This project studied roadway lighting’s impact on altering growth and development of the soybean. This effort evaluated light spill from roadways (i.e., light trespass) into soybean fields in situ and then compared those levels of light to the development, growth, and yield of soybeans planted in the same field without light trespass. In the past, there has been overwhelming evidence that artificial light affects the growth and maturity of soybean plants. However, such research has been conducted predominantly in a controlled laboratory setting. The effect of roadway lighting on the maturity of soybean plants in an actual field adjacent to a lighted roadway has never been reported before. This project aimed to provide an initial assessment of the effects of lighting level on soybean growth for both overhead lighting and vehicle headlamps. The study answered the following questions: - What is the impact of light level on soybean growth and maturity? - What is the impact of vehicle headlamps on soybean growth and maturity? - What is the cost and benefit relationship of modifying or replacing lighting in terms of soybean impact? Seven farms were selected at various locations in Illinois based on the trespass lighting measured in the unplanted fields, farmer participation, and planned soybean crop. The lighting was surveyed robotically immediately after the fields were planted but before plant emergence in order to minimize soil compaction and to prevent damaging any plants. The lighting data collected included vertical and horizontal illuminance from the roadway edge of the field inward until the lighting levels were minimal. Any moonlight or other lighting trespass, such as sky glow, was measured. Headlamp light trespass into the field and the roadway lighting levels were also characterized. During the growing season, the plant data collection included minimally invasive, periodic height, reproductive-stage, and Normalized Difference Vegetation Index (NDVI) measurements, performed on site. Just before the farmer harvested, a 1-m (3-ft) strip of plants was collected from rows at 130 sample locations across the seven sites for final analysis. The data measured included final height measurement, plant moisture content, and dried seed weight after harvest. The study found three main effects of lighting on soybean plants: development delays, yield reduction, and height increase. Based on the data collected, soybean development can be delayed anywhere from 2 to 7 weeks when exposed to light trespass from typical high-pressure sodium (HPS) lighting used on Illinois roadways. Although development was delayed, most of the plants sampled matured (R7 stage, physiological maturity) before the farmer harvested the field. From a harvesting standpoint, the limits for trespass illuminance are 5.7 lux (lx) horizontal and 4.5 lx vertical to enable mechanical harvesting and threshing. Yield is also limited by horizontal illuminance, which should be kept at no more than 5.7 lx each to keep yield above 87% . Height and stage of plant maturity are both affected by trespass illuminance values, as shown from periodic measurements during the growing season, but the limit for the effect seemed to be greater than for the yield measurements. The study attempted to determine soybean variety differences, as different varieties were grown in the field, and this did not appear to affect the results obtained. The project found that house side shields attached to the luminaires could potentially be effective in minimizing the impact of lighting on soybean growth on the house side as observed in one field. Draft specifications were developed for horizontal, vertical, and the combination of the two for lighting trespass maximums for roadway lighting to minimize soybean growth impact. Trespass light from the roadway luminaire into soybean fields should be limited to the values listed in in the following table. These values are based on the limits found from the analysis of the R-Stage data and from the yield data. These values will ensure that the plants are eventually harvestable and that the yield will be at least 87—88% of the norm for the field. (Author/publisher)
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