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III. Nutrient Returns in Feces and Urine

III. Nutrient Returns in Feces and Urine

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NUTRIENT CYCLING UNDER GRAZED PASTURE



131



Table I11

Mean Nutrient Content in Urine and Feces of Lactating Cows on Seven North Carolina

Dairy Farmsa



Parameter



Urine content (g liter')



Feces content (%

fresh weight)



Percentage excreted

in feces



Total solids

Total N

Total P



6.1

11.5

0.2

2.5

7.95

0.17

0.56

1.18

0.00 1

0.002

0.006

0.0002



15.4

2.9

1.2

0.6 1

0.84

1.28

0.63

0.22

0.005

0.02

0.16

0.02



85

48

95

47

28

97

78

41

95

98

99

99



C1



K

Ca

Mg

Na



cu



Zn

Fe

Mn



Data from Safley ef al. ( 1984).



100



-



ao -



Retention



0,



Y



Milk



m



.-cE

m



60 -



Urine



c

0

c



Dung



Lc



0

Q)



40



-



CI)



m



c



E



0,



2



20 -



cr"



n

--



N



(2562)



P



(237)



K



(1720)



Ca



(726)



M9



(222)



Na



(279)



Figure 3. Percentage excretion and retention of nutrient intake in lactating dairy cows.

Nutrient element intake totals (grams per day) are shown in parentheses. (Data from Hutton

etal., 1965, 1967.)



132



R. J. HAYNES A N D P. H. WILLIAMS



animals and physiological differencesbetween animals in the percentage of

feed intake excreted and its partitioning between dung and urine (Hutton

et al., 1967; Betteridge et al., 1986). Betteridge et at. (1986), for example,

measured intake and fecal and urinary output of N, K, and P by steers

grazing high-quality pasture. They observed that urinary excretion of N

and K vaned between 81 and 137 g N day-' and 58 and 90 g K day-',

respectively. Urinary N and K concentrations were higher at night than

during the day. Similarly, fecal nutrient content varied greatly, i-e., 3662 g N day-', 12-46 g K day-', and 10-23 g P day-'. Notwithstanding

the great variability in the amounts of nutrients excreted in dung and urine

by individual animals, the general trends in the amounts and forms excreted are discussed below.



B. FORMOFRETURN

1. Nitrogen



The proportion of total N intake that is excreted and its partition between urine and feces is dependent on the type of animal, the intake of dry

matter, and the N concentration of the diet (Whitehead, 1970, 1986). For

sheep and cattle, fecal excretion of N is usually about 0.8 g N 100 g-I of

dry matter consumed, regardless of the N content of the feed (Barrow and

Lambourne, 1962; Barrow, 1987). As shown in Fig. 4, as the N concentration of sheep fodder was increased from 1.0 to 5.0%, the N excreted as

dung remained constant. Similarly for dairy cows, Lantinga et al. (1987)

found that feces contained an average of 132 g N cow-' day-' irrespective

of whether their level of intake was 450 or 775 g N cow-' day-'.

The remainder of the N is excreted in the urine and as the N content of

the diet increases, so too does the proportion of N in the urine (Fig. 4).

Barrow and Lambourne (1962) found that for sheep ingesting herbage

containing more than 4% N, 80% of the N was excreted as urine, whereas

with herbage containing 0.8% N the proportion of the excreted N present

in the urine was only 43%. In most intensive high-producing pasture

systems, where animal intake of N is high, more than half of the N is

excreted as urine. For instance, data for Netherlands dairy cows showed

that approximately 60-65% of excreted N was present in urine (Lantinga

et al. 1987; Van Vuuren and Meijs, 1987), whereas for sheep grazing

grass/clover pastures in New Zealand, 70-75% of the excreted N occurred

in the urine (Sears et al., 1948; Sears, 1950).

The average N content of feces is 2.0-2.896 N on a dry matter basis

(Floate and Torrance, 1970; Whitehead, 1970). There are small amounts



NUTRIENT CYCLING UNDER GRAZED PASTURE



133



U



Q



CI

v)



D



En



A



Q



.-r



s



2



I



o



1



Total excretion

Fecal excretion



2



3



4



5



Nitrogen content of feed (%)

Figure 4. Effect of fodder nitrogen concentration on the excretion of N by sheep. Total

excretion (feces plus urine) and excretion in feces alone are shown. (Redrawn from Barrow

and Lambourne, 1962.)



of mineral N in feces but the bulk of the N is in organic form. About

20-25% of fecal N is water soluble, representing the metabolic products of

the animal and microbial population in the gut; about 15-25% is undigested dietary N and the remaining 50-65% is present in bacterial cells

(Mason, 1969, 1979; Mason et al., 1981). Partial chemical fractionation of

fecal N from cattle by Van Faassen and Van Dijk (1987) showed an

ammonium content of 1 - 10’30, an a-amino N content of 20-35%, and an

amide N content of 10- 15%. Much of the remaining 40-70% is presumably present mainly as hexosamines (amino sugars), because these are

major components of the cell walls of bacteria (Stevenson, 1982).

The concentration of N in urine varies widely because of factors such as

N content in the diet and consumption of water, but is normally in the

range of 8 - 15 g N liter-’ (Whitehead, 1970). As the digestible N intake

increases, so too does the proportion of urine N present as urea (Topps and

Elliott, 1967). Typically over 70% of the N in urine is present as urea and

the rest consists of amino acids and peptides (Doak, 1952; Bathurst, 1952).

There is little mineralization of dietary organic N during passage through

the animal because the majority of N in both dung and urine is in organic

form. Thus, about 99% of dietary N is in organic form (Floate, I970a) and

about the same percentage of excreted N is in organic form. However, after



134



R. J. HAYNES AND P. H. WILLIAMS



passage through the animal, much of the organic N is in a more rapidly

mineralizable N form. This is because over 60% of excreted N is usually in

the form of urine and 70 - 90% of this is in urea N form. Thus, typically at

least 48% of excreted N is present as urea and this is very rapidly hydrolyzed to NHt N in the urine patch (see Section IV,C,3).

2.



sulfur



Sulfur is excreted in significant proportions in both urine and feces.

Barrow and Lambourne ( 1962) observed that the proportion of S excreted

in the urine varied from 90% for pasture herbage of high S content (0.5% S)

to 6% for herbage with low S content (0.1% S). Kennedy and Till (1981)

calculated that for Merino wethers grazing a grass/legume pasture, about

5390 of the excreted S would be in the form of urine. Similarly, our

unpublished results have indicated that for sheep grazing typical New

Zealand pastures (0.25-0.30% S), 50-70% of excretal S is voided as urine.

Although Barrow and Lambourne (1962) observed that fecal excretion

of S remains constant at about 0.11 g S 100 g-I of dry matter consumed,

other workers have found that fecal S content increases with increasing S

intake for both sheep and cattle (Bray and Hemsley, 1969; Bird, 1971;

Langlands et al., 1973; Kennedy, 1974). Most of the S excreted in feces is

in organic forms (Bird, 1971; Bird and Hume, 1971). Bird (197 1) observed

that after infusion of 35Sinto the rumen of sheep, 87 - 94% of fecal S was C

bonded, 4-5.4% was in ester sulfate form, and only 0.5 -4.0% was present

as inorganic sulfate. The C-bonded fraction consists mainly of bacterial

protein (Bird, 1971; Langlands et al., 1973).

Sulfur is present in urine in both organic and inorganic forms. The

amount of S excreted in urine is strongly related to S intake (Bird, 1971;

Kennedy, 1974). The relative proportion of the different S forms in the

urine is also dependent on the S status of the diet, and the inorganic sulfate

content of urine increases markedly as S intake increases (Bird, 1972;

Kennedy, 1974). Thus, Bird and Hume (1971) reported that the urine

excreted by sheep fed a diet supplemented with cysteine contained 84%

sulfate whereas the urine of the control animals on an unsupplemented

diet contained only 14%sulfate. Under intensively grazed farming systems,

sulfate S often represents 50-60% of urine S. The organic S content of

urine is made up of roughly similar proportions of ester sulfate and Cbonded S (Bird and Hume, 1971).

It appears that a significant amount of mineralization of dietary S occurs

during passage through the animal (Till, 1981). Sulfate S makes up a small

but variable proportion of the total S content of herbage (1 -20%) (Blanchar, 1986).If an animal excreted 60% of its S in the form of urine and 60%



NUTRIENT CYCLING UNDER GRAZED PASTURE



135



of that were in sulfate form, then 36% of ingested S would be returned to

the pasture in readily available sulfate S form. However, there are few if

any direct data to show the exact extent of animal-induced S mineralization.

3. Phosphorus



Fecal P represents the predominant pathway for animal returns of P to

grazed pasture. Only trace amounts of P are normally detected in the urine

of ruminants, although the amount of P increases slightly when P intake

increases (Braithwaite, 1976) and there can be considerable variation between individual animals (Grace, 1983). Total fecal P content is strongly

correlated with total P intake (Bromfield and Jones, 1970; Blair et al.,

1977) and thus P content of the diet. Rowarth et al. (1988) found a highly

significant linear relationship between P concentration in pasture on offer

for grazing and P concentration of the feces deposited subsequently during

a grazing period (Fig. 5).

The major form of inorganic P present in feces is dicalcium phosphate

(Barrow, 1975). Gerritse ( I 978) identified inositol hexaphosphate and

adenosine triphosphate as the main organic phosphates in pig feces. The

proportion of inorganic P in feces increases as total P intake increases

(Bromfield, 1961; Barrow and Lambourne, 1962), whereas organic P content remains relatively unchanged. Thus, Rowarth ( 1987) found that fecal



1.6



1.2



0.8



-am



/



0.4



0



a



U



01

0



1



I



0.1



0.2



I



0.3



I



0.4



Pasture P concentration



I



0.5



1



0.6



(%I



Figure 5. Relationshipbetween pasture P concentration and the fecal P concentrationof

sheep grazing the pasture. (Redrawn from Rowarth et al., 1988.)



136



R. J. HAYNES AND P. H. WILLIAMS



inorganic P contents increased with increasing rates of P fertilizer (and

increasing herbage P concentrations)and showed a similar seasonal pattern

to pasture P concentrations, whereas organic fecal P concentrations were

little affected by either fertilizer rate or season.

Dung contains a higher content of both organic and inorganic P than

does ingested pasture (Floate and Torrance, 1970; Rowarth et al., 1988),

although there can be considerable conversion of plant organic P to inorganic P during passage through the animal (Bromfield and Jones, 1970;

Floate, 1970a,b). Thus, Floate and Torrance (1970) found that feces contained 80% inorganic P but ingested plant material contained only 64%

inorganic P. Bromfield and Jones (1970) observed that in the spring, when

P content and digestibility of pasture were high, up to 80% of the ingested

organic P was mineralized via passage through the animal. They found that

by summer, when P content and digestibility had decreased, mineralization became slight.

4. Other Nutrients



Potassium is mostly excreted as urine, with only 10- 30%being excreted

in feces (Barrow, 1987). The K content of urine can vary widely (Williams

et al., 1990a) but is usually in the range 6- 1 1 g K liter-' (Hutton et al.,

1967; Ledgard et al., 1982; Williams et al., 1989). The K in urine and dung

is in ionic form and is therefore readily plant available. Davies et al. ( 1962),

for example, reported that virtually all the K in cattle dung was water

soluble and therefore readily available.

Potassium commonly represents 60- 70% of the equivalent cation content of urine. The major balancing anions in urine are C1- and HCO;,

which often represent 20- 50% and 40-70%, respectively of the equivalent

sum of anions. Urine is also the main form in which B and I are excreted

(Barry, 1983; Barrow, 1987). With diets high in S, Mo is also readily

excreted in urine, but when sheep are fed diets low in S, Mo is mostly

excreted in small amounts in the feces (Barrow, 1987).

The feces are the main excretory pathway for Ca and Mg; the concentration of these ions in urine is usually less than 1 g liter-'. The Ca and Mg

content of feces is usually in the range 1.2-2.5% and 0.3-0.896, respectively (Hutton et al., 1965, 1967; Weeda, 1977; H o g , 1981). The high

concentrations of fecal Ca and Mg result in an excess content of nutrient

cations over anions in dung. This imbalance is made up by carbonate

(Barrow, 1987). Barrow (1975) showed that Merino sheep feces had a

CaCO, content of about 1.3%, and it seems probable that much of the Mg

is also present as magnesium carbonate. Certainly, a significant proportion

of the total Mg and Ca content of feces is not readily soluble in water.



NUTRIENT CYCLING UNDER GRAZED PASTURE



137



Davies et al. (1962), for example, observed that only 62% of Mg in dairy

cow dung was water soluble whereas other workers (R. J. Haynes and P. H.

Williams, unpublished observations, 1989) found that 52% of Mg and 32%

of Ca in cow dung was readily water soluble. As a result of the presence of

calcium carbonate, animal feces usually have a pH in the range 7.0-8.0

(Underhay and Dickinson, 1978; Omaliko, 1984).

Feces represent the major pathway for the excretion of many trace

elements (e.g., Cu, Zn, Fe, Mn, Co, and Se) (Underwood, 1981; Safley et

al., 1984; Barrow, 1987) and heavy metals such as Cd (Smith, 1984) and

Pb (Quarterman, 1986). Most of such excretion consists of unabsorbed

dietary elements.



C . PATTERN

OF RETURN

The amount and availability of nutrients returned to pasture in dung

and urine are influenced not only by the amount and forms of nutrients in

excreta but also the number of excretions per day, the size of each excretion, and the surface area covered by the excreta. In addition, the pattern of

excretal return is important because the more even the pattern, the more

efficiently the nutrients are likely to be recycled within the pasture system.

1. Number, Size, and Area Covered by Excretions



The reported urination and defecation events per 24-hr period for cattle

and sheep are shown in Table IV. For cattle, a range of 8 - 12 urinations

and 1 1 - 16 defecations per day is common. Data for sheep are limited, but

a range of 18-20 urinations and 7-26 defecations per day has been

reported.

The number of defecations and urinations per day can be greatly influenced by grazing conditions and environmental factors. Barrow ( 1967),

for instance, observed that cattle grazing in rangeland conditions defecated

less than half as often per day as cattle in intensive conditions. The number

of urinations per day can be greatly influenced by water intake and therefore by the water content of the herbage (Doak, 1952), the season of the

year (MacDiarmid and Watkin, 1972b),and the weather (Betteridge et al.,

1986).

The reported mean volume of a single urination and weight of a single

defecation for cattle and sheep is shown in Table IV. Each urination event

by cattle and sheep has a mean volume of 1.6-2.2 liters and 0.10-0.18

liters, respectively. The mean weight per defecation is 1.5-2.7 kg for cattle

and 0.03 - 0.17 kg for sheep.



Table IV



Number and Weight or Volume of Defecstions and Urinations per D a y and Surface Area Covered by Excreta Produced by Cattle and Sheep



Reference



E

O0



Johnstone-Wallaceand

Kennedy ( 1944)

Castle et al. ( 1950)

Hancock (1950)

Goodall(1951)

Waite ef af. (1951)

Doak(1952)

Hardison et al. (1956)

Petersen et al. (1956)

MacLusky (1960)

Davies et al. (1962)

Wardrop ( 1963)

H o g (1968)

Weeda ( 1967)

Frame (1971)

MacDiarmid and Watkin

(1972b)



Stock type



Mean number

of defecations

per day



Beef COW



11.8



Daily COW

Dairy COW

Dairy COW



11.6

12.2

12



Daily COW

Dairy COW



-



Dairy COW

Dairy COW

Dairy COW

Dairy COW



15.4

12

11.6

12

16.1



Dairy COW

Dairy COW

Beef steer

Dairy COW

Dairy cow



Weight of single Area covered

defecation

by defecation

(kg wet weight)

(m2)

1.77



8.5

9.8



I .48

2.27

-



10.5



-



I1

13.9



2.7

1.82



-



0.06



Mean number

of urinations

per day



0.09

0.05

0.07



-



0.07



10.1

11



-



9.4

8



10



12.1

-



11



-



Volume of

single urination

(liters)



Area covered

by urination

(m2)



w

\o



Robertson (1972)

During and Weeda (1973)

Richards and Wolton (1976)

Weeda (1979)

Williams et al. ( 1990b)

Sears and Newbold (1942)

Sears(1951)

Doak (1952)

Raymond and Minson (1955)

Bromfield ( 1961)

Hemott and Wells (1963)

Frame(l971)

Robertson ( I 972)

Morton (1984)

Morton and Baird ( 1990)

J. S. Rowarth (personal

communication, 1990)

P. H. Williams and R. J. Haynes

(unpublished observations,

1990)



Dairy cow

Beef steer

Dairy cow

Beef steers

Dairy cow

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep

Sheep



Sheep



Data calculated based on 20 defecations or urinations per day.



_.



-



0.07"



-



0.09"

0.06"

0.075"

0.17



-



0.03

-



0.05

0.05



-



0.008

0.0 12

0.025

-



0.02



140



R. J. HAYNES A N D P. H. WILLIAMS



Such mean values are subject to considerable variation. For example,

urinations and defecations by individual cattle have been measured at

0.85-2.85 liters (Doak, 1952) and 0.45-6.79 kg (Goodall, 1951), respectively. Many factors can contribute to this variation in excretal output

(Barrow, 1967). The volume of urine excreted is strongly correlated with

the amount of water absorbed (Paquay et al., 1970a,b), and on hot days

water intake and urinary volumes are much greater than on mild, overcast

days (Betteridge et al., 1986). As a result, seasonal differences in urinary

volumes can occur (Vercoe, 1962). The quantity of feces produced is

greatly influenced by the quantities of feed ingested (Hutton and Jury,

1964) and consequently factors affecting feed intake will also affect fecal

output.

The surface area reported to be covered by a single urination event is

0.16-0.49 m2 for cattle and 0.03-0.05 mz for sheep (Table IV). The

variation in area is partly due to variations in the volumes excreted and

may be also partially due to difficulties in measuring the wetted area

accurately. The most accurate measurements are those that involve the use

of tracers that can be observed or chemically measured, for example, chalk

(During and McNaught, 196l), fluorescent dye (Morton and Baird, 1990),

or bromide (Williams et al., 1990b). Other factors causing variations in the

surface area covered by a urination include wind and slope (During and

McNaught, 1961), soil moisture content, and other soil physical conditions, such as water-repellent or compacted soil surfaces (Williams et al.,

1990b).

The surface area covered by individual cattle and sheep dung patches

ranges from 0.05 to 0.09 mz and 0.008 to 0.025 m2 (Table IV). Although

the range of measurements for cattle is small, that for sheep is much

greater. This reflects the difficulty of defining the area covered by sheep

dung because it is often in the form of pellets, which can be scattered over a

relatively wide area (Morton and Baird, 1990).

2. Distribution of Excretal Returns



The pattern in which nutrients are returned to the pasture in the form of

dung and urine is nonuniform. The pattern of return is greatly influenced

by stock behavior (e.g., camping of stock in small areas of the field) and

stock management (e.g., having separate fields for daytime and nighttime

grazing). Excreta can also be deposited in nonproductive parts of the farm,

such as raceways and stock-handling sheds.

Animals generally deposit more excreta on areas where they congregate

(stock camps)-beneath trees and hedges, around gateways and water

troughs, on areas away from roadsides, and on ridges and hillcrests on hill



NUTRIENT CYCLING UNDER GRAZED PASTURE



141



country farms (Hilder, 1966; Gillingham and During, 1973; Hakamata,

1980). For example, fertility transfer was studied by Hilder (1966) using

flat land stocked with Merino sheep. Because of stock camping, about

one-third of the total dung deposited was found on less than 5% of the total

area of the field. The distribution of urine appeared to follow a similar

trend. On dairy farms during winter, there can be a concentration of

excreta in areas of the paddock where hay or silage are fed out (MacDiarmid and Watkin, 1972b).

On hill country pastures the stock tend to camp on flat areas of land and

significant quantities of nutrients are transported to these areas from the

steeper slopes where the sheep graze (Gillingham and During, 1973; Gillingham et d.,1980; Saggar et d.,1988; Rowarth and Gillingham, 1990).

Measurements on hill country lands have shown that 60% of dung and

55% of urine are deposited in campsite areas, which occupy only 15 - 3 1%

of the total land area (Saggar et al., 1988). As a result of this uneven

pattern, there is a buildup of nutrients in the campsite areas and a depletion in nutrient status on the remainder of the pasture. Nutrient balance

studies on hill country pastures have shown that the annual net accumulation of nutrients on campsite areas can be about 2 10 kg N ha-', 200 kg K

ha-l, 30 kg P ha-l, and 15 kg S ha-' (Gillingham and During, 1973;

Gillingham et al., 1980; Saggar et al., 1988; Rowarth and Gillingham,

1990).

In the New 'Zealand hill country, pasture improvement by topdressing

with superphosphate is slow and withdrawal of fertilizer can lead to a rapid

decline in production (Williams and Haynes, 1990a). The major reason for

this is thought to be the continual transfer by grazing stock of P away from

the main grazing slopes to the relatively small stock camp areas (Gil1980; Rowarth and Gillingham, 1990). As stocking rate

lingham et d.,

increases there is less tendency for animals to camp and consequently there

is a more even distribution of excreta over the paddock. This leads to

reduced transfer losses of nutrients and more efficient cycling of nutrients

within the system. Thus, increasing the stocking rate through subdivision

of paddocks and the use of rotational grazing rather than set stocking can

reduce the camping effects.

On dairy farms where separate paddocks are grazed during the day and

night periods, a transfer of fertility has often been observed from day to

night paddocks (Sears, 1950, 1956; Hancock and McArthur, 1951). On

grass/clover pastures the night paddocks can become grass dominant

through high N returns and conversely the day paddocks become more

clover dominant because of lowering of the soil N status (Haynes, 1981).

Some workers have reported that a greater proportion of dung and urine is

excreted in the nighttime compared with daytime (Castle et al., 1950;



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