Andrew Lee, Technical Services Manager at GRODAN explains the company’s philosophy on Precision Growing and gives examples of how this is enabling greenhouse growers to produce crops more sustainably.
Most people will be familiar with Precision Agriculture, a farm management concept with the goal of optimising returns on inputs whilst preserving our planet’s natural resources. A well-known protagonist of this concept is John Deere, a manufacturer of tractors and other farm equipment, which incorporates GPS and sensor technology on its machinery, allowing farmers to optimise machinery usage, irrigation and fertiliser application to fields.
Precision Growing uses exactly the same philosophy only in this case production takes place inside a greenhouse. Modern commercial greenhouses are large, complex facilities. Sensors and computers are used to monitor and adjust the greenhouse climate and irrigation systems where crop production has moved from soil to soilless ‘hydroponic’ cultivation (Image 1). In this way greenhouse growers can optimise the growth of crops, fine tuning growing temperatures and fertigation strategies in accordance with the prevailing weather conditions and crop growth stage.
Image 1: Inside a large commercial tomato green house. The plants are no longer grown in soil but hydroponically in stone wool substrate suspended on ‘hanging’ gutters.
Improving the sustainability of greenhouse vegetable production
Hydroponic greenhouse vegetable production is already a highly efficient method of food production, for example it uses significantly less water than field based systems (Image 2). Understanding whether further intensification of the sector could make it more sustainable than it is today requires a clear definition of sustainability.
The classic definition of sustainable development, first described at the United Nations ‘Earth Summit’ in Rio de Janiero in 1992 is: ‘development which meets the needs of the present without compromising the ability of future generations to meet their own needs’. It is now generally accepted that sustainable development is a balance between economic growth, environmental protection and social equality.
Image 2: Water use efficiency of field based production systems versus hydroponic cultivation in run-to-waste or where drain water is collected and recycled
Measuring sustainability performance using LCA
In order to introduce improvements in sustainable greenhouse production, it is necessary to measure performance. The 19th century physicist Lord Kelvin said ‘To measure is to know’ and ‘If you cannot measure it, you cannot improve it.’
Whilst not a perfect system, Life Cycle Analysis (LCA) is a useful tool. LCA is defined by the International Standards Organization (ISO) as the ‘Compilation and evaluation of the inputs, outputs and the potential environmental impacts of a product system throughout its life cycle’ (ISO 14040, 1997). As this definition suggests, LCA focuses primarily on the environmental aspects of sustainability, although other measurement systems are also beginning to consider the economic and social aspects.
Within the horticultural value chain, the LCA will consider a wide range of issues including:
- Energy consumption
- Use of other raw materials
- Emission of hazardous substances
- Contamination of ground water, rivers and seas
- Use of agricultural land
The higher the LCA score, the greater the impact of the activity being measured. Importantly an LCA will also highlight the impact areas which contribute most towards the final score – sometimes referred to as ‘hotspots’. These hotspots are the areas which should be addressed first to generate the largest improvements in sustainability performance. A standard set of ‘impact areas’ is used to cluster the influences from different parts of the process being studied.
An LCA study in a typical north European greenhouse considered all the inputs for tomato production . It identified three main impact categories, which are responsible for more than 90% of the total life cycle impact. These are:
- Fossil depletion: the environmental impacts resulting from the extraction and use of fossil based energy sources (such as coal, oil and gas).
- Climate change, ecosystem: the impacts of CO2 methane, nitrous oxide and other greenhouse gas emissions on ecosystems.
- Climate change, human health: the impacts of CO2 , methane, nitrous oxides and other greenhouse gas emissions on human health.
Further analysis of the tomato production process revealed the impact sources within each of these critical impact categories (Figure 1).
Figure 1: the sources of impacts for each of the three most important
This clearly shows that energy use is the major hotspot contributing to the three most important impact categories. The greenhouse itself, meaning the steel, aluminum, glass and concrete’ is the next most significant. Third are the impacts from fertilisers, largely due to their manufacturing process. A greenhouse tomato grower can use this information to improve sustainability performance:
- Energy consumption should be the main area of focus. So innovation in greenhouse design that lowers the total energy input or investments in greenhouse heating systems using non-carbon fuel sources, will significantly reduce LCA scores.
- The impacts from fertilisers can also be addressed simply by optimising their application via a precise irrigation strategy, regular monitoring and adjustment of the base feed recipe and the use of drain water collection systems from the start of the cultivation (Image 3). While fertiliser and water use are relatively small costs when compared to energy, they are increasingly a focus of attention from retailers and legislators due to the fact that nutrient solution draining from greenhouses can cause serious pollution of ground and surface water supplies.
Image 3: Sensors in the substrate measure water and nutrient levels providing valuable management information to the grower. Irrigation is adjusted so that precise volumes of water and nutrients are applied. The water & nutrients exiting the slab are collected by the gutter system and re-applied to the crop, lowering growing costs & eliminating run-off to the environment.
a thermal screen was installed to insulate the greenhouse at night and conserve significant amounts of energy.
The impact of energy
Figure 2 shows the actual energy use (m3 gas / m2), crop yield (kg/ m2) and yield (kg/m2 per m3 of gas) from a tomato crop in a Dutch greenhouse over a 10-year period (2001-2011). In 2005/06 a thermal screen was installed (Image 4) to insulate the greenhouse at night and conserve significant amounts of energy. By focusing on the principles of Precision Growing, ventilation levels and heating pipe temperatures were reduced and irrigation strategies were also adapted to the different greenhouse climate. All of these elements contributed to greatly improved efficiency moving from gas consumption of 47m3/m2 giving a yield of 52kg/m2 in 2001 to gas consumption of 33m3 / m2 yielding 62kg/m2 in 2011. This is a good example of how Precision Growing can deliver a more sustainable and efficient cultivation process.
|Figure 2: Yield and energy use in a Dutch tomato greenhouse 2001-2011
Image 4: Thermal screens placed above the crop, when closed are used to insulate the greenhouse at night conserving significant amounts of energy
This change in the production process had a dramatic impact on the LCA score (Figure 3). The total LCA impact was reduced by 27% per hectare over the 10-year period. However, when the increased yield is taken into account and the impact per ton of tomatoes is calculated, the reduction in the impact rises to 40%.
The life cycle impact directly attributable to the substrate (in this case GRODAN stone wool) makes a negligible contribution to the impact of tomato cultivation (Figure 3). Stone wool is therefore an ideal substrate for hydroponic cultivation giving the grower total control over water and nutrients in the root zone. It is made from basalt rock melted at 1600°C and blown into fibres, which are then compressed before the resulting stone wool slabs are wrapped in plastic foil (Images 1 & 2).
In many industries, supplier sustainability performance is already one of the criteria used by procurement departments to compare suppliers.
Sustainability measurement in practice
Retailers are turning their attention to ways in which they can more accurately and consistently assess the sustainability performance of their suppliers. Leading this development is The Sustainability Consortium (TSC), a non-profit organisation comprised of members from the global retail sector, product manufacturers and suppliers, non-Governmental organisations and universities.
In association with university academic teams, TSC is developing sustainability measurement tools and systems to facilitate the conversation between retailers and their suppliers. TSC has developed guidance in the form of ‘Category Sustainability Profiles’ (CSP). These identify the sustainability hotspots and the ways in which they can be addressed using ‘improvement opportunities’ for any particular crop. In the case of tomatoes, TSC highlights energy use, fertiliser consumption and water use issues as being important hotspots when assessing sustainability performance, confirming the outcomes of the LCA highlighted above.
Sustainability of crop production, measured either by academic calculation models, such as those used for LCA, or by using more practical tools, such as those being developed by TSC, is increasingly being adopted by the global retail sector. Measurement highlights the largest impact areas or hotspots where action via Precision Growing can be taken to deliver the most significant improvements in sustainability performance.
Looking at current greenhouse crop production in Europe it is clear that ‘sustainable greenhouse production’ can be defined as:
- Greenhouse production which fully addresses energy use as the sector’s biggest single sustainability hotspot
- Greenhouse production which makes measurably more efficient use of fertilisers and water preventing ground and surface water pollution
- Greenhouse production which addresses the sustainability concerns of global food retailers: using academically developed measurement tools
- addressing hotspots and ‘improvement opportunities’.
In many industries, supplier sustainability performance is already one of the criteria used by procurement departments to compare suppliers. Therefore, paying attention to these issues can not only save money via greater production efficiency in the short-term but can also serve as a means of differentiating and adding value to a business.
Andrew Lee, Technical Services Manager, GRODAN, Roermond, the Netherlands
GRODAN supplies innovative, sustainable stone wool substrate solutions for the professional greenhouse horticultural sector based on Precision Growing principles. These solutions are used in the cultivation of vegetables and flowers, such as tomatoes, cucumbers, sweet peppers, aubergines, roses and gerberas. Sustainability plays a prominent role at GRODAN, from the production of stone wool substrates to end-of-life solutions.
1.LCA Study of tomato production in the Netherlands February 2011 by Blonk Milieuadvies, Guoda, The Netherlands. Commissioned by Rockwool BV, Externally reviewed by Pré Consultants BV.