A study started in 1998 was continued through 2001 to compare the effects
of liquid hog manure and urea applied at similar N rates on corn production and N and P
movement in the soil and into the tile lines. In November 2001, the study was expanded
to include pathogen movement from higher rates of liquid manure into subsurface, tile
drainage. This study was continued in 2003. Hog manure was spiked with Salmonella
anatum and sweep-injected into moldboard-plowed continuous corn in Nov. 2002 at a
rate of 5000 gal/A (268 lb “available N/A). Urea was applied at a rate of 160 lb N/A in
April 2003 and incorporated immediately. Corn production was not affected differently
by the two sources of N. Grain yields were excellent, ranging from 169 to 180 bu/A.
Rainfall for the growing season was 7.8” below normal and was below normal each
month. Tile flow occurred for 49 days from mid-April to mid-June. Drainage totaled only
3.8”, which probably was insufficient to leach N or P from the treatments applied for
2003 into the subsurface drainage water. Nitrate-N concentrations in the drainage
averaged 14% higher (1.9 mg/L) for the urea treatment compared to manure. This was
likely due to greater residual N carryover from 2002 in the urea plots. Nitrate-N losses in
the drainage water were small, ranging from 10.2 lb/A for the manured treatment to 11.1
lb/A for urea. Seventy six percent of the annual loss occurred in May. Even though soil
test P (Bray P1) was increased from 26 ppm in the urea plots to 141 ppm in the
manured ones, losses of total P and ortho P were minimal. Total P exceeded detection
limits in 84% of the drainage water samples and averaged < 0.036 mg/L. Ortho-P
exceeded detection limits in 81% of the water samples and averaged < 0.015 mg/L.
Differences in P loss were negligible between the manure and urea treatments.
Salmonella anatum was not found in any of the water samples, indicating that this
organism either did not survive the winter or was retained in the upper layers of soil and
not transported to drainage water. Numbers of fecal coliforms (found in only the last two
sampling weeks), male-specific phages, and somatic phages were similar in both ureatreated
and manure-treated plots. This suggests these organisms did not survive over
winter in the added manure and that levels seen during the seven-week drainage period
were probably background levels.