Leaf and Stem Yields and Forage Quality of Three N‐fertilized Warm‐Season Grasses1

Abstract

AbstractNitrogen fertilization of warm‐season tall grasses may increase dry matter yields, percentage crude protein, and in vitro dry matter disappearance (IVDMD). Leaf and stem portions of total dry matter may vary among grasses, years, and fertility levels and during the growing season. Established pure field stands of switchgrass (Panicum virgatum L.), indiangrass [Sorghastrum nutans (L.) Nash], and big bluestem (Andropogon gerardi Vitman) were fertilized annually with 0, 45, and 90 kg N/ha and harvested at six biweekly dates beginning in mid‐June during 1973 and 1974 to determine leaf and stem yields and forage quality of these warm‐season grasses as influenced by N‐rate and plant maturity. Leaf and total dry matter yields decline 50% following the 1st year of clipping due to below average precipitation of 1974 as compared with 1973. Leaf yields increased with N fertilization more at the later harvests. Big bluestem responded with more than double the dry matter (leaf and total) production per kg of N and showed less decline the 2nd year than the other grasses. Leaf material of all grasses comprised approximately 85% of the total forage yield at most N levels both years. Leaf crude protein percentages were increased with N fertilization during the first three harvests; whereas, leaf IVDMD ercentages were increased with N fertilizer during the first five harvests. Leaf IVDMD was highest in indian. grass followed by big bluestem and switchgrass. Rapid declines occurred in leaf crude protein and IVDMD throughout the growing season, indicating that leaf maturation primarily is responsible for declining forage quality rather than increasing plant development, i.e., increasing stem growth, in these grasses.