INDIANGRASS AND CAUCASIAN BLUESTEM RESPONSES TO DIFFERENT NITROGEN-SOURCES AND RATES IN THE OZARKS

Alternatives to cool-season grasses are needed for summer forage produ ction on droughty, infertile soils in the Ozarks. The objective of thi s research was to compare nitrogen (N) sources and application rates f or improving forage production, crude protein concentration, and appar ent fertilizer N recovery by 'Rumsey' indiangrass [Sorghastrum nutans (L.) Nash] and caucasian bluestem [Bothriochloa caucasia (Trin.) C.E. Hubbard]. Pure stands of each species were treated with urea, NH4NO3, or (NH4)(2)SO4 at 0, 56, 112, and 168 kg N ha(-1) from 1985-1987. In 1 988 the (NH4)(2)SO4 treatment was discontinued and in 1990 the N rates were increased to 0, 78, 157, and 235 kg N ha(-1). Forage yields, cru de protein concentrations or both were greater with NH4NO3 compared to urea in 3 out of 6 years for indiangrass and 4 out of 6 years for cau casian bluestem. Indiangrass forage yields increased with increasing N rates up to 168 kg N ha(-1). Caucasian bluestem forage yields peaked at 101 kg N ha(-1) in 1985, 132 kg N ha(-1) in 1986, 122 kg N ha(-1) i n 1987, 129 kg N ha(-1) in 1989, and 161 kg N ha(-1) in 1990. Crude pr otein concentrations of both species increased linearly with N rates i n most years. At the lowest N rate (56 kg N ha(-1)) caucasian bluestem was more efficient than indiangrass in apparent fertilizer N recovery , but at greater N rates the 2 species were similar in fertilizer N re covery. Forage yield and crude protein concentration of both species r esponded similarly to (NH4)(2)SO4 and NH4NO3.