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Daniel C. Bowman

An experiment was conducted in nutrient solution culture to examine the effects of salinity on N uptake by tall fescue (Festuca arundinacea Schreb.) turfgrass. The cultivars `Finelawn' and `Monarch' were chosen for study, representing a salt-sensitive and salt-tolerant tall fescue. Nitrogen treatments were imposed to produce N-replete turf (no N stress) and moderately N-deficient turf. Rootzone salinity was increased gradually over four weeks to final salt concentrations of 0, 40, 80 and 120 mM using a combination of NaCl and CaCl2 at a molar ratio of 8:1. Uptake of both NO3-N and NH4-N, each labeled with 99.8% enriched 15N to determine N partitioning, was measured over a 24 hr period as depletion from solution. Nitrate and ammonium uptake by N-replete tall fescue turf were similarly affected by salinity in both cultivars, with moderate inhibition (10-25%) at 40 and 80 mM and severe inhibition (60-70%) at 120 mM salt. Uptake by the N-deficient turf was much faster than by the N-replete turf, with the controls absorbing all the added N by 8-12 hours. Inhibition of uptake by `Monarch' tall fescue was roughly 30% at both 40 and 120 mM salt, whereas 80 mM salt had essentially no effect. Nitrogen uptake by `Finelawn' was progressively inhibited by higher salt concentrations. It is possible that these differences are related to the relative salt tolerances of the two cultivars, but the mechanism is presently unknown.

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Daniel C. Bowman and Jack L. Paul

The absorption and assimilation of 15N-labeled urea, (NH4)2 S O4, and KNO applied to the foliage of perennial ryegrass (Lolium perenne L.) turf were examined under a controlled environment. Each source of N was dissolved in deionized water to a final concentration of 25 g N/liter and spray-applied at a rate of 5 g N/m2. Absorption of the fertilizer-N over 48 hours, as measured by 15N analysis of tissue digests, amounted to 35%, 39%, and 40% for the urea, (NH4)2 S O4, and KNO3, respectively. Absorption was also estimated by a washing procedure that measured the urea remaining on the foliage and by the increase in total N in the ryegrass tissue. There were no significant differences between the three methods for absorption of (NH4) 2SO4 and KNO3. The washing method, however, significantly overestimated absorption of urea. Partitioning of the absorbed N between tissues was similar at 48 hours for all three N sources, averaging 32% in new leaves, 52% in old leaves and shoot tissue, and 16% in the roots. Most of the absorbed urea- and NH4 -N was assimilated by 48 hours, whereas only half of the NO3 -N was reduced during that period.

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Daniel C. Bowman and Richard Y. Evans

Hydration of a commercial hydrophilic polyacrylamide gel in 20 meq Ca(NO3)2/liter was reduced to <10% of the maximum hydration in deionized water. Repeated soaking with deionized water to remove soluble salts restored hydration to ≈ 30% of maximum. Incorporating KNO3 at concentrations ranging from 5 to 40 meq·liter-1 with the Ca(NO3)2 in the hydration solution partially reversed the Ca2+ inhibition of hydration following repeated soaking. Potential hydrogel hydration increased to 50% of maximum with 40 meq K+/liter. Potassium nitrate supplied separately following hydration in Ca(NO3)2 was much more effective at reversing Ca2+ inhibition of hydrogel hydration than joint application. Potential hydrogel hydration (following repeated soaking) was doubled after treatment with 5 meq KNO3/liter and reached 77% of maximum at 40 meq KNO3/liter.

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Daniel C. Bowman, Richard Y. Evans, and J.L. Paul

Hydration of three commercial hydrophilic polyacrylamide gels in deionized water ranged from 340 to 420 g per gram of gel. Hydration was progressively inhibited by fertilizer salt concentrations from 0 to 20 meq·liter-1. Hydration of the gels in the presence of divalent cations (Ca2+ and Mg2+) and monovalent cations (K+ and NH4 +) at 20 meq·liter-1 was reduced to ≈10% and 20% of maximum, respectively. The valence of the accompanying anion did not affect hydration. Gel hydration was unaffected by urea over the range of 2 to 20 mm. Sequential rinses of the hydrated gels with deionized water completely reversed the inhibition due to the monovalent, but not the divalent, cations. The electroconductivity (EC) of the external solution increased during gel hydration. In the presence of fertilizer salts, the physical properties of a 2 redwood sawdust : 1 sand (v/v) container mix were unaffected by hydrophilic gel additions of 1.2 and 2.4 kg·m-3 (1 × and 2 × the recommended rate, respectively).

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Cale A. Bigelow, Daniel C. Bowman, and D. Keith Cassel

sand-based rootzones are specified for golf course putting greens because they resist compaction and maintain drainage, even under heavy traffic. Although sands provide favorable physical properties, nutrient retention is generally poor and soluble nutrients like nitrogen (N) are prone to leaching. Laboratory experiments were conducted to evaluate several inorganic soil amendments (clinoptilolite zeolite (CZ), diatomaceous earth, and two porous ceramics), which varied in cation exchange capacity (CEC), and sphagnum peat for their ability to limit N leaching. Columns (35 cm tall × 7.6 cm diameter) were filled with 30 cm of sand-amendment mixtures (8:2 v/v) and NH4NO3 was applied in solution at a N rate of 50 kg·ha-1. Leaching was initiated immediately using 2.5 pore volumes of distilled water in a continuous pulse. Leachate was collected in 0.1 pore volume aliquots and analyzed for NH4 +-N and NO3 --N. All amendments significantly decreased NH4 + leaching from 27% to 88% which was directly proportional to the CEC of the amendments. By contrast, NO3 - losses were consistently high, and no amendment effectively decreased loss compared to nonamended sand. Two amendments with the highest CECs, CZ and a porous ceramic, were selected to further study the effects of amendment incorporation rate, depth, and incubation time on N leaching. Ammonium but not NO3 - leaching was decreased with increasing amendment rate of both products. At 10% amendment (v/v) addition, only 17% to 33% of applied NH4 + leached from the amended sands. Depth of amendment incorporation significantly affected NH4 + leaching, with uniform distribution through the entire 30 cm tall column being more effective than placement within the upper 2.5 or 15 cm. Allowing the NH4NO3 to incubate for 12 or 24 hours following application generally did not affect the amount leached. These results suggest NH4 +-N leaching is inversely related to CEC of the root-zone mixture and that uniform distribution of these CEC enhancing amendments in the root-zone mixtures reduced N leaching to a greater extent than nonuniform distribution.

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Daniel C. Bowman, Richard Y. Evans, and Linda L. Dodge

A study was conducted to determine the potential for using ground automobile tires as a container medium amendment. Rooted cuttings of chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] were planted in 1.56-liter pots containing 1 sand:2 sawdust (v/v) or media in which coarsely or finely ground particles of rubber substituted for 33%, 67%, or 100% of the sawdust. Amendment with the coarse material decreased total porosity and container capacity and increased air-filled porosity and bulk density relative to the sawdust control. Amending the medium with the fine material did not appreciably alter total porosity, container capacity, or bulk density, but did increase air-filled porosity. Plant height, fresh weight, dry weight, and number of open flowers were reduced significantly in rubber-amended media compared to sawdust controls. Rubber amendment reduced shoot tissue concentrations of N, P, K, Ca, Mg, and Cu, but increased Zn as much as 74-fold over control values. There was no accumulation of other heavy metals (Cd, Cr, Ni, Pb) or Na in the tissue due to rubber amendment. This study demonstrates that ground tires might be used as a component of container media in the production of greenhouse chrysanthemums. However, growth reductions and the potential for Zn toxicity may limit the usefulness of ground tires as a substitute for conventional organic amendments.

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Yuguang Zhao, George C.J. Fernandez, Daniel C. Bowman, and Robert S. Nowak

Cumulative evapotranspiration (ETcum) patterns of 10 commercially available cool-season turfgrass species and cultivars were evaluated under progressive water stress in the semi-field conditions using a gravimetric mass balance method in three studies. At the end of water stress, the cultivars were visually scored for green appearance on a 0 (no green) to 10 (100% green) scale. A Gompertz nonlinear model gave a best fit to ETcum vs. days adjusted for pan evaporation variation. Two of the ETcum attributes (ti, the time during which the rate change in ET is zero, and ETmax, the maximum ET rate) estimated from the Gompertz model appeared to reflect efficient water-use attributes in the turfgrass. Among the physiological screening techniques studied, electrolyte leakage, relative water content, and the difference between canopy and air temperature appeared to separate cultivars by drought resistance and water use efficiency (WUE). These physiological attributes were also relatively easy to measure and had high correlations with color score and WUE. Biplot display is a graphical technique in which the interrelationships between the cultivars and water-use attributes can be displayed together. Based on ti, ETmax, color score, and physiological attributes, `Wabash' and `Bristol' Kentucky bluegrass (Poa pratensis L.), `Aurora' hard fescue (Festuca ovina var. duriuscula L. Koch.), and `FRT-30149' fine fescue (F. rubra L.) were identified as cultivars with higher WUE.

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Dale A. Devitt, Lena Wright, Daniel C. Bowman, Robert L. Morris, and Michelle Lockett

Irrigators in arid and semiarid regions that use reuse water must maintain positive leaching fractions (LFs) to minimize salt buildup in root zones. However, with the continuous feed of NO3-N in reuse water, imposing LFs can also lead to greater downward movement of NO3-N. It is therefore essential that deep movement of NO3-N be assessed relative to nitrogen loading under such conditions. We conducted a long-term monitoring program on nine golf course fairways in southern Nevada over a 1600-d period. The fairways were predominantly bermudagrass [Cynodon Dactylon (L.) Pers.; 35 of 36 site × years] overseeded with perennial ryegrass (Lolium perenne L.; 8 of 9 courses). Courses were irrigated with fresh water, reuse water (tertiary treated municipal sewage effluent), or transitioned to reuse water during the study. Solution extraction cups were inserted at depths of 15, 45, 75, and 105 cm on fairways and sampled and analyzed for NO3-N on a monthly basis. Distribution patterns of NO3-N varied from site to site. Concentrations exceeding 100 mg·L−1 were observed at the 105-cm depth on all three long-term reuse courses. On the transitional courses, 72% of the variation in the yearly average NO3-N concentrations at the105-cm depth could be accounted for based on knowing the amount of fertilizer nitrogen (N) applied, the amount of reuse N applied, and the LF (Y = –42.5 + 0.18 fertilizer N + 0.26 reuse N –62.0 LF). Highest N fertilizer applications occurred on transition courses with little or no reduction in N applications after courses had transitioned to reuse water (pretransition courses 394 + 247 kg·ha−1 N/year versus posttransition courses 398 + 226 kg·ha−1 N/year). The results of this study indicate a need for a more scientific approach to N management on reuse irrigated courses.