Reflection on reflection in action: a case study of growers conception of irrigation strategies in pot plant production

Abstract

A case study of growers conception of irrigation strategies indicates that pot plant growers in Scandinavia base their management approaches on experientially based art. The study also indicates that there is a gap between experientially based art and available greenhouse technology. In order to standardize production and produce quality, both the grower’s experience and available technology should be taken into account. In order to achieve this, the present study proposes to arrange reflection on reflection in action with a group of growers by means of the dialogue seminar method. The concept of reflection on reflection in action is novel to horticultural practice. Therefore, we suggest future inter- and multidisciplinary research within this domain.

Appendix: material and methods

General considerations

Access to water and water supply is one of the main factors limiting crop production. In horticulture, in particular in pot plant production, water supply is an important factor for production timing, produce design and transportability (Dole and Wilkins 1999). Interactions between growing medium moisture and biomass production, as well as growth, are well established facts in the literature (Raviv and Blom 2001). The comparative study associated with the present experiment with Kalanchoë blossfeldiana as a model plant supports these findings. As a transport medium for nutrients and constituents, water plays an important role for photosynthesis and for maintaining the turgor pressure which both are conditions for growth (Milburn 1979; Kramer and Boyer 1995; Raviv and Blom 2001). Both excess and deficiency of water leads to morphological and physiological changes in plant performance as further outlined by several researchers (Laan et al. 1989; Marschner 1995; Bray 1997; Kage et al. 2000; Larcher 2001; Raviv and Blom 2001; Taiz and Zeiger 2002; Earl and Davis 2003).

Irrigation regime is a result of complex interaction between moisture of the growing medium, external growth factors, such as light irradiation, temperature and relative humidity as well as plant performance and changes in state variables, e.g., potential or actual evapotranspiration (Gisleröd et al. 1989; Moe 1990; Hansen et al. 1996; Katsoulas et al. 2002; Nagler et al. 2003). Moisture content of the growing medium can be determined by tensiometer measurement (Rana and Katerji 2000) and time domain reflectrometry (TDR) (Pepin et al. 1992; Anisko et al. 1994; Kipp and Kaarsemaker 1995; Da Silva et al. 1998; Mojid and Cho 2004; Kritz and Khaled 2004) allowing continuous monitoring. These might, however, imply problems under the specific conditions prevailing in pot plant production. Only micrometric assessment stem diameter (Lemaire et al. 2003) and digital scales (Morel et al. 1992; Raviv and Blom 2001) meet the specific conditions in pot plant production.

Material and methods

A triangular approach consisting of inquiry, interview and greenhouse block experiment was chosen.

Questionnaire

A questionnaire was sent to the 324 pot plant growers who were registered as members in Swedish growers association (GRO), corresponding to 900,000 m² (50%) of the total production area of pot plants in Sweden (Jordbruksverket 2005). The questionnaire (Ejlertsson 2005) consisted of a general part with three questions dealing with background questions on the company and a part with five questions on factors decisive for irrigation strategies in pot plant production. In a final question the respondents were given the option to describe gaps of knowledge concerning irrigation that they experience. Apart from the final question, there were options for at least two fixed alternatives and for an open free choice alternative. More than one option could be chosen. The background part took on the definition of the respondent (owner, foreman, free choice), person in charge of irrigation management (shared responsibility between xx persons, responsibility of one person, free choice) and the crop (no specific crop; all irrigation management takes place in the same way for all crops within the company, free choice). The part on factors decisive for irrigation strategies concerned the decisive factors for (1) irrigation event based on the plants and substrates condition (physiognomic perceptual, tactile, free choice), (2) external factors of importance for the irrigation incidence (outdoor temperature, irradiation, event for the last irrigation, free choice), (3) irrigation volume and irrigation time (drought level of the plants, standard configurations for the specific type of table, free choice), (4) time of the day for irrigation [before 6 am (immediately before sunrise), before 9am (immediately after sunrise), 12 noon (mid day), 3 pm or later (after noon), no specific time of the day], (5) company internal factors affecting the choice of event for irrigation (irrigation groups, crop specificity, event for irrigation is without importance).

In-depth interviews

Based on the answers given in the questionnaire in-depth interview were outlined, focusing on deeper inquiry into (1) technical preconditions of interest for irrigation in the greenery, (2) general assessment of water need as well as decisive factors, such as plant physiognomy, substrate, climate and climate factors and season, (3) irrigated volume as well as (4) self-evaluation on the powerfulness of the present irrigation strategy. A total of five growers were chosen for the interview. Selection was based on their production of crop. The interviews were done at the growers place and were all recorded on tape complemented with written notes. The interviews lasted 1 h and no longer time for consideration was available.

Greenhouse experiment

In order to scrutinize different irrigation procedures, a confirming greenhouse experiment was conducted in the experimental greenhouse at SLU, Alnarp. Within the framework of a pre-trial, the properties of the peat-based growing medium were defined with respect to volume weight, air as well as water volume at a suction of pot capacity (0 kPa) as well as 10, 50 and 100 cm water column (1, 5 and 10 kPa) (Gabriëls and Verdonck 1991) and compared to time domain reflectometry (TDR, Kritz and Khaled 2004) measurements. Four distinct levels were elected (i, 60 m s⁻¹; ii, 40 m s⁻¹; iii, 24 m s⁻¹; iv, 16 m s⁻¹ corresponding to pot capacity, 0, 10, 50 and 100 cm of water pressure head, respectively). Pre-treated Kalanchoë blossfeldiana cv. Simone was grown in peat-based growing medium in three blocks at a density of five plants per treatments (temperature set point, day time 19°C; night time 20°C; ventilation started when temperature deviated +2°C; relative humidity, 75%) and exposed to the above-named moisture set points and compared to the commercially used approach referred as “golden grip” (treatment 1, 16; treatment 2, 24; treatment 3, golden grip; treatment 4, 40; treatment 5, 60). Assimilation light was provided between 7 am and 5 pm, in order to insure a minimum of light of 40 Wm⁻² during these hours. During other hours of the day the plants were kept in the dark.

The plants were continuously connected to the TDR equipment and the time of irrigation management were made manually by evaluating the TDR levels keeping them as close to the wanted level as possible. Supplied amount of water was measured individually with a volumetric cylinder. Fertilizer was added simultaneously to all treatments and adopted to treatment 1.

Analyses

Alternative responses in the introductory questionnaire were transformed into binary numbers and frequencies were calculated (Minitab version 14; U.K.). Alternatives including free answers as well the in-depth interviews were analyzed using the SOLO-scale with five levels of cognitive complexity (Biggs and Collis 1982), (1) prestructural level, (2) unistructural level, i.e., direct and concrete, but minimalistic conception, (3) multi-structural level, comprising an understanding of boundaries, but not of systems, (4) relational level, revealing a level of involvement where facts, theory, action and purpose are integrated and (5) the extended abstract level, i.e., a conceptualizing, metacognitive level of involvement.

The plants were weighed before and 1 h after each irrigation event. Once a week the plants total surface area (Löfkvist et al. 2008) and plant height were measured. At five occasions, evenly distributed over the experimental period, three plants per block were removed to monitor the total leaf area using a Licor Li 3100 Area meter (Glen Spectra, UK) as well as plant fresh and dry weight. Dry weight of shoot and leaf were determined after drying at 80°C for 3 days. All data were analyzed using one- and two-way ANOVA and Tukey test (P < 0.05; Minitab version 14).

Greenhouse experiment results

Biomass production was not constant during the period of observation irrespective of the treatment displaying a significant decrease in the ratio of leaf area to leaf dry weight from 0.07328 m² g⁻¹ (P < 0.001) in the beginning and 0.009006 m² g⁻¹ (P < 0.001) in the end. Canopy fresh and dry weight as well as canopy fresh weight and total leaf area were positively correlated (R ² = 88.4%, P = 0.001 and R ² = 87.6%, P = 0.001, respectively) irrespective of the treatment; a similar trend was found for the interaction between the total leaf and the total canopy surface area (R ² = 59.7%, P < 0.001).