greenhouse vegetable species grown in hydroponic culture ( Bar-Yosef, 2008 ; Conesa et al., 2009 ; Ikeda and Osawa, 1983 ; Imas et al., 1997 ; Savvas et al., 2006 ; Sonneveld and Voogt, 2009 ). Edible crop species are also grown in peat-based soilless
Ryan W. Dickson and Paul R. Fisher
Michael R. Evans, Johann S. Buck and Paolo Sambo
, 1988 ; Nelson, 1998 ). One of the most common materials used in the formulation of substrates is sphagnum peat (peat). Environmental concerns ( Barkham, 1993 ; Buckland, 1993 ; Robertson, 1993 ) in the European Union and cost in markets, such as
Canadian sphagnum peat moss has long been the preferred base for growing media of horticulturists in North America and Europe. Growers, horticultural scientists, and soil media producers have been using peat moss for several decades with excellent results. In the past 5 years, there has been some concern raised, especially in the U.K., that harvesting peat is harmful to the environment. The situation in Canada is far different from that in Europe. The Canadian peat industry is a world leader in restoration research because of its efforts to find the best ways to return harvested bogs to functioning wetlands. The first stage of research just completed by Laval Univ. shows that peat bogs can be effectively, economically, and easily restored. Additional research findings will be described in this paper. But, the conclusion is clear: Peat moss is a safe, environmentally friendly growing medium. This paper also will describe the state of resource in Canada as outlined by an independent environmental group, the steps taken by the Canadian Sphagnum Peat Moss Assn. to ensure that resource development is sustainable, as well as the process of how peat is harvest and how bogs are restored to functioning wetlands.
Brad B. Hawcroft and Steven E. Newman
Kenaf is an alternative fiber crop being evaluated in Mississippi. Kenaf, primarily grown in Asia, can be used in the manufacture of paper, fiber board, acoustical tiles and compost. The bark is the source of the fiber used, leaving the fiber core or pith for use as a paper additive, poultry litter, or is discarded. The objective of this study was to evaluate the potential use of kenaf fiber core as a vermiculite substitute in a sphagnum peat moss-based medium.
Plugs of Celosia argentea, Viola × wittrockiana, and Impatiens wallerana were transplanted into 10 cm pots containing 5 different sphagnum peat moss-based media modified with the milled fiber core (pith) of kenaf (Hibiscus cannabinus) and/or vermiculite. The media were as follows: 5 peat: 0 kenaf : 5 vermiculite (v/v/v); 5 peat : 1 kenaf : 4 vermiculite (v/v/v); 5 peat : 2 kenaf : 3 vermiculite (v/v/v); 5 peat : 3 kenaf : 2 vermiculite (v/v/v); 5 peat : 4 kenaf : 1 vermiculite (v/v/v); and 5 peat : 5 kenaf: 0 vermiculite (v/v/v). Water holding capacity, pore space, pH and media shrinkage were monitored throughout the study along with plant growth and plant quality.
Janet F. M. Rippy, Paul V. Nelson and Ted Bilderback
Problems of inconsistent initial pH in peat moss-based substrates that are created using standard formulas for limestone additions, and pH drift from the target in those substrates may be due to variations in the CEC and BS of peat moss. This study was conducted to determine whether such variation exists. Sixty-four peat moss samples were obtained from several bogs across Alberta, Canada. Adsorbed cations on each peat moss sample were displaced with hydrochloric acid (HCl), and flushed out with three deionized water washes. The displacing/flushing solution was collected and later analyzed for concentration of bases (Ca, Mg, K, and Na) using atomic absorption spectrometry. After cations were removed, the peat moss exchange sites were saturated with barium acetate [Ba(OAc)2] to displace the H+, which were then collected by a second flushing with deionized water. This second displacing/flushing solution was titrated with measured amounts of NaOH to a phenolphthalein end point. Base saturation and CEC were calculated. There were significant variations in CEC (ranging from 108.12 to 162.25 cmol·kg-1) and BS (ranging from 13.52% to 63.97% of CEC) among the peat moss samples. Ca accounted for 78.08% of the BS. For a given peat moss, the higher the BS, the lower the neutralization requirement to achieve a target pH. Also, high CEC peat mosses may have greater buffering capacity than those with low CEC, which may result in less pH drift.
Shravan Dasoju, Michael R. Evans and Brian E. Whipker
Paclobutrazol drench applications of 0, 2, and 4 mg a.i./pot were applied to `Pacino' potted sunflowers (Helianthus annuus L.) and `Red Pigmy' tuberous rooted dahlias (Dahlia variabilis Willd.) grown in substrates containing 50%, 60%, 70%, or 80% (by volume) sphagnum peat or coir, with the remainder being perlite, to study the efficacy of paclobutrazol (Bonzi). Potted sunflower plant height differed significantly for peat- and coir-based substrates, with greater plant height being observed in coir-based substrates. Plant diameter was significantly greater at higher percentages of peat or coir in the substrate at 2 and 4 mg of paclobutrazol. Inflorescence diameter also was significantly decreased as paclobutrazol concentration increased. When the percent of height control from the untreated plants for potted sunflower was compared between coir and peat-based substrates, the percent height reduction was similar for peat- and coir-based substrates at 2 mg of paclobutrazol and height control was greater at 4 mg of paclobutrazol in coir-based substrates. The differences in plant growth observed in peat- and coir-based substrates can be attributed to differences in physical properties of these substrates. Dahlia plant height, diameter, and number of days until anthesis were not influenced by substrate type or percentage. However, dahlia growth was significantly reduced as paclobutrazol concentration increased. Coir-based substrates did not reduce the activity of paclobutrazol drenches compared to peat-based substrates, although to compensate for the greater amount of plant growth in coir-based substrates, paclobutrazol concentrations may need to be increased slightly to achieve a similar plant height as with peat-based substrates.
Manuel Abad, Fernando Fornes, Carolina Carrión, Vicente Noguera, Patricia Noguera, Ángel Maquieira and Rosa Puchades
Selected physical properties of 13 coconut coir dusts from Asia, America, and Africa were compared to physical properties of sphagnum peat. All properties studied differed significantly between and within sources, and from the peat. Coir dusts from India, Sri Lanka, and Thailand were composed mainly of pithy tissue, whereas most of those from Costa Rica, Ivory Coast, and Mexico contained abundant fiber which was reflected by a higher coarseness index (percentage by weight of particles larger than 1 mm in diameter). Coir dust was evaluated as a lightweight material, and its total porosity was above 94% (by volume). It also exhibited a high air content (from 24% to 89% by volume) but a low easily available and total water-holding capacity which ranged from <1% to 36% by volume and from 137 to 786 mL·L–1, respectively. Physical properties of coir dust were strongly dependent on particle size distribution. Both easily available and total water-holding capacity declined proportionally with increasing coarseness index, while air content was positively correlated. Relative hydraulic conductivity in the range of 0 to 10 kPa suction dropped as particle size increased. Coir dusts with a particle size distribution similar to peat showed comparatively higher aeration and lower capacity to hold total and easily available water. An air–water balance similar to that in peat became apparent in coir dust at a comparatively lower coarseness index (29% vs. 63% by weight in peat). Stepwise multiple regression analysis showed that particles with diameters in the range of 0.125 to 1 mm had a remarkable and highly significant impact on the physical properties studied, while particles <0.125 mm and >1 mm had only a slight or nonsignificant effect.
Mary M. Gachukia and Michael R. Evans
species. Evans and Gachukia (2007) also reported how PBH affected the physical properties of sphagnum peat-based substrates compared with perlite. However, the effects that PBH has on the chemical properties of sphagnum peat-based substrates compared
J. Norrie, M.E.D. Graham, P.A. Dubé and A. Gosselin
An automatic irrigation system was designed for use on green-house tomatoes growing in peat-based substrates. This system uses electronic tensiometers to monitor continuously substrate matric potential (SMP) in peat-bags. The system also uses the Penman equation to evaluate potential evapotranspiration (PET) through the acquisition of many greenhouse environmental parameters. Through a series of linear equations, estimates of PET are used in a computer-controller system to vary the electrical conductivity (EC) of irrigated nutrient solutions, as well as SMP setpoints at which irrigations are started. Such modifications to current irrigation management systems may improve fruit quality and reduce the risk of water stress during periods of high PET by irrigating more frequently with less-concentrated nutrient solutions. Conversely, during periods of low PET, irrigation is less frequent with more-concentrated nutrient solutions. Although no differences were found in fruit number or overall yield using variable nutrient solution EC, plant fresh weight was higher in those treatments. It is concluded that an integrated tensiometer-PET system may give increased precision to irrigation management and the control of crop growth in the greenhouse.
Kenneth G. McCabe, James A. Schrader, Samy Madbouly, David Grewell and William R. Graves
technologies that help improve WUE ( Beeson et al., 2004 ). Water usage during crop production in fiber containers has been studied, and Evans and Karcher (2004) reported that crop production in peat-fiber containers used 2.25 times the water needed for