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Dimitrios Savvas, Gerasimos Meletiou, Spiridoula Margariti, Ioannis Tsirogiannis, and Anastasios Kotsiras

In a completely closed hydroponic system, Na and Cl commonly accumulate in the root zone, at rates depending on the concentration of NaCl in the irrigation water (rate of Na and Cl inlet) and the Na to water and Cl to water ratios at which they are taken up by the plants (rates of Na and Cl outlet). However, while the concentration of NaCl in the irrigation water is commonly a constant, the Na to water and Cl to water uptake ratios are variables depending on the concentrations of Na and Cl in the root zone and, hence, on the rates of their accumulation. To quantify this feed-back relationship, a differential equation was established, relating the rate of Na (or Cl) accumulation to the rate of water uptake. This equation was solved according to the classical Runge-Kutta numerical method using data originating from a cucumber experiment, which was conducted in a fully automated, closed-loop hydroponic installation. Four different NaCl concentrations in the irrigation water, 0.8, 5, 10 and 15 mm, were applied as experimental treatments. The theoretically calculated curves followed a convex pattern, with an initially rapid increase of the Na and Cl concentrations in the root zone and a gradual leveling out as the cumulative water consumption was rising. This was ascribed to the gradual approaching of the Na to water and Cl to water outlet ratios via plant uptake, which were increasing as NaCl was accumulating in the root zone, to the constant NaCl to water inlet ratio (NaCl concentration in irrigation water). The model could predict the measured Na and Cl concentrations in the drainage water more accurately at 10 and 15 mm NaCl than at 0.8 and 5 mm NaCl in the irrigation water. Possible explanations for these differences are discussed. Plant growth and water uptake were restricted as salinity was increasing, following a reverse pattern to that of Na and Cl accumulation in the root zone. The leaf K, Mg and P concentrations were markedly restricted by the increasing salinity, while that of Ca was less severely affected.

Open access

Michael R. Sweatt and Fred T. Davies Jr.

Abstract

To determine the role of endomycorrhizae on water relations and plant growth of geraniums under nonrate-limiting soil P conditions, hybrid seedlings (Pelargonium X hortorum Bailey cv. Cherry Glow) were planted in moderately high P (40 ppm) media, grown under high (−0.4 MPa) or low (−1 MPa) soil water potential (ψs), and either inoculated with VA mycorrhizal fungi [Glomus mosseae (Nicol. & Gerd.) and G. fasciculatus (Thaxt. sensu Gerd.) Gerd. & Trappe] (VAM) or left as noninoculated controls. Geraniums grown under high moisture had greater shoot growth, more advanced floral development, and higher P uptake than the low moisture plants. Mycorrhizal plants under high moisture conditions had higher P levels than noninoculated plants, while mycorrhizal plants under low moisture regimes had greater shoot growth, more advanced floral formation, and greater N uptake than noninoculated plants. Xylem water potential in leaves (ψL) was lower under −1 MPa than −0.4 MPa ψS moisture regimes and lowest in mycorrhizal geraniums grown under −1 MPa ψS. One hundred minutes after plants had recovered from water stress, the greatest change in ψL was recorded for mycorrhizal geraniums acclimatized to low moisture regimes. Geraniums under low moisture regimes are more mycorrhizal-dependent. Total estimated root length and root water conductivity were lower with mycorrhizal geraniums under high water and P regime. Under water stress, the larger mycorrhizal geraniums have greater total water demands than controls. Consequently, mycorrhizal geraniums stressed more rapidly yet more efficiently recovered from water deficits. Data suggests that VAM plants acclimate more efficiently to water stress because of more frequent or extreme drought.

Free access

Tina Wilson, Robert Geneve, and Brent Rowell

One possible influence film-coating may have on seeds is modifying water uptake and electrolyte leaking during imibibition. Film-coating is a seed treatment that can improve sweet corn germination, especially under cold soil conditions. Two shrunken-2 sweet corn varieties (`Even Sweeter' and `Sugar Bowl') were treated with a polymer film-coating and evaluated for water uptake patterns during imibibition. `Even Sweeter' is a low-vigor sweet corn, while `Sugar Bowl' is a high-vigor variety. Standard germination tests were performed according to AOSA rules and suggest film-coated seeds germinated at a slower rate than untreated seeds. After 4 days of imibibition, `Sugar Bowl' film-coated seeds had 5% germination, while untreated seeds had ≈20% germination. However, after 7 days, film-coated seeds had 94% germination with untreated seeds at 80% germination. Results were similar for `Even Sweeter'. Bulk electrical conductivity readings were taken over 24 h to determine the amount of electrolyte leakage during imibibition. Low-vigor `Even Sweeter' had 92% higher overall leakage than high-vigor `Sugar Bowl'. Additional conductivity readings were taken for both seed lots every 2 h for 12 h. Film-treated seeds leaked 15% less than untreated seeds for `Sugar Bowl'. However, `Even Sweeter' film-coated seeds actually leaked 17% more than the untreated seeds. In both cases, 70% of electrolyte leakage occurred within the first 12 h of imibibition. An imibibition curve was established for the two seed lots comparing untreated and film-coated seeds. During the first 6 h of water uptake, film-treated seeds weighed ≈50% more than the untreated seeds for both `Even Sweeter' and `Sugar Bowl'. Pathways for water uptake as influenced by film-coating shrunken-2 seeds will also be presented.

Free access

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.

Open access

I. Levin, R. Assaf, and B. Bravdo

Abstract

Six irrigation treatments consisting of replenishing the water extracted from the 0-60 cm or 0-120 cm layer, were applied to a 10-year-old apple orchard. The highest yield and fruit size were obtained by irrigating to 60 cm depth when soil moisture to this depth dropped to 40% available water during the 2 months of intensive fruit growth. During the rest of the season this treatment was irrigated to 60 cm whenever the 0-60 cm layer dropped to wilting point and to 120 cm whenever the 60-120 cm layer dropped to 60% available water. The relative water extraction from the 60-90 cm layer was the highest in this treatment. Increasing water uptake from layers below 120 cm by watering them was not effective. Climatic conditions favoring high rates of evaporation increased the relative contribution of layers deeper than 90 cm in all plots. The proportion of water loss from the 0-30 cm layer increased with the number of irrigations.

Free access

Timothy K. Broschat

Queen palms (Syagrus romanzoffiana) were grown in containers of sand to determine the effects of irrigation water salinity and liming rate on cation uptake by the plants. Dolomite was incorporated at rates of 0, 3, or 6 kg/m3. Within each lime rate palms were irrigated with a solution of NaCl and CaCl2 (molar ratio =5Na:1Ca) at conductivities of .25, 1, 2, 4, or 6 dS/m. Plant height and dry weight and leaf Mg were decreased with increasing irrigation water salinity, whereas leaf Ca was increased at higher salinities. Leaf Mn and Zn increased, then decreased as salinity was increased. Leaf Ca and Mg increased with increased lime, but leaf Mn and Cu were decreased by increasing the lime rate. Leaf K increased, then decreased as lime rate was increased.

Free access

Timothy K. Broschat

Queen palms (Syagrus romanzoffiana) were grown in containers of sand to determine the effects of irrigation water salinity and liming rate on cation uptake by the plants. Dolomite was incorporated at rates of 0, 3, or 6 kg/m3. Within each lime rate palms were irrigated with a solution of NaCl and CaCl2 (molar ratio =5Na:1Ca) at conductivities of .25, 1, 2, 4, or 6 dS/m. Plant height and dry weight and leaf Mg were decreased with increasing irrigation water salinity, whereas leaf Ca was increased at higher salinities. Leaf Mn and Zn increased, then decreased as salinity was increased. Leaf Ca and Mg increased with increased lime, but leaf Mn and Cu were decreased by increasing the lime rate. Leaf K increased, then decreased as lime rate was increased.

Free access

Troy M. Buechel, David J. Beattie, and E. Jay Holcomb

A characteristic problem with peat moss is its difficulty in initial wetting and rewetting, especially in a subirrigation system. Wetting agents improve wetting characteristics primarily by reducing the surface tension of water. This results in a rapid, uniform movement of water by capillary rise through the growing medium.

Two methods were used to compare the effectiveness of different wetting agents: gravimetric and electrical. Ten cm pots containing peat moss were placed in a subirrigation system. The gravimetric method used a laboratory scale where pots were periodically weighed to determine the amount of water absorbed. The electrical method utilized thin beam load cells, which have strain gages bound to the surface, to determine the weight of a suspended object. Load cells were coupled with a Campbell Scientific datalogger to collect data every minute without removing the pot from subirrigation. Because the effect of buoyancy altered the true weights, equations were generated to adjust the water uptake values. Corrected weights were used to create absorption curves for comparison of the slopes to determine which wetting agent has the fastest rate of absorption. The load cell reliably and accurately described the wetting characteristics of Peat moss and we found good agreement with the gravimetric method.

Free access

S. Gamiely, W.M. Randle, H.A. Mills, D.A. Smittle, and G.I. Banna

Nitrogen applied as NH4-N or NO3-N (75 mg·liter-1) affected onion (AIlium cepa L.) plant growth when grown in solution culture. Nitrate alone or in combination with NH4-N increased leaf fresh and dry weight, leaf area, root fresh and dry weight, and bulb dry weight when compared to growth with NH4-N as the sole N source. Bulb fresh weight was highest with an NH4-N: NO3-N ratio between 1:3 and 3:1. Maximum leaf fresh weight was not necessary to produce maximum bulb fresh weight when onions were subjected to different N-form ratios. Precocious bulbing resulted when NH4-N was the sole N source; however, high bulbing ratios early in plant development were not correlated with final bulb fresh weight. Nitrogen form also influenced water uptake and pungency, as measured by enzymatically developed pyruvate concentration, but did not affect bulb sugar concentration.

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Holger Weichert, Carina von Jagemann, Stefanie Peschel, Moritz Knoche, Dieter Neumann, and Wilfried Erfurth

Water uptake through the exocarp of intact sweet cherry [Prunus avium (L.)] fruit was determined gravimetrically in an immersion assay (25 °C). Fruit with sealed pedicel/fruit juncture were incubated in water during the first interval (0 to 0.75 hour) and in 10 mm salt solutions of selected cations during the second (0.75 to 1.5 hours) and third interval (1.5 to 2.25 hours) of an experiment. Rates of water uptake (F) were calculated for first, second and third intervals (FI, FII and FIII, respectively) and salt effects indexed by the ratios FII/FI and FIII/FI. AgNO3 (FII/FI = 0.65), NaCl (0.70), BaCl2 (0.67), CdCl2 (0.69), CuCl2 (0.42), HgCl2 (0.58), and SrCl2 (0.69), and the salts of trivalent cations AlCl3 (0.50), EuCl3 (0.58), and FeCl3 (0.49), significantly decreased water uptake into mature `Sam' fruit as compared to the water control (0.87). KCl (0.82), NH4Cl (0.85), CaCl2 (0.75), MgCl2 (0.88), MnCl2 (0.81), and ZnCl2 (0.72) had no effect, LiCl (1.00) increased uptake. Similar data were obtained for FIII/FI. The effect of FeCl3 on water uptake was independent of the presence of CaCl2, AlCl3, or CuCl2, as sequential or simultaneous treatment with these salts reduced water uptake to the same extent as with FeCl3 alone. Increasing FeCl3 concentration up to 1 mm decreased uptake, higher concentrations had no further effect. FeCl3 and CaCl2 to a smaller extent decreased water uptake in developing `Regina' sweet cherry fruit (55 to 91 days after full bloom). FeCl3 had no significant effect on water uptake along the pedicel/fruit juncture, but markedly reduced uptake through the exocarp of all cultivars investigated (`Burlat', `Early Rivers', `Hedelfinger', `Knauffs', `Regina', `Sam', `Summit', and `Van'). Effects of CaCl2 on water uptake were limited to `Burlat', `Early Rivers', and `Hedelfinger'. CaCl2 and FeCl3 both decreased fruit cracking, but FeCl3 was more effective. The mode of action of mineral salts in decreasing water uptake and fruit cracking and their potential for field use are discussed.