Stimulation of Alfalfa Bud and Shoot Development with Cytokinins

As the number of alfalfa (Medicago sativa L.) plants in a stand declines, a compensatory increase in number of shoots per plant maintains production; however, when plant density declines below a critical level, compensatory shoot production is insufficient to maintain yield. Stimulating new shoots to grow in low density alfalfa stands may allow for continued economic alfalfa production in low density stands. Cytokinins have increased shoot growth in other plants. Our objective was to determine the effect of cytokinin on alfalfa development, yield, and quality. Two cytokinins, kinetin (6-furfurylaminopurine) and BAP (6-benzylaminopurine), were applied foliarly at several concentrations to alfalfa grown at different densities in both a greenhouse and field environment. Cytokinins increased shoots per plant, shoot length, and leaf area per plant. Increases in these plant characteristics were positively correlated (r > 0.74) with increased yield per plant. Average herbage dry matter (DM) yields per plant were increased by 35% in the greenhouse study and 79% in the field study, by application of cytokinins. The stimulatory effects of cytokinin were similar between low and high plant density stands. In the greenhouse study, delaying cytokinin application from immediately after harvest until 3 or 7 d after harvest reduced the yield per plant by 9 or 15%, respectively. Alfalfa quality was unaffected in the field and reduced in the greenhouse (average of 13 g kg⁻¹ less crude protein and 29 g kg⁻¹ more acid detergent fiber) by cytokinin application. Cytokinin application to alfalfa stubble increases the number of shoots and DM yield per plant and may prove to be a method of increasing or maintaining yield under field production situations. Idaho Exp. Stn. Res. Paper no. 90744.