Determining the Environmental Impact
of
Irrigating with Swine Effluent
Charles A. Shapiro, Crop Nutrition
Bill Kranz, Biological Systems Engineering
Mike Brumm, Animal Science
Northeast Research and Extension Center-Norfolk
Bruce Anderson
Agronomy
University of Nebraska-Lincoln
Nebraska swine annually produces 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 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 is 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 1). The implication is that
producers can reduce the land base for effluent distribution by over 50% when compared to
the 200-pound removal rate for corn followed by winter rye (Table 1). 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; 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 corps grown in Nebraska.
Methods
A line source sprinkler system is 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 is designed so that the distribution patterns of both
the fresh and effluent waters produce an even amount of water application. Therefore, only
effluent rates change. Rates of effluent are chosen that provide from 0 to 140% of the
predicted nitrogen harvest for the corn-winter rye and alfalfa treatments. Irrigation of
each crop can be controlled and is applied based on soil moisture and crop nitrogen needs.
Laboratory analysis shows that the effluent contains about 80 lbs total
nitrogen, 100 lbs K2O, and 10 lbs P2O5 per acre-inch of
water. The goal is to apply sufficient effluent so that at the end of the growing season
both the corn and alfalfa will have plot areas with an excess of applied N. Sampling soil,
leachate and crop harvest takes place at five equally spaced areas across each cropping
system plot for a range of 0 to 140 percent of nitrogen application versus estimated
harvest removal.
At each sampling site a porous cup extractor is installed 6.5 feet in
the ground. The soil water solution passing the cup is sampled and analyzed for nitrate.
Other instruments determine the rate of water flow at that point. This information is used
to determine the amount of nitrate leaching at each sampling site.
The original alfalfa stand was planted in the fall of 1992. 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 non-nodulating alfalfa variety was planted
along with the conventional variety, Saranac. Unlike the conventional variety, the
non-nodulating line can not use atmospheric nitrogen for crop growth needs. Use of the
non-nodulating alfalfa allows a determination of how much nitrogen harvested in the
alfalfa came from the soil and applied effluent versus nitrogen fixed from the atmosphere
by symbiosis.
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 sufficient rainfall and the use of irrigation scheduling
the maximum nitrogen applied in 1996 was 75 lbs total nitrogen/acre. A severe winter in
1996 caused winterkill in the experiment, so the alfalfa was replanted in 1997.
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.
Soil samples taken in the spring of 1997 indicated that a buildup of
both phosphorus and potassium at the higher application rates is occurring (Table 2).
Continued buildup of soil potassium could cause soil structure problems in the future. At
some point, effluent might need to be reduced until soil phosphorus and 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. In addition,
manure storage capacity considerations may necessitate land application regardless of soil
moisture availability, thus, increasing the risk of a drainage event. In 1994 there was
drainage. Porous cup data summarized for the season indicated nitrogen leaching from all
treatments (Table 3). If 10 ppm nitrate-N concentration is the limit for acceptable
nitrate concentration then 340 lbs of nitrogen in the effluent can be applied per acre.
This would result in less than 15 lbs nitrate-N leached per acre per year. Drainage was
greater in the zero effluent treatments because less alfalfa dry matter was produced and
total water use per acre was less. Alfalfa is an excellent target crop for swine effluent
since it harvests more nitrogen then the corn-rye cropping system studied and drainage
nitrate levels can be controlled by irrigation scheduling and application rates.
Acknowledgments
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. Total nitrogen harvested after irrigation with swine
effluent as alfalfa hay and in a corn/rye system. Concord, NE.
Year |
Alfalfa type |
Nitrogen lbs/acre |
Crop |
Nitrogen lbs/acre |
1993 |
Nodulating |
230 - 250 |
Corn/rye |
154 |
1994 |
Nodulating |
680 - 745 |
Corn/rye |
213 |
1995 |
Nodulating |
337 - 520 |
Corn/rye |
162 |
1996 |
Nodulating |
270 - 383 |
Corn |
205 |
1996 |
Non-nodulating |
189 - 396 |
|
|
Alfalfa was established in 1993 and
1996.
Rye cover crop did not survive winter in 1996. |
Table 2. Effect of lagoon water on soil phosphorus and
potassium after four years of irrigation with swine effluent. Concord, NE.
Swine Effluent
Application Intensity
% of Estimated N removal |
Soil P |
Soil K |
-------ppm------- |
0 |
31 |
188 |
35 |
42 |
213 |
70 |
51 |
306 |
105 |
70 |
383 |
140 |
66 |
364 |
Soil sampled spring 1997;
corn grown 1996-97 and alfalfa 1993-95.
Effluent rates differed each year. |
Table 3. Effect of swine effluent application on
drainage, leachate nitrate nitrogen and nitrate nitrogen leached.1994. Concord, NE.
Effluent |
Nitrate-Nitrogen |
N-Rate (lb/ac) |
Drainage (inches) |
Concentration
(ppm) |
Nitrate-Leaching (lb/ac) |
0 |
6.3 |
4.9 |
7.0 |
90 |
5.7 |
8.2 |
10.6 |
210 |
5.5 |
8.2 |
10.2 |
340 |
6.3 |
10.0 |
14.2 |
450 |
4.7 |
19.9 |
21.2 |
560 |
3.9 |
37.1 |
33.1 |
Mean |
5.4 |
14.1 |
16.0 |
Figure 1. Field layout, water distribution and porous cup
installation. Concord. NE.
![](20524/manuremgmt/Image46.gif)
To Top |