Where coarse-textured materials, such as gravel, underlie the root-zone layer of sports turf soil profiles, water retention in the root-zone layer is increased. The objective of this research was to determine the water retention characteristics in sand and sand: peat mixtures placed over coarse-textured layers and to determine how sand particle size and type of peat in the mixtures influenced water distribution after drainage. Soil profiles consisted of 30 cm of sand or sand: peat mixtures over 5 cm of predominantly coarse and very coarse sand, which in turn was over 10 cm of gravel. Excess water was added to the profile and allowed to drain for 24 or 48 h, following which water content and air-filled porosity (AFP) in the mixtures were evaluated. Regardless of the root-zone mixture, the coarse-textured sublayers resulted in a wet zone in the lower portion of the root-zone mixture. An unamended, predominantly medium and coarse sand, when used in the 30- cm root-zone layer, maintained ≈10% AFP in the lower 6 cm after drainage. Sand: peat mixtures using this sand generally maintained 3% to 8% AFP in the lower 12 cm of the root-zone layer. An unamended, predominantly fine and medium sand root-zone layer had ≈6% AFP in the lower 9 cm and sand: peat mixtures using this sand had <5% AFP in the lower 12 to 18 cm of the root-zone layer, with significant portions remaining at or near saturation after 24 or 48 h of drainage.
Summer decline of annual bluegrass (Poa annua L.) putting greens is a major concern of golf course superintendents. Low soil water infiltration rates and high concentrations of salts in the root zone are contributing factors. This study was conducted to determine the effects of summer cultivation treatments on field infiltration rates of water, soil salinity, oxygen diffusion rates (ODR), bulk density, total and air-filled porosity, and root weight density. This research was conducted during two summer seasons (1996 and 1997) on a practice putting green located at Industry Hills Golf Courses, City of Industry, Calif. The green was constructed to U.S. Golf Association (USGA) specifications in 1978. Cultivation treatments consisted of: 1-3) water injection cultivation (WIC) applied with a Toro HydroJect every 21 d (raised position), and every 14 or 21 d (lowered position); 4) solid tine cultivation (STC) applied every 14 d; and 5) no cultivation (check). Results showed WIC and STC significantly increased field infiltration rates of water and lowered overall soil electrical conductivity of the extract (ECe) at depths of 2.5 to 7.5 cm and 7.5 to 15.0 cm in the root zone. The effects of WIC, raised position, did not differ significantly from those of STC, but infiltration rates of water were greater on all rating dates. Cultivation treatments had no significant effects on overall soil ODR, bulk density, and porosity or on overall root weight density.
Hydrophilic polymers or hydrogels have shown potential to increase water retention of media and to reduce irrigation frequency. This property would be particularly useful in the production of fast growing species in which large amounts of water are needed. This study evaluated the effect of two acrylic-based hydrogels on water desorption curve and hydraulic conductivity of substrates and on plant growth. The duration of their effects was also investigated. Rooted cuttings of Surfinia (Petunia ×hybrida `Brilliant Pink') were transplanted into 30-cm pots containing one of three different substrates amended with one of two types of hydrogels, a commercial acrylic polymer, and a commercial acrylic-acrylamide copolymer, and grown for 9 weeks under well watered conditions and then imposed with a drought. Results indicated that both polymer types gave similar results. The substrates' physical properties (air-filled porosity, available water) at potting time were significantly affected by hydrogel addition, but differences vanished within 9 weeks of growth. Hydrogels had no significant effect on the point at which plant wilted and on the substrate's unsaturated hydraulic conductivity. Shoot dry weight was affected by substrate and hydrogel and was positively correlated to water content between container capacity and -10 kPa of water potential, or between container capacity and the soil water potential at plant turgor loss.
Physical characteristics of two media were studied concerning water availability to roots, as reflected in specific transpiration rate, stomatal conductance, and specific growth rate of very young leaflets of `Kardinal' rose (Rosa ×hybrida L.), grafted on Rosa canina L. `Natal Brier'. Plants were grown in UC mix [42% composted fir bark, 33% peat, and 25% sand (by volume)] or in coconut coir. Water release curves of the media were developed and hydraulic conductivities were calculated. Irrigation pulses were actuated according to predetermined media moisture tensions. Transpiration rate of plants was measured gravimetrically using load cells. Specific transpiration rate (STR) was calculated from these data and leaf area. STR and stomatal conductance were also determined using a steady-state porometer. Specific growth rate (RSG) of young leaflets was calculated from the difference between metabolic heat rate and respiration rate, which served as an indicator for growth potential. Low STR values found at tensions between 0 and 1.5 kPa in UC mix suggest this medium has insufficient free air space for proper root activity within this range. Above 2.3 kPa, unsaturated hydraulic conductivity of UC mix was lower than that of coir, possibly lowering STR values of UC mix-grown plants. As a result of these two factors, STR of plants grown in coir was 20% to 30% higher than that of plants grown in UC mix. STR of coir-grown plants started to decline only at tensions around 4.5 kPa. Yield (number of flowers produced) by coir-grown plants was 19% higher than UC mix-grown plants. This study demonstrated the crucial role of reaching sufficient air-filled porosity in the medium shortly after irrigation. It also suggests that hydraulic conductivity is a more representative measure of water availability than tension.
saturation. Above the 18-cm depth, about a third of total soil volume is occupied by air in the 100% sand mix, whereas a very small percentage is occupied by air when 20% or more of the mix is fines ( Fig. 2 ). Air-filled porosity decreased drastically from 0
soil oxygen concentration ( Johnson, 1968 ). The root system is easily damaged by irregular moisture levels of substrates. Substrates suitable for the root growth of begonias require at least 10% to 20% air-filled porosity ( Johnson, 1968 ). Drip
-aerated) substrate ( Ingram et al., 1993 ). Poorly aerated media may concentrate roots in the top portion of the container and increase the susceptibility to root rot pathogens and micronutrient deficiencies ( Ingram et al., 1993 ). Although air-filled porosity was
-based root zones that are often used to characterize its hydraulic performance in the field are the CP, air-filled porosity, and saturated hydraulic conductivity (Ks). Because these properties of an organic amendment alone are of little value in predicting
with thin but firm cell walls, which are excellent for transmitting water and holding shape ( Puustjarvi, 1977 ). These characteristics make it an ideal substrate to retain water and air for epiphytic orchids. The air-filled porosity (v/v) of sphagnum
) was calculated as follows: (W 2 − W 1 )/V; total porosity (% volume) = (W 3 − W 2 )/V × 100, air-filled porosity (% volume) = (W 3 − W 4 )/V × 100; water-holding capacity (% volume) = total porosity-air-filled porosity. The pH was determined with a