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  • Author or Editor: D. C. Bowman x
  • Journal of the American Society for Horticultural Science x
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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.

Free access

Abstract

Nitrogen uptake by two N-deficient turfgrass species was characterized by measuring N depletion from a complete nutrient solution. The uptake rate of both NO 3 and NH 4 + was enhanced up to 6-fold in N-deficient perennial ryegrass (Lolium perenne L.) compared to N-sufficient controls, reaching a maximum of about 0.3 and 0.4 g N/m2 per hr for NO 3 and NH 4 + , respectively. Deficiency-enhanced uptake exceeded uptake by controls for about 72 hr following resupply of N. Nitrogen uptake was enhanced to a similar degree by N deprivation in Kentucky bluegrass (Poa pratensis L.). Mowing had no effect on NO 3 uptake by N-deficient perennial ryegrass turf, whereas mowing inhibited uptake by N-sufficient turf by ≈60%. Deficiency-enhanced uptake was found to be the result of an increased capacity for N absorption (Imax) rather than an increased affinity for N (K m). Imax values increased from 0.24 and 0.73 mg N/g dry weight per hr for N-sufficient ryegrass turf for NO 3 and NH 4 + , respectively, to 1.44 and 2.68 mg N/g dry weight per hr for N-deficient turf. K m values increased slightly, from 14 μm for both N forms for N-sufficient turf to 24 and 39 μm for NO 3 and NH 4 + , respectively, for N-deficient turf.

Open Access

Abstract

The depletion of N applied to a moderately N-deficient Kentucky bluegrass (Poa pratensis L.) turf was measured using a soil sampling procedure. Nitrogen as either Ca(NO3)2 or (NH4)2SO4 was applied in solution at 5 g N/m2 and washed into the thatch and soil with an additional 0.3 cm of water. Both N forms were located primarily in the thatch and upper 1 cm of soil. The NO 3 was present in the soil solution, while the NH 4 + was mainly exchangeable (86%). The concentrations of NO 3 and NH 4 + in the soil solution were 452 and 56 μg N/ml, respectively, in the upper 1 cm of soil. Depletion of both NO 3 and NH 4 + from the turf was very rapid, with 70% to 80% of the applied N disappearing during the first 24 hr. Essentially all of the applied N was depleted by 48 hr. Results using (l5NH4)2SO4 indicate that ≈75% of the NH 4 + depletion is attributable to absorption by the turf. Similar results were obtained following fertilization of perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinaceae Schreb.), and creeping bentgrass (Agrostis palustris Huds.).

Open Access