, Rodriguez (2009) demonstrated progressively unavailable water in horticultural substrates, leading to incipient water stress at pressures above −1.5 MPa. Regardless, the results herein demonstrate P. kamtschaticus may be accessing water previously assumed
Whitney N. Griffin, Steven M. Cohan, John D. Lea-Cox and Andrew G. Ristvey
James E. Altland and Charles R. Krause
mean of the core. Bulk density was determined using oven-dried (60 °C) substrate in 347-cm 3 cores. Unavailable water, held in the substrate at 1.5 MPa or greater, was determined with 116-cm 3 cores (2.5 cm tall × 7.6 cm i.d.) using a porous ceramic
Florida. Iron deficiency on vegetable crops in Florida. Ninety-five percent of the growers in calcareous and alkaline soils (man-made or natural), or with irrigation water sources with high pH (≥7.5), experienced Fe chlorosis ( Table 3 ). Seventy percent
William C. Fonteno, Matthew S. Drzal and D. Keith Cassel
The influence of substrate physical properties on water transport and plant growth must be known if irrigation water use efficiency is to be improved. Three fundamentally different substrates were examined: 1 peat moss: 1 vermiculite (v/v), 3 pine bark: 1 peat: 1 sand, and 1 mineral soil: 1 peat: 1 sand. Capacity analyses included total porosity, container capacity, air space, available water and unavailable water. Water transport was characterized by saturated and unsaturated flow analyses. A new method, Pore Fraction Analysis, was developed to characterize substrate pore structure into fractions based on function with the substrate. This method is based on soil moisture retention curves, pore size distributions, and average effective suction at container capacity (AEScc) This method is offered to expand the traditional terms of macropore and micropore into new definitions: macropores, mesopores, micropore, and ultramicropore; each based on a range of pore sizes and functions. Computer simulation models of air and water profiles were run on several container sizes with the three test substrates. Pore fraction analysis indicated that under traditional production practices macropores indicate the volume of a substrate that be filled with air at container capacity, the mesopore fraction effectively fills and drains with daily irrigation, the micropore fraction functions as a measure of water reserve, while the ultramicropores contain water unavailable to the plant.
Anne-Marie Hanson, J. Roger Harris, Robert Wright, Alex Niemiera and Naraine Persaud
Newly transplanted container-grown landscape plants are reported to require very frequent irrigation. However, container nurseries in the U.S. commonly use growing substrates that are mostly bark, even though the contribution of bark-based growing substrates to water relations of transplanted root balls is unknown. Therefore, a field experiment was undertaken to determine water relations of a pine-bark substrate (container removed) within a drying mineral soil over a three week period. A range of common production container sizes—3.7 L (#1), 7.5 L (#2), 21.9 L (#7), 50.6 L (#15), and 104.5 L (#25)—was used. The fraction of substrate volume that is water [total volumetric water (TVW)] within the top and middle zones of substrate was compared to TVW at corresponding depths of adjacent mineral soil. The fraction of substrate and soil volume that is plant-available water [plant-available volumetric water (PAVW)] was calculated by subtracting the fraction of substrate or soil volume below where water is unavailable to most plants (measured with pressure plates) [plant-unavailable volumetric water (PUVW)] from each TVW measurement. The pine-bark substrate had a PUVW of 0.32 compared to a PUVW of 0.06 for soil. Top sections of substrate dried to near zero PAVW 6 days after irrigation for all containers. Larger container sizes maintained higher PAVW in middle sections than smaller container sizes, and PAVW was always higher in the adjacent soil than in the embedded substrate. Overall, very little PAVW is held by the embedded pine-bark growing substrate, suggesting the need for container substrates with greater water retention once transplanted to mineral soils.
Sloane M. Scheiber, Richard C. Beeson and Heather Bass
Native plants are often promoted as an approach for water conservation in urban landscapes. However, information regarding plant water needs is based primarily upon anecdotal observations of plant performance. Direct comparisons between native and introduced species using physiological measures of plant water stress are unavailable to support or refute such recommendations. Ligustrum japonicum and Myrica cerifera, representing an introduced and native species, respectively, were transplanted into a fine sand soil to evaluate establishment rates and growth characteristics under two irrigation regimes. Each species was irrigated either daily or every 3 days and received 1.3 cm of irrigation per event for 8 months after transplant. Predawn, midday, and dusk water potentials were recorded on three consecutive days monthly, with cumulative stress intervals calculated. Height, growth indices, shoot dry mass, root dry mass and leaf area were also recorded. Water potential was significantly influenced by day of water stress level. On days without irrigation, water stress was generally greater and affected growth. Myrica irrigated daily had the greatest growth, yet plants receiving irrigation every 3 days had the least growth and greater leaf drop. In contrast, for Ligustrum there were no differences between irrigation regimes in growth responses except for growth index.
W.C. Fonteno and T.E. Bilderback
Addition of a polyacrylamide hydrogel to pine bark and pine bark + sand substrates had no effect on total porosity, regardless of incorporation rate. Container capacity was increased with increasing rate of hydrogel in both substrates. Air space in pine bark was slightly increased at the lowest rate but was reduced with higher incorporation rates. Air space in pine bark + sand was reduced with all hydrogel additions. The dry weigh', of hydrogel cubes recovered from both substrates was similar to amounts predicted. This result indicates that blending hydrogel granules into the substrates was uniform and did not contribute to variability in hydrogel studies. After allowing dry hydrogel granules to expand freely in distilled water for 24 hours, hydrogel granules expanded 317 and 372 times their dry weights at the lowest and highest rates, respectively. Reduction of expansion (in water) at higher rates may have been due to physical restriction of expansion. Conversely, recovered hydrogel cubes from substrates watered to drainage (-10% excess) for 6 weeks absorbed 25 to 55 times their dry weight while in the container. Subsequent rehydration of extracted gels in distilled water was greater for hydrogel cubes from the pine bark + sand medium (104 to 130) than in pine bark alone (51 to 88). Because of anomalies in hydraulic conductivity and pressure plate contact, three techniques were used to study unavailable water content in gels expanded in distilled water. Hydrogel cubes placed in direct contact with the pressure plate released ≈95% of their water at pressures ≤ 1.5 MPa. Effectiveness of ployacrylamide gels in coarse-structured substrates is influenced by physical restrictions to expansion in the substrate and hydraulic conductivity between the hydrogel cubes and the surrounding substrate.
Marc W. Van Iersel, Sue Dove, Jong-Goo Kang and Stephanie E. Burnett
Managing global water resources is one of the most pressing challenges of the 21st century. Population growth and increased urbanization have increased competition for water by agricultural, industrial, and domestic users. Agricultural water use
Satriyas Ilyas, Claudinei Andreoli and Anwar A. Khan
Seeds of six pepper (Capsicum Anuum L.) cultivars were treated with tetcyclacis (TCY), an inhibitor of the oxidative steps from ent-kaurene to ent -kaurenoic acid in the gibberellin biosynthetic pathway. Seeds were soaked in TCY solutions for 24h in darkness at 25° to 30°C, washed with water and then air-dried. Various concentrations of TCY were needed to induce dormancy in `Yolo Wonder', `Cayenne', `California Wonder', `Sweet Banana', `El Paso' and `Anaheim'. TCY-treated seeds were germinated in water and in various concentrations of GA4+7 in darkness. Dormancy induced by TCY was released with 10 μM GA4+7. The germination inhibitor, abscisic acid (ABA), failed to induce dormancy in pepper seeds even when treated at a concentration of 400 μM for up to 14 d. Similar results were obtained with tomato seeds and will be reported elsewhere. The results indicate that the absence or the unavailability of GA rather than the presence of ABA determines the dormant state in pepper seeds.
The first weed disc (Weed Guard) was introduced to Ontario in the early 1980s. They were made of semirigid plastic similar to 45-rpm records. Small holes allow water to penetrate but weeds germinating on the substrate often grow through them. In the 1990s, we obtained 85% reduction of container weeds using discs made from geotextile fabric (Mori Guard) or foam (similar to polyfoam used for container winter protection). The foam disc tended to curl upward at the edges, become easily windblown, and tended to partially expose the surface of the container mix. During the past 15 years, we have annually reused the same fabric discs (now unavailable due to high unit cost), and have tested various other weed discs, including several new-generation types and also the Mori Weed Bag. The new-generation discs are fabricated from materials such as fabric (Tex-R Geodisc), pressed peat moss (Biodisc), corrugated cardboard (Corrudisc), and plastic (Enviro LID). Both Tex-R Geodisc and Enviro LID were as effective or better in controlling weeds than weekly hand-weeding, herbicides, or the Mori Guard fabric disc. The Mori Weed Bag, a patented black polyethylene sleeve with prepunched holes fitted around the container like a florist's plant prepared for market, is used effectively and almost exclusively by one Ontario nursery. We also tested two types of insulated blanket covers, which when placed around the ball of above-ground container-grown trees, prevented weed growth during the summer and also protected the root ball against cold during the winter. We introduced the garbage bag sleeve, the ultimate no-weed method for pot-in-pot tree culture, which also reduces water use and frequency of irrigation. Due to factors such as under-performance, insufficient demand, and/or high costs, only certain discs are currently manufactured: Weed Guard, Tex-R Geodisc, Biodisc, and Enviro LID. The Mori Weed Bag is available but not the insulated blankets.