Abstract
The projected increase of the world’s population, coupled with the shrinking area of arable land required to meet future food demands, is building pressure on Earth’s finite agricultural resources. As an alternative to conventional farming methods, crops can be grown in protected environments, such as traditional greenhouses or the more modern plant factories. These are usually more productive and use resources more efficiently than conventional farming and are now receiving much attention—especially in urban and peri-urban areas. Traditionally, protected cropping has been predominantly practised in temperate climates, but interest is rapidly rising in hot, arid areas and humid, tropical regions. However, maintaining suitable climatic conditions inside protected cropping structures in warm climates—where warm is defined as equivalent to climatic conditions that require cooling—is challenging and requires different approaches from those used in temperate conditions. In this paper, we review the benefits of protected cropping in warm climates, as well as the technologies available for maintaining a controlled growing environment in these regions. In addition to providing a summary of active cooling methods, this study summarises photovoltaic (PV)-based shading methods used for passive cooling of greenhouses. Additionally, we also summarise the current humidity-control techniques used in the protected cropping industry and identify future research opportunities in this area. The review includes a list of optimum growing conditions for a range of crop species suited to protected cropping in warm climates.
Highlights
Over the past 20 years, the concept of maximising a sustainable yield per unit area has been the primary goal of agriculture and horticulture industries, due to population growth, climate change, water shortage, declining arable land and biotic and abiotic stresses to crops [1,2,3]
The arable land per capita of the global population has already decreased from 0.37 ha in 1961 to 0.19 ha in 2015 (Table S1), with similar trends seen in individual countries [2]
Plant factories do significantly improve water-use efficiency and yield of vegetable production [15], they make no use of abundant solar energy especially in warm climates
Summary
Over the past 20 years, the concept of maximising a sustainable yield per unit area has been the primary goal of agriculture and horticulture industries, due to population growth, climate change, water shortage, declining arable land and biotic and abiotic stresses to crops [1,2,3]. The result is an environment that is conducive for plant growth and development [11,12] This cropping typology is semi-controlled and mostly relies on solar energy for crop photosynthesis and heating. Plant factories do significantly improve water-use efficiency and yield of vegetable production [15], they make no use of abundant solar energy especially in warm climates. Heating, cooling and dehumidification in lettuce-production greenhouses accounted for an estimated 30%–40% of energy use per cultivation area (MJ/m2 ), this depended on climatic conditions [15]. Due to the growing global population and the decline in available arable land, research interest in protected cropping in warm and arid regions has recently increased. Findings from our review of both greenhouse climate control and the recently growing area of plant factory systems are discussed
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