SOIL MANAGEMENT FOR INTENSIVE GRAZING

K. L. WELLS and C. T. DOUGHERTY

	Recycling of plant nutrients is of major concern in managing paddocks
in pasturefields for intensive grazing.  Redistribution of nutrients present 
in fecal and urine deposits is an important issue in growing climatically and 
seasonally-adapted forage species and for efficient conversion of herbage into
animal products while adding to the sustainability of the system.  Some of 
the questions that arise in managing soils for intensive grazing are discussed 
below.

How Soil Affects Other Factors in the System

	Requirements of the photosynthetic and growth process of pasture plants 
include air, water, and nutrients ... 16 specific nutrients, 95% by weight 
originating from air and water (carbon, hydrogen, and oxygen) and 5% by weight 
coming from soil minerals and organic matter (the remaining 13 nutrients).  
With the exception of carbon, nearly all the other 15 nutrients are obtained by 
plants either from or through the soil.  To best operate any soil-plant system, 
the manager needs to know the basic physical and chemical characteristics of 
soils in terms of their capability to provide air, water, and nutrients for 
plants and to anchor and support them.  Then, armed with a thorough 
understanding of the growth habits and requirements of the plants being 
grown, he can most effectively match specific plant requirements to specific 
soil characteristics so as to render his soils as least limiting as possible 
and give plants the opportunity to strive for their productive potential.  
Climatic factors, recognizing that their range can be fairly extreme, must 
also be considered in management of each grassland ecosystem.  Seasonal 
growth/productivity patterns of grasslands are a good illustration of the 
significance of climatic factors that influence management.
	Variability of soil characteristics and microclimate results in 
several distinctive sites within and among fields that may require somewhat 
different management on the same tract of farmland.  The importance of a 
good working knowledge of soil-plant-climatic factors acting on a specific 
land tract cannot be overemphasized, because these factors exert monumental 
control over total forage production, and thereby, animal carrying capacity.
	To this basic framework of specific fields on the farm being uniquely 
managed for production of specific plants, the producer adds forage-consuming 
livestock as a means to generate added values.  Potential forage production 
and seasonal yield distribution per unit area basically controls livestock 
production per unit area, which in turn, exerts much control over economic 
returns per unit area.  This further adds to management complexities and 
results in a system of 4 major components ... soil, climate, plants, and 
animals.  For further purposes of this discussion, only the effect of 
cattle on soil management will be considered.  Their major diet consists 
of living plants, which they must harvest from the landscape, retaining 
some 65% of total biomass for their metabolism and recycling the remainder.  
The major management concepts involved are:

(1)	Manage to maximize forage production relative to soil capabilities.    
This involves establishment of field boundaries based on the potential 
productivity of the soils while maintaining soils in a sustainable productive 
state.
(2)	Manage cattle to achieve desired consumption of the forages produced 
in each field.  This requires following a management rationale that treats 
grazing cattle herds as biologic mowing machines and that utilizes sound 
grazing management to maximize utilization of the forages produced.
(3)	Evaluation of the effectiveness in managing soils, pastures, and 
livestock in this manner in terms of units of animal output (pounds of beef 
or milk) per unit of land area (acre).

The Effect of Grazing Cattle on Soil Management

	Cattle can exert both beneficial and detrimental effects on a grazed 
field.  The greatest detrimental concerns, perhaps, are the physical effects 
of treading.  The interaction of several factors will determine the amount of 
potential damage that may result.  Soil moisture content, soil physical 
properties, type of forage, stocking rate, and number of days grazed all 
interact greatly in managing paddocks to minimize treading damage.  The most 
basic concept to keep in mind is that application of weight (cattle) 
to soil which is wet, will compress more soil into smaller volumes, thereby 
increasing bulk density of soil (weight per unit volume).  The effect of 
compaction is to diminish the volume of soil in the plant rooting zone that 
can store oxygen and water (pore space), thereby limiting rooting volume of 
the plants.  The remaining pore space remaining will likely be affected by 
having relatively fewer large pores (those which store air) and 
relatively more small pores (those which hold water).  Because the effect 
of treading is greatest at the soil surface, this can lead to decreased 
soil permeability of both air and water.  Lowered rates of water 
infiltration may lead to higher rates of surface runoff 
dudring heavy rains and to greater soil erosion, a problem often related 
to overgrazing.
	Nature of the forage can also affect the rate at which treading 
damage occurs.  Established forages that have a prolific rooting system 
in the top 6 to 10 inches of soil (form a good sod), can absorb more 
treading energy than those forages that do not form a dense rooting mass, 
thereby slowing the rate at which soil damage can occur.  
However, the forage plant itself may be physically affected by treading, 
and the nature of the species (how it recovers) may also have an effect.  
Non-rhizomatous, non-stoloniferous species (e.g. orchardgrass) can more 
easily be damaged than rhizomatous/stoloniferous species (e.g. bermudagrass).  
And, of course, the stocking rate and how long the animals are kept there 
will influence the degree of treading damage.
	Management to minimize potential treading damage should be aimed 
at keeping cattle off fields when the soil is too wet, or if that is not 
possible, putting them onto well-sodded fields at a lowered stocking rate 
(more acres).  Alternatively, at such times, cattle could be moved to 
"sacrifice" fields (stubble fields/run-down pastures/drylots, etc.).
	From the positive standpoint, large quantities of dung and 
urine are deposited within paddocks as a result of intensive grazing 
management.  In addition to nutrient recycling, organic matter in the 
dung will increase the rate of organic matter buildup in 
the soil, which also leads to improved soil physical properties.

The Effect of Grazing Cattle on Plant Nutrient Recycling

	One of the obvious consequences of using cattle to harvest forages, 
so as to give them added value, is that nutrient content of ingested 
forages may be transported from some parts of a field to other parts and 
re-deposited in urine and feces.  In addressing the issue of how nutrient 
recycling by grazing cattle affects sustainability (also utilization) of 
forages growing in that field, a few behavorial aspects of grazing 
cattle behavior should be kept in mind.

	The Proportion of Nutrients Ingested by Grazing Cattle Excreted in 
Urine and Feces.

  Most estimates indicate that about 25%, 20%, and 15%, 
respectively, of nitrogen (N), phosphorus (P), and potassium (K) contained 
in forages consumed by grazing cattle is retained in their bodies for support 
of their various metabolic processes.  This means that about 75%, 80%, and 
85%, respectively, of N, P, and K passes through the animal and are excreted 
in urine and feces.  Most of the nutrients ingested are, thereby, recycled by 
the animals, perhaps many times.  On grazed fields, these recycled animal 
nutrients are, or can become, available as plant nutrients.  One 
point of concern, though, is that urination and defecation patterns of grazing 
cattle do not result in recycling of nutrients uniformly over the field.  
Grazing practices affect the distribution of recycled nutrients.  From the 
perspective of a pasture, nutrients in the soil are non-point sources while 
those in dunghills and urine spots are point sources.

	Quantification of Urine and Fecal Deposits in Pasture Fields. 
 
In order to determine recycling patterns, it is useful to know the frequencies 
of defecation and urination per day, and the area covered 
per elimination.  A rule-of-thumb value would be 10 defecations per bovine 
animal per day, each covering about 1 square foot, for a daily total of 10 
square feet per head.  Urination events are harder to quantify because they 
leave no visible short-term deposit on the surface.  Some researchers estimate 
that the daily number of urinations are about the same as defecation, and are 
deposited very similarly over the field.  There is a key difference in the 
nutrient content of feces and urine.  About half the N eliminated from the 
animal's body is in urine and the remainder in feces.  This proportion can 
increase to nearly two-thirds in urine if cattle are grazing on a high 
N-containing forage (grass, well-fertilized with N, or legumes) which provides 
excessive amounts of their N requirements.  Nearly all the N in urine is 
present as urea, which when deposited onto the field, behaves just as 
commercial urea fertilizer (some surface volatilization occurs).  The N content 
of feces exists in various organic structures (including microbial and plant 
protein), some of which break down fairly quickly to ammonium N (NH4+), and 
others which are very resistant to decomposition, and may remain in the soil 
for weeks, months, or even years.
	In contrast to N, most of the P is contained in feces, largely bound in 
organic compounds, which, even though they are not immediately available for 
plant uptake, contribute very effectively to increasing soil test levels of P.  
Consequently, all the P in feces is credited to soil buildup of available P 
within a year after deposition. 
	And, in contrast to P, most of the K passing through the animal is in 
the urine.  It is as effective as fertilizer K and is immediately available for 
plant uptake after deposition.
	Factors Affecting Patterns of Fecal and Urine Deposits.

  Several factors 
have been shown to affect the pattern of nutrient recycling by grazing cattle. 
 Perhaps the most notable of these are landscape features, such as shade, field 
shape, and topography of the landscape.  Shade tends to promote loafing areas 
for cattle, so that more defecations and urinations occur in shaded than 
unshaded areas.  Similarly, the presence of depressions on the landscape, such 
as swales, hollows, draws, etc., results in more animal use of such areas, with 
resulting increased urination and defecation patterns there.  It has been 
reported that soil test K levels in these special 
areas increased 4 to 10 fold over that from the remainder of the field.
	Cattle also tend to defecate more during the night in areas where they 
rest, than during the day while they move about and graze.  However, they tend 
to urinate more frequently during the daytime.  These differing patterns are 
related to the rapid rate of absorption and excretion of water, compared with 
the slow rate of passage of undigested plant herbage through the digestive tract, 
and may also contribute to uneven distribution of recycled plant nutrients.
	Source of water is another factor having major impact on elimination 
patterns by cattle.  Concentrations of feces and urine are greater around water 
sources.  Supplemental feeding sites (hay, mineral, and concentrate feeders) 
within the field have a similar effect.  One study of intensive rotational 
grazing practices showed that if animals have to travel through a lane at 
distances greater than 450 feet to get to water, nearly one fourth (22%) of 
the total manure deposits were made in the water lane.
	Another factor impacting patterns of dung and urine deposition is 
stocking density.  The more animals per acre, the more uniform will be the 
distribution.  Duration of grazing must also be considered.  If the field size 
is large enough to provide several days, or weeks, of grazing by the number 
of animals present, manure deposits will not be as uniform as if field size 
is restricted to provide only a few days grazing.  Missouri studies suggest 
that if paddock size or animal numbers are restricted to provide less 
than 6 days feed to the number of cattle present, and if water is available 
in the paddock, manure distribution will be fairly uniform over the paddock.  
This would represent the optimum situation for managing grazing cattle to 
recycle nutrients uniformly over the grazed area.  Otherwise, and to varying 
degrees, as influenced by the factors discussed above, recycling will result 
in a net movement of nutrients from within the field to areas where cattle 
congregate, thereby non-uniformly re-distributing them and increasing the 
potential for increased nutrient, fecal material, and fecal 
bacteria runoff into surface water sources, following rainfall.

	Are Commercial Fertilizers Required on Fields Grazed by Cattle?  

If fertility levels of fields are low, it should be obvious that grazing will 
not raise overall fertility levels.  It is quite likely, though, at low 
fertility and at low stocking rates, that grazing cattle will concentrate 
nutrients in special areas of the field, with the result that soil 
fertility in some areas of the field may be depleted while other areas are 
enriched.  On the other hand, if soil fertility is or has been built to 
desirable levels (medium to high) and if management is designed to concentrate 
animals onto areas with no more than a few days (less than 6) of grazing 
(intensive grazing), and are provided water within the 
area being grazed, recycling of nutrients will be fairly uniform, and 
existing fertility levels may be maintained for several years before 
additional commercial fertilizer is needed.  Above and beyond the uniformity 
of defecation and urination which can be obtained by confined, mob grazing of 
a few days duration, additional benefits in uniformity can be attained rather 
economically by use of a chain drag harrow, perhaps following clipping of 
ungrazed stubble, within a few days after removing cattle from the 
paddock.  A soil testing program of sampling each paddock to a depth of 4 
inches every 3 to 4 years should be sufficient to monitor soil fertility 
levels so as to maintain sustainability of the paddock.
	For larger fields with low grazing pressure and in which areas exist 
where cattle congregate, avoid sampling (or at least sample separately) 
within and around such areas because they will test higher in P and K than 
the remainder of the field.  Also, avoid spreading P and K fertilizers in 
such areas.  Confine P and K applications to the lower testing areas of the 
field.  For legume-grass mixtures, manage fertilizer applications to favor 
legumes, rather than grasses.  This means development of 
medium to high soil test levels of P and periodic liming to maintain soil 
pH around 6.5.  Urination and defecation by grazing livestock has little 
effect on soil acidification.


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