Optimal row spacing improves the yield and quality of alfalfa cultivated in alpine areas of China.

Unprecedented pressures stemming from climate change and anthropogenic activities endanger grasslands, making well-designed forage cultivation practices essential for sustainable grassland management. We conducted a field experiment to determine the optimal planting density and cultivar to be used in the alpine region of Inner Mongolia. The experiment included 3 alfalfa cultivars cultivated at 4 different row spacings (20, 40, 60, and 80 cm) and we evaluated the responses of alfalfa yield and quality to these treatments. We found that the row spacing significantly affected the fresh and dry matteryield of alfalfa, and the effects differed by the cultivars. Specifically, cultivar polar bear (PB) and Longmu 806 (LM) cultivated with a 20 cm row spacing yielded significantly higher fresh and dry matter compared to the 60 cm and 80 cm treatments. Regarding the forage quality, the crude protein and crude fat of PB cultivated at 20 cm row spacing were more than those at 80 cm for both of two cuts, respectively, while the relative feed value (RFV) at 40 cm row spacing was 38.1% higher than that at 80 cm for the 2nd cut. On the other hand, the acidic detergent fiber and neutral detergent fiber at 80 cm row spacing were significantly higher than those of 60 and 20 cm for the 2nd cut. Regarding the LM cultivar, the ash and P contents in the 20 cm row spacing treatment were significantly higher than those at 80 cm. Different row spacing showed similar effects on the yield and quality indexes of the Gongnong (GN) cultivar. Principal component analysis indicated that quality factors, including crude protein and RFV, had the highest contribution rate, followed by yield factors and mineral element factors. We concluded that the PB should be the preferred cultivar for alfalfa planting in China's northern alpine regions, with a recommended row spacing of 20-40 cm, followed by LM, with a recommended row spacing of 40-60 cm.