Greenhouse technology for sustainable production in mild winter climate areas: Trends and needs

Greenhouse production in the near future will need to reduce significantly its environmental impact. For this purpose, elements such as the structure, glazing materials, climate equipments and controls have to be developed and wisely managed to reduce the dependence on fossil fuels, achieve maximum use of natural resources such as solar radiation and water, and minimize the input of chemicals and fertilizers. This paper discusses the most relevant developments in greenhouse technology for mild winter climates. Regarding greenhouse structures, recent studies based on computational fluid dynamics have been conducted to investigate the effect of parameters such as ventilator size and arrangement, roof slope and greenhouse width and height on the air exchange rate. Next generation greenhouses are expected to incorporate some of the innovations derived from recent ventilation studies. Covering crops with screens is becoming a common practice. Main advantages and limitations of screenhouses are discussed in this paper. Thermal storage is increasingly applied in closed or semi-closed greenhouses. Under some conditions semi-closed greenhouses could mitigate day/night while reducing the use of water and the entrance of pest. Photo selective films that reflect a fraction of NIR radiation are effective at lowering greenhouse temperature and, in some cases, may be cost effective. NIR reflective films have side effects of major importance in greenhouse production. The CO2 enrichment strategy in computer-controlled greenhouses is based on determining the benefits of increasing the CO2 concentration against the cost of it. No clear strategies have been defined for the application of CO2 in unheated greenhouses, where most of the time the source of carbon dioxide is the external air. Some authors suggest ventilating as little as possible and fertilizing with bottled carbon dioxide at least up to the external concentration. Improving greenhouses by introducing new technologies may have an additional impact on the environment. From an environmental point of view, the incorporation of technology needs to increase yield to compensate for its associated environmental burden. Previous results have shown that forced ventilation and heating are the main reasons for the increase in environmental impact in climate controlled greenhouses. Additional results on the area of technology and its associated impact are discussed in this pape

Greenhouse engineering: New technologies and approaches

Firstly, this article discusses the greenhouse engineering situation in three geographic areas which are relevant in the field of protected cultivation: Northern Asia, The Netherlands and the Mediterranean. For each area, the prevailing greenhouse type and equipment is briefly described. Secondly, the main technological constraints are pointed out and finally the research directions are discussed. For all areas under consideration, attempts to design more efficient greenhouse systems are under way. In Northern Asia progress is being made towards the optimisation of greenhouses as a solar collector and to the development of new heating strategies. Important subjects addressed in The Netherlands are energy conservation and the replacement or alleviation of human labour by increasing mechanisation. In the Mediterranean there is growing interest in semi-closed greenhouses with CO2 enrichment and control of excessive humidity. All geographic areas share the need of having an optimised climate control based on the crop response to the greenhouse environment. All areas also share the requirement of being respectful to the environment, therefore future greenhouses are expected to use engineering to produce with minimal or zero emissions

Resource use efficiency in protected cultivation: towards the greenhouse with zero emissions

Protected cultivations are expanding all over the world, particularly in otherwise marginal agricultural land. However, protected cultivation involves the intensive use of resources such as soil, water, fertilizers, pesticides and energy. As a consequence, such intensive production systems are perceived by many as artificial and highly pollutant processes. Protected cultivation, and more particularly green-house production, has to be – and to be seen – more respectful of the environment. The greenhouse of the future will have nearly zero environmental impact. This goal can be achieved by developing a sustainable greenhouse system that: does not need any fossil energy and minimizes carbon footprint of equipment; with no waste of water nor emission of fertilizers and full recycling of the substrate; with minimal need of plant protective chemicals, yet with high productivity and resource use efficiency. An environmental and economic study of the current situation is a tool to identify the most critical elements of the production process, in various climatic and market conditions, so that suitable technologies may be developed to address the locally relevant bottlenecks. The greenhouse of the future can fulfil the need for safe use of resources (energy, water, pesticides) through modification of greenhouse design and management. Coatings and additives can be used to improve the performance of greenhouse covers in terms of light transmission vs. thermal insulation. More efficient greenhouse ventilation is expected to have a positive effect on the cutback of inputs as well. The greenhouse can benefit from the reduction of waste through better manage¬ment of irrigation and climate. This article will discuss the current expectations and limitations on resource use efficiency in protected cultivatio

Directional vortex motion guided by artificially induced mesoscopic potentials

Rectangular pinning arrays of Ni dots define a potential landscape for vortex motion in Nb films. Magnetotransport experiments in which two in-plane orthogonal electrical currents are injected simultaneously allow selecting the direction and magnitude of the Lorentz force on the vortex-lattice, thus providing the angular dependence of the vortex motion. The background dissipation depends on angle at low magnetic fields, which is progressively smeared out with increasing field. The periodic potential locks in the vortex motion along channeling directions. Because of this, vortex-lattice direction of motion is up to 85o away from the applied Lorentz force direction.Comment: PDF file includes figure

Report on economic & environmental profile of new technology greenhouses at the three scenarios

The EUPHOROS project is co-funded by the European Commission, Directorate General for Research, within the 7th Framework Programme of RTD, Theme 2 – Biotechnology, Agriculture & Food, contract 211457. The views and opinions expressed in this Deliverable are purely those of the writers and may not in any circumstances be regarded as stating an official position of the European Commission. This Deliverable 5 Annex is the latest updated version in September 2011

Experimental results and modelling of humidity control strategies from greenhouses in continental and coastal setting in the Mediterranean regíon. I : Experimental results and model development.

Experimental strategies for controlling humidity were compared in a greenhouse sited in Madrid, a continental site in the Mediterranean region. Small roof window apertures significantly reduced the relative humidity with only a limited increase in associated energy consumption. A simplified climate model with four energy exchange terms (heating, insolation, losses through structure, and losses through windows) and three mass exchange terms (evapotranspiration, losses through structure, and losses through windows) was validated, allowing relative humidity to be predicted with an error of < 9%. - Se ensayaron una serie de estrategias experimentales para el control de la humedad en un invernadero de Madrid, España. Se comprobó que pequeñas aperturas de la ventana cenital reducían significativamente el nivel de humedad con limitados incrementos del consumo de energía en calefacción. Se validó un modelo climático simplificado con cuatro términos de intercambio de energía (calefacción, radiación solar, pérdidas a través de la cubierta y pérdidas a través de las ventanas) y tres términos de intercambio de humedad (evapotranspiración, pérdidas a través de la cubierta y pérdidas a través de las ventanas), modelo que permitió predecir la humedad relativa con un error inferior al 9%

Environmental and economic profile of present greenhouse production systems in Europe. Annex

The EUPHOROS project is co-funded by the European Commission, Directorate General for Research, within the 7th Framework Programme of RTD, Theme 2 – Biotechnology, Agriculture & Food, contract 211457. The views and opinions expressed in this Deliverable are purely those of the writers and may not in any circumstances be regarded as stating an official position of the European Commission. This Deliverable 5 Annex is the latest updated version in September 2011

Evaluating observed versus predicted forest biomass: R-squared, index of agreement or maximal information coefficient?

The accurate prediction of forest above-ground biomass is nowadays key to implementing climate change mitigation policies, such as reducing emissions from deforestation and forest degradation. In this context, the coefficient of determination ($${R^2}$$) is widely used as a means of evaluating the proportion of variance in the dependent variable explained by a model. However, the validity of $${R^2}$$ for comparing observed versus predicted values has been challenged in the presence of bias, for instance in remote sensing predictions of forest biomass. We tested suitable alternatives, e.g. the index of agreement ($$d$$) and the maximal information coefficient ($$MIC$$). Our results show that $$d$$ renders systematically higher values than $${R^2}$$, and may easily lead to regarding as reliable models which included an unrealistic amount of predictors. Results seemed better for $$MIC$$, although $$MIC$$ favoured local clustering of predictions, whether or not they corresponded to the observations. Moreover, $${R^2}$$ was more sensitive to the use of cross-validation than $$d$$ or $$MIC$$, and more robust against overfitted models. Therefore, we discourage the use of statistical measures alternative to $${R^2}$$ for evaluating model predictions versus observed values, at least in the context of assessing the reliability of modelled biomass predictions using remote sensing. For those who consider $$d$$ to be conceptually superior to $${R^2}$$, we suggest using its square $${d^2}$$, in order to be more analogous to $${R^2}$$ and hence facilitate comparison across studies