2.1. Study area
The experimental site is located at the Horticulture and Agroforestry
Research Center (HARC) of the University of Missouri in
New Franklin, MO (92◦74W and 37◦2N; 195m above sea level).
Four small watersheds under grazed pasture (GP) were used for
the study, which include replicate watersheds with agroforestry
buffers (AgB) (tree-grass buffers) and grass buffers (GB). Pastures
were seeded with red clover (Trifolium pratense L.) and lespedeza
(Kummerowia stipulacea L.) in 2003. The size of each watershed is
about 0.64 ha (6420m2) and this area was divided into six paddocks.
The size of each buffer is about 0.16 ha (1605m2). The cattle
were introduced in 2005 and were rotationally grazed (Kumar
et al., 2008). The previous land use for GP, AgB and GB was similar.
The land was under tall fescue grass (Festuca arundinacea Schreb.)
without grazing before the establishments of watersheds. The GB
buffer areas were reseeded with tall fescue (F. arundinacea; Kentucky
31) in 2000. The AgB buffers consisted of eastern cottonwood
trees (Populus deltoides Bortr. ex Marsh.) which were planted into
fescue sod in 2001. Soils for the row-crop (RC) treatment were
sampled from an adjacent corn field on the north side of the pasture
areas. This area was under corn (Zea mays L.)-soybean [Glycine
max (L.) Merr.] rotation and during the sampling year the crop was
corn. The size of row-crop treatment was similar to the grazing
watersheds. Soil at the pasture and row-crop sites was classified
as Menfro silt loam (fine-silty, mixed, superactive, mesic Typic
Hapludalfs). Average slope for the site is 12.5%. The annual precipitation
of the experimental site for the last 50 years is 925mm;
mean maximum temperature is 18.8 ◦C and minimum temperature
is 6.9 ◦C. The mean annual temperature in 2009 was 12.6 ◦C
(http://agebb.missouri.edu/weather/history/index.asp).