Report to the Stapledon Memorial Trust Evaluation of rootzone mixes and water retentive amendment materials in sports surface constructions Dr. Stanislav Hejduk Department of Animal Nutrition and Grassland Management, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic [email protected] Details of the fellowship Contact in UK: Dr. Stephen W. Baker Sports Turf Research Institute St. Ives Estate Bingley West Yorkshire, BD 16 1AU [email protected] Research and Fellowship Dates: 9 August – 8 October 2010 The main Purpose of the Fellowship was to undertake a research project to investigate the use of various organic and inorganic rootzone amendment materials to improve both water retention and surface stability. Research Report INTRODUCTION Sand-dominated rootzones are now widely used for high quality sports facilities because of their good drainage properties, greater air-filled pore space after compaction and more consistent playing characteristics, particularly in respect to the firmness of the surface (Adams 1986, Baker 1989). Two of the potential problems associated with sand-dominated media are ensuring adequate water and nutrient retention. Accordingly, amendment materials are regularly added to the sand material and there has been a considerable amount of research on the effect of different amendment materials and application rates for sports turf rootzones (eg. Waddington et al. 1974, Cook & Baker 1998, Baker et al. 1999, Baker et al. 2010). There has, however, been relatively little research work on the effects of the depth of the amended layer on water retention properties of rootzones. There is a need to assess whether it is better for the amendment material to be applied through the whole profile or concentrated in the surface layers where most of the root system is found. It is also important to be able to predict the potential implications for water retention, particularly within the main rooting depth of the grass plant, when a specific amendment material is used. Laboratory data can be obtained relatively easily for different combinations of amendment materials and incorporation rates. The laboratory tests can give water release curves which indicate the volume of water retained at a range of moisture potentials (SWB papers with water release curves, ASTM F 1815-06). Knowledge of the water release characteristics of rootzone materials should give a relatively easy method of predicting water retention of different amendment materials through the depth of the profile. The objectives of the current study were therefore: 1) To assess the effects of a number of amendment materials and the depth of incorporation on water retention within typical profiles used for sports turf construction. 2) To examine how effectively water release curves can be used to predict the vertical distribution of water within sports turf rootzones. MATERIALS AND METHODS The study was carried out under laboratory conditions using 150 mm diameter plastic cylinders. Within each column, a profile was constructed with a 300 mm rootzone layer over a 50 mm gravel drainage layer. The rootzone was based on uniform medium sand (Table 1) and the gravel was a fine gravel where all particles fell within a 2-5 mm size range. The gravimetric moisture of the sand was 4.7 %. The sand and gravel coincided with the normal ranges for golf green construction (STRI 2006, Baker 2006). TABLE 1: Particle size distribution of the used sand Category Particle diameter (mm) % Coarse gravel 3.4-8.0 0.0 fine gravel 2.0-3.4 0.2 Very coarse sand 1.0-2.0 2.1 Coarse sand 0.5-1.0 52.2 Medium sand 0.25-0.5 41.4 Fine sand 0.15-0.25 2.9 very fine sand 0.053-0.15 0.4 silt+clay under 0.053 0.9 Experimental design A randomised block design was used with three main treatments: profile characteristics, amendment type and amendment rate. a) There were three profile arrangements. All contained the amendment at the appropriate rate in the upper profile (0-150 mm) but for the lower profile (150-300 mm) three alternatives were included, i.e. amendment at the same rate as the upper profile, amendment at half the rate of the upper profile and no amendment in the lower profile (sand only). b) Five amendment materials were used as follows: Sphagnum peat (commercially available material) Composted green waste (Re-do, Bathgate Silica sand) Zeolite (Clinoptilolite, grade 0.5-1.0 mm, Zeocem Inc., Slovakia) TerraCottem Turf (mixture of hydroabsorbent polymers of acrylamide and acrylic acid, partially neutralized by potassium and ammonia salts, humic acids and zeolite, TerraCottem n.v. Belgium) Stockosorb M (cross-linked potassium polyarylate/polyacrylamide co-polymer, grade 0,8 – 2.0 mm; The Resource Management Group, Inc. Atlanta GA 30350) Three rates were used for each material, nominally 0.5, 1.0 and 1.5 times a typical rate for each material based on either earlier research or manufacturer’s recommendations). Rates of 10, 20 and 30% by volume were used for the two organic materials and the zeolite. For the TerraCottem the recommend rate was 600 g m-3 and for Stockosorb 1200 g m-3. A control with no amendment was also included. All combinations were included using three randomised blocks. Preparation of the profiles Each column was 375 mm high and had a voile membrane attached at the base and was supported on a perforated plastic mat to allow free drainage and ease of handling. The 50 mm drainage gravel was added to the base of the column and then the lower rootzone (including any amendment as appropriate) was added in two layers, each of 75 mm. Each layer was consolidated using four blows from a 2.82 kg weight dropped from a height of 0.39 m (packing energy for each layer = 2.5 kg m-2). After each compaction treatment, the upper 5 mm was lightly raked to prevent layering and any adjustments to the height of the layer were made to give the desired 150 mm depth. The upper rootzone was then added again in two layers with the same compaction treatments to give a total depth of the rootzone of 300 ±10 mm. The rootzone finished 25 mm from the top of the cylinder allowing space for water to be ponded in the cylinder as part of the wetting procedure. The mixes were prepared with moist sand (gravimetric water content approximately 5 %). To saturate the cylinders, 2650 cm³ of water (50% of the total rootzone volume) was added and the materials were left overnight. A further 2650 cm³ was added the following morning. Photo 1: Cylinders filled with different rootzone mixtures Measurements To monitor changes in water content during drainage, volumetric water content in the upper 60 mm was measured using a Theta probe. Initial measurements were made within the first minute after the ponded water had completely percolated into the surface of the rootzone. Further measurements were made after 1, 2, 4, 6, 24 and 48 hours. In all cases, three replicates were made per cylinder. After gravitational drainage for 48 hours, the surface was lightly compacted (one blow of the 2.82 kg mass from 0.39 m) to firm the surface after the theta probe measurements. Hardness was then measured again using a Clegg soil impact tester (0.5 kg test mass released from 0.55 m. Three measurements of peak deceleration during impact were made per cylinder. After the hardness measurements, shear strength was measured using a Geonor shear vane fitted with four blades of 50 mm length and 12 mm width. Measurements were made in the area of impact from the hardness measurements as these areas had more uniform consolidation because of the greater compaction. To determine the bulk density and the volumetric water content after gravitational drainage, the columns were excavated in increments of 50 mm. The exact height of each layer was recorded and the total weight of material removed was determined. A sub-sample of around 100-150 g was taken for measurement of gravimetric water content after drying at 105˚C. Bulk density was calculated as the dry weight of material per unit volume, and volumetric water content for each layer was calculated from bulk density x gravimetric water content. Water release characteristics Samples were taken from each rootzone for determination of hydraulic conductivity measurements and water retention measurements using USGA methods (ASTM F 1815-06). The range of tensions was extended to give a sequence of 10, 20, 30, 40, 50 and 60 cm tension. Measurements were taken after 24 hours at each tension. Photo 2: Water release characteristics measurement on a tension table Statistical analysis Statistical analyses were performed using ANOVA (Statistica 7.1, StatSoft) with a randomised block design where all the treatments were analysed separately. Results and discussion Water retention Individual amendment materials increased water retention in a rootzone unevenly. The greatest water retention was measured for the 30% sphagnum peat and the 1.5 recommended rate of Stockosorb (Table 1). Both these treatments increased water retention in the rootzone top layer (150 mm) almost by 150% compared with pure sand (36 mm at Stockosorb rate 1800 g m-3, 35.5 peat 30% vs. 14.6 mm at pure sand). The lowest water retention was recorded for the Terracottem amended rootzones, even when added at the highest rate (17.9 mm at 1.5 RR). Average water consumption of turfgrasses during summer sunny days in climatic condition of temperate zones is cc. 3 mm. Under these circumstances a 150 mm layer of pure sand would provide enough soil water for 5 days while the most retentive treatments could provide plants with water for 12 days.