Indiangrass and caucasian bluestem responses to different nitrogen sources and rates in the Ozarks.

Abstract

Alternatives to cool-season grasses are needed for summer forage production on droughty, infertile soils in the Ozarks. The objective of this research was to compare nitrogen (N) sources and application rates for improving forage production, crude protein concentration, and apparent 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)2SO4 at 0, 56, 112, and 168 kg N ha-1 from 1985-1987. In 1988 the (NH4)2SO4 treatment was discontinued and in 1990 the N rates were increased to 0, 78, 157, and 235 kg N ha-1. Forage yields, crude 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 caucasian 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 in 1987, 129 kg N ha-1 in 1989, and 161 kg N ha-1 in 1990. Crude protein concentrations of both species increased linearly with N rates in 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 recovery. Forage yield and crude protein concentration of both species responded similarly to (NH4)2SO4 and NH4NO3.