Farmers know that manure is an important aspect of the crop
cycle, but it’s easy to forget that value when manure is stored and winter work
takes precedence on the farm.
Dr. Rick Koelsch, department of biological systems at the University
of Nebraska, says we’ve always recognized the value of fertility from manure,
but sometimes forget how manure enhances soil quality.
Koelsch quotes an Iowa State University article from 1907
that lauds manure as ‘one of the most effective means at the disposal of the
farmer to permanently improve his soil … its value to the soil can scarcely be
measured, for no other substance has equal power in maintaining permanent
fertility.’
“It has always boggled my mind that we’ve ever equated the
term ‘manure’ with ‘waste’ and use them in the same context,” said Koelsch.
“It’s such a tremendous disservice to manure.”
Dr. Charles Wortmann, soil scientist at the University of
Nebraska-Lincoln, addresses the ways in which manure affects soil physical
properties. “Soil is mostly inanimate,” he said, “99.5 percent on a dry weight
basis. But it does provide habitat for much plant and microbial life, and also
a lot of chemistry.”
Wortmann says some soil physical properties, such as
landscape position, texture, aggregation and susceptibility to erosion can
affect crop response to manure. Properties such as aggregation and soil/water
infiltration can also be influenced by manure.
Understanding soil associations in the landscape is
important to good soil management. “Soil texture is the result of sand, silt
and clay content of the soil,” said Wortmann. “Soil texture is fundamental to
other properties and interactions. We might expect greater manure effect on
soils that are relatively high in sand content or high in clay content.”
The concept of aggregation is important. Soil particles are
microscopic and require an electron microscope for examination. “If we didn’t
have soil aggregation, soil would be a massive, inert block,” said Wortmann.
“The size and strength of the aggregates are affected by other soil properties
such as soil organic matter (SOM) and by management practices including manure
application.”
Susceptibility to erosion is another property that
influences soil response to manure. “We’re most concerned with sheet erosion —
the gradual movement of fine particles along the surface,” said Wortmann.
“Water erosion tends to be downslope. Some (erosion) occurs due to raindrop
splash effect. Sheet erosion is the most erosive process, but it’s often not
noticed. Much more visible to us are rill and gully erosion, which occur with
concentrated flow.” Small aggregates are easily carried by wind and water,
while weak aggregates break down for easy transport and sealing of soil, which
leads to crusting and reduced water infiltration.
Wortmann cites a study during which compost was surface
applied, and in the first three years, runoff was reduced by about 60 percent.
The following four years, there was additional runoff reduction due to the
residual effect. Sediment loss was also reduced over the total seven-year
period. Wortmann says there’s approximately a 2 percent reduction in runoff and
erosion per ton, per acre per year of dry weight of manure application.
During the study, there were no effects on runoff or losses
of sediment or phosphorus comparing winter and spring application without any
incorporation. “If you have one or two moderate rainfall events that do not
cause runoff before you have a runoff event,” said Wortmann, “there is enough
reaction of the soil with manure that there is not an increase in phosphorus
loss with surface application as compared to where manure was applied.”
Manure application reduces sediment and runoff, but
increases runoff phosphorus concentration. The quantity of phosphorus loss may
be increased or decreased, depending on ‘does the reduction in runoff and
sediment loss fully compensate for increased runoff P concentration?’
Linda Schott, graduate research assistant and PhD candidate
at University of Nebraska-Lincoln, says there are many studies on the effect of
cover cropping and crop rotations on soil health, but not as much focus on how
manure affects soil health. “In general, practices that increase soil organic
matter (SOM) increase soil quality,” she said. “Manure increases soil organic
matter, so it increases soil quality.”
Schott’s research focused on summarizing short and long term
studies reporting the effects of livestock manure and municipal biosolids on
soil physical, chemical and biological properties, and indirect indicators of
soil quality such as climate resilience, crop yield and crop quality.
When soil organic carbon is increased through organic
amendments such as manure, a lot happens. Water holding capacity increases,
nutrient retention increases, and structure and biological qualities improve.
“All of these lead to a increase in soil organic matter because as biology
breaks down and consumes carbon, it stabilizes and eventually becomes organic
matter,” said Schott. “Manure increases soil organic carbon 10 to 100+ percent.
It’s variable because it depends on a lot of factors such as climate and soil
type.” Schott also found that about 20 percent of carbon in manure persists
after the first year. The carbon that remains in the soil contributes to the
buildup of soil organic matter.
In reviewing soil physical properties over time, Schott says
manure helped increase aggregate stability and soil infiltration. Water holding
capacity was variable – sometimes it increased, sometimes it decreased;
depending on soil type.
Soil biological properties are greatly enhanced by manure.
Schott says an abundance of bacteria and microbes influence soil biology.
“Included in abundance are bacteria and fungi, earthworms, nematodes and
microarthropods,” she said, adding that soil is also affected by microbial
diversity and the activity of bacteria and microbes. “In general, manure
significantly increased bacteria and fungi abundance in soil compared to
inorganic fertilizer.”
Schott says this is important because soil is 95 to 99
percent mineral particles, and depending on location, the remainder is
comprised of valuable soil organic matter. Soil organic matter includes stable
humus, decomposable plant matter, bacteria, fungi and other biological
components such as yeast, algae, protozoa and nematodes; all of which are
important for nutrient cycling and plant health and growth.
The bottom line doesn’t change. “Manure significantly
increases soil organic matter, which allows bacterial and fungal populations to
increase,” said Schott. “In comparison to inorganic fertilizer, manure
increases these populations 10 to over 100 percent. Nematodes that feed on
fungi and bacteria increased, and earth worm populations also significantly
increase.”
As composted manure piles, manure pits, pumps and spreaders
remain idle until the ground is fit and regulations allow spreading, remember
how manure is always ready to contribute to building better soil.
