Influence And Optimization Of Light Intensity And Airflow On Lettuce Growth And Tip Burn Disease In A Plant Factory

With the advantages of high efficiency,energy saving,and environmental control,artificial light based plant factories have become one of the important trends in agricultural development.Cultivating multiple vegetable varieties simultaneously within the same plant factory space,as well as synchronizing the cultivation of different growth stages of the same vegetable variety,can better meet the needs of plant factory users and promote the application of plant factory technology in more fields.Achieving precise environmental control in different zones within the plant factory is an essential prerequisite for zone specific cultivation.In this study,lettuce was selected as the research object,with the aim of controlling tip burn disease incidence and improving lettuce quality.By focusing on two major environmental factors,light intensity and airflow,the study conducted zone specific optimization of the plant factory environment for cultivating lettuce during the seedling and growth stages,utilizing CFD technology.The specific work content includes the following aspects:(1)In response to the simultaneous cultivation of lettuce in the seedling and growth stages in a plant factory,response experiments were conducted on light intensity and airflow for both stages of lettuce.The optimal environmental factor comfort zones for lettuce at different growth stages were determined.By using principal component analysis and path analysis,it was found that leaf water potential was the main physiological and ecological factor inducing tip burn disease in the seedling stage of lettuce,while stomatal conductance and calcium ions were the main physiological and ecological factors inducing tip burn disease in the growth stage of lettuce.Based on the analytic hierarchy process,the comprehensive quality indicators of lettuce in different light intensity and airflow treatment groups were assessed,including "leaf area,tip burn disease incidence rate,plant height,fresh weight,SPAD,AsA,soluble sugar,and nitrate".The optimal environmental factor ranges suitable for the seedling and growth stages of lettuce were determined.When plants were within the suitable range of environmental factors,the comprehensive quality was optimized,and tip burn disease was effectively suppressed.(2)Based on heat transfer and energy balance theory,a coupled numerical model was established to investigate the transmission and flow process of humid air within a plant factory.The model incorporated components such as the walls of the plant factory,cultivation racks,LED light sources,mixed air,crop plants,and air conditioning fresh air systems.In conjunction with fluid dynamics theory,this study utilized the STAR-CCM+software and employed a structured grid to discretize the calculations.The Realizable k-ε turbulence model was used to solve the turbulent transport process of indoor humid air,while the standard wall function method was adopted to handle the airflow near the wall,ensuring rapid computation and convergence.Additionally,to address turbulent airflow issues within the plant factory,a numerical solution method based on airflow control equations and component transport equations was applied.This method accurately and efficiently described the distribution of humid air within the plant factory,providing an effective numerical simulation tool for optimizing plant factory design and environmental control.(3)Aerodynamic experiments were conducted on lettuce during its seedling and growth stages in a low speed wind tunnel,considering lettuce as a porous medium model.The viscous drag coefficient D and inertial drag coefficient C2 of lettuce were determined in the x,y,and z directions for both the seedling and growth stages.These parameters were then input into a CFD numerical model of the plant factory.The solution of porous medium parameters for seedling and growth stage lettuce in this study allowed for a more accurate elucidation of the transmission and flow patterns of humid air within the plant factory.(4)Based on the airflow simulation results from the unloaded plant factory,a cultivation plan was proposed that divided the cultivation areas into high and low wind speed zones,achieving mixed closed loop cultivation of lettuce during the seedling and growth stages.Seedling lettuce was cultivated in the low wind speed zone,while growth stage lettuce was cultivated in the high wind speed zone.Through the regulation of environmental factors in various cultivation areas within the plant factory,efforts were made to maximize the assurance that lettuce in different growth stages remained within the suitable growth range.Experimental results showed that the standard deviation of the suitable humidity area percentage for different positions of cultivation racks was 19.4%,the suitable airflow area percentage standard deviation was 20.1%,and the suitable temperature area percentage standard deviation was 22.5%.Considering the disturbance caused by LED light source heat dissipation on various environmental factors in the plant factory,a disturbance coefficient θ was introduced to quantitatively analyze the impact of LED light source heat dissipation on humidity,airflow,and temperature.Combining the results of lettuce responses to light intensity and airflow during the seedling and growth stages with the disturbance coefficient θ,the lighting mode for the light period in the plant factory was determined.(5)To further optimize the distribution of environmental factors in different cultivation areas,differential fans were installed outside each cultivation rack.The differential fans device for the light period operated in an intake mode,referred to as the TLOpt mode.The differential fans device for the dark period operated in a blowing mode,known as the TNOpt mode.The uniformity of environmental factors significantly improved in the optimized plant factory.In the TLOpt mode,the uniformity coefficient for humidity UIRH was 0.9212,for vertical air velocity UIV was 0.9661,and for temperature UIT was 1.In the TNOpt mode,the humidity uniformity coefficient UIRH reached 0.9564,the vertical air velocity uniformity coefficient UIV reached 0.9986,and the temperature uniformity coefficient UIT reached 1.By alternating between the TLOpt and TNOpt modes,the comprehensive quality evaluation score for lettuce in the seedling stage was 0.7281,and in the growth stage was 0.6778.Both the seedling and growth stages effectively suppressed lettuce tip burn disease.This study investigated the effects of light intensity and airflow on the comprehensive quality and tip burn incidence of lettuce at different growth stages in a plant factory.The AHP fuzzy comprehensive evaluation method was used to assess the lettuce during the seedling and growth stages,obtaining the suitable growth ranges for the main environmental factors of lettuce at different growth stages.Rational planning of the cultivation space in the plant factory was achieved through computational fluid dynamics numerical analysis.The placement of LED light sources in the cultivation area was optimized to improve various environmental factors in the plant factory.This research aims to guide plant factory production,minimize or prevent the occurrence of lettuce tip burn disease,and provide theoretical and technical support for achieving high yield,high quality,and efficient plant production in plant factories.