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Yanjun Guo, Terri Starman, and Charles Hall

drop. Additionally, using water deficit as a plant height control was reported ineffective ( Dole and Wilkins, 1999 ; Schuch et al., 1996 ). However, more recent studies reported that a constant 20% substrate moisture content (SMC) could be used as a

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Yanjun Guo, Terri Starman, and Charles Hall

relative humidity was 65.1%. Substrate moisture content treatments. Two irrigation treatments (20% and 40% SMC) were applied in two experiments (one species per experiment) starting at production week 8 and ending at production week 13 (the greenhouse

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William K. Harris, Joyce G. Latimer, John F. Freeborn, Margaret Aiken, and Holly L. Scoggins

container-grown plants from damaging winter temperatures ( Smith, 2004 ). Several cultural factors, such as the use of substrate moisture content ( Smith, 2004 ), protective covers ( Perry, 1998 ), and fertility level ( Bilderback and Bir, 2007 ) have been

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Ka Yeon Jeong and James E. Altland

forms are transformed between inorganic forms (NH 4 + and NO 3 − ). The objective of this research was to determine over time how initial substrate moisture content and storage temperature affect the chemical properties and available nutrients derived

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Alison Bingham Jacobson, Terri W. Starman, and Leonardo Lombardini

Wilting during shelf life is a major cause of postharvest shrink for bedding plants shipped long distances from production greenhouses to retail outlets. The objective of this research was to determine if irrigation at lower, constant substrate moisture content (SMC) during greenhouse production would be a feasible way to acclimate plants for reduced shrinkage during shelf life while potentially conserving irrigation water. In two separate experiments conducted in the fall and spring seasons, rooted plugs of Angelonia angustifolia ‘Angelface Blue’ (angelonia) were grown in greenhouse production until a marketable stage in substrates irrigated at SMC levels of 10%, 20%, 30%, and 40% using a controlled irrigation system. At the end of the greenhouse production stage, plants were irrigated to container capacity and subjected to a simulated shipping environment in shipping boxes in the dark for 2 days. After shipping, plants were placed back in the greenhouse and watered minimally to simulate a retail environment. Data were taken at the end of each stage, i.e., greenhouse production, simulated shipping, and simulated retail. Results indicated that as SMC decreased from 40% to 10%, plants were shorter in height but had proportional and more compact flowering sections. The volume of water received by the 40% SMC plants was three times greater (fall) and 12 times greater (spring) than the 20% SMC plants during greenhouse production and two times greater (fall) and nine time greater (spring) during simulated retail. During production, midday water potentials decreased as the SMC levels decreased, but at the end of the simulated retail, the midday water potentials were the same, suggesting that plants that were drought-stressed during production were acclimated to lower water levels experienced in retail settings. Overall, the 20% SMC treatment produced the best postharvest quality plant resulting from reduced plant height without detrimental effects on flowering. The results demonstrate that while conserving water, controlled irrigation at a lower SMC can produce high-quality plants that have equal shelf life to those that are irrigated at high levels.

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Adam F. Newby, James E. Altland, Daniel K. Struve, Claudio C. Pasian, Peter P. Ling, Pablo S. Jourdan, J. Raymond Kessler, and Mark Carpenter

Greenhouse growers must use water more efficiently. One way to achieve this goal is to monitor substrate moisture content to decrease leaching. A systems approach to irrigation management would include knowledge of substrate matric potentials and air-filled pore space (AS) in addition to substrate moisture content. To study the relationship between substrate moisture and plant growth, annual vinca (Catharanthus roseus L.) was subject to a 2 × 2 factorial combination of two irrigation treatments and two substrates with differing moisture characteristic curves (MCCs). A gravimetric on-demand irrigation system was used to return substrate moisture content to matric potentials of −2 or −10 kPa at each irrigation via injected drippers inserted into each container. Moisture characteristic curves were used to determine gravimetric water content (GWC), volumetric water content (VWC), and AS at target substrate matric potential values for a potting mix consisting of sphagnum moss and perlite and a potting mix consisting of sphagnum moss, pine bark, perlite, and vermiculite. At each irrigation event, irrigation automatically shut off when the substrate-specific weight of the potted plants associated with the target matric potential was reached. Irrigation was triggered when the associated weight for a given treatment dropped 10% from the target weight. VWC and AS differed between substrates at similar matric potential values. Irrigating substrates to −2 kPa increased the irrigation volume applied, evapotranspiration, plant size, leaf area, shoot and root dry weight, and flower number per plant relative to irrigating to −10 kPa. Fafard 3B had less AS than Sunshine LB2 at target matric potential values. Plants grown in Fafard 3B had greater leaf area, shoot dry weight, and root dry weight. Leachate fraction ranged from 0.05 to 0.08 and was similar across all treatment combinations. Using data from an MCC in conjunction with gravimetric monitoring of the container–substrate–plant system allowed AS to be determined in real time based on the current weight of the substrate. Closely managing substrate matric potential and AS in addition to substrate water content can reduce irrigation and leachate volume while maintaining plant quality and reducing the environmental impacts of greenhouse crop production.

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Holly L. Scoggins and Marc W. van Iersel

Several probes have been been recently developed that can be inserted directly into the growing medium of container-grown crops to get electrical conductivity (EC) or pH measurements. However, for many floriculture and greenhouse crops, EC interpretation ranges are based on substrate solution extraction methods such as the 1:2 v/v dilution, saturated media extract (SME), and more recently, the pour-through. We tested the sensitivity and accuracy of four in situ EC probes at a range of substrate moisture content and fertilizer concentrations. We also compared results from in situ probes with currently used methods of EC measurement. Concerning the effects of substrate volumetric water content (VWC) on the in situ probes, our results indicate little differences exist among probes when VWC exceeds 0.50, though drier substrates yielded differences depending on the measurement method. The SigmaProbe and W.E.T Probe measure the EC of the pore water specifically and show a decrease in EC with increasing water content, as the fertilizer ions in the pore water becomes more diluted as VWC increases. Results with the Hanna and FieldScout probes increased with increasing water content as the added water helps conduct the current of these meters. The EC measured with the various in situ probes differed slightly among the probes, but was highly and positively correlated with all three of the solution extraction methods over the range of fertilizer concentrations. It would be possible to convert substrate EC guidelines that have been established for any of the laboratory methods for use with the in situ probes, though our results indicate the substrate VMC must be above 0.35 for the interpretation to be valid.

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Xiaoya Cai, Terri Starman, Genhua Niu, and Charles Hall

irrigation of that container depend on another Acclima sensor programmed to the same SMC. There were no sensor failures in this experiment. Substrate moisture content treatment. The SMC is defined as V W /V T (V W is the volume of water; V T is the total

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James E. Altland and Ka Yeon Jeong

. Educ. 68 642 Jeong, K. Altland, J.E. 2017 Initial substrate moisture content affects chemical properties of bagged substrates containing controlled release fertilizer at two different temperatures HortScience 52 1429 1434 Jeong, K. Nelson, P

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Marc W. van Iersel and Sue Dove

Efficient water use in nurseries is increasingly important. In recent years, new soil moisture sensors (ECH2O probes) have become available, making it possible to monitor the moisture content of the growing medium in containers. One piece of information that is lacking for fully-automated irrigation systems is how much water actually needs to be present in the growing medium to prevent detrimental effects of drought on plants. We determined the effect of substrate moisture on photosynthesis and plant water relations of hydrangea and abelia. Growth rates of these species were measured during two subsequent drying cycles to determine how drought affects the growth rate of these species. Whole-plant photosynthesis, an indicator of growth rate, of both species remained stable as the volumetric moisture content of the substrate dropped from 25% to 15%, with pronounced decreases in photosynthesis at lower substrate moisture levels. Abelias and hydrangeas wilted when the substrate moisture level dropped to 6.3% and 8.3%, respectively. At wilting, abelias had lower leaf water potential (–3.7 MPa) than hydrangeas (–1.8 MPa). After the plants were watered at the end of the first drying cycle, the photosynthesis of the plants did not recover to pre-stress rates, indicating that the drought stress caused a long-term reduction in photosynthesis. Despite the more severe drought stress in the abelias (both a lower substrate water content and lower water potential at wilting), abelias recovered better from drought than hydrangeas. After the plants were watered at the end of the first drying cycle, the photosynthetic rate of abelias recovered to ≈70%, while the photosynthetic rate of the hydrangeas recovered to only 62% of the pre-stress rate.