The objectives of this study were to evaluate the leaching, degradation, uptake, and mass balance of indaziflam, as well as its potential to produce phytotoxicity effects on young pecan trees. Pecan trees were planted in pots with homogeneous porous media (sandy loam soil), preferential flow channels open to the soil surface, and shallow tillage at the soil surface. Pots were treated with indaziflam at two application rates of 25 and 50 g a.i./ha in 2014 and 2015. Each pecan tree was irrigated with 7 L of water every 2 weeks during the growing season. An irrigation volume of 2 L was used to maximize indaziflam retention time in the soil from Dec. 2015 until the end of the trees’ dormant stage. In 2014, leachate samples were collected after each irrigation for quantifying indaziflam mobility. Soil samples were collected at depths of 0 to 12 and 12 to 24 cm after 45, 90, and 135 days of indaziflam application, and leaf samples were collected at the end of the growing season to quantify mobility and uptake. Indaziflam was detected in leachate samples, and the leaf indaziflam content increased with increasing application rate. Indaziflam and its breakdown products were detected at both sampling depths. Mass recovery and half-life values for indaziflam in the soil ranged from 38% to 68% and 63 to 99 days, respectively. No phytotoxicity effects were observed from increasing application rate and retention time of indaziflam in the soil. Most of the applied indaziflam was retained in the soil at shallow depth.
Amir M. González-Delgado and Manoj K. Shukla
Joshua Sherman, Richard J. Heerema, Dawn VanLeeuwen and Rolston St. Hilaire
and poorly available for root uptake by pecan trees in those alkaline soils ( Chang, 1953 ; Lindsay, 1979 ; Sims, 1986 ; Sparks, 2000 ) and this results in micronutrient deficiency symptoms that are commonly visible in southwestern U.S. pecans
Anil P. Ranwala, Garry Legnani and William B. Miller
Several experiments were conducted to find effective ways of utilizing gibberellin4+7 (GA4+7) and benzyladenine (BA) to prevent leaf chlorosis during greenhouse production of Easter lilies (Lilium longiflorum Thunb.) while minimizing the undesirable side effects on stem elongation. On an absolute concentration basis, GA4+7 was much more effective than BA in preventing leaf chlorosis. Excessive levels of GA4+7, however, tended to cause stem elongation. When applied at around the visible bud stage, if the foliage was well covered with the spray solution, 25 mg·L-1 of GA4+7 was adequate for maximum protection against leaf chlorosis. Increasing the GA4+7 concentration above 25 mg·L-1 gave no additional benefit on leaf chlorosis. Two possible modes of GA4+7 uptake during a foliar spray application (absorption through leaves and stems, and root uptake of the extra run-off) were studied in terms of their relative contribution to leaf chlorosis and stem elongation. Although both modes of uptake prevented leaf chlorosis, foliar uptake was much more effective than root uptake. However, GA4+7 taken up by the roots contributed mainly to stem elongation. When sprayed to leaves on only the lower half of the plant, a 10-mL spray of either 25 or 50 mg·L-1 of each GA4+7 and BA was enough for complete protection against leaf chlorosis. Increasing volumes had no additional benefit on leaf chlorosis, but increased the chances of unwanted stem elongation.
R.L. Qu, D. Li, R. Du and R. Qu
Turfgrass, which is widely grown and produces a large amount of biomass, could act as a sink for industrial pollutants in urban and suburban regions. Little research has been conducted regarding heavy metal uptake by turfgrasses. The objective of this study was to evaluate root uptake of lead (Pb) in four turfgrass species. Grasses were grown hydroponically in solutions containing from 0 to 450 mg·L-1 Pb, at either pH 4.5 or 5.5, for 4 or 8 days. A significant quadratic relation existed between Pb accumulation in roots and solution Pb concentration within the tested range. The maximum Pb accumulation in roots of the four species was in the range of 20 mg·g-1 dry root weight. Tall fescue (Festuca arundinacea Schreb.) and Spartina patens survived at 450 mg·L-1 Pb solution without showing obvious damage while centipedegrass [Eremochloa ophiuroides (Munro) Hack.] and buffalograss [Buchlöe dactyloides (Nutt.) Engelm.] deteriorated or died at this concentration. This study showed that turfgrass plants can absorb heavy metals efficiently and tolerate high Pb concentration in hydroponic solutions and thus may have a potential use in environmental remediation as a biological extractor of lead.
Regina L. Reickenberg and Marvin P. Pritts
The dynamics of nutrient uptake from foliar applied 15N-urea and Rb (a K analog) were quantified in red raspberries. Both N and Rb in an aqueous solution were absorbed rapidly into the leaf and transported throughout the plant. In the greenhouse, about half of the urea and a third of the Rb were absorbed within 32 hours of application. The addition of a surfactant to the foliar solution reduced uptake, while solution pH, time of application and leaf age had little effect. The lower leaf surface exhibited a faster rate of absorption than the upper surface, but the difference was not large. In the field, some foliar N appeared to have been washed off leaves and taken up by the root system; however, none of the foliar applications affected plant growth. We conclude that significant uptake of foliar applied N and K occurs in raspberry, but the absolute amount delivered through a single foliar application is small. The percentage of total plant nutrient supplied through a foliar application is reduced to < 5% over time as the plant grows, so multiple applications would be required to maintain levels significantly higher than would exist through root uptake alone.
Louise Ferguson and Steven R. Grattan
There are two ways salinity can damage citrus: direct injury due to specific ions, and osmotic effects. Specific ion toxicities are due to accumulation of sodium, chloride, and/or boron in the tissue to damaging levels. The damage is visible as foliar chlorosis and necrosis and, if severe enough, will affect orchard productivity. These ion accumulations occur in two ways. The first, more controllable and less frequent method, is direct foliar uptake. Avoiding irrigation methods that wet the foliage can easily eliminate this form of specific ion damage. The second way specific ion toxicity can occur is via root uptake. Certain varieties or rootstocks are better able to exclude the uptake and translocation of these potentially damaging ions to the shoot and are more tolerant of salinity. The effect of specific ions, singly and in combination, on plant nutrient status can also be considered a specific ion effect. The second way salinity damages citrus is osmotic effects. Osmotic effects are caused not by specific ions but by the total concentration of salt in the soil solution produced by the combination of soil salinity, irrigation water quality, and fertilization. Most plants have a threshold concentration value above which yields decline. The arid climates that produce high quality fresh citrus fruit are also the climates that exacerbate the salt concentration in soil solution that produces the osmotic effects. Osmotic effects can be slow, subtle, and often indistinguishable from water stress. With the exception of periodic leaching, it is difficult to control osmotic effects and the cumulative effects on woody plants are not easily mitigated. This review summarizes recent research for both forms of salinity damage: specific ion toxicity and osmotic effects.
Gene E. Lester, John L. Jifon and Gordon Rogers
Muskmelon [Cucumis melo L. (Reticulatus Group)] fruit sugar content is directly related to potassium (K)-mediated phloem transport of sucrose into the fruit. However, during fruit growth and maturation, soil fertilization alone is often inadequate (due to poor root uptake and competitive uptake inhibition from calcium and magnesium) to satisfy the numerous K-dependent processes, such as photosynthesis, phloem transport, and fruit growth. Experiments were conducted during Spring 2003 and 2004 to determine if supplemental foliar K applications during the fruit growth and maturation period would alleviate this apparent inadequate K availability in orange-flesh muskmelon `Cruiser'. Plants were grown in a greenhouse and fertilized throughout the study with a soil-applied N-P-K fertilizer. Flowers were hand pollinated and only one fruit per plant was allowed to develop. Starting at 3 to 5 days after fruit set, and up to 3 to 5 days prior to fruit maturity (full slip), entire plants, including the fruit, were sprayed with a glycine amino acid-complexed potassium (potassium metalosate, 24% K) solution, diluted to 4.0 mL·L-1. Three sets of plants were sprayed either weekly (once per week), biweekly (once every 2 weeks) or not sprayed (control). Fruit from plants receiving supplemental foliar K matured on average 2 days earlier than those from control plants. In general, there were no differences in fruit maturity or quality aspects between the weekly and biweekly treatments except for fruit sugar and beta-carotene concentrations, which were significantly higher in the weekly compared to the biweekly or control treatments. Supplemental foliar K applications also resulted in significantly firmer fruit with higher K, soluble solids, total sugars, ascorbic acid (vitamin C) and beta-carotene concentrations than fruit from control plants. These results demonstrate that carefully timed foliar K nutrition can alleviate the developmentally induced K deficiency effects on fruit quality and marketability.
Kirk W. Pomper and Michael A. Grusak
Understanding the mechanisms that regulate xylem transport of calcium (Ca) to snap bean (Phaseolus vulgaris L.) pods could allow approaches to increase pod Ca concentration and enhance the nutritional value of edible pods. Using the snap bean cultivars Hystyle and Labrador, which exhibit high and low pod Ca levels, respectively, we wished to determine whether there were differences between the two cultivars in stem xylem-sap Ca concentration and whether any differences in sap Ca concentration were related to differences in whole-plant water uptake or Ca import between the cultivars. Well-watered greenhouse-grown plants were placed in a growth chamber at a constant light intensity for an equilibration period. Pot weight loss was measured to determine whole-plant water use and stem xylem exudate was subsequently collected from the severed base of the shoot at flowering and at two stages of pod development. `Hystyle' displayed an exudate Ca concentration that was 50% higher than `Labrador' during pod development. `Labrador' showed 35% greater total water transport through the stem than `Hystyle'. `Labrador' plants also showed a significantly larger leaf area than `Hystyle' plants. Additional plants were used to determine total, long-term Ca influx. No difference was observed between cultivars in total Ca influx into the aerial portion of the plant. With whole-shoot Ca influx being equivalent and pod transpiration rate identical in the two cultivars, our results suggest that the higher whole-plant water uptake in `Labrador' led to a dilution of Ca concentration in the xylem stream and thus less total Ca was transported to developing pods, relative to that in `Hystyle'. Increased transpiration efficiency, enhanced root uptake of Ca, or reduced Ca sequestration in the xylem pathway of the stem could lead to an enhancement in pod Ca concentration in future cultivars of snap bean.
D. Neilsen and G.H. Neilsen
In irrigated apple orchard systems, the magnitude and timing of plant demand for nitrogen (N) and retention of N in the root zone to allow root interception are important factors for efficient management of N fertilizer. Results from five experiments in high-density plantings of apple (Malus domestica) on dwarfing (`Malling 9') rootstocks are reported. All experimental plots received daily drip irrigation and N applied through the irrigation system (fertigation) with different regimes according to experimental design. Labelled fertilizer applications, whole tree excavation and partitioning and removal of N in fruit and senescent leaves were used to assess tree N demand. Nitrogen requirements ranged from 8 to 40 lb/acre (8.8 to 44 kg·ha-1) over the first 6 years after planting and N use efficiency was often low (<30%), likely because supply exceeded demand. Annual growth is supported by N remobilized from storage and taken up by roots. Root uptake of labelled fertilizer was negligible during early spring and the commencement of rapid uptake was associated with the end of remobilization and the start of shoot growth, rendering prebloom fertilizer applications ineffective. Thus timing of N supply to periods of high demand is crucial for improving efficiency. Comparisons were made to determine the effects on N leaching and tree N utilization of irrigation scheduled to meet evaporative demand and irrigation applied at a fixed rate. Water losses beneath the root zone were greater for fixed rate than scheduled irrigation during the coolest months (May, June and September) of irrigation application. Nitrogen leaching followed a similar pattern during times of N fertigation (May and June). Greater N use efficiency was also measured for trees when irrigation was scheduled to meet evaporative demand rather than applied at a fixed rate. The most N efficient management system was for trees receiving a low [50 ppm (mg·L-1)] fertigated N supply, at 0 to 4 or 4 to 8 weeks following bloom with scheduled irrigation.
Gene E. Lester, John L. Jifon and D. J. Makus
Netted muskmelon [Cucumis melo L. (Reticulatus Group)] fruit quality (ascorbic acid, β-carotene, total free sugars, and soluble solids concentration (SSC)) is directly related to plant potassium (K) concentration during fruit growth and maturation. During reproductive development, soil K fertilization alone is often inadequate due to poor root uptake and competitive uptake inhibition from calcium and magnesium. Foliar applications of glycine-complexed K during muskmelon fruit development has been shown to improve fruit quality, however, the influence of organic-complexed K vs. an inorganic salt form has not been determined. This glasshouse study investigated the effects of two K sources: a glycine-complexed K (potassium metalosate, KM) and potassium chloride (KCl) (both containing 800 mg K/L) with or without a non-ionic surfactant (Silwet L-77) on melon quality. Orange-flesh muskmelon `Cruiser' was grown in a glasshouse and fertilized throughout the study with soil-applied N–P–K fertilizer. Starting at 3 to 5 d after fruit set, and up to 3 to 5 d before fruit maturity at full slip, entire plants were sprayed weekly, including the fruit, with KM or KCl with or without a surfactant. Fruit from plants receiving supplemental foliar K had significantly higher K concentrations in the edible middle mesocarp fruit tissue compared to control untreated fruit. Fruit from treated plants were also firmer, both externally and internally, than those from non-treated control plants. Increased fruit tissue firmness was accompanied by higher tissue pressure potentials of K treated plants vs. control. In general, K treated fruit had significantly higher SSC, total sugars, total ascorbic acid, and β-carotene than control fruit. Fall-grown fruit generally had higher SSC, total sugars, total ascorbic acid and β-carotene concentrations than spring-grown fruit regardless of K treatment. The effects of surfactant were not consistent but in general, addition of a surfactant tended to affect higher SSC and β-carotene concentrations.