Summary
Much native Mixed Prairie in Nebraska (central USA) is degraded due to livestock overgrazing, with resultant shortgrass communities dominant. Previously these grasslands would have been dominated by mid- and tall-grass species, primarily big bluestem Andropogon gerardii. This study in Nuckolls County, evaluated the ability of existing desirable, native species to increase in degraded prairie following rest from grazing and/or soil discing, and combined with native seedings.
Vegetation was dominated by short-grasses. Cool-season species were primarily western wheatgrass and Kentucky bluegrass; warm-season species primarily blue grama Bouteloua gracilis and buffalograss Buchloe dactyloides. Within blocks, treatments (and controls) were randomly assigned to 23 x 11 m plots (4 replicates):
Discing - one plot in each block disced (8-10 cm depth) on 1 May 1979. Cover (plants, litter and bare ground) was determined in late May 1979, 1980 and 1981 using a point frame. Four quadrats (30 x 60 cm) per plot were clipped in May, July and October (1979-1980) to estimate standing biomass.
Discing and seeding - plots disced (as above) and drill seeded with a mix (30 PLS (pure live seed)/0.1 m): big bluestem (25%), little bluestem Schizachrium scoparium (30%), indiangrass Sorghastrum nutans (10%), switchgrass Panicum virgatum (l0%) and sideoats grama Bouteloua curtipendula (25%).
Discing, herbicide and seeding - plots disced (as above) sprayed with glyphosate (1.1 kg active ingredient/ha) on 7 May and drill seeded 12 May 1979. Plant suppression was about 90% 10 days after spraying.
Herbicide and lo-till sod seeding - on 7 May 1979, glyphosate was applied. Plant suppression was about 60-70%. On 12 May 1979, a power-till seeder was used to ‘sod seed’ a mix (30 Pure Live Seed/0.1 m) of: big bluestem (35%), indiangrass (15%), switchgrass (15%) and sideoats grama (35%).
To assess seedling establishment, frequency of occurrence within 160 (30 x 30 cm) quadrats/plot was recorded in August 1980 and July 1981. Above-ground standing crop was assessed in September 1982.
Vegetation cover of controls (26.4%) in 1979 was dominated by Kentucky bluegrass and blue grama (14.0%). Discing reduced cover to 12%. Cool-, warm-season and total vegetation cover declined from 1980 to 1981 in both control and disced plots (primarily due to 48% lower than average June-September 1980 rainfall, as well as litter build up). Discing did not induce a shift to desired grasses; in the second and third growing seasons, warm-season shortgrasses in fact increased relative to controls.
In lo-till sod-seeding with glyphosate seedling establishment was rapid for all four ‘desirable’ warm-season grasses sown (66% frequency all species, 1981).
Whilst establishment was slower in the two other seeded treatments, both were deemed to produce adequate grass stands by 1981: drill seeded disced plots (53% frequency) or disced plus glyphosate (60%).
Yield was similar for seeded treats (6.8-7.6 Mg/ha) by September 1982 (controls 5.0 Mg/ha).
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