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  • Author or Editor: Daniel C. Bowman x
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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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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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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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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.

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