Cytokinins Effect on Protein and Chlorophyll Content of Big Bluestem Leaves

Abstract

Four concentrations of the synthetic cytokinin benzyladenine (BA) were applied to ungrazed tallgrass prairie near Manhattan, Kans., in 1979 on 4 biweekly dates beginning in mid-June. Changes in chlorophyll and crude protein content of big bluestem (Andropogon gerardi Vitman) leaves from the different treatments were monitored weekly from August until early October. BA did not significantly delay chlorophyll breakdown in big bluestem, but leaves sprayed with 5 ppm BA contained higher mean chlorophyll contents throughout the sampling period than leaves from other treatments. Big bluestem receiving 5, 20, and 40 ppm BA applied in July had significantly more crude protein than untreated leaves, but 10 ppm BA had no effect on leaf protein content. Applying BA in mid-June was ineffective in maintaining high crude protein levels, regardless of concentration. BA did not alter protein or total nonstructural carbohydrate content in big bluestem rhizomes, indicating that it had no deleterious effect on internal nutrient reserve cycles. Applying 5 ppm BA in either mid- or late-July significantly increased herbage yields the next year in comparison with yields of untreated plots.