Figure 1. Dan Anderson, Assistant Professor Agriculture and Biosystems Engineering and Agriculture Engineering Extension Specialist of Iowa State University, performs manifold testing on Bazooka Farmstar’s timed tank manifold at a field day hosted by Eldon C. Stutsman in Hills, IA during Summer 2017.
Injecting liquid livestock manure into the land to restore nutrients that are lost during
harvest, is a growing trend across the nation and a practice that is well-established in our
home state of Iowa.
A mass of factors plays a role in the effectiveness of the application, but in this instance,
we turn our focus to the distribution of the liquid manure through the manifold that is
found on tool and tank bars used in the injection process.
The Iowa State University Extension and Outreach has mimicked a coefficient of variation
(CV) statistical test, used by the American Society of Agriculture and Biological Engineers
(ASABE) to measure the uniformity of pesticide sprayers, to similarly the uniformity of
liquid manure application manifolds. Figure 1 below, constructed by the ISU Extension
and Outreach, shows the manifold distribution operation at a high level.
Figure 2. On-board application rate controls and distribution of liquid manure through a seven-outlet manifold. (Sketch is not to scale)
Proper nutrient placement is the ultimate goal of any manure injection application, and
when done correctly, reaps the greatest benefit for the everyday farmer in the numbers
of next year’s crop yields.
Equal distribution of manure across the tool or tank bar, is an important element in
achieving proper nutrient placement throughout the entirety of a field. In a perfect
application, the delivery of manure would be equal throughout each port with zero
variation. Due to land, manure and equipment diversification, entirely equal distribution is
nearly impossible to achieve. Applicators should strive for uniformity, with a very low
variation rate across the bar. (Ideally achieving variation below 10%)
The ISU Extension and Outreach has evaluated test results and determined which
manifolds on the market for dragline and tank applications alike, provide the lowest
coefficient variation and likewise, the most accurate nutrient placement.
Figure 3. Bazooka Farmstar Dragline Manifold
Figure 4. Bazooka Farmstar Tank Manifold
Size, port number, inlet location, etc. varies from manufacturer to manufacturer, producing differing performance capabilities
Manure applicators apply liquid manure at a specific gallon per acre (GPA) that is heavily
based on the following:
This measure (GPA) provides measurement of the amount of manure that is being
applied per acre, however, it does not warrant the uniformity of the manure within each
Picture this: an applicator has an 8-port manifold, 2 of which, lack outflow throughout
several passes of a field before the applicator realizes an issue. The desired GPA was
achieved, but the 6 ports with outflow will have an excess of the desired amount of
manure injected, while the other 2 go without manure injection entirely. This scenario will
result in a very high CV, ununiform application and an unideal field like the photo below.
In conjunction, a producer may incur an additional expense to apply commercial fertilizer
which can lead to nutrient accumulation in the soil and consequently, water quality
Result of uneven nitrogen fertilizer application
The Iowa State University Extension and Outreach conducted CV testing on six different
manifolds in 2015 & 2016, using a drive speed of 5mph with water from rural water supply
or a farm pond. The water from each manifold discharge hose was collected in a 55-
gallon drum, using tractor control settings for application rates ranging from 2,000 to
6,000 GPA (Figure 1).
Each of the 6 manifolds tested had different shapes and number of outlets, as well as
different inlet locations. The differentiated designs created an independent coefficient of
variation across all manifolds. By design, certain manifolds are capable of achieving the
ideal, 10% CV or less running low application rates, while others are not. The results of
this test indicate that low application rates with a CV of less than 10% are feasible with
appropriate manifolds, which proves especially effective for liquid swine manure
applications. Smaller manifold chambers, along with a reduced inlet-to- outlet area ratio,
appeared to aid the achievement of a lower CV.
The discharge hoses that span from the outlet ports to the injection units loop on some
manifold set-ups. The manifolds with loops in the discharge hose throughout the
configuration were inspected during testing. The study found that the “sags” in the
discharge hose can hold liquid from previous runs that can create a pressure plug,
preventing the outlet to discharge. This again, results in an ununiform application.
Mounting the manifold at the highest possible location can provide adequate elevation to
minimize hose loops contributing to the increased CV.
Manifold distribution is not the only factor in a perfect liquid manure application, but it
plays an enormous role in the end result. It can be concluded that it is important to use
caution when choosing the appropriate manifold for your operation in order to achieve
the lowest CV possible. Each manifold ISU tested proved its performance capabilities
and limitations in terms of the GPA each can sufficiently support.
In a general sense, the coefficient of variation can be improved by increasing the drive
speed of your tractor, which will in turn increase the flow rate through the manifolds
chamber. (See figure 5 below for graphed results of the tests conducted by ISU below)
Strive for equal distribution and uniformity, it will thrill your local farmers.
Figure 5. Coefficient of variation for the nine different manifolds tested using a drive speed of 5 mph by September 30, 2016. Coefficient of variation (%) is plotted on the y-axis and application rate in gallons per acre is plotted on the x-axis. (Manifold 7 – Bazooka Farmstar dragline manifold | Manifold 2 – Bazooka Farmstar tank bar manifold)