Vegetation management on solar farms can be accomplished through targeted grazing with sheep. No data currently exists informing management for contract grazers on solar farms. Therefore, our objectives were to investigate both the effects of solar panels on sheep grazing behavior and the grazing management strategy (i.e., rotational grazing or continuous grazing) best suited for vegetation management on a solar array facility. Data were collected on Gold Tree Solar Farm in San Luis Obispo, CA, USA. In the experiment, conducted in January 2021 for 16 days, sheep with predominately Dorper genetics (over 99%; n = 80) were stratified by body weight (BW) and age in a crossover design to 1 of 2 respective treatment grazing locations: (1) solar farm, or (2) native rangeland (control). Grazing location treatments were then randomly assigned to 1 of 2 grazing management styles: (1) continuous (paddock size = 0.405 ha, 4 days/paddock), or (2) rotational (paddock size = 0.101 ha, 1 day/paddock, 4 paddocks), resulting in a 2 × 2 factorial arrangement of treatments (Solar Continuous (S-C), Solar Rotational (S-R), Control Continuous (C-C), and Control Rotational (C-R)). All sheep were equipped with a HOBO Pendant G data logger (Onset Computer Corporation, Bourne, MA, USA) on the top of their necks using vet wrap (Dura-Tech), to record grazing behavior. The sensitivity, accuracy, and precision were > 90% for grazing behavior with 2-minute intervals. Grazing behavior exhibited a treatment × management (P < 0.01) interaction. Both solar (S-C and S-R) groups spent more time (P < 0.01) on grazing than both control (C-C and C-R) groups. The presence of solar panels may have provided sheep relief from heat, wind, and rain, which could increase grazing activity. Sheep spent less time grazing under rotational management when compared with continuous management (P < 0.001). During the experiment, forage was senescent and low-quality in terms of nutritive value. Rotational grazing management is considered superior for sheep weight gain during the green feed period, while continuous grazing management is more effective during forage senescence. The use of sheep for vegetation management on solar farms has great potential. Sheep are effective grazers, easily able to maneuver between solar panels and can graze on steep slopes utilizing the panels to provide for them shade and protection from climatic conditions. In conclusion, utilizing a mix of rotational and continuous grazing according to forage conditions may be the most effective grazing management strategy in solar farms.


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Linda Poole

Hi Emma, and thank you for sharing your research.

Your study makes an excellent case for the grazing of sheep beneath solar arrays. I think this is a marvelous melding of sustainable agriculture and energy. My area of interest is in rangeland and wildlife ecology, and I am a shepherd, so I am eager to learn about grazing programs that meet the specific, long-term needs of solar farms.

Your conclusions touch on a constant tension point in grazing management between caring for the land versus caring for the livestock. Grazing senescent vegetation can be a challenge to animal performance, and as your research revealed, sheep will then forage selectively to boost their nutritional status. But allow too much of that and we predictably set back the health of vegetation and soils as the sheep nibble favored plants to their roots while leaving less palatable species or individual plants to dominate the land. Year-round rotational grazing has proven beneficial to the land -- and thus to the long-term health of livestock -- in many studies across a diversity of seasonal landscapes. The pace of rotation between paddocks typically slows, but does not stop, during dormant seasons. Well-managed rotational grazing throughout the year helps desirable vegetation maintain vigor, helps build soils, prevents erosion and improves water cycles -- and these things together can then extend the active growing season and increase the amount of palatable vegetation available to sheep. Continuous grazing can be somewhat less of an issue in low-diversity swards of sod-forming grasses and legumes, so long as there is adequate leaf area left to maintain plant health and sufficient stubble left to protect the soil surface. Rotational grazing is especially important for maintaining or building health in more diverse plant communities, or if more than 40% of the annual growth of the forage species is removed.

In solar arrays, the concurrent needs to maintain healthy, low vegetation; reduce fire danger; and provide for healthy livestock is an interesting challenge. One of the pitfalls of masters research is the short duration of the work. A one to two year study is unlikely to detect significant impacts of continuous versus rotational grazing. Animal behavior and performance will change in relation to changes in plant vigor and species composition, but these changes will take time. I hope you are successful in securing a PhD grant to delve further into this over a longer period of time. The questions you are asking are important! Thanks again for sharing your research results.
Emma, are you familiar with the ASGA ? I guess you might be , but just in case : American Solar Grazing Association . Check it out if you have not already.. Cheers.. Joe

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