Climate and Yield in a closed greenhouse

The so-called closed greenhouse (closed ventilation windows) is a recent innovation in Dutch greenhouse industry. The technical concept consists of a heat pump, underground (aquifer) seasonal energy storage as well as daytime storage, air treatment units with heat exchangers, and air distribution ducts. Savings of up to 30% in fossil fuel and production increases by up to 20%, mainly because of the continuously high CO2 concentration, have been reported. Economic feasibility of this innovative greenhouse highly depends on the yield increase that can be obtained. In this simulation study the effects of greenhouse climate on tomato yield in a closed greenhouse are presented. The explanatory model INTKAM was used, which has several submodels e.g. for light interception, leaf photosynthesis and biomass partitioning. The closed greenhouse offers possibilities for combinations of light, temperature, air humidity and CO2 concentration that are impossible in a conventional greenhouse. At high CO2 concentration and high light intensity, leaf photosynthesis shows a more narrow optimum for temperature than at high CO2 and moderate light intensity. However, the response of crop photosynthesis to temperature has a much broader optimum than that of leaf photosynthesis. Besides photosynthesis, temperature also influences aspects like partitioning, leaf area development and fruit development. Yield potential reduces at temperatures above 26°C, with fruit set being one of the first processes that is negatively influenced by supra-optimal temperatures. Based on actual climatic conditions in a conventional and a closed greenhouse (same crop management) measured during two years, INTKAM predicts an increase in yield by about 17%. Hence, in a closed greenhouse a higher stem density can be maintained for obtaining the same average fruit weight (size) as in a conventional greenhouse. In 2005 actual yield increase was similar to the simulated one (16%), but in 2004 only a 9% higher yield was realized, at least partly because of botrytis infection in the closed greenhouse

Comparative investigation into the effect of fertigation and of broadcast fertilization on the yield and nitrate content of lettuce (Lactuca sativa L.).

Three [unnamed] cultivars were grown successively during March to May, June to July, and July to August 1983 on a sandy soil. For each of these field experiments the treatments were: no N application, and fertilization with various amounts of ammonium nitrate, either as split applications via irrigation water or as a single broadcast application. Fertigation increased the availability and uptake of N and increased the nitrate content of the crop compared with broadcast fertilization. A second-degree polynomial model fitted the fertilization:NO3-content data. In the first cropping, yield was significantly higher when N was applied by fertigation compared with broadcast application, but in the following croppings there was no significant difference. However, it is suggested that the yield difference in the first cropping may be related to the very wet spring conditions (a 56 mm rain surplus compared with 105 and 116 mm deficits in the following two experiments) when leaching of NO3 from the upper soil layer would be expected. (Abstract retrieved from CAB Abstracts by CABI’s permission

Passion for work: Work engagement versus workaholism.

Introduction: Nothing great in the world has been accomplished without passion. Georg Wilhelm Friedrich Hegel (1770-1831) Is passion needed for excellent performance? The question of what predicts outstanding performance at work remains timely and relevant. The term “passion for work” emerged from qualitative research on entrepreneurs’ motivation, and has been defined as a selfish, passionate love for the work (Shane, Locke & Collins, 2003). Passion for work has been proposed as key to understanding entrepreneurial behavior and performance. Passion is “… the enthusiasm, joy, and even zeal that come from the energetic and unflagging pursuit of a worthy, challenging and uplifting purpose” (Smilor, 1997, as cited in Shane at al., 2003). However, few attempts have been made so far as to operationalize the construct, let alone relate it to entrepreneurial behaviour. The current chapter aims to fill this void, by focusing on work engagement and workaholism as two motivational concepts indicating “passion for work”

The effect of the PPARgamma ligand rosiglitazone on energy balance regulation

BACKGROUND AND AIM: Fat mass generation requires an energy surplus and the activity of the peroxisome proliferator-activated receptor gamma (PPARgamma). We investigated if the PPARgamma ligand rosiglitazone influences substrate usage, energy expenditure (EE) and energy intake (EI) and, thereby, how PPARgamma activity contributes to susceptibility to obesity. METHODS: Twenty healthy males (20-29 years) were randomly assigned to receive a placebo (n = 10) or rosiglitazone (8 mg/d) (n = 10) for seven consecutive days, while staying in a respiration chamber. Food intake was ad libitum. Body composition was determined by underwater weighing (day 1) and deuterium dilution (day 1 and 8). RESULTS: Mean (+/-SE) EI was 15.9 +/- 0.9 MJ/d in the placebo group and 18.9 +/- 1.2 MJ/d in the rosiglitazone group. Mean EE was 11.3 +/- 0.3 MJ/d and 12.5 +/- 0.5 MJ/d for the placebo and rosiglitazone groups respectively. This resulted in a cumulative positive energy balance (EB) of 32.3 +/- 5.1 MJ for placebo and 44.7 +/- 6.9 MJ for rosiglitazone. There were no significant differences in EI, EE, and EB between treatments. Both groups did not adjust their fat oxidation to the increased fat intake, but fat oxidation decreased faster in the rosiglitazone group (significantly lower on days 6 and 7). During treatment with rosiglitazone, significantly more fat storage was seen in overweight subjects while this was not the case in the placebo group. CONCLUSIONS: Our results suggest a shift in substrate usage during PPARgamma stimulation leading to a preference for fat storage, especially in subjects with a higher BMI. Copyright (c) 2005 John Wiley & Sons, Ltd

Measuring very negative water potentials with polymer tensiometers: principles, performance and applications

In recent years, a polymer tensiometer (POT) was developed and tested to directly measure matric potentials in dry soils. By extending the measurement range to wilting point (a 20-fold increase compared to conventional, water-filled tensiometers), a myriad of previously unapproachable research questions are now open to experimental exploration. Furthermore, the instrument may well allow the development of more water-efficient irrigation strategies by recording water potential rather than soil water content. The principle of the sensor is to fill it with a polymer solution instead of water, thereby building up osmotic pressure inside the sensor. A high-quality ceramic allows the exchange of water with the soil while retaining the polymer. The ceramic has pores sufficiently small to remain saturated even under very negative matric potentials. Installing the sensor in an unsaturated soil causes the high pressure of the polymer solution to drop as the water potentials in the soil and in the POT equilibrate. As long as the pressure inside the polymer chamber remains sufficiently large to prevent cavitation, the sensor will function properly. If the osmotic potential in the polymer chamber can produce a pressure of approximately 2.0 MPa when the sensor is placed in water, proper readings down to wilting point are secured. Various tests in disturbed soil, including an experiment with root water uptake, demonstrate the operation and performance of the new polymer tensiometer and illustrate how processes such as root water uptake can be studied in more detail than before. The paper discusses the available data and explores the long term perspectives offered by the instrument

Work Engagement and Workaholism: Comparing the Self-Employed and Salaried Employees

Abstract: This study among a Dutch convenience sample of self-employed individuals (n = 262) and salaried employees (n = 1900) tested to what extent workaholism and work engagement relate to self-reported work performance. After controlling for measurement inequivalence, results of structural equation modelling showed that the self-employed score higher on engagement and working excessively then employees, but not on working compulsively. In addition, work engagement related positively to task performance and innovativeness for both groups. However, engagement only related to contextual performance (performance beyond role requirements) for employees. Workaholism had positive and negative relationships with self-reported performance. Working excessively related positively to innovativeness for both groups, and to contextual performance for the self-employed. Working compulsively suppressed this positive relationship between excessive working and innovativeness in both groups, and between excessive working and contextual performance for the self-employed. In contrast to our expectations, working compulsively related positively to contextual performance for employees