The PURR‐WICK system, as developed at Purdue University in 1966, provides an impermeable underlay, plus possible retention of free water by outflow drainage control. What would be the effect in this system of sand texture, depth of water reserve, and temperature? ‘Penncross’ bentgrass (Agrostis palustris Huds.) was grown in columns of finer and coarser sand mixes with water tables maintained at depths of 11, 25, and 40 cm in constant temperature chambers of 15 and 30 C for 9 weeks. Temperature had the greatest effect. At 15 C root growth was slow initially but steadily maintained. At 30 C initial root growth was rapid but declined to little or no growth, so that total root length at 15 C was three times that for 30 C. Within each temperature the water table ✕ sand interaction was significant. Root growth was better in the coarser sand for the 11‐ and 25‐cm water tables and better in the finer sand for the 40‐cm treatment. The deepest root growth was found at 15 C in the finer sand mix with the water table at 40 cm. Where oxygen diffusion was favored by coarse texture, roots were still limited by higher temperature.

Recent developments in plastic barrier placement under compacted sand for regulated availability and retention of water (PURR‐WICK Rootzone) raises questions of duration of availability. Creeping bentgrass (Agrostis palustris Huds) was studied under putting green conditions when grown on replicated 1‐m2 plastic‐lined plots containing dune sand, mortar sand, calcined clay, diatomaceous earth, and peat. Soil was not included in any of the rootzone mixtures because of its inherent structural instability. In 1968 and 1969, some infiltration rates exceeded 150 cm/hr and all were greater than 7 cm/hr, therefore, water movement was considered ample. The relative ability of the material in plots to retain moisture was measured by allowing the plots to dry‐down for 15 days between rains during August 1968 and for 17 days during July 1969. No irrigation was added to any plot until turf showed severe wilt. Bentgrass on plots containing the finer fractions of the dune sand, diatomaceous earth, various mixtures of sand, calcined aggregates, and peat did not require water for either period. Comparison of the dune sand treatments with and without subsurface irrigation showed that a constant moisture level could be maintained in the subirrigated plots. Depth ranged from 20 to 50 cm with 40 cm proving ample.

Dicyandiamide (DCD), a nitrification inhibitor, is a 67% N compound of low volatility that can be incorporated into fertilizer granules. Urea, ammonium sulfate (AS), and a complete fertilizer (COMP), all amended with DCD so that I 0% of the N was derived from DCD, were evaluated in field studies at West Lafayette, IN, on 'Wabash' Kentucky bluegrass (Poa pratensis L.) grown on Toronto silt loam (fine-silty, mixed, mesic Udollic Ochraqualfs). Urea, AS, sulfur-coated urea (SCU), and isobutylidene diurea (IBDU) were included for comparison. Equal treatments were applied two or four times per season to provide 196 kg N ha-•yr-•. Clipping yields in response to DCDamended fertilizers were similar to those of urea and AS at both N regimes. Initial response to DCD-amended fertilizers was rapid and response to residual N shorter than that of IBDU and SCU; however, recovery of applied N in the tissue was similar between DCD fertilizers and IBDU, and SCU. Averaged over 3-yr, recovery of N ranged from 41.1% for IBDU to 36.4% for AS at 2 X 98 kg N ha-•, and 39.0% for COMP + DCD to 32.6% for AS at 4 X 49 kg N ha-1 , respectively. Turf quality of plots receiving IBDU was superior to all N sources. Measurements 24 days after a 15 November application in 1984 indicated DCD inhibited N0.3 formation at the 2 X 98 kg N ha-• rate (14.6 kg DCD ha-1 ). Fall-applied DCD did not influence soil NHt and N03 concentrations at 0 to 0.20 m the next spring. The short period of effectiveness of DCD would seldom warrant its use as a nitrification inhibitor in turf.Additional index words: Isobutylidene diurea, Sulfur-coated urea, Soil inorganic N, Nitrogen recovery, Poa pratensis L. W ITH the ~ncreasing cost of N fertilizers and the potential for N03 pollution of lakes and groundwater, efficiency inN management is extremely important. Applications of slow-release N tend to minimize leaching losses by reducing concentration of NO) in the soil solution. Bredakis and Steckal (1963) reported N03 release in this order: (NH 4 hS0 4 = urea > sewage sludge > ureaformaldehyde (UF). Residual N was found to be greater with sulfur-coated urea (SCU) applications, however, leaching losses of N03 were less than 11% of a 400 kg N ha-1 application for all soluble and insoluble N sources (Allen et al., 1978). Others have reported higher residual N with SCU than isobutylidene diurea (IBDU); however, split applications of these materials were necessary to produce 1

Slow-release N fertilizers are used in turfgrass fertilization programs to reduce foliar burn and N losses, and to extend the response period between applications. In this study, oxamide (31% N), an amide of oxalic acid, and a 7:3 N ratio of oxamide and urea were evaluated as slow release N sources on Kentucky bluegrass (Poa pratensis L.) at West Lafayette, IN, on a Toronto silt loam soil (finesilty, mixed mesic, Udollic Ochraqualfs). Two particle sizes of oxamide, C (1-2.8 mm) and F ( <0.85 mm), were applied as a granular and liquid suspension treatment, respectively. Additional treatments consisted of applying isobutylidene diurea (IBDU), sulfur-coated urea (SCU), and urea. Two and four applications were made, with a total annual application rate of 196 kg N ha~• yr~•. Recovery of N in the tissue from applications of oxamide C was 51% compared to 41, 39, and 38% for IBDU, oxamide F, and SCU, respectively, averaged over 3 yr. Initial change in visual turf quality and clipping yields in response to oxamide C was slow, similar to that of IBDU; however, residual N release was equal to that of IBDU and greater than that of SCU. Adding urea to oxamide C increased initial yields and turf quality but reduced the duration of turf response as compared to applications of oxamide C alone. At two applications of 98 kg N ha~ 1 , oxamide proved to be a good, slow-release source of N. At four applications per year, initial clipping yields resulting from spring oxamide F applications were lower than those from urea, but turf quality in response to residual N tended to be greater than that of urea. Late fall applications of oxamide F reduced soil N03 concentrations shortly after application and in early spring as compared to fall applications of urea. Oxamide F at four applications generally produced a more desirable turf response than did similar applications of urea.Additional index words: Isobutylidene diurea, Sulfur-coated urea, Nitrogen recovery, Soil inorganic nitrogen, Poa pratensis L. Agron. J. 79:720-725 (1987). Published in

A root zone for natural grass of sports fields (planted surfaces) based on suction applied to a water control system has been developed and patented. Controlled water management by surface and/or subirrigation, conservation, and suction removal is automatically regulated by soil moisture sensing. The availability of sports fields for scheduled events regardless of weather is enhanced and wear tolerance increased. The Prescription Athletic Turf system is patented by Purdue Research Foundation as USA 3908385, 13 SE 75 and Canada 985516, 16 MR 76.