Summary
On abandoned Nebraska Sandhills cropland (former tallgrass prairie) of north-central USA, it is difficult to re-establish perennial grasses due to low soil fertility, organic matter content and water holding capacity, erosion, unpredictable precipitation, and weed competition. This study (in Custer and Milburn Counties) evaluated the effect of seedbed preparation on establishment of two native warm- (sand bluestem Andropogon gerardii var. paucipilus [syn: A.hallii] and switchgrass Panicum virgatum), and two cool-season grasses (native smooth brome Bromus inermis and intermediate wheatgrass Thinopyrum intermedium (a Eurasian species introduced for fodder)), and weeds.
Plots were established on two abandoned cropland sites.Four 36 x 72 m areas were delineated at each, divided in half (36 x 36 m block) and seeding year (1985 or 1986) randomly assigned. Within blocks, three seedbed treatments (12 x 36 m) were likewise assigned:
1) untilled (weeds at one site; corn Zea mays residue and rye Secule cereale at the other);
2) disced to 10 cm on 1 May 1985 and 1986;
3) dead oat Avena sativa cover (DOC) - disced to 10 cm on 23 March 1985 and 1986. Oats sown two days later (to stabilize the soil and suppress weeds); on 1 May each year, glyphosate was applied (by backpack sprayer) to kill the oats.
Grasses were drilled in strips across randomly assigned seedbeds (i.e. 6 x 12 m subplots; 430 PLS/m²) on 3-4 May 1985 and 3 May 1986. In 1985, one site was irrigated (25 mm/week 1 June-15 August). Neither was irrigated in 1986.
Sampling (areas seeded 1985 sampled June and August 1985, and June 1986; areas seeded 1986 sampled June and August 1986, and June 1987) was undertaken in the central 3 x 9 m of each subplot. Seeded grass densities were determined on 10 randomly located l-m row lengths. Density of weeds was evaluated within 20 (0.1 m²) quadrats.
In 1985, seedling establishment was poor (< 5/m²) on the non-irrigated site: rainfall was erratic (intense events separated by long dry periods), although above average. Grasshopper (Tettigoniidae)herbivory (especially of brome and wheatgrass) occurred at both sites in both years, but particularly at the non-irrigated site in 1985.
Irrigation enhanced grass seedling establishment: in June 1986, these plots (established 1985) had 38, 46 and 61 plants/m² for the untilled, disced and DOC seedbeds, respectively (i.e. all of the preparation techniques gave good results for all four species 1 year after sowing).
In 1986 when moisture conditions were more favorable at both locations, plots established in that year (all non-irrigated) were successful (i.e. > l0 grass plants/m²) when seedbeds were prepared by discing or DOC. Sand bluestem was the only sown species to establish in both years.
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