For many growers, established and newcomers, the determination of the optimal light spectrum for growing crops can be challenging and highly dependent on crop species and variety. With the increased popularity of LED lighting, the capability to fine-tune a light spectrum has never been greater. Here, we break down the fundamental roles of the major spectral regions (ultraviolet, blue, green, red, and far-red) and explain the effect on plant growth, yield, and crop quality (i.e., greenness, coloration, flavor) when applied in isolation or combination. The first part of this review examines plant responses to light stimuli and the potential benefits for growers. We also discuss how LED lighting can be used to manipulate plant growth and development to improve crop productivity and/or value. We suggest some basic LED light “recipes” that could be used by growers to deliver specific growth effects and provide an easy-to-use visual reference guide. The second part of this review explores the impact of light treatments on crop productivity. Increased productivity is weighed against the ongoing costs associated with various light treatments, modeled in the context of UK electricity pricing.

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Climate change from elevated [CO2] may reduce water availability to crops through changes in precipitation and higher temperatures. However, agriculture already accounts for 70% of human consumption of water. Stomata, pores in the leaf surface, mediate exchange of water and CO2 for the plant. In crops including barley, the speed of stomatal response to changing environmental conditions is as important as maximal responses and can thus affect water use efficiency. Wild barleys and landraces which predate modern elite lines offer the breeder the potential to find unexploited genetic diversity. This study aimed to characterize natural variation in stomatal anatomy and leaf physiology and to link these variations to yield. Wild, landrace and elite barleys were grown in a polytunnel and a controlled environment chamber. Physiological responses to changing environments were measured, along with stomatal anatomy and yield. The elite barley lines did not have the fastest or largest physiological responses to light nor always the highest yields. There was variation in stomatal anatomy, but no link between stomatal size and density. The evidence suggests that high photosynthetic capacity does not translate into yield, and that landraces and wild barleys have unexploited physiological responses that should interest breeders.

Low onion (Miura cepa L.) seed yields uoccur without obvious reasons izy=cularly with hy. varieties. Solutions to the need to be found to insure seed for bul re Water and ttemperaturestress in the um b el may be factors during hot, dry, sunny weather. We investigated the relationship of umbel temperature to ambient and umbel conditions and the effects of periodic wetting of the umbels. Onions were grown in a field n'iment at Kimberly, Idaho on Panne& silt loam sail (Durixerollic Calciorthids; coarsesihy, mixed, metric) using commercial practices except that periodicsling was provided with a rotating-head sprinkler irrigation system when temperatures exceeded certain levels. Sprinkling for five min reduced floret temperatures as much as 15 C below ambient. The florets remained cool for 20 to 40 min, depending on umbel maturity, wind speed, and air temperature and humidity. Nearly mature umbels were hotter and uired more sprinkling to keep cool. Five min of sprinkl ing every 20 to 30 min usually provided adequate cooling. A speciallydesigned temperature sensor was found to successfully simulate the behavior of an onion floret during wetting and drying, permitting direct control of the Initiation, duration, and frequency. of winkl. Excessive tem.ratures did not occur d the ex t, so seed yields were similar on and unsyrinkled plots. While we have shown that periodic sprinkhn will provide umbel cooling and minimize undesirable effects on pollination, similar studies need to be conducted in hotter, major seed producing areas to establish economic benefits.