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Abstract
Machinery traffic can negatively impact alfalfa (Medicago sativa L.) yield and nutritive value. The objective of this research was to simulate machinery traffic through the effect of downforce on the alfalfa crowns and soil, and quantify its impact on alfalfa yield and nutritive value. Treatments evaluated include the impacts of compaction on ‘Ameristand 435TQ RR’ and ‘Alfagraze 600 RR’ when compacting 1) the crown of the plant (C), 2) the surrounding soil (S), 3) both the surrounding soil and crown of the plant (CS), and 4) neither as an untreated control (UC) with compaction occurring at 5 timings to mimic machinery traffic in the field during dry hay and silage production. Measurements included: yield, number of shoots per plant, damage to the roots, and nutritive value. Regardless of variety, yield gradually decreased throughout the season, and there was a threshold in which there was a significant difference between harvests 3 and 4 (5.69 g DM plant-1 and 3.14 g DM plant-1) where compaction started to damage the plant significantly. Ameristand overall had greater crude protein (CP) values and lower NDF and ADF, which is desirable. CP was greater for no compaction controls for both varieties. The bulk density increased throughout the season but not to a level that restricted root growth. However, the S treatment had higher bulk density compared to other treatments. For the root evaluations, Ameristand had more total root mass, but the controls of both varieties had the least amount of cracks and damages to the top 8 cm of roots.