82 PROCEEDINGS OF THE ELEVENTH NORTH AMERICAN PRAIRIE CONFERENCE



establishment. While essential to a full understanding of the effect
of herbicides on native plant establishment, the proximal causes
of any observed effects were not part of the design. The study,
therefore, implies, but does not attempt to determine, whether the
results are a consequence of direct effects of the herbicide on seeds
or seedlings, of excessive biomass resulting in reduced solar ra-
diation reaching the prairie seedlings, of effects of allelochemicals
that are known to be produced by several of the species identified
in this study (Rice 1984), or of any other possible causes.

                METHODS AND MATERIALS

Study Site
  The study was conducted from 1975 through 1978 on two,
previously cultivated fields located at a recently developed flood-
control dam site situated about 20 km northwest of Omaha, Ne-
braska. This area is locally designated Dam Site 11 or Cunningham
Reservoir. Soils of the site are mostly of the Mollisol soil order.
One field, the Lowland Site (SEI/4 of SE1/4, Section 22, T16N,
Rl2E), was located on a Colo/Kennebec Series (Ck) soil complex
(Cumulic Haplaquolls and Hapludolls). These soils are deep, nearly
level, somewhat poorly drained to well-drained fine-silty clay loam
soils that typify the occasionally-flooded bottomlands along major
streams of this portion of eastern Nebraska. The second field, the
Upland Site (SWI/4 of SWI/4, Section 22, T16N, R12E), was
situated on a Monona/Ida Series (MoD and MsE2) soil complex
(Typic Hapludolls and Typic Udorthents the latter of the Entisol
Soil Order). These are deep, well-drained, sloping fine-silty and
silty loam soils (7-11% slopes) formed over 9-15 m of loess.
Climate of the region varies from average high temperatures of
31 C in July to - 11 C in January; annual precipitation averages 71
cm with 75% falling from April to September. The growing season
averages 167 days. Soil and climatic data are from Bartlett (1975).



Treatments
  At each of the two sites, a 0.82 ha study plot was permanently
marked and divided into 22 treatment plots (12 x 30 mi). The study
plots were disked and harrowed just prior to seeding to provide a
weed-free seed bed (Cox and McCarty 1958). From 21 to 23 May
1975, 16 species of native prairie forbs and 7 of native prairie
grasses were seeded in each study site at rates averaging 19 pure
live seed (PLS) per m2 for grasses and 28 seeds per m2 for forbs
(Table 1). Seeds were obtained from the Soil Conservation Serv-
ice's Plant Materials Center in Manhattan, Kansas. Seeding was
accomplished using a Nesbit drill and planting at a depth of 0.6
cm. Forb seeds were mixed with bran to prevent size-sorting during
drilling. The bran-forb seed mixture was uniformly drilled across
both upland and lowland sites on 21 May 1975 at a rate of 26 kg/
ha.
  Grasses were drilled evenly across each study site on 22 and
23 May 1975, but the species seeded varied for each topographic
location (Table 1). Eastern gammagrass [Tripsacum dactyloides
(L.) L.] was an exception. It was broadcast, followed by harrow.
ing, because of the large size of the seed.
  Atrazine and 2,4-D treatments were applied at rates of 0.6, 1.1,
1.7, and 2.2 kg/ha. All treatment plots evaluated, including un-
treated controls, were separated by buffer plots of equal size to
reduce the effects of pesticide drift or edge effect. In 1975, atrazine
was applied in the 80% wettable powder form on 23 May, the
time of grass seeding, while 2,4-D was applied as a liquid spray
on 10 July 1975. Mowed plots were mulch-mowed to a height of
approximately 5-10 cm on 17 July and 8 August 1975 for the
lowland site, and 24 July and 8 August 1975 on the upland site.
Untreated control plots were not treated in any way. One half of
each treatment plot was retreated in 1976 at the same rate applied
the previous year. Atrazine was applied in the wettable powder



Table 1. Seeded species coding and application rates. Species indicated with
an asterix (*) were seeded but not found in any treatment plot.



Scientific and Common! Varietal Name



Forbs - upland/lowland seeding:
AscTub                Asclepias tuberosa L. (butterfly milkweed).
CeaHer                Ceanothus herbaceous Raf. var. pubescens T. & G.
(inland ceanothus; New Jersey Tea) .
DalCan                Dalea candida Michx. ex Willd. (white prairie clover).
DalPur                Daleapurpurea Vent. (purple prairie clover).
DesIll                Desmanthus illinoensis (Michx.) MacM. (Illinois bundleflower).
EchAng                Echinacea angustifolia DC. (purple coneflower) .
HelMax                Helianthus maximilianii Schrad. (Maximilian sunflower).
He1Hel                Heliopsis helianthoides (L.) Sweet var. scabra (Dun.)
Fern. (false sunflower).
LesCap                Lespedeza capitata Michx. (round-head lespedeza).
LiaAsp                Liatris aspera Michx. (rough gay-feather).
LiaPun                Liatrispunctata Hook. (dotted gay-feather).
LiaPyc                Liatris pycnostachya Michx. (thickspike gay-feather)
. ...........................................
PenGra                Penstemon grandiflorus Nutt. (shell-leaf penstemon)
.
RatPin                Ratibida pinnata (Vent.) Barnh. (grayhead prairie coneflower).
SalAzu                Salvia azurea Lam. (Pitcher sage) ......................................
SchNut                Schrankia nuttallii (DC.) Stand. (catclaw sensitive
brier).

Grasses upland seeding:



AndSco
BouCur
BouGra



Andropogon scoparius Michx. ('Aldous' little bluestem)..........................................
Bouteloua curtipendula (Michx.) ('El Reno' sideoats grama) ......................................
Bouteloua gracilis (H.B.K.) Lag. ex Griffiths ('Nature' blue grama) ......
..........................



Grasses lowland seedinl
AndGer
AndSco
PanVir
SorNut
TriDac



AndropogongerardiiVitman ('Kaw'bigbluestem) ..............................................
       2.136
Andropogon scoparius Michx. ('Aldous' little bluestem) .6..........................................
 68
Panicum virgatum L. ('Blackwell' switchgrass) ..................................................
  .73
Sorghastrum nutans (L.) Nash ('Oto' indiangrass) ...........................................
     2.12
Tripsacum dactyloides (L.) L. (eastern gammagrass) .............................................



'Based on estimates of counts of disseminules of each species; total estimate
= 442,500 disseminules.



Code



Quantity



  f10 trt'
  0.7*
  5.7
  11.4
  12.1'
  1.8'
  2.9
  3.8
  3.1
  8.0
  7.2
  4.8*
  7.7*
  12.0
  21.9
  2.7
  0.7

kg PLS/ha
  1.74
  2.56
  1.27



I :