Plant factories are overturning traditional agricultural cultivation methods

"Manufacturing" a ray of sunlight for plant factories

No soil, no sunlight, yet the vegetables here are especially green and lush, with yields several times higher than open-field cultivation.

The nutrient solution is the soil, and the alternating red and blue LED lights are the sunlight. There is no pollution or pest infestation. Here, through high-precision control of the environment, the growth of vegetables is almost free from the constraints of natural conditions. Recently, reporters saw at the Nongzhong IoT Plant Factory in Mafang Town, Pinggu District, Beijing, that six-tier-high cultivation racks were filled with more than 10 kinds of hydroponic leafy vegetables, including lettuce, bok choy and ice plant.

Today, this kind of plant factory, which has completely overturned traditional agricultural cultivation methods, is changing or is about to change our dining tables.

"A plant factory is a highly technology-intensive agricultural production method with highly efficient resource utilization, and it is an important development direction for countries around the world to ensure food security," said Yang Qichang, one of China's earliest experts to research plant factories and a researcher at the Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences.

However, because plant factories carry out production under precisely controllable environmental conditions, problems such as high energy consumption and high operating costs are prominent and have become an important bottleneck for their development. Under the leadership of Yang Qichang, the project team went through 12 years of dedicated research and achieved a number of original results in areas such as the theory and methods of light source adaptation for plant factories, improvement of light efficiency and energy efficiency, regulation of nutritional quality, and multi-factor coordinated control technology. They formed multiple series of products, including popularized plant factories, island and reef plant factories, and low-carbon intelligent household plant factories, which have been promoted and applied in more than 200 parks and agricultural enterprises and institutions in more than 20 provinces, municipalities and autonomous regions including Beijing, as well as in the military system, with significant economic and social benefits. In 2016, the project won the second prize of the Beijing Science and Technology Award.

An important indicator of a country's high-level agricultural technology

"A plant factory is an efficient agricultural production method that achieves continuous year-round crop production through high-precision environmental control within a facility. Its yield per unit area can reach more than 40 times that of open-field production, so it is regarded by countries around the world, especially those with scarce arable land resources, as an important development direction for ensuring food security," said Yang Qichang.

China is a country with extremely scarce per capita resources. Its per capita arable land is only 40% of the world average, and its per capita water resources are only 25% of the world average. The task of ensuring food security is arduous, and vigorously promoting the development of the high-tech plant factory industry is in line with China's long-term strategic deployment.

A prominent feature of plant factories is the high degree of technology integration and application, so they are also regarded as an important indicator of a country's high-level agricultural technology. Just like aerospace engineering, maglev trains and large aircraft, developed countries will not easily let other rivals master such technologies, and they must rely on independent research and development.

It is understood that Japan, the Netherlands and other countries began research in the 1970s and have already made important progress in some key technologies such as plant factory system structures, nutrient solution cultivation and environmental control. However, due to prominent bottlenecks such as high system energy consumption and high operating costs, large-scale application is still subject to certain limitations.

"How to break through the prominent technical bottlenecks of plant factories such as high system energy consumption and high operating costs, substantially reduce the energy consumption of artificial light sources and air-conditioning systems, improve vegetable quality and achieve intelligent control of plant factories, and build a 'low-carbon, intelligent and efficient' plant factory production technology system, is the key to the rapid popularization and promotion of plant factories," said Yang Qichang.

Growing vegetables without relying on the sun

All things grow relying on the sun. Sunlight is not only the energy source for basic physiological activities such as photosynthesis in plants, but also the driving force for morphogenesis such as flower bud differentiation, flowering and fruiting. But in plant factories, the light needed by vegetables is provided through LED lamps.

Yang Qichang told reporters that the artificial light sources currently used in plant factories are mainly fluorescent lamps and light-emitting diodes. LEDs can emit the monochromatic light needed for plant growth (such as blue light with a peak at 450nm and red light with a peak at 660nm, etc.), and after red and blue LEDs are combined, they can also form a spectrum that basically matches plant photosynthesis and morphogenesis.

"Compared with ordinary fluorescent lamps and the like, LEDs mainly have the advantages of energy saving, environmental protection, long life, monochromatic light that can be combined, and being a cold light source, and are considered the ideal light source for artificial-light plant factories," said Yang Qichang. "Through different combinations of light quality and regulation of light intensity and photoperiod, artificial light sources can replace sunlight and meet the photosynthesis needs of vegetables and other crops throughout their entire growth period in plant factories."

Apart from not relying on sunlight, the vegetables in plant factories have another magical feature: they do not need soil. These thriving vegetables all grow in professionally customized cultivation modules. There is no soil beneath the modules; instead, they rely entirely on nutrient solution.

According to reports, this special "dietary" method of plants, commonly known as soilless cultivation technology, is one of the technical cores of plant factories. These nutrient solutions are carefully formulated by professionals and can promptly and effectively provide plants with various nutrients, maximize satisfaction of the nutritional requirements of plants at different growth stages, and also coordinate conditions such as water, fertilizer, air (oxygen) and temperature needed for plant growth, so that vegetables grow quickly and have high yields.

In response to the prominent problem of autotoxic substance accumulation in the nutrient solution cultivation system of plant factories, which is difficult to remove by conventional methods, the project team invented a technical method that combines UV (ultraviolet)-nano TiO2 treatment to handle autotoxic substances in nutrient solution; it proposed and invented a vegetable quality regulation technology that combines short-term continuous lighting before harvest with regulation of the nitrogen level in the nutrient solution.

"This technology can reduce the nitrate content of leafy vegetables by more than 30%, and significantly increase Vc and soluble sugar content," said Yang Qichang.

However, not all vegetables can be grown in plant factories. "In terms of technical conditions, all vegetables can be grown in plant factories," said Yang Qichang. "But because plant factories use a three-dimensional multi-layer cultivation model, in order to make full use of cultivation space, low-growing leafy vegetables (lettuce, small rape, celery, spinach, etc.), Chinese medicinal herbs, edible fungi, strawberries and the like are generally chosen for cultivation. For tall solanaceous and cucurbit vegetables such as tomatoes, peppers, eggplants and cucumbers, they are not suitable for cultivation, and even if cultivated, low-growing varieties must be selected."

Mastering the core technology of plant factories

However, realizing plant factories is not easy. During the course of the research, the biggest challenge Yang Qichang and his team encountered was the development of dedicated LED light sources. Before 2005, the light quality of common LED light sources on the market did not sufficiently match the photosynthetic needs of plants, and the light intensity was also weak.

Through exploration on many fronts and cooperation with other semiconductor light source research institutions, the project team developed a dedicated LED light source panel for plant factories in 2005 and built a small-scale LED artificial-light plant factory laboratory. Only then did the research and development progress of artificial-light plant factories accelerate.

Yang Qichang told reporters that when plants grow in the artificial environment of a plant factory, the core element is the light environment. The first difficulty to solve is research on plant light formulas, which is the core of creating plant LED light sources. At the same time, because plant factories consume relatively large amounts of energy, energy-saving environmental control technology can be called the "life" of plant factories. "If energy consumption is very large, development will be limited."

In addition, the realization of intelligent control is also one of the difficulties. "The detection and control of environmental and nutritional factors are very different from traditional agriculture," said Yang Qichang. "High-tech means are needed, including the integration and application of information technology, intelligent equipment technology, internet technology and other technologies."

How to break through key technical bottlenecks of plant factory systems such as high energy consumption and high operating costs, substantially reduce the energy consumption of artificial light sources and air-conditioning systems, improve vegetable quality and achieve intelligent control of plant factories, and build a "low-carbon, intelligent and efficient" plant factory production technology system, is the key to the rapid popularization and promotion of plant factories.

"To develop China's high-tech plant factory industry, we must rely on independent research and development to achieve breakthroughs in core key technologies such as plant light formulas and the creation of artificial light sources, energy-saving environmental control, and intelligent control; otherwise we will inevitably be controlled by others," said Yang Qichang.

After long-term intensive study and exploration, Yang Qichang led the research team to take the lead in systematically exploring plant light formulas, identified optimized LED-based plant light formula parameters, and invented a multi-light-quality combined plant LED energy-saving light source centered on AIGaInP red light 660nm chips and InGaN blue light 450nm chips; they developed horizontal and vertical movable LED dynamic light environment regulation technology based on plant development characteristics, significantly reducing light source energy consumption.

The project team also developed environment-nutrition multi-factor synergistic technology for improving light efficiency, energy efficiency and nutritional quality in plant factories, and integrated and created three series of complete intelligent LED plant factory products. They identified the logical control strategies and algorithms for multi-factor coordinated regulation based on light formulas, light-temperature coupling and nutritional quality improvement, developed IoT-based intelligent control technology for plant factories, and realized online detection, remote access, program updates and networked intelligent control of factors such as temperature, humidity, light, CO2 concentration and nutrient solution EC, pH and DO in plant factories. They integrated and created three series of complete intelligent LED plant factory technology products: large-scale mass-production type, movable type, and household micro plant factory.

Conditions for large-scale promotion are already in place

It is understood that China is already the country with the fastest industrialization development of plant factories, having covered in just a few years the development path that developed countries took decades to traverse. At present, China's total number of artificial-light plant factories has reached more than 100, making it a major plant factory development country second only to Japan in number. More and more people are beginning to taste vegetables produced in plant factories.

Among them, Yang Qichang's team made important contributions. Since 2003, the research group has gone through 12 years of innovative research and development, successively developing multiple series of products such as popularized plant factories, building-type plant factories, island and reef plant factories, and low-carbon intelligent household plant factories, and took the lead in demonstration and promotion in Beijing. It has now been promoted to more than 200 application units in more than 20 provinces and regions across the country as well as in the military, achieving energy savings of 280 million kWh.

As the earliest research and development and industrialization demonstration base for the project, Beijing has seen widespread application of the project results. It cultivated the two largest plant factory production enterprises in China - Beijing Zhonghuan Yida Facility Horticulture Technology Co., Ltd. and Beijing Jingpeng Global Technology Co., Ltd. These two companies have become leading enterprises in the promotion of plant factories.

"At present, people's demand for high-quality vegetables is rising, and they are gradually accepting the prices of hydroponic vegetables from plant factories. More and more enterprises are joining the construction and production operations of plant factories, while plant factory technology and equipment are becoming increasingly mature, and conditions for large-scale promotion are already in place," said Yang Qichang. (Source: Science and Technology Daily)