ROOTZONE COMPOSITION AND THE PERFORMANCE OF GOLF GREENS. III. SOIL PHYSICAL PROPERTIES

Transcription

1 J. Sports Turf es. Inst. Vol. 69 OOTZONE COPOSITION AND THE PEFOANCE OF GOLF GEENS. III. SOIL PHYSICAL POPETIES By S.W. BAKE & C.W. ICHADS The Sports Turf esearch Institute, Bingley, West Yorkshire, BD6 AU SUAY The soil physical properties of Festuca/Agrostis turf receiving simulated wear and grown on sixteen different sand and sand-soil rootzones were examined over a period of four years. There was a marked overall decline in infiltration rates during the course of the trial with the mean for all mixes falling from 56 mm h - in June 989 (before wear) to 9 mm h - in April 992. After three years of wear infiltration rates ranged from a mean of 52 mm h - for pure sand materials to 4 mm h - for mixes containing approximately 3% silt plus clay. Infiltration rates were higher when coarser sands were used. The volume of larger pores (>75 µm diameter) also increased with sand content and the coarseness of the sand. Depth was also important because of the effects of compaction and averaged over all the mixes there was a pore volume of 24% >75 µm diameter in the 0-80 mm depth but only 5% >75 µm diameter for the -90 mm depth. Sand content and type both strongly influenced air-filled pore space and moisture content, although the moisture content of the immediate surface was also affected by the sward and thatch layer. Only those mixes with >94% sand gave acceptable soil physical properties in terms of adequate infiltration rates and air-filled pore space. Significant problems of drought stress, at times when irrigation was reduced, only occurred on the pure sand rootzone based on a medium-coarse sand ( mm diameter) with no amendment. INTODUCTION The soil physical properties of golf green rootzones strongly influence their ability to support a healthy sward and also affect the playing quality of the surface. There has been a considerable amount of work to identify those factors which contribute to a high quality rootzone material and this has concentrated mainly on the effects of sand type and amount (e.g. Lunt 956, Swartz & Kardos 963, Brown & Duble 975, Blake 980, Baker 983) and on the effects of various amendment materials (e.g. Davis et al. 970, Waddington et al. 974, Baker 984). Detailed specifications for rootzone materials used for golf green construction have been published on the basis of much of this work (e.g. USGA 960, 989, Davis 973). However, with some notable exceptions (e.g. Davis et al. 970, Schmidt 980, Waddington et al. 974), much of the work on rootzone materials for golf has been based on laboratory compacted soils with no turf cover or on greenhouse studies in which the time for grass development is relatively restricted. This means that the effects of the complex interaction between compaction, pore blockage by roots and organic matter accumulation may not have been adequately studied in all cases. Furthermore, many of the studies on sand-soil mixes have been restricted to soils of heavy texture (Swartz & Kardos 963, Schmidt 980), rather than the lighter sandy loam soil used in this project. The present study has particular relevance as there has been relatively little published work concerning the effect of construction type on golf green performance under United Kingdom conditions. Lodge et al. (99) and Lodge & Baker (99, 992) studied the performance of golf greens constructed from a sandy loam soil, a pure sand rootzone and a sand-soil-peat mix conforming the USGA specifications. Soil physical properties for these rootzone materials 38

2 are given in another paper in this volume (Lodge & Baker 993). In two previous papers from the current study (Baker 99, Baker & ichards 99) the effects of 6 different rootzone materials on ground cover, species composition and playing quality were examined. In this paper the effect of these rootzone materials on soil physical properties are examined and the implications for construction methods under United Kingdom conditions are discussed. ATEIALS AND ETHODS Trial area The trial was constructed at the Sports Turf esearch Institute, Bingley (NG SE ) and consisted of a suspended water table design with a 250 mm deep rootzone layer, formed from 6 different rootzone materials, overlying a coarse sand blinding layer and a gravel drainage layer. Full details of the construction method and materials are given by Baker (99) but in summary the 6 mixes were formed by combining four different sand types in four mixing ratios of sand and soil. Details of the sand materials and mixes are summarised in Table. The trial was laid out in a split plot, randomised block design with four replications. The different mixing ratios formed the main plots, with sand type as the sub-plots. Sub-plot size was 2 m x 2 m. The trial was sown on 24 June 988 with an 80: mix of Festuca rubra L. ssp. commutata Gaud. Frida and Agrostis castellana Boiss. & eut. Highland. aintenance and wear treatments The objective of the management programme was to simulate that used for a good quality golf green. Details of trial maintenance for 988 to 990 are given by Baker (99). A similar programme was used in 99 and 992 and details for these two years are given in Table 2. TABLE Characteristics of the rootzone sands and mixing ratios [a] ootzone sands Sand type id particle diameter Uniformity coefficient (D 50 )* (D 90 /D )* edium-fine (F) edium () edium-coarse (C) ange of particles () [b] ixing ratios ixing ratio (soil:sand) % fines % silt + clay % clay (<0.25 mm diameter) (<0.05 mm diameter) (<0.002 mm diameter) : : : : (pure sand) 0 0 * The D x values are a measure of particle size whereby D x is the particle size corresponding to x% of the material (by mass) passing. Low values of the D 90 /D index indicate a sand with a uniform size distribution. the percentage figures presented in part [b] are for mixes with sands F, and C. Sand has 8% of its particles <0.25 mm diameter and therefore mixes using this sand have proportionately more fine material. 39

3 Oversowing owing TABLE 2 Trial maintenance during 99 and 992 Because of heavy wear and an associated loss of ground cover the trial was oversown with an 80: F. rubra:a. castellana mix at 8 g m -2 on April 99. The trial was mown at a height of 5 mm during the late spring, summer and early autumn and at 7 mm during the winter. After the oversowing on April 99 cutting height was relaxed to mm and was reduced gradually to 5 mm by 5 ay 99. Fertiliser Annual total (kg ha - ) N P 2 O 5 K 2 O Irrigation Aeration Top dressing Verticutting Fungicides Wear applications of ammonium nitrate in solution plus application of superphosphate. application of ammonium nitrate in solution plus 2 applications of compound granular fertiliser (for part of season only, last application 2 July 992). In 992 one application of sulphate of iron at 8 g m -2 was made on 4 April. Applied using a pop-up system linked to an automatic weather station and a Toro Network 8000 system. The aim was to supply 25 mm of water in dry weather to replace an estimated evapotranspiration loss of 8 mm per week, with an allowance of 7 mm per week for wind drift and evaporation during watering. Slit tine aeration was carried out at approximately monthly intervals during the late autumn, winter and spring periods and chisel tine aeration was used at approximately monthly intervals during the summer and early autumn. In 99 a total of 4 kg m -2 of top dressing was applied in four applications and in kg m -2 was applied in one application. In each case the top dressing material matched the composition of the rootzone layers. Used on six dates in 99 (2 ay - Sep.) and seven dates in 992 (3 Apr. - 6 July). Carbendazim was applied on 5 Oct. 99 for treatment of fusarium patch disease. Wear was applied using a differential slip wear machine (Canaway 982) fitted with golf studs and a pulley ratio of :8. Wear was carried out at the rate of pass per week from 2 Jan. 99, 2 passes per week from 24 ay 99, 4 passes per week from 9 July 99, 2 passes per week from 2 Oct. 99, pass per week from 2 Jan. 992 and 2 passes per week from 8 ay 992 with the last application on 2 July 992. Wear was not carried out in conditions of snow, frost or saturated ground and the total number of passes were: 99 = 82, 992 = 35. Data collection The main soil physical properties which were measured were water infiltration rate, soil moisture content, total porosity, pore size distribution, air-filled porosity and water retention. However, supplementary information on visual symptoms of drought stress is also given in this paper. Water infiltration rates were measured using a double ring infiltrometer with ring diameters of c. 0 mm and c. 500 mm. Water was ponded

4 in the rings for approximately 5- minutes before each measurement was made and the drop in water level over time from an initial depth of mm was recorded. Infiltration rates were standardised to a temperature of C by considering the viscosity of water at the measurement temperature relative to that at C. Three measurements were made for each sub-plot. Infiltration rates were measured in June 989 (before wear) and in April of the three following years (990 to 992). The soil moisture content of the surface layer (0- mm) was measured on six dates between 22 January 99 and 8 July 992. Approximately twenty cores per sub-plot were taken with a hollow tine fork. The cores, which included their surface vegetation, were oven dried at 5 C to determine the gravimetric moisture content on a dry weight basis. In June 992, at the end of the trial, undisturbed soil cores were taken to measure total porosity, pore size distribution, air-filled porosity, water retention and loss on ignition. Four cores per sub-plot were taken from each of two depths -90 mm (i.e. excluding any surface thatch) and 0-80 mm. The cores were taken in 80 mm deep, 54 mm internal diameter, brass rings using a corer similar to that described by Dagg & Hosegood (962). After weighing to enable the subsequent calculation of field moisture content, the cores were saturated before being placed on a sand tension table (Hall et al. 977) and successively equilibrated at water potentials of 2, 4 and 8 kpa so that the moisture retention characteristics could be established. The cores were then dried at 5 C for 24 hours and weighed. A sub-sample from each core was taken to allow the loss on ignition to be measured after the material had been placed in a muffle furnace at 0 C for 8 hours. Total porosity was calculated from the dry weight of soil per unit volume and its loss on ignition value which was used to calculate particle density (Baker & Isaac 987). Water retention was measured as the volumetric moisture content at each tension and air-filled pore space at each tension was obtained by subtracting the volumetric moisture content from the total porosity. Pore diameter (d, in mm) can be related to soil suction (h, in millibars) by the equation: d = 3/h (ussell 973) Thus pores drained at water potentials of 2, -4 and 8 kpa correspond approximately to sizes of 50 µm, 75 µm and 37 µm equivalent pore diameters. Drought stress was recorded visually on a 0-6 scale (6 = best, <3 being regarded as unacceptable) in August 99 and June 992. The mean value from three observers was used. Data analysis elationships within the data were examined using analysis of variance and the least significant difference (LSD) for p = 0.05 was used to detect significant differences between treatments. In the split plot design, two values of the LSD can be calculated at the sub-plot level: that appropriate to comparisons within a given mixing ratio and that appropriate to comparisons between mixing ratios. In the figures the larger of these two LSDs is presented. The infiltration data were transformed as log (x + ) to stabilise the variance. ESULTS Water infiltration rates Infiltration rates fell considerably during the course of the study (Fig. ). In June 989, before wear, infiltration rates averaged 25 mm h - for the : mixes and 449 mm h - for the pure sand rootzones, but after three years of wear the corresponding figures were 4 mm h - and 52 mm h -. 4

5 - INFILTATION ATE (mm h ) 00 0 JUNE 989 F C - INFILTATION ATE (mm h ) 00 0 APIL INFILTATION ATE (mm h ) 00 0 APIL 99 FIGUE. Changes of infiltration rate over time in relation to mixing ratio and sand type. In this and subsequent similar graphs, sand types are as follows: F = medium-fine, = medium, C = mediumcoarse, = range of particle sizes. (Note: vertical bars show the LSD.) - INFILTATION ATE (mm h ) 00 0 APIL 992 There were considerable differences between the rootzone materials on all four sampling dates. As well as the effects of sand content, the particle size of the sand also had a major influence on infiltration rates. For example, in April 99 the infiltration rates for the :4 mixes using the medium-fine sand were 5 mm h - compared with 4 mm h - when the medium-coarse sand was used. Similarly on the pure sand rootzones the infiltration rates were 68 mm h - and 269 mm h - for the mediumfine and medium-coarse sands respectively. On the pure sand rootzones, the sand with a wide spread of particles gave the lowest infiltration rate but it gave intermediate performance in the sand-soil mixes. Pore size distribution Differences in total porosity after three years of wear were relatively small with porosity ranging from % in the upper layer and % for the mm depth (Fig. 2). There were, however, significant effects of both mixing ratio and sand type with total porosity being slightly higher for sand types F and and for the : mixes. There was no significant difference between the overall means for the upper and lower depths. Differences in pore size distribution were much greater, with the proportion of large pores increasing with the higher sand contents (Fig. 2). Sand type also had an important influence with the coarsest sand, inevitably giving the highest proportion of large pores especially with those mixes with high sand contents. Depth also had a significant effect with, for example, the total volume of pores >37 µm 42

6 POE SPACE (%) POE SPACE (%) mm DEPTH POE SIZE >50 µ m µ m µ m <37 µ m F C F C F C F C 0-80 mm DEPTH F C F C F C F C SAND TYPE AND FIGUE 2. Pore size distribution (equivalent pore diameter) in relation to mixing ratio and sand type. (Note: vertical bars show LSDs for total porosity and the cumulative pore space below 50, 75 and 37 µm respectively.) diameter being only 2.6% in the : mixes for the upper layer but 22.2% for the mm depth. Comparable figures for the pure sand mixes were a pore volume 26.7% >37 µm diameter for the upper layer but 33.7 >37 µm diameter for the underlying material. Air-filled porosity and water retention Values for air-filled porosity and water retention relate directly to pore size distribution and they are summarised in Figs. 3 and 4. For the airfilled porosity at a water potential of 4 kpa (Fig. 3) the medium-coarse sand gave the highest air-filled pore space figures for all mixing ratios and generally the medium-fine sand gave the lowest values. For example, air-filled pore space for the medium-fine sand at the -90 mm depth ranged from 7.8% for the : mix to 5.9% for the pure sand rootzone. In contrast, the corresponding figures for the mediumcoarse sand were 2.5% for the : mix and 27.9% for the pure sand treatment. AI-FILLED POOSITY (%) AI-FILLED POOSITY (%) 0-90 mm DEPTH 0-80 mm DEPTH F C FIGUE 3. Air-filled porosity at a water potential of 4 kpa in relation to mixing ratio and sand type. The trend in values for volumetric moisture content for the laboratory cores (Fig. 4) was virtually the reverse of those for air-filled porosity with moisture content decreasing as the amount of sand in the mix and its particle size increased. For example, volumetric moisture content at the -90 mm depth averaged 29.9% for the : mixes but only.6% for the pure sand rootzone with the medium-coarse sand. oisture content for the immediate surface layer was measured as part of the work on the playing quality of the rootzone mixes (Fig. 5). These values of field moisture content were not as strongly influenced by the effects of mixing 43

7 VOLUETIC OISTUE CONTENT (%) -90 mm DEPTH 0 FIGUE 4. Volumetric moisture content at a tension of 4 kpa in relation to mixing ratio and sand type. (Note: vertical bars show LSD.) OISTUE CONTENT (%) OISTUE CONTENT (%) OISTUE CONTENT (%) 0 22 JANUAY 99 F C 28 AUGUST AY 992 VOLUETIC OISTUE CONTENT (%) OISTUE CONTENT (%) OISTUE CONTENT (%) 0-80 mm DEPTH F C 5 AY 99 5 FEBUAY JULY 992 FIGUE 5. Surface moisture content (0 mm, including sward) in relation to mixing ratio and sand type. (Note: vertical bars show LSD.) 44 OISTUE CONTENT (%)

8 ratio as the moisture content measurements obtained from the undisturbed cores and this undoubtedly reflects moisture held by the grass blades and within the thatch layer. Nevertheless, the effect of mixing ratio was significant on four of the six sampling dates and sand type was also important with the medium-coarse sand consistently giving the lowest moisture content values. Organic matter content Organic matter content was strongly influenced by mixing ratio and to a lesser extent sand type and sampling depth (Fig. 6). The original soil had an organic matter content of 6% and it is inevitable that this figure should have been reduced by the addition of sand. Organic matter content in the -90 mm depth averaged.4%, compared to.% for the 0-80 mm depth. This no doubt reflects the greater root LOSS ON IGNITION (%) LOSS ON IGNITION (%) mm DEPTH F C 0-80 mm DEPTH FIGUE 6. Loss on ignition in relation to mixing ratio and sand type. (Note: vertical bars show LSD.) mass in the upper depth. There was a small, but significant effect of sand type; averaged over all combinations of mixing ratio and depth, the lowest values were for sand C at.2% and the highest value.34% for sand. Whether this has any practical significance is open to debate. Ponding and drought stress The main surface manifestations of poor soil physical properties are ponding in wet conditions and, in the absence of irrigation, drought stress in dry weather. The incidence of surface ponding was considerably less than when the same trial area received football-type wear (Baker 988). Over the period October ay 992 surface water (at 0 hours) was recorded on 8 dates for the : mixes, 3 dates each for the :2 and :4 mix but never on the pure sand rootzones. As the trial area had a full irrigation system drought stress was generally not a problem. However, in August 99 irrigation was temporarily suspended so that the response of the turf to moisture stress could be examined. In addition, in June 992 an irrigation fault led to a period of systematic under-watering. This led to symptoms of drought stress which were recorded on 25 June 992, immediately before normal irrigation was resumed. The scores in Fig. 7 are on a 0-6 scale with values below 3 being considered to be unacceptable. In general, the effect of sand type was greater than that of mixing ratio and the mediumcoarse sand gave the lowest visual rating for all mixing ratios on both dates. Only two rootzone materials gave values less than 3, i.e. the pure sand rootzone with the C sand and the :4 mix with the C sand. In particular, the pure sand rootzone with the finest sand (F) retained good colour during the two periods of drought stress. Indeed, on August 99 this gave the highest visual rating, a fact possibly explained by the relatively deep rooting in the pure sand material. 45

9 DOUGHT STESS DOUGHT STESS AUGUST JUNE 992 F C FIGUE 7. Drought stress based on visual assessments (0 6 scale, 6 = best) in relation to mixing ratio and sand type. (Note: vertical bars show LSD.) DISCUSSION There is relatively little published work which defines the optimum soil physical conditions for golf rootzones under field conditions. However, for laboratory compacted cores performance requirements are well established and, for example, USGA (989) requires a total porosity of 35-50%, an air-filled porosity at a water potential of 4 kpa of 5-25% and a water retention value for gravimetric moisture content at 4 kpa of 2-8%. For golf green turf in the USA, Waddington et al. (974) suggested that 25 mm h - should be regarded as a minimum acceptable value. Infiltration requirements for sports pitches in the United Kingdom have been reviewed by Gibbs & Baker (989). Ideally, values should be above mm h - to cope with the most periods of intensive rainfall. An infiltration rate of mm h - can be regarded as a minimum requirement for areas of good quality sports turf. Although USGA (989) give a minimum requirement of 5% air-filled pore space at a water potential of 4 kpa for laboratory compacted figures, both Bingaman & Kohnke (970) and Adams et al. (97) suggest that a minimum value of % is appropriate for sports fields. After three years of wear in the present trial, infiltration rates on the : soil:sand mixes averaged 4 mm h -. This is well below the suggested acceptable threshold of mm h -. Ponding did occur during heavy rainfall, although the frequency of standing water would have meant that the turf would have been unusable for only short periods. However, this makes no allowance for further deterioration in drainage performance or for the possibility on a more contoured green of water retaining hollows. Higher drainage rates are therefore preferred. Infiltration rates on the :2 mixes also fell below mm h - when the finer sands were used but remained just above mm h - when the medium-coarse sand was included in the mix. Infiltration rates for the :4 mixes ranged from to 9 mm h - in April 992 and for the pure sand constructions all values were >26 mm h -. To make allowance for future reductions in drainage performance it is suggested that the sand content for high quality rootzones should at least be comparable to that on the :4 mixes, i.e. approximately 94% or more. Values for total porosity ranged from 39.2% to 43.3% for the -90 mm depth and 38.8% to 44.0% for the 0-80 mm depth. None of these values are considered to be unacceptable. Air-filled porosity at a water potential of 46

10 4 kpa was above 5% for all mixes at the 0-80 mm depth. However, for the -90 mm depth air-filled pore space at 4 kpa was generally below 5% for those mixes containing >7% silt + clay and below % for the : mixes with the finer sand materials. Sand type had virtually as much effect as mixing ratio on water retention in drier conditions, with the mixes with the medium-coarse sand consistently giving the lowest moisture retention values. However, with an efficient irrigation system only the pure sand construction, based on the medium-coarse sand and which contained no amendment, would be likely to cause problems in terms of irrigation management. CONCLUSION On the basis of the soil physical results from the 6 rootzone mixes the following recommendations can be made: [a] To achieve good infiltration characteristics the silt plus clay content of the rootzone mix should be no more than 6%. [b] In sand-soil mixes, medium sands (mainly m diameter) and medium-coarse sand ( mm diameter) are more effective than medium-fine sands ( mm diameter) and sands with a wide spread of particles. [c] In pure sand constructions medium-fine and medium sands are preferable because of their greater water retention although this situation may be modified if any water retentive amendments are incorporated into the sand. [d] There often has to be a compromise where a single green on a golf course requires redevelopment and it is important that this green does not have entirely different playing characteristics and maintenance demands to other soil based greens on the same course. ixes with up to % silt plus clay may be suitable in these cases but it must be recognised that this will be at the expense of good infiltration rates. This work has specifically examined sand-soil mixtures for golf green construction and the role of organic materials and other amendments has been excluded. However, there is very little published information to evaluate such materials under United Kingdom conditions and this is an area where further experimental work is required. ACKNOWLEDGEENTS The authors wish to thank r.a. Baines, rs D.S. Hill and r B.J. West for their help in data collection, analysis and presentation. We are also grateful to the staff of our experimental ground for their diligence in trial management and to r D.. Stansfield for his helpful discussions on the maintenance programme. EFEENCES Adams, W.A., Stewart, V.I. & Thornton, D.J. (97). The assessment of sands suitable for use in sportsfields. J. Sports Turf es. Inst. 47, Baker, S.W. (983). Sands for soil amelioration: analysis of the effects of particle size, sorting and shape. J. Sports Turf es. Inst. 59, Baker, S.W. (984). Long-term effects of three amendment materials on the moisture retention characteristics of a sand-soil mix. J. Sports Turf es. Inst. 60, Baker, S.W. (99). ootzone composition and the performance of golf greens. I. Sward characteristics before and after the first year of simulated wear. J. Sports Turf es. Inst. 67, Baker, S.W. & Isaac, B.J. (987). The assessment of soil porosity in sports turf rootzones using measured and calculated values of particle density. J. Sports Turf es. Inst. 63,

11 Baker, S.W. & ichards, C.W. (99). ootzone composition and the performance of golf greens. II. Playing quality under conditions of simulated wear. J. Sports Turf es. Inst. 67, Bingaman, D.E. & Kohnke, H. (970). Evaluating sands for athletic turf. Agron. J. 62, Blake, G.. (980). Proposed standards and specifications for quality of sands for soilsand-peat mixes. Proc. 3rd Int. Turfgrass es. Conf., Blacksburg, Virginia, USA (Ed. E.C. oberts), pp Brown, K.W. & Duble,.L. (975). Physical characteristics of soil mixtures used for golf green construction. Agron. J. 67, 5, Canaway, P.. (982). Simulation of fine turf wear using the differential slip wear machine and quantification of wear treatments in terms of energy expenditure. J. Sports Turf es. Inst. 58, 9-5. Dagg,. & Hosegood, P.H. (962). Details of a hand sampling tool for taking undisturbed soil cores. E. Afr. Agric. For. J. Supplement to special issue, Davis, W.B. (98). Sand green construction. Calif. Turfgrass Culture 3,, 4-7. Davis, W.B., Paul, J.L., adison, J.H. & George, L.Y. (970). Evaluating sands and amendments used for high trafficked turfgrass. AXT n 3 Agric. Extension Service, Univ. Calif., 93 pp. Hall, D.G.., eeve,.j., Thomasson, A.J. & Wright, V.F. (977). Water retention, porosity and density of field soils. Soil Survey Tech. ono. No. 9, Harpenden, 75 pp. Lodge, T.A. & Baker, S.W. (99). The construction, irrigation and fertiliser nutrition of golf greens. II. Playing quality assessments after establishment and during the first year of differential irrigation and nutrition treatments J. Sports Turf es. Inst. 67, Lodge. T.A., & Baker, S.W. (992). Soil moisture content and evapotranspiration rates of three types of golf green construction in response to different rates of irrigation. J. Sports Turf es. Inst. 68, 4-3. Lodge, T.A. & Baker, S.W. (993). Pore structure, moisture release characteristics and infiltration rates of three golf green rootzones. J. Sports Turf es. Inst., in this volume. Lodge, T.A., Baker, S.W., Canaway, P.. & Lawson, D.. (99). The construction, irrigation and fertiliser nutrition of golf greens. I. Botanical and reflectance assessments after establishment and during the first year of differential irrigation and nutrition treatments. J. Sports Turf es. Inst. 67, Lunt, O.. (956). A method for minimising compaction in putting greens. S. California Turfgrass Culture 6, 3, -4. ussell, E.W. (973). Soil Conditions and Plant Growth th Ed. Longman, London, 849 pp. Schmidt,.E. (980). Bentgrass growth in relation to soil properties of typic Hapludalfs soil variously modified for a golf green. Proc. 3rd Int. Turfgrass es. Conf., Blackburg, Virginia, USA (Ed. E.C. oberts), pp Swartz, W.E. & Kardos, L.T. (963). Effect of compaction on physical properties of sandsoil-peat mixtures at varous moisture contents. Agron. J. 55, 7-. USGA Green Section Staff (960). Specifications for a method of putting green construction. USGA Journal and Turf anagement, September, pp. -5. USGA Green Section Staff (989). Specifications for a ethod of Putting Green Construction (Ed. W.H. Bengeyfield). United States Golf Association, 24 pp. Waddington, D.V., Zimmerman, T.L., Shoop, G.J., Kardos, L.T. & Duich, J.. (974). Soil modification for turfgrass areas. I. Physical properties of physically amended soils. Pennsylvania State Univ. Agric. Exp. Sta. Progress eport 337, 96 pp. 48