Jayalath Theekshana C, van Iersel Marc W, Ferrarezi Rhuanito Soranz
Department of Horticulture, University of Georgia, 1111 Miller Plant Sciences Building, Athens, GA 30602, USA.
Plants (Basel). 2024 Feb 27;13(5):652. doi: 10.3390/plants13050652.
The sunlight greenhouse crops receive varies and is often insufficient for consistent year-round growth in greenhouses. Supplemental lighting is commonly applied in winter, but this practice has a significant energy cost, accounting for 10-30% of operating expenses and impacting greenhouse profitability. Greenhouse lights are traditionally adjusted based on sunlight intensity to meet crops' daily light requirements. However, if plants can withstand lower daily light integrals (DLI) after a sunny day without reducing the growth, there is potential to reduce the energy required for supplemental lighting and increase the profit. To determine whether excess light received one day can be 'carried over' to the next, we grew oakleaf lettuce ( 'Green Salad Bowl' and 'Red Salad Bowl') under six lighting regimes inside a vertical farm. Plants in all treatments received an average DLI of 15 mol·m·d, but DLIs alternated from day-to-day (15/15, 17.5/12.5, 20/10, 22.5/7.5, 25/5, and 27.5/2.5 mol·m·d), resulting in DLI fluctuations from 0 to 25 mol·m·d. Plants had similar leaf area (800 cm/plant) and dry weight (1.8 g/plant) when grown with DLI fluctuations from 0 to 15 mol·m·d, while higher DLI fluctuation reduced growth. To confirm this DLI "carrying-over" effect on plants grown under sunlight with supplemental light, we conducted a second study in a greenhouse with 'Green Salad Bowl' lettuce. In this study, plants were grown with five different DLI fluctuations (15/15, 16.75/13.25, 18.5/11.5, 20.25/9.75, and 22/8 mol·m·d), ranging from 0 to 14 mol·m·d, while maintaining an average DLI of 15 mol·m·d in all the treatments. We observed similar leaf area (750 cm/plant) and dry weight (1.8 g/plant) in lettuce plants grown with DLI fluctuations from 0 to 10.5 mol·m·d. Higher DLI fluctuations reduced growth. Hence, carrying excess light from a sunny to an overcast day is possible within limits. Our study concluded that the DLI requirement can be reduced by approximately 5.25 mol·m·d on the day following a sunny day. By analyzing historical weather data from five US locations, we quantified the potential annual energy savings from incorporating this 'carrying-over DLI' concept. This approach resulted in annual energy savings of approximately 75-190 MWh/ha in greenhouse lettuce production. Such reductions in supplemental lighting energy will enhance the profitability and sustainability of the greenhouse industry.
日光温室作物所接受的光照各不相同，且往往不足以维持温室中全年持续生长。冬季通常会使用补光，但这种做法能源成本高昂，占运营成本的10%-30%，影响温室的盈利能力。传统上，温室灯光是根据阳光强度进行调节，以满足作物的每日光照需求。然而，如果植物在晴天后能够承受较低的每日光积分（DLI）而不影响生长，那么就有可能降低补光所需的能源并提高利润。为了确定一天中接收到的过量光照是否可以“留存”到第二天，我们在垂直农场内的六种光照条件下种植了橡叶生菜（“绿色沙拉碗”和“红色沙拉碗”）。所有处理组的植物平均每日光积分均为15摩尔·米²·天，但每日光积分每天交替变化（15/15、17.5/12.5、20/10、22.5/7.5、25/5和27.5/2.5摩尔·米²·天），导致每日光积分在0至25摩尔·米²·天之间波动。当每日光积分在0至15摩尔·米²·天之间波动时，植物的叶面积（约800平方厘米/株）和干重（约1.8克/株）相似，而较高的每日光积分波动会降低生长。为了证实这种每日光积分“留存”效应在有补光的日光下种植的植物上是否成立，我们在温室中对“绿色沙拉碗”生菜进行了第二项研究。在这项研究中，植物在五种不同的每日光积分波动条件下生长（15/15、16.75/13.25、18.5/11.5、20.25/9.75和22/8摩尔·米²·天），波动范围为0至14摩尔·米²·天，同时所有处理组的平均每日光积分为15摩尔·米²·天。我们观察到，在每日光积分波动为0至10.5摩尔·米²·天的生菜植株中，叶面积（约750平方厘米/株）和干重（约1.8克/株）相似。较高的每日光积分波动会降低生长。因此，在一定限度内，将晴天的过量光照留存到阴天是可行的。我们的研究得出结论，在晴天后的第二天，每日光积分需求可降低约5.25摩尔·米²·天。通过分析美国五个地点的历史天气数据，我们量化了采用这种“留存每日光积分”概念可能实现的年度能源节约。这种方法在温室生菜生产中每年可节约约75-190兆瓦时/公顷的能源。补光能源的这种减少将提高温室产业的盈利能力和可持续性。
