- Intensification of livestock operations has enhanced the problem
of animal waste disposal. Since high application rates of the
waste to soils would help elevate the problem, a study was established
to determine water quality as affected by applications of dairy
waste slurries to tiled and untiled soils.
Dairy cow waste slurries were applied to tiled and untiled
Amity sicl soil at rates of 0, 400 and 1000 gallons per plot or 0, 3.0
and 8.0 acre-inches per acre. The waste was applied during the
winter, summer and fall of 1971. In a subsidiary study several
acre inches of dairy waste slurry were applied to an agricultural
tiled field of Amity silty clay loam (sicl) soil during the winter of 1972.
Dairy cow waste slurries, tile drain effluents and groundwater
were assayed for total solids, total-N, total P, NH₄-N and NO₃-N
content. Water samples were collected prior and subsequent to
waste application. During the winter application period the NH₄-N concentration in
both groundwater and tile effluent was < 50 ppm and with time
decreased to <10 ppm. The NH₄ -N concentration in the applied
waste slurry averaged 100 ppm. The NH₄-N concentration in tile
effluent and groundwater from control plots was <1 ppm. The total
-N concentration in the tile effluent and groundwater were approximately
twice the assayed NH₄-N concentration.
During the summer application period, the NH₄-N concentration
in tile effluent and groundwater was higher than in the winter
months after the waste slurry application. The Amity sicl soil
cracked severely during the summer months and allowed some
preferential flow of the waste directly to the tile drains or groundwater
The NO₃-N concentration in the effluent and groundwater
increased from <1 ppm in the winter to 9 ppm in the summer due to
the increased microbiological activity.
The total P fixed by the undrained Amity soil decreased from
90% during the January application to 40% during the May 1971 application.
The total P fixation by the undrained Amity sicl soil was 50
to 90% for both the sodded and desodded plots during the summer
application period. The total P fixed by the tile drained Amity sicl
decreased from 80% in January to 40% in February and remained
constant for the duration of the winter application period. The percent total P fixation for both the medium and high application rates
was similar, The total P fixed by tile drained Amity sicl soil during
the summer waste applications was similar to the low percent total P
fixation of the winter application period. The low percent total P
fixation resulted largely from minimal soil-waste contact time due to
cracks in the undisturbed soil, channel formation in the tile trench
backfill and the high hydraulic conductivity of the Amity sicl soil.
The fall, 1971 waste applications' included soil moisture criteria
to determine waste application frequency. The use of soil moisture
criteria for waste applications did not improve water quality; but,
water quality was improved when the surface soil became sealed to
thus reduce the water percolation rate and extend the soil-waste
Nitrogen and P accumulated in the surface 12 inches of the
Amity soil; however, the accumulations were lower than would be
expected from the large elemental applications. Only 260 pounds
of total-N per acre accumulated in the surface 12 inches of the Amity
soil after receiving over 4400 pounds of total-N. Considerable NH₃
was probably lost at the time the waste slurries were applied.
Besides NH₃ volatization, NO₃-N
leaching, gaseous losses of N₂ or
nitrogen oxides and the waste slurries rapid percolation through the
soil contributed to the low total-N accumulation. The total-N,
total P and NH₄-N level in the subsoil, 22 to 28 inch depth, remained
relatively constant. The NO₃-N concentration in the 0 to 12 inch layer of tile
drained Amity soil increased from <1 ppm during the winter to 35
ppm in the summer and then decreased to <10 ppm in the fall. The
NO₃-N concentration in the undrained Amity soil was 5 to 10 ppm
greater than in the tile drained plots.
Approximately 80% of the applied total-P was fixed in the 0 to
12 inch layer of the Amity sicl soil. The percent total-P fixed by
the soil very likely would be higher if P accumulations in the entire
soil profile had been considered.
When the waste slurries were applied to the agricultural tiled
soil, the soil removed 95 to 99% of the N and P. The total-N concentration
in the ground water was < 10 ppm. The NH₄-N, NO₃-N and
total P concentrations in the groundwater were generally < 2 ppm.
Although very little difference in water quality occurred
between sodded and desodded plots in this research project, sodded
application areas would increase retention and infiltration of waste
slurries on steep slopes.
A. recommended application rate to agricultural tiled soils
would be one to two acre-inches of <2% total solids waste slurry
applied every three to four weeks. This application rate would
prevent formation of a manure thatch and would reduce surface runoff
A possible crop rotation program of corn, barley and pasture could be used. Corn and grasses are high utilizers of N. Corn
utilizes approximately 400 pounds of N per acre. The net accumulation
of total-N, before the crop is planted, ideally should not exceed
400 pounds of N per acre.
The application of waste slurries during the summer to soils
that have a moderate to high content of shrink-swell clays is not
suggested because of rapid waste percolation through the soil cracks
into groundwater with minimal soil-waste contact.