, to detect and avoid toxic levels of H⁺ and inorganic Al. Alevins were tested in steep gradient choice tanks using a range of H⁺ (pH 4.0 to 5.5) and Al (0 to 500 μg L^?1) concentrations in low Ca (2.0 mg L^?1) water. The young brook charr actively avoided acidic water with a pH < 5.0. Aluminum additions of 500 μg L^?l increased the avoidance response. The observed behavioral response of alevins to low pH and elevated levels of Al, may be of significant adaptive advantage in systems undergoing acidification.     

Response of ‘Jonagold’ Apple Trees in the First Three Years after Planting to Mono-Ammonium Phosphate Fertilization Under Replant Problem Conditions

Abstract

The objective of the experiment was to examine response of immature apple trees to application of mono-ammonium phosphate (MAP) fertilizer on replant problem soil. The study was carried out during 2001–2003 under a greenhouse on ‘Jonagold’ apple trees/M.9 EMLA planted singly in 50 L polyethylene containers filled with a sandy loam soil with low status of both organic matter and phosphorus (P) in soil solution. This soil originated from an apple orchard unfertilized with P for 23 years. The biological test showed the presence of specific replant disease in the soil. Immediately before apple tree planting, the soil was mixed with MAP at rates of 1, 2, and 3 g L^{? 1}. Trees grown in the soil untreated with MAP served as a control. Each year apple trees were drip-irrigated and supplied with nitrogen (N) at differentiated rates to achieve a level of 50 g N per plant. The results showed that MAP application increased soil solution P status. Simultaneously, MAP supply at rates of 2 and 3 g L^{? 1} caused a drop in soil pH value in the last two years of the experiment. MAP treatments increased both dry weight and length of fine roots (< 2 mm in diameter), vigor of trees, the number of flower clusters per tree, flower intensity, the number of fruits per tree, and P concentrations in leaf and fruit tissues. Fruits from MAP-supplied trees were firmer than those of the control trees. Mean fruit weight, titratable acidity, and soluble solids concentration of ‘Jonagold’ apples at harvest were not influenced by MAP treatment. Fruits from MAP-supplied apple trees had increased calcium concentration only in one year. It is concluded that pre-plant application of MAP at a rate of 1g L^{? 1}can be recommended on coarse-textured soils with low P status in soil solution to increase precocity of apple trees. However, MAP-supplied apple trees have to be watered to avoid the risk of osmotic stress.     

Foliar sensitivity of eight eastern hardwood tree species to ozone

As part of a larger 3-yr study, container-grown seedlings of black cherry (Prunus serotina) red maple (Acer rubrum), red oak (Ouercus rubra), sweetgum (Liquidambar styraciflua), white ash (Fraxinus americana), white oak (Ouercus alba), yellow-poplar (Liriodendron tulipifera), and yellow birch (Betula allegheniensis) were exposed to 0,0.075, or 0.15 μL L-¹ O₃ in laboratory controlled-environment chambers for 6 hr d^?1 on 2 consecutive days for 12 weeks. On the third consecutive day of each week, plants were treated for 45 min with precipitation at pH 3.0 or 4.2. The only significant foliar symptoms were induced by the O₃ treatments, and the severity of symptoms was not influenced by precipitation pH. The most common symptom was a dark, adaxial stipple which was most severe on the oldest leaves. Equations were developed to express the influence of leaf position on percent leaf injury following 4, 8, and 12 weeks of treatment. Based on percent leaf tissue showing stipple and defoliation following exposure to 0.15 μL L^?1 O₃, the most sensitive species to O₃ was black cherry, followed by sweetgum, yellow-poplar, white ash, red maple and yellow birch. Red oak and white oak foliage did not exhibit stipple.