LEAF NUTRITIVE-VALUE RELATED TO TILLER DEVELOPMENT IN WARM-SEASON GRASSES

Assessing nutritive value of key grass species in relation to plant de velopment is essential for producers to efficiently manage livestock e nterprises, Changes in nutritive value for tiller populations of 2 com mon Nebraska Sandhills grasses, prairie sandreed [Calamovilfa longifol ia (Hook.) Scribn.] and sand bluestem [Andropogon gerardii var. paucip ilus (Nash) Fern.], in response to morphological development was evalu ated at the Gudmundsen Sandhills Laboratory (GSL) during the 1990 and 1991 growing seasons, Morphological development was determined on a 40 to 60-tiller sample from each block (12 blocks in 1990 and 8 blocks i n 1991) at ten-day intervals using a comprehensive staging system, In vitro dry matter digestibility (IVDMD), crude protein (CP), neutral de tergent fiber (NDF) and lignin were determined for leaves and correlat ed with the morphological index (Mean Stage by Count), growing degree days and day of the year, Leaf NDF values of both species remained con stant while leaf IVDMD declined throughout the summer indicating that decline in leaf IVDMD was caused by declining cell wall digestibility, Leaf IVDMD was influenced more by tissue aging than advancing morphol ogical stage, Leaf CP was significantly different between years but no t between species indicating leaf CP was largely influenced by environ mental factors, In both species and for both years, leaf CP initially declined rapidly to low levels and then stabilized during the vegetati ve phase, Nutritive value of a single vegetative morphological stage o ver the growing season was similar to the leaf tissue of the tiller po pulations, Management decisions by producers depend on accurate assess ment of changes in nutritive value during the growing season in tiller populations of these 2 important grasses.