Search Results

You are looking at 1 - 7 of 7 items for :

  • Author or Editor: Dariusz Swietlik x
  • HortScience x
Clear All Modify Search

The purpose of this study was to determine the effect of Ca: NH4 ratio in the rhizosphere of hydroponically grown sour orange seedlings (SO) (Citrus aurantium L.) on the plants' vegetative growth and N uptake. The experiment was prompted by our observation that application of N in the form of NH4 in conjunction with CaCl2 was more efficient in eliminating N deficiency in field-grown grapefruit trees than the same rates of N applied in the form of NH4NO3 without CaCl2. About 40-cm-tall SO were pruned back to the 4th leaf and grown for 6 weeks in nutrient solutions containing 5 mm NH4 + at CaCl2: NH4 + molar ratios of 1.0, 1.3, 1.6, 1.9, 2.2, or 2.5. In an additional treatment, NO3 was used as the sole source of N at CaCl2: NO3 ratio of 1:1. The level of Ca:NH4 ratio had no effect on new leaves number, shoot growth, total and average leaf area, specific leaf weight, as well as leaf, stem, and tap root dry weight. However, lateral root dry weigh decreased at Ca: NH4 ratio of 2.5. No growth differences were found when the plants were supplied with NH4 + vs. NO3 at Ca:N molar ratio of 1:1.

Free access

The public is increasingly concerned with the danger of ground water pollution with fertilizer nitrogen and other chemicals. This is because slow water movement in underground aquifers assures the long lasting existence of contaminants. Citrus orchards commonly are heavily fertilized with nitrogen and other mineral nutrients. Fertigation through a low volume irrigation system is a promising new method of efficient use of fertilizer materials because it places mineral nutrients only in the wetted zones where roots are most active. Preliminary studies in Texas indicate that applying nitrogen fertilizers through a low volume irrigation system is a potentially powerful tool in minimizing N fertilizer leaching. When coupled with partial sodding in close tree proximity further reductions in NO3 leaching may be achieved presumably through uptake into the cover plants and/or indirectly by enhancing biological fixation in the soil. Other potential benefits of frequent N fertigations in citrus orchards will also be discussed based on the experimental data collected in various parts of the world.

Free access

Root distribution of trickle–and flood-irrigated 4-year-old `Ray Red' grapefruit (Citrus paradisi Macf.) trees on sour orange (C. aurantium L.) rootstock was studied utilizing a trench method. Irrigation treatments were: flooding at 50% soil water depletion, trickle irrigation (2 drippers per tree) at 0.5 Class A Pan evaporation or at 0.02 MPa soil tension. Two trees from each treatment were studied. Five 2.5 m deep trenches positioned perpendicular or parallel to the tree row at 0.6, 2.1, or 4.3 m from the tree trunks were dug per tree. After washing off a 0.5 cm thick layer of soil from the trench wall, 0.5 cm long root sections were marked on a transparent plastic film attached to the wall. Many roots of trickle-irrigated trees grew past the trickle wetted zone and extended beyond 2.1 but not 4.3 m of the trunk. However, the roots of flood-irrigated trees were present at all distances from the trunk. From 26 to 51% of the roots of trickle–irrigated trees were found 90-230 cm deep, despite the clayey texture of the top 1 m of soil which was underlaid by a sandy clay loam. The root systems-of flood-irrigated trees were shallower and in most cases confined to the top 90 cm soil layer.

Free access

Sour orange seedlings were grown in water culture to which one of seven aromatic compounds, associated with allelopathic effects, was added to produce concentrations ranging from 0.5 to 2.0 mM. Leaf water potential (ψ1), leaf stomatal conductance (gs), and whole plant transpiration (T) were measured during a 7-day treatment period. At the end of that period, the total and average leaf surface area, shoot elongation, and fresh weight gain of seedlings were determined. Solutions of vanillic, coumaric, and ferulic acids of 2mM concentration reduced ψ1, gs, and T. Reductions of gs, and T but not (ψ1) occurred when vanillic acid of 1mM concentration was applied. Solutions of vanillic (0.5; 1.0; 2.0mM), coumaric (1; 2mM), cinnamic (1mM), or chlorogenic (1; 2mM) acids reduced fresh weight gain of seedlings. Only the coumaric and chlorogenic acids treatments of 2mM concentration reduced shoot elongation. No treatment affected total or individual leaf area. Gallic and caffeic acids had no effect on sour orange water relations and growth.

Free access

Abstract

The efficacy of glyphosate in controlling bermudagrass (BG) (Cynodon dactylon L.), guineagrass (GG) (Panicum maximum Jacq.), and purple nutsedge (PN) (Cyperus rotundus L.) was determined when the herbicide was used alone or in combination with adjuvants: Frigate, LI-700, or VPG in a volume of 378 liters of water/ha. No loss of BG control was noted as the glyphosate level was lowered from 4.5 to 2.25 kg·ha-1 with Frigate added, but control decreased with VPG or no adjuvant addition (LI-700 not used). No reduction in control of PN was observed when glyphosate amount was lowered from 3.4 to 1.7 kg·ha-1, provided LI-700 was present in the spray solution. With Frigate, VPG, or no adjuvant, however, the degree of PN control was less at 1.7 than 3.4 kg·ha-1. Frigate, LI-700, and VPG were equally effective in improving glyphosate efficacy on GG when the herbicide was used at 3.4 kg·ha-1, but the adjuvants had no effect at the herbicide level of 1.7 kg·ha-1. Chemical names used: α-(p-alkyl phenyl) Ω-hydroxypoly (ethylenoxy) phosphate ester, propylene glycol (VPG); fatty amine ethoxylate (Frigate); isopropylamine salt of N-(phosphonomethyl) glycine (glyphosate); phosphatidylcholine methylacetic acid (LI-700).

Open Access

Water extracts of cocklebur,CBX (Xanthium spinosa L.) and velvetleaf,VLX (Abutilon theophrasti Medic.) shoots and Mexican ash,AshX (Fraxinus Berlandieriana A.DC.) roots were added to 9 month-old sour orange Citrus aurantium L.) seedlings(SOs) in water culture. Final extract concentrations represented either 50 or 12.5 g. of plant material liter-1 of culture solution, i.e. 1/20 or 1/80 dilutions. Leaf water potential(ψ); stomatal conductance(gs);transpiration(T) and growth responses were measured for 13 days. After 1 day, SOs in AshX and CBX had lower ψ than controls. After 11 days SOs in CBX had higher ψ than the others. ψ responded similarly to both extract concs.. Thru day 5, AshX decreased gs vs. the controls and VLX. By day 11, gs of SOs in AshX was less than for VLX but not the others. On days 1 and 5, gs for VLX at 1/20 was lower than controls but at 1/80, gs's were the highest of all treatments. These results supported by the T rates, growth responses and others findings suggest AshX and VLX induce water stress by reducing water absorption and/or transport in addition to possibly disrupting normal root/shoot communications

Free access

Abstract

Foliar application of CaCl2 at concentrations of 60 to 100 meq·liter-1 to in vitro-propagated ‘Jonathan’ apple (Malus domestica Borkh.) trees reduced stomatal conductance (gs). Responses in gs were not associated with visible leaf injuries. No reduction in gs was observed when Ca at 100 meq·liter-1 was applied to the leaves in conjunction with nonabsorbable anions (IDA or DMDADS), indicating that Ca2 alone was not responsible for stomatal closure after CaCl2 application. Foliar-applied Cl- at 100 meq·liter-1 with the organic cation 2-amino-2-hydroxymethyl-1,3-propanediol (Tris), induced stomatal closure. However, no changes in gs were observed after Tris application alone or when Cl- was applied with K- as an accompanying cation. These results indicate that CaCl2-induced reductions of gs derive from the interaction between Ca2 and Cl- rather than the effect of Ca2- or Cl- alone. CaCl2 sprays lowered transpiration for 2 days and increased stem water potential of water-stressed and unstressed trees. Transpiration was reduced less in stressed than unstressed trees. Chemical names used: iminodiacetate (IDA); 4,4-dimethyl-4,7-diazadecane-1,10 disulfate (DMDADS).

Open Access