Multiyear Use of Killed Strips for Forage and Grain Sorghum Production in a Tall Fescue Pasture

Abstract

Tall fescue (Festuca arundinacea Schreb.) is an excellent perennial grass for spring and fall forage production and for erosion control on sloping land. Tall fescue forage production is poor during the summer, however. Our objective was to improve pasture productivity without increasing erodibility by planting a sorghum × sudan hybrid [Sorghum bicolor (L.) Moench × Sorghum bicolor L. Moench] (S × S) or grain sorghum [Sorghum bicolor (L.) Moench] (GS) in 12 in. killed strips of tall fescue and to determine if strips could be used in subsequent years without additional herbicide treatment. Forage from a block of tall fescue was harvested in May 1990, and plants were allowed to regrow for 1 wk before application of glyphosate in 12 in. strips on 30 in. centers at two rates of 1.2 and 0.6 lb ai/acre (strip-kill). For control treatments, the entire tall fescue sod was killed (complete-kill) or tall fescue was not sprayed in order to measure forage production from the grass monoculture. The S × S (cv. FFR 201) was planted into strip-kill and complete-kill pilots 1 wk after glyphosate treatment in 1990 and again in 1991 and 1992 without additional glyphosate treatment. In May 1991, GS (cv. MFA GS-10) was planted into strip-kill and complete-kill plots and these strips were used again in 1992. Tall fescue was successfully killed with a single application of each rate of glyphosate in the strip-kill and complete-kill systems. There was little difference in S × S dry matter yield or GS grain yield between glyphosate treatments. Dry matter yield of S × S in strip-kill plots decreased each year after initial treatment in 1990, probably a result of increased competition from tall fescue encroachment into the killed strips. Dry matter yield of S × S in strip-kill plots was 16,49, and 52% less than that of the complete-kill plots in 1990,1991, and 1992, respectively. Tall fescue yield in strip-kill plots was only slightly less than that of tall fescue (monoculture) control plots. Total forage yield (S × S plus tall fescue) in the strip-kill plots was 3.49, 2.39, and 1.63 tons/acre greater than that of the tall fescue (monoculture) control in 1990, 1991, and 1992, respectively. Grain sorghum yield in strip-kill plots was 25 bu/acre less than that in complete-kill plots in 1991 and 53 bu/acre less than that in complete-kill plots in 1991. Planting S × S into the same strip-kill plots is feasible for 3 yr, however for GS to be successful in a strip-kill system, tall fescue strips must be killed annually. Research Question Tall fescue is a source of high quality forage during the spring and fall; however, the productivity of tall fescue is poor during the summer. One major attribute of tall fescue pastures is that they prevent erosion on hilly landscapes. The objective of this study was to determine the feasibility of supplementing forage or grain production in tall fescue pastures during the summer by growing sorghum × sudan (S × S) or grain sorghum (GS) in 12 in. killed strips of tall fescue sod and by using the same strips in subsequent years. If successful, this system would increase productivity of hilly landscapes without causing erosion. Literature Summary There are several reports that corn or S × S were successfully grown in grass pastures within 8 or 16 in. strips sprayed with paraquat or glyphosate, when water and N were in abundant supply. For production in subsequent years, however, strips were again treated with herbicides. Planting S × S into killed strips would be more attractive economically, if the strips could be used for more than 1 yr. Permanently killing tall fescue with glyphosate is not always easy and often requires more than one application. Some research has shown that planting forage sorghum into tall fescue pastures after spraying with glyphosate apparently helped kill the tall fescue. Study Description Tall fescue (Ky 31) was sprayed with glyphosate at two rates, 0.6 and 1.2 lb ai/acre, in 12 in. bands on 30 in. centers in May 1990. Sorghum × sudan (FFR 201) was planted 1 wk after spraying when the tall fescue was turning yellow. The killed strips were used for two additional years without glyphosate treatment. In May 1991, 12 in. strips were killed in another block of tall fescue and GS was planted the following week and in 1992. As one control in both studies, entire plots of tall fescue were killed with glyphosate at rates of 1.5 and 3.0 lb/acre (complete-kill). This control was identical to a S × S or GS no-till production system. As another control, tall fescue was not sprayed in order to measure forage production from the grass monoculture. The experiments were carried out in central Missouri on a poorly drained silt loam soil. Applied Questions Did strips in tall fescue pastures killed with glyphosate remain open and useful for forage sorghum production for more than one year? Strips in the tall fescue killed with either of two rates of glyphosate remained open throughout the 3 yr of the experiment. There were some encroachment of tall fescue into strips and this may have been responsible for reduced forage yields in subsequent years. Planting S × S into the killed strips may have aided in both initial killing of tall fescue and in keeping strips open either through shading or through the release of allelopathic chemicals. How successful was S × S and GS production in killed strips in the years after establishment? Sorghum × Sudan dry matter yield in strip-kill treatments decreased each year after establishment of the 12 in. strips. In the second and third year after establishment, S × S dry matter yield was only 50% that of the complete-kill controls. Total forage production (S × S plus tall fescue) of strip-kill plots, however, was equal to or greater than that of complete-kill plots during the first 2 yr (Fig. 1). Total forage production in strip-kill treatments was 2 to 3 tons greater than in the tall fescue monoculture each year. Grain yield of GS was satisfactory only during the first year, thereafter competition from the tall fescue severely reduced grain yield. Figure 1Open in figure viewerPowerPoint Total forage production from tall fescue monoculture, strip-kill (S × S plus tall fescue), and complete-kill (S × s) plots. The 12 in. killed strips were established in 1990 and used again in 1991 and 1992. * Letters indicate significant differences during each year at the 0.05 probability.