IRRIGATING WITH SWINE EFFLUENT
Bill Kranz
Extension Irrigation Specialist
University of Nebraska
Norfolk, Nebraska
Voice: 402-370-4012
Fax: 402-370-4010
Email: wkranz@unlnotes.unl.edu
Charles Shapiro
Extension Crop Nutrition Specialist
University of Nebraska
Concord, Nebraska
Voice: 402-584-2803
Fax: 402-584-2859
Email: cshapiro@unlnotes.unl.edu
INTRODUCTION
`
Nebraska swine annually produced manure containing 40 million pounds of
nitrogen. The trend toward increased concentration of animals in large
production units makes it difficult to find enough available land for economical
manure distribution at agronomic application rates. In Nebraska, pigs per farm
have increased from 250 in 1982 to 507 in 1997. As the number of pigs per
enterprise has increased, there has not been a corresponding increase in the
number of acres per enterprise available for land application and crop utilization
of the stored swine manure.
The goal of our research was to evaluate alfalfa as a nitrogen sink for swine
effluent. Data from our experiment has shown that alfalfa receiving 600 pounds
of swine effluent nitrogen per acre removed about 100 pounds more nitrogen per
acre than alfalfa receiving no swine effluent. Established, irrigated alfalfa can
remove more than 700 pounds of nitrogen per acre in the harvested hay (Table
4). The implication is that producers can reduce the land base for effluent
distribution by more than 50% when compared to the 200 pound removal rate for
corn followed by winter rye (Table 4). This could be beneficial to producers who
do not have sufficient land to apply effluent at agronomic rates to corn or other
row crops.
Additional advantages to alfalfa are: it covers the ground all year round which
reduces the erosion potential; the nitrogen use curve is more constant through
the season than for annual crops; uptake of phosphorus and potassium are
relatively high; effluent application can occur at times that are not possible in a
corn system; and alfalfa is deep rooted and can scavenge nitrogen from deeper
in the soil than most other crops grown in Nebraska.
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METHODS
A line-source sprinkler system was used to distribute a range of effluent rates to
both alfalfa and corn. Figure 1 shows the distribution of the effluent and of fresh
water. The experiment was designed so that the distribution patterns of both the
fresh and effluent waters produce an even amount of water application.
Therefore, only effluent rates changed. Rates of effluent were chosen that
provided from Oto 140% of the predicted nitrogen harvest for the corn-winter rye
and alfalfa treatments. Irrigation of each crop could be controlled and was
applied based on soil moisture and crop nitrogen needs with the caveat of
needing to apply up to 600 lb-N per acre near the centerline.
Laboratory analysis showed that the effluent contained about 90 lbs. total
nitrogen, 100 lbs. K20, and 10 lbs. P205 per acre-inch of water (Table 1). The
goal was to apply sufficient effluent so that at the end of the growing season both
the corn and alfalfa would have plot areas with an excess of applied N. In 1994,
soil samples, leachate and crop harvest took place at 6 equally spaced areas
across each cropping system plot for a range of Oto 140 percent of nitrogen
application versus estimated harvest removal.
At each sampling site a porous cup extractor was installed 6.5 feet in the ground
(Insert, Figure 1). The soil water solution passing the cup was sampled and
analyzed for nitrate. Neutron readings were recorded to determine the rate of
water flow past the 6.5 foot depth. This information was used to determine the
amount of nitrate leaching at each sampling site (Table 3).
The original alfalfa stand was planted in the fall of 1992 and replanted in 1993. In
1996 the corn-rye and alfalfa areas were switched. However, the gradient of
increasing levels of swine effluent remained the same. In 1996, a nonnodulating alfalfa variety (Saranac) was planted along with the conventional
variety and the number of subplots was reduced from 6 to 5 (Figure 1). Unlike
the conventional variety, the non-nodulating isoline could not use atmospheric
nitrogen for crop growth needs.
In each year, alfalfa samples were collected from each subplot using a flail-type
forage harvester. Sampling protocol was designed to mimic a range of harvest
management schemes. Thus, each replicate contained subplots that were
harvested 3x, 4x, or Sx times per year. The 3x treatment was harvested at full
bloom and the 4x and Sx at tenth bloom. The 5x treatment had the 5th harvest
after a killing frost. Plant dry matter was collected from a 30 square foot area
and used to estimate total dry matter production for the treatment. Laboratory
analysis provided the N content in each alfalfa sample.
278
1996 was 75 lbs total nitrogen/acre. Actual N removal in the forage was within
10 lb-N per acre for the non-nodulating and nodulating isolines (Table 4).
•
A severe winter in 1996 caused winter kill in the experiment, so the alfalfa was
replanted in 1997. Subsequent work continues to support the notion that nonnodulating alfalfa will produce forage of the same quality and quantity as
nodulating alfalfa if N is applied to meet crop needs. Failure to apply sufficient N
tends to reduce plant stand by allowing weed competition, and it appears to
increase the potential for winter-kill in the isoline we tested. Plant breeding
efforts will likely reduce the winter-kill problems.
DISCUSSION
Documenting the environmental effects of swine effluent application is the major
objective of this research. Two indicators have been monitored 1) soil nutrient
levels in the spring and fall and 2) nitrate leaching.
Using book-values, 9 tons of alfalfa would remove about 500 lb-N, 135 lb-P205,
540 lb-K20 per acre. In 1994, laboratory analysis of the dry matter indicated that
about 700 lb-N were removed in the forage. Field data indicate that alfalfa can
remove more applied N than a more traditional crop like corn. Thus, the lagoon
water can be distributed over fewer acres of land when alfalfa is used as a
scavenger crop.
Soil samples taken in the spring of 1997 indicated that a buildup of both
phosphorus and potassium at the higher application rates was occurring (Table
5). The phosphorus levels were increasing despite removal at rates up to 50 lbP205 per acre greater than the application rate. Research evaluating the long
term impacts of manure applications have suggested that manures high in NH4-N
can change soil pH sufficiently to allow additional phosphorus to enter the
available pool from the organic pool. In addition, increased microbial activity
tends to increase P mineralization rates. Both of these factors are likely present
in fields where swine lagoon water is applied. Thus, long term application of
swine lagoon water may need to account for the additional P in the management
plan.
Potassium application was in excess of the removal rate so a buildup was
anticipated. However, continued buildup of soil potassium could cause soil
structure problems in the future. At some point, effluent might need to be
reduced until potassium levels decrease.
Leaching of nitrate may occur when drainage through the soil profile occurs.
When irrigation scheduling techniques are used correctly, drainage is held to a
minimum. When rainfall is greater than crop use, drainage is inevitable.
Research using commercial fertilizer applications tend to suggest that off-season
losses are a definite concern in Nebraska. So even if good irrigation
279
RESULTS
In 1994, dry matter production ranged from 9 to 10 tons of alfalfa per acre.
Thus, the addition of 560 lb-N resulted in an additional ton of dry matter
production (Table 2) and a slight increase crude protein of about 1.5% (data not
shown). Yields were highest when the alfalfa was harvested 4 times per season
at approximately 10% bloom. Apparently, the harvest after a killing frost reduced
yields for the 5x treatment.
Subsurface drainage was greater than would be typical of a field managed using
irrigation scheduling techniques (Table 3). This was due in large part due to
near normal precipitation and below normal temperatures so little irrigation was
necessary. Drainage ranged from 6 inches in plots receiving no lagoon water to
4 inches in plots receiving 560 lb-N. This reduction· in drainage is attributed to
the additional production (1 ton/ac) resulting from the lagoon water application.
The N concentration of soil water at the 6.5 foot depth had flow-weighted
average concentrations that ranged from 4.9 ppm in plots receiving no lagoon
water to 37 ppm where 560 lb-N were applied (Table 3). The acceptable N
concentration is up for discussion, however, if the maximum contaminant level
for drinking water of 10 ppm N03-N is used, our data would suggest that
approximately 340 lb-N could be safely applied to irrigated alfalfa. We were not
in a position to estimate losses of N to the atmosphere during and after
application, but published values are typically greater than 30%. Assuming 30%
application loss, the actual removal in the alfalfa dry matter would be close to
235 lb-N. This level of utilization agrees with laboratory research from Minnesota
that suggests that alfalfa will preferentially fix up to 2/3 of the N removed in the
forage. This happened despite N applications that would have met crop needs.
Thus, a high percentage of the N contained in the alfalfa forage will continue to
be fixed from the atmosphere.
Nitrate leaching losses ranged from 7 to 33 lb-N per acre (Table 3). Though a
zero tolerance rule could be applied, these levels are within the range recorded
for crops fertilized with commercial fertilizer. Leaching losses would be reduced
if subsurface drainage could be reduced by irrigation management strategies
that allow plants to lower soil water content near the end of the season. Another
beneficial practice would be to leave room in the soil profile for rainfall by
accounting for the deep rooting depth of the crop. Both of these practices were
not possible during this research due to timely rainfall events and the need to
apply 6-7 inches of lagoon water.
In 1996, the non-nodulating alfalfa nitrogen harvest was 70 percent of the
nodulating alfalfa at the zero effluent rate, but equal to the nodulating alfalfa at
the higher nitrogen rates. Due to it being a crop establishment year, sufficient
rainfall, and the use of irrigation scheduling, the maximum nitrogen applied in
280
.
`b
management is practiced, over application of N may lead to leaching losses.
This is of particular significance where manure storage capacity considerations
necessitate land application regardless of soil water availability, thus, increasing
the risk of a drainage and N leaching event.
Application of swine effluent to alfalfa shows considerable promise based on the
results of this research. Alfalfa uses large amounts of nutrients contained in
animal manures and provides ample opportunities to spoon feed applications in
much the same was as commercial fertilizers. Further development of the nonnodulating alfalfa isolines will enhance the value of alfalfa as a crop suitable for
use in crop rotations used by animal producers.
Acknowl
函
gments
Research funded by Burlington Northern Endowment. The non-nodulating alfalfa was
donated by Joanne Lamb at the USDA Dairy Forage Laboratory in Minnesota. Previous
funding for this project included support form the Nebraska Pork Producer's Council and
the UNL Water Center.
Table 1.
Nutrient concentrations of monthly water samples collected from
the swine lagoon in parts per million. Concord, NE.
No.
Sample
Year
Total
N
NH4-N
一
民
P20s
s
O
--.----
ppm
Zn
Na
Ca
Mg
----..-一
1993
12
400
310
9.8
401
4.1
0.13
103
59
23
1994
12
420
371
12.8
554
2.1
0.14
114
65
26
410
340
11 .3
472
3.1
0.13
108
62
24
mean
Table 2.
Mean dry matter yields as affected by swine effluent application
in1994. Concord. NE.
Alfalfa Harvests Rer Season
Effluent
N Rate
lb N / acre
4x
3x
I —·一-
Mean
5x
tons OM per acre
------..------一
。
8.5
9.3
8.9
8.9
90
8.3
9.7
9.1
9.0
210
8.4
10.4
9.5
9.4
340
8.4
10.0
9.7
9.3
450
8.7
10.7
10.0
9.8
560
8.8
10.1
10.3
9.7
281
Table 3.
Total nitrogen harvested after irrigation with swine effluent as
alfalfa hay and in a corn/rye system. Concord, NE.
Year
Alfalfa type
Nodulating
Nodulating
Nodulating
Nodulating
Non-nod ulating
1993
1994
1995
1996
1996
Nitrogen
lbs/acre
230 - 250
680- 745
337 - 520
270 - 383
189 - 396
Crop
Nitrogen
Corn/rye
Corn/rye
Corn/rye
Corn
lbs/acre
154
213
162
205
Alfalfa was established in 1993 and 1996.
Rye cover crop did not survive winter in 1996.
Table 5.
Effect of swine effluent application on drainage, leachate nitrate
nitrogen and nitrate nitrogen leached. 1994. Concord, NE..
Effluent
N-Rate
Nitrate-Nitrogen
Concentration
Drainage
(inches)
6.3
5.7
5.5
6.3
4.7
3.9
5.4
(lb/ac)
。
90
210
340
450
560
Mean
Nitrate-Leaching
(lb/ac)
7.0
10.6
10.2
14.2
21.2
33.1
16.0
(ppm)
4.9
8.2
8.2
10.0
19.9
37.1
14.1
Effect of lagoon water on soil phosphorus and potassium after four
years of irrigation with swine effluent. Concord, NE.
Table 4.
Swine Effluent
Application Intensity
SoiI P
Soil K
% of estimated N removal - p p m 188
213
306
383
364
計 7066
11
3142
05O5O
37O4
Soil sampled spring 1997; corn grown 1996-97 and alfalfa 1993-95.
282
Figure 1.
Field layout, water distribution and porous cup installation. Concord.
NE.
p
c
Top view of plot layout, showing sampling
sites and water distribution system.
Nodulatlng AH'alfa
Sampling Levels
.。
/'
Sprlnklen
35./o
.。
70%
35%
…
………
户.
105%
…
……
U-om
·J=cup
户.
105%
Non-nodulatlng Alfalfa
Sampling Levels
g
』]
ir
eOn
.
..
♦
70./4
…
Blowup drawing of instrume
矗 tion
installed at each samplinc leveL
4
Water and effluent water application patterns
Total
W:
正
』
rApl
.. .. ..... . . . .. . . . . . . .
Fresh
Water
Line
二「
E ffluent
Water
Line
Field plot detail of instrumentation and water
application system for fresh and effluent waters.
283