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J Sci Food Agric 1998, 76, 289È297
Eþects of Sodium and Potassium Fertilisers on the
Composition of Herbage and its Acceptability to
Dairy Cows
Paul C Chiy,” Abdul-latif A Al-Tulihan, Mohammed H Hassan and
Clive J C Phillips*¤
School of Agricultural and Forest Sciences, University of Wales, Bangor, Gwynedd, UK
(Received 20 January 1997 ; revised version received 14 May 1997 ; accepted 30 June 1997)
Abstract : Fertilisation of herbage with Na can increase acceptability to cows, but
the inÑuence of fertiliser rate and fertilisation by K is unknown. In experiment 1,
ten cows were grazed on pasture plots that had just been fertilised with 0È132 kgNa ha~1 (current Na) and had received 0È64 kg-Na ha~1 in the previous grazing
season (residual Na). Herbage Na concentration increased in proportion to
current Na from 2É7 to 4É9 g-Na kg~1 dry matter (DM) and also increased with
increasing residual Na from 2É2 to 4É5 g-Na kg~1 DM. Herbage K concentrations were low (10 g kg~1 DM at 0 kg-Na ha~1) and were only slightly reduced
by Na fertiliser. Herbage Mg and Ca concentrations and DM digestibility were
maximum at 66È99 kg-current-Na ha~1. Cows grazed current-Na-fertilised plots
to a lower height and spent more time grazing them. In experiment 2, pasture
plots received no fertiliser, low and high isomolar and independent applications
of Na and K or a combination of the two. The herbage was more mature than in
experiment 1 and Na concentration of the herbage without Na fertilizer was high
(5 g kg~1 DM). Na fertiliser, therefore, only slightly increased Na concentration,
more in clover than in grass, and had little e†ect on K concentration. K fertiliser
increased K concentration from 16 to 20 g kg~1 DM and reduced Na concentration to 3É5 g kg~1 DM. Sodium fertiliser, therefore, only increased the acceptability of herbage to cattle when herbage Na concentrations were initially low
(less than 5 g kg~1 DM) and were increased substantially by the application of
the fertiliser. ( 1998 SCI.
J Sci Food Agric 76, 289È297 (1998)
Key words : herbage ; fertiliser ; palatability ; sodium ; potassium ; ryegrass ; white
clover
INTRODUCTION
the plant. The e†ects on magnesium (Mg) and calcium
(Ca) concentrations and dry matter digestibility (DMD)
vary between the di†erent plant fractions and depend
on initial herbage Na concentration (Chiy and Phillips
1996, 1997).
At herbage concentrations between 2É9 and 4É9 g-Na
kg~1 DM cows graze for longer on Na-fertilised pastures (Chiy et al 1993a) and prefer them to unfertilised
pasture, leading to increased milk production (Chiy and
Phillips 1991). Apart from this, no information is available on the e†ect of Na or K concentrations in pasture
on the grazing preference of dairy cows. Schneider et al
Mammals have an instinctive appetite for sodium (Na)
(Richter 1956), and the ability to taste it is inherent in
ruminants (Denton 1966). Applying Na fertiliser to
herbage increases herbage Na, but decreases its potassium (K) concentration (Chiy and Phillips 1993). Na
and K, therefore, are competitors for absorption sites in
* To whom correspondence should be addressed.
” Present address : Department of Clinical Veterinary Medicine, University of Cambridge, Cambridge, CB3 0ES, UK.
289
( 1998 SCI.
J Sci Food Agric 0022-5142/98/$17.50.
Printed in Great Britain
P C Chiy et al
290
(1986) found that the DM intake of cows o†ered Nasupplemented silage was greater at 5É5 than at 8É8 or
1É8 g-Na kg~1 DM. The extent to which herbage Na
concentrations can be increased by Na fertiliser without
adversely a†ecting herbage nutrient concentration has
not been reported previously, but it is relevant when Na
fertiliser is used to correct Na deÐciencies in grazing
ruminants. Recent genetic improvements that have
increased dairy cow milk yields, and hence the output of
Na in milk, may predispose dairy cows to an increased
risk of Na deÐciency (Hemingway 1995). Both pregnancy and lactation increase the physiological requirement for Na, and restricted DM intakes at the end of
pregnancy limit voluntary Na intake at this time (ARC
1980).
The objective of the present experiments was to
examine the e†ects of Na fertiliser application with and
without K fertiliser on herbage chemical composition
and the grazing preference of pregnant dairy cows.
MATERIALS AND METHODS
Experimental design
Experiment 1
Ten non-lactating, autumn-calving British Friesian
cows with similar calving dates, lactation number, live
weight and milk yield were selected at drying o† for
grazing on the treatment area. This was a 3-ha Ðeld of
predominantly perennial ryegrass (L olium perenne L cv
S23). Herbage comprised 964 g perennial ryegrass per
kilogram herbage freshweight. The area was divided
into Ðve main plots of equal area (0É6 ha), identiÐed
with corner posts (Fig 1). Water was available in all of
these areas.
The following Na fertiliser treatments were allocated
at random to the experimental plots : 0 (nil treatment),
33 (low treatment), 66 (medium treatment), 99 (high
treatment) and 132 (very high treatment) kg-Na ha~1
(Fig 1). Fertiliser Na was applied on 17 July 1991 as
commercial granular NaCl (994 g-NaCl kg~1 fertiliser
applied) with a 3-mm particle size. Application was by
broadcasting with a Vicon land-geared fertiliser spinner,
with a 5 m spread that ensured minimum inaccuracy at
edges and corners of the plots. There were no bu†er
zones between plots. All plots additionally received
85 kg-N ha~1 in March, 65 kg-N ha~1 in April and
May and 85 kg-N, 43 kg-P O and 85 kg-K O ha~1 in
2 5
2
June. Prior to the experimental grazing period between
25 July and 25 August the entire area had been uniformly grazed by dairy cows. Each main plot was
further subdivided by corner posts to indicate the three
equal areas of residual Na treatments (1 ha
treatment~1) applied in the previous year (Fig 1). These
consisted of 0 (RN), 32 (RL) or 64 (RH) kg-Na ha~1,
applied as NaNO in Ðve isonitrogenous applications at
3
monthly intervals in the year prior to the current trial,
beginning from 9 April 1990 (Chiy and Phillips 1993).
All plots had received a uniform management regime
and fertiliser application of 300 kg-N, 30 kg-P O and
2 5
40 kg-K O ha~1 yr~1 in the previous 7 years before
2
1990.
Experiment 2
Twelve cows were selected as in experiment 1 for
grazing on a 3É5-ha pasture area of similar botanical
composition. The area was divided into 14 equal plots
of 0É25 ha each, identiÐed with corner posts, and allocated at random to seven fertiliser treatments : no fertiliser, Na low rate (40 kg-Na ha~1), Na high rate (80 kgNa ha~1), K low rate (69 kg-K ha~1), K high rate
(138 kg-K ha~1), Na ] K low rate (20 kg-Na and
35 kg-K ha~1, respectively) or Na ] K high rate
(40 kg-Na and 69 kg-K ha~1, respectively). This gave
isomolar applications of the monovalent cations Na
and K at the low and high application rates. Fertilisers
used were NaCl, KCl and a combination of the two
(Silvinit, Cleveland Potash Ltd, Whitby, UK) (Table 1).
The fertilisers were applied on 30 August as in experiment 1 and the swards grazed from 3 September to 7
October. Prior to the start of the experiment the entire
area had received 130 kg-N ha~1 in March before a
Ðrst cut of silage in May. After this silage cut, 125 kg-N
and 80 kg-K O were applied and a second silage cut
2
taken in August. The area was then grazed by dairy
cows between the second silage cut and the start of the
experiment, when the twelve cows were introduced.
Sward measurements and chemical analysis
Herbage height was measured using a sward stick on
the day before the experiment began and subsequently
TABLE 1
Fertiliser application rates in experiment 2 (kg ha~1)
T reatment
Fertiliser application rate
L ow
Fig 1. Layout of current and residual treatment applications
in the Ðeld in experiment 1.
Na
K
Na ] K
High
NaCl
KCl
NaCl
KCl
102
È
51
È
130
65
204
È
102
È
260
130
E†ects of Na and K fertiliser on cattle pasture
291
TABLE 2
E†ects of current Na fertiliser treatment in experiment 1 on herbage chemical composition (g kg~1
DM, except where otherwise stated)
T reatment
Na
K
Mg
Ca
DM (g kg~1
fresh weight)
DMD
MADF
CP
Ash
Nil
L ow
Medium
2É73
10É17
1É79
4É42
3É63
9É61
1É95
5É48
4É10
9É38
2É16
5É55
5É18
9É34
1É87
5É62
4É93
9É13
1É69
5É10
219
712
212
246
91É1
229
744
222
250
92É2
221
854
214
244
94É6
210
807
222
245
94É1
209
735
218
242
91É7
every 2 days during the experimental period. Twelve
(experiment 1) and 16 (experiment 2) measurements
were taken in a W-pattern across each plot.
Ten hand-plucked herbage samples of approximately
200 g were collected at random in each plot at the time
of fertiliser application and at three (experimental 1)
and four (experiment 2) day intervals during the experiment. An additional sample was taken by the same
method at the end of experiment 2 and separated into
clover and grass leaf fractions for individual analysis
to investigate the response of these two species to the
fertiliser treatments. Individual samples were dried at
High
SED
Prob
0É286
0É312
0É079
0É204
\0É001
0É02
\0É001
\0É001
V ery high
2É1
15É6
4É8
2É6
0É44
0É04
0É001
0É16
0É06
\0É001
90È100¡C for 16 h to determine DM concentration.
They were then hammer-milled through a 1 mm screen
and a sub-sample used for the determination of crude
protein (CP, N ] 6É25) and modiÐed acid-detergent
Ðbre (MADF) according to the methods of AOAC
(1984), and DMD by a modiÐed technique (Omed et al
1989) of incubation in faecal liquor (El Shaer et al 1987).
The remainder was ashed in a muffle furnace at 600¡C
and a solution prepared by dry combustion, which was
used for the analysis of Na, K, Mg and Ca by atomic
absorption spectrophotometry (Model 951, Instrumentation Laboratory, Lexington, USA).
TABLE 3
Residual e†ects of Na fertiliser applied in the previous year at a low (RL) or high (RH) rate,
compared with no fertiliser (RN), on herbage chemical composition in experiment 1 (g kg~1 DM,
except where otherwise stated)
T reatment
Na
Na start
Na end
K
Mg
Ca
Ca start
Ca end
DM (g kg~1 fresh weight)
DMD
MADF
CP
Ash
RN
RL
2É24
1É22
3É25
9É73
2É00
6É06
6É76
5É35
199
837
216
256
95É7
3É15
2É70
3É59
9É71
2É02
6É92
8É29
5É55
188
815
216
265
97É2
SED
Prob
0É186
\0É001
0É264a
\0É001a
0É517
0É158
0É327
NSb
NS
NS
0É462a
\0É10a
RH
4É54
4É08
3É19
9É81
1É86
6É20
7É90
4É49
195
784
217
272
98É2
a `Interaction between residual and start/end sampling dates.
b NS \ P [ 0É10.
H
H
5É43
37É5
3É50
3É32
1É52
NS
NS
NS
\0É005
NS
P C Chiy et al
292
Animal measurements
Animals had free access to the entire grazing area, and
the location of each grazing cow in the treatment grid
was recorded at 5-min intervals for 90 min each day.
The 90-min period was randomly assigned within the
main grazing period of the day, from 09.00 to 18.00 h.
The sward biting rate was recorded for each cow in
the morning, afternoon and evening for 5 days per week
and the treatment area occupied by the cow on each
occasion. The number of bites was counted over a 90 s
period of continuous biting. Cows were allowed 30 s
after the start of biting before counting commenced.
The record was abandoned if the cow stopped grazing
for more than 10 s.
The distance walked by each cow during 60 s grazing
was measured once every 2 days using a calibrated
wheel and the treatment area occupied by the cow
during the recording noted. The position of the hind
right foot was used as the reference point.
Statistical analysis
The signiÐcance of di†erences between treatments was
determined by analysis of variance of a generalised
linear model using Genstat 5 (Lawes Agricultural Trust
1980). Factors included in the model were the treatment
and sampling date, and cow in grazing behaviour measurements. Residual Na treatment was also included in
experiment 1. If the probability of treatment e†ects was
10% or greater, they were assumed not to be signiÐcant.
RESULTS
Experiment 1
E†ects of the current Na treatments on herbage chemical composition are given in Table 2. E†ects of the
residual Na treatments are given in Table 3, and the
signiÐcant interactions between current and residual
treatments (herbage Na concentration, grass height and
proportion of time spent grazing) are shown in Fig 2.
Other residual ] current treatment interactions were
not signiÐcant.
Herbage chemical composition
Current Na fertiliser application increased herbage Na
concentration from the nil to high application rates,
with no further e†ect at the very high rate (Table 2).
Herbage Na concentration also increased in proportion
to residual Na fertiliser application (Table 3). There
appeared to be a maximum herbage Na concentration
of approximately 5 g kg~1 DM. The signiÐcant interaction between current and residual Na application
(SED 0É26, P \ 0É001) (Fig 2) demonstrated that, in the
Fig 2. E†ect of current Na fertiliser application level on
herbage Na content, herbage height and proportion of time
cows spent grazing for residual nil (L), low (K) and high (|)
treatments in experiment 1.
E†ects of Na and K fertiliser on cattle pasture
293
TABLE 4
Current treatment e†ects on herbage height and grazing behaviour in experiment 1
T reatment
Herbage height (cm)
Grazing time (proportion of
total time)
Biting rate (no min~1)
Walking rate (m min~1)
Nil
L ow
Medium
High
V ery high
8É65
0É137
8É03
0É150
8É01
0É159
7É53
0É160
7É66
0É152
69É0
2É47
73É6
3É64
residual high treatment, Na concentration in herbage
was greater at low and medium application rates than
in residual nil and low. There was also a signiÐcant
interaction between the time of the recording and the
residual treatment e†ect (Table 3). Herbage at the start
of the experiment showed a response in Na concentration to residual Na fertiliser application, but by the end
of the experiment this response had disappeared.
Herbage K concentration was signiÐcantly reduced
by current Na fertiliser application at the medium, high
and very high application rates (Table 2). Residual Na
treatment did not a†ect herbage K concentration (Table
3). Herbage Mg concentration increased up to the
medium application rate but thereafter decreased. It
was not a†ected by residual Na treatment. Ca concentration was increased at all levels of Na fertiliser application, but especially at the medium and high rates.
There was a signiÐcantly increased herbage Ca in
residual low and high treatments at the start but not at
the end of the experiment. Herbage DM content was
increased at the low application rate, una†ected at the
medium rate and thereafter decreased. Herbage DM
digestibility increased linearly up to the medium rate
and thereafter declined. Ash concentrations were
increased in the medium and high treatments. There
were no e†ects of residual Na treatments on herbage
DM, DMD or ash concentrations. There were no
TABLE 5
Residual treatment e†ects on herbage height and grazing
behaviour in experiment 1
T reatment
SED
Prob
RN
RL
RH
8É0
8É7
8É3
0É15
\0É001
0É161
0É149
0É143
0É0043
\0É001
78É0
3É80
76É8
3É09
67É6
3É11
SED
Prob
0É219
0É005
\ 0É001
\ 0É001
1É46
0É313
0É03
0É03
current or residual Na treatment e†ects on herbage
MADF concentration, but CP concentrations tended to
be slightly increased in the low treatment. There was a
linear increase in CP concentration with increasing
residual Na fertiliser.
Herbage height and cow behaviour
Current and residual treatment means of herbage height
and grazing behaviour are given in Tables 4 and 5,
respectively. Cows grazed herbage to a lower height in
the current treatments where Na was applied, particularly in high and very high treatments. There was a signiÐcant current ] residual Na treatment interaction in
herbage height (SED \ 0É332, P \ 0É001). In residual
nil treatment, and to a lesser extent residual low,
herbage height declined with increasing current treatment Na application rate (Fig 2). However, in residual
high herbage height increased for the medium, high and
very high current treatments.
There was a signiÐcant interaction between current
and residual treatments in grazing time (Fig 2) (SED
0É174, P \ 0É001). Where there was no residual Na fertiliser, grazing time increased with current Na fertiliser.
In the residual low treatment, grazing time increased up
to the medium application rate and then declined ; in
residual high, grazing time decreased with current Na
application rate above the low level. Biting rate was
increased in the low, medium and high current treatments (Table 4). It was not a†ected by residual treatment and there was no current ] residual treatment
interaction. Walking rate was increased with Na application rate up to the medium rate and declined thereafter.
Experiment 2
Herbage height
(cm)
Grazing time
(proportion of
total time)
Biting rate
(no min~1)
72É8
73É9
72É2
1É13
0É31
Herbage chemical composition
Herbage Na concentration was high (5 g kg DM~1)
when no Na fertiliser was applied (Table 6). Na fertiliser
increased and K fertiliser decreased herbage Na concentration, with greater responses at the high application
rate. The combined fertiliser had little e†ect on herbage
P C Chiy et al
294
TABLE 6
Treatment e†ects on herbage chemical composition in experiment 2 (g kg~1 DM unless otherwise stated)
Cation level
None
Na
L ow
Na
Herbage
5É01
Grass leaf
5É31
Clover
4É99
K
Herbage
16É1
Grass leaf
16É0
Clover
20É3
Mg
Herbage
1É28
Grass leaf
2É05
Clover
2É20
Ca
Herbage
4É83
Grass leaf
7É69
Clover
9É50
P
Herbage
3É16
Grass leaf
3É09
Clover
3É77
Cl
Herbage
38É4
Grass leaf
43É9
Clover
41É5
DM (g kg~1 freshweight)
Herbage
212
Grass leaf
198
Clover
127
MADF
Herbage
277
Grass leaf
234
Clover
182
CP
Herbage
106
Grass leaf
146
Clover
263
Ash
Herbage
83É9
Grass leaf
78É5
Clover
118
5É37
5É58
4É28
16É1
19É8
13É9
Na ] K
K
High
5É43
6É07
8É85
15É4
18É5
18É2
L ow
4É62
4É28
4É79
18É8
19É5
22É4
High
3É52
4É72
4É62
20É1
22É4
24É9
L ow
5É18
5É65
4É04
18É2
20É6
18É5
SED
Prob
0É331
0É550
0É979
\0É001
0É10
0É02
0É67
1É02
2É79
\0É001
0É01
0É08
High
4É61
5É96
4É76
19É3
21É3
20É9
1É22
1É84
1É69
1É17
2É13
1É93
1É24
1É54
2É14
1É21
1É76
2É06
1É21
1É38
1É78
1É25
1É88
1É86
0É035
0É366
0É271
0É11
0É46
0É49
4É64
6É51
8É61
4É42
7É43
9É52
4É56
6É64
9É52
4É60
7É69
9É00
4É46
7É04
8É08
4É66
6É77
7É82
0É190
0É840
0É728
0É42
0É66
0É20
2É86
2É95
3É05
3É09
3É48
3É58
3É17
2É85
4É08
2É89
3É02
4É09
3É05
2É94
3É92
3É00
3É18
4É38
0É144
0É259
0É598
0É22
0É36
0É47
2É96
8É25
12É10
\0É001
0É23
0É49
39É4
52É5
28É1
44É6
50É7
44É4
46É6
59É0
50É9
49É7
62É4
53É9
47É9
59É2
39É6
54É3
67É2
49É4
212
205
169
205
191
155
215
200
142
211
200
146
206
197
162
201
191
160
5É3
6É1
19É8
0É09
0É33
0É47
260
228
167
266
227
184
271
224
193
271
236
193
260
221
177
268
228
174
4É6
4É6
15É3
0É01
0É10
0É60
101
140
228
106
148
242
102
143
269
102
141
270
106
147
247
112
157
256
2É9
7É1
24É6
0É06
0É37
0É61
86É1
80É5
136
92É9
81É9
140
91É7
87É5
135
94É0
91É4
133
93É2
84É7
133
99É6
90É5
134
2É76
2É54
28É1
\0É001
0É01
0É60
Na concentration at the low application rate and slightly decreased it at the high rate. Grass leaf and clover
tended to respond in a similar manner.
Herbage K concentration showed little change with
Na fertiliser, and was increased by K fertiliser, particularly at the high rate. K fertiliser increased the K concentration of grass leaf and to a lesser extent clover, and
Na fertiliser increased the K concentration of grass leaf.
The combined fertiliser increased herbage and grass leaf
K concentrations, but not clover. There was a trend for
Mg, Ca and P concentrations to be reduced with all
fertiliser treatments compared with no fertiliser, but this
was not statistically signiÐcant. Herbage Cl concentration was increased by all fertiliser treatments, particularly the K and combined fertilisers and at the high
level. The same trend was evident for grass leaf but this
was not statistically signiÐcant. Clover Cl concentration
was variable and not signiÐcantly a†ected by treatment.
The DM and CP concentrations were not a†ected by
treatment. MADF concentration tended to be reduced
by the fertiliser treatments, especially Na. Ash concentration was increased by fertiliser treatment compared
with no fertiliser, particularly the K and combined fertilisers and at the high rate.
E†ects of Na and K fertiliser on cattle pasture
295
Herbage height and cow behaviour
Herbage height was increased in the Na and to a lesser
extent K and combined fertiliser treatments, compared
to no fertiliser (Table 7). The proportion of time spent
grazing and the walking rate on pasture treatments
were not a†ected by treatment, but the biting rate
tended to be reduced for the fertiliser Na and K treatments and the combined Na ] K treatments.
DISCUSSION
Herbage composition
The herbage Na concentrations of approximately
5 g kg~1 DM in the high and very high Na current
treatments in experiment 1 have previously been
achieved at lower rates of Na fertiliser application and
have been accompanied by reductions in herbage K and
increases in Ca, DMD and ash concentrations (Chiy
and Phillips 1991, 1993). This herbage Na concentration
appears to be the maximum that can be achieved under
these conditions and with the application of Na fertilisers. As a result, the herbage Na : K ratio was only
increased up to the high rate of Na application (0É27,
0É38, 0É44, 0É56 and 0É54 for treatments low to very
high, respectively).
In experiment 2 the application of Na fertiliser had
relatively little e†ect on herbage Na concentration
because it was already high, probably due to the maturity of the herbage. In the absence of Na fertiliser, Na
contents of herbage at this site had been observed to
increase with herbage maturity (Chiy and Phillips 1997).
The proximity of the sea (250 m) and inadequate drainage may also have contributed to the high herbage Na
concentrations. Higher herbage Na concentrations of 6È
8 g kg~1 DM have been reported following Na fertiliser
application at 30È100 kg-Na ha~1 (Moseley 1980 ; Chiy
et al 1993b), but only where herbage is cut before being
fed to livestock, thus avoiding urine and faecal K return
to the pasture.
The Na : K ratio in experiment 2 increased in clover
in response to fertiliser Na, but not in grass (Fig 3). In a
separate experiment, Chiy and Phillips (1997) found
that there was only an increase in older clover leaves
Fig 3. E†ect of Na fertiliser application on Na : K ratio in
herbage (K), grass (È) and clover ()) in experiment 2.
([50% unfolded) and young grass leaves (at least 95%
of the surface area being green). In accordance with this,
the herbage in experiment 2, being tall and relatively
mature, would have mainly contained older grass and
clover leaves, and therefore the response was only seen
in clover. In experiment 1 the herbage was not separated into grass and clover but was predominantly shorter,
younger grass than in experiment 2 ; hence, there was a
response in herbage Na, K and Na : K ratio.
The reduction in Na : K ratio with application of K
fertiliser was evident for grass and clover in experiment
2 (Fig 4). In terms of uptake kinetics, the binding sites
on the plasma membrane of the root cells have a high
affinity for K and low affinity for Na, and it is therefore
Fig 4. E†ect of K fertiliser application on Na : K ratio in
herbage (K), grass (È) and clover ()) in experiment 2.
TABLE 7
Herbage height and grazing behaviour in experiment 2
Cation level
Herbage height (cm)
Grazing time (proportion of
total time)
Biting rate (no min~1)
Walking rate (m min~1)
None
Na
Na ] K
K
SED
Prob
L ow
High
L ow
High
L ow
High
12É6
0É118
14É0
0É132
13É5
0É117
13É5
0É145
13É0
0É163
13É5
0É125
13É1
0É152
0É25
0É019
\0É001
0É12
68É4
2É72
66É2
2É97
67É6
2É88
66É6
2É65
66É1
2É69
65É7
3É02
65É7
2É73
1É01
0É198
0É07
0É43
P C Chiy et al
296
to be expected that K fertiliser will induce a response in
Na : K ratio of the herbage under a range of Na : K
ratios in the soil solute.
The low herbage K concentrations (c 10 g kg~1 DM)
may have prevented any reduction in herbage Mg
uptake with Na fertiliser in experiment 1, which occurs
mainly at high K levels due to competition by monovalent cations for plant absorption sites (Mengel and
Kirby 1978 ; Whitehead et al 1978). In experiment 2
with higher K concentrations there was evidence of a
reduction in Mg and Ca concentrations with fertiliser
treatment.
Cow grazing behaviour
A preference by dairy cows for pasture fertilised with
18 kg-Na ha~1 compared with unfertilised pasture has
been reported (Chiy and Phillips 1991). An increase in
grazing time has also been reported when cows are
grazed on pastures containing 5 compared to 3 g-Na
kg~1 DM, accompanied by an increase in cow biting
rate and a reduction in herbage height (Chiy and Phillips 1991 ; Chiy et al 1993a). The interaction between
current and residual treatment e†ects on herbage Na
concentrations in experiment 1 demonstrated that the
e†ects were only additive up to 5 g-Na kg~1 herbage.
Residual Na accelerated the response of herbage Na
concentration up to a maximum level with additional
current Na (Fig 2), but the residual e†ects were eliminated by the end of the experiment. Despite the similarity across residual treatments of herbage Na
concentrations at high current Na application, grazing
time decreased and herbage height increased on swards
with both high current and residual Na treatments. The
cause of this adverse e†ect on grazing preference is
uncertain, but it may relate to the decline in DMD at
high Na application rates. Previous research (Chiy and
Phillips 1993) has related the change in DM digestibility
with Na fertiliser to a change in water-soluble carbohydrate concentration, which, together with Na, is likely
to be a major gustatory signal to regulate feeding preferences.
It is assumed that the reduction in herbage height
with increased sodium content of herbage in experiment
1 reÑected more grazing at a faster intake rate, rather
than reduced herbage growth. Perennial ryegrass has
been observed to show positive responses to Na fertiliser, and is generally accepted to be natrophillic (Chiy
and Phillips 1993).
The increased biting rates in the low, medium and
high treatments in experiment 1 may partly represent an
attempt by the animal to maintain intake rate at the
reduced herbage heights. However, herbage height was
also reduced in the very high treatment where biting
rate was reduced, suggesting that Na might be having
speciÐc e†ects on biting rate at the highest application
rate independent of grass height. Biting rate may be
related to herbage DMD if herbage of lower digestibility
(and
higher
structural
carbohydrate
concentration) takes longer to sever from the sward.
It is perhaps surprising that, in experiment 1, cattle
walked faster on pasture on which they spent longer
grazing, suggesting that, Ðrstly, they made the conscious
decision to graze the Na-fertilised pasture for longer. To
do this they would have a identify and learn which
areas of the Ðeld had high Na concentrations. Secondly,
less searching was done as the cow moved her head
from side to side whilst walking. Thirdly, at the lower
grass height they may have been walking faster in
search of taller herbage of the same palatability. Evidence for the latter is reported by Fraser and Broom
(1990), who found that walking rate increased from
1É9 m min~1 on long herbage to 2É5 m min~1 on short
herbage.
The increase in herbage height and tendency for
slower biting with fertiliser treatments in experiment 2
suggests that the palatability of the treated herbages
was not increased. This corresponds to the absence of
major e†ects on herbage Na concentration of Na fertilisers, but the reduction, from 5É0 to 3É5 g kg~1 DM, in
herbage Na concentration with K fertiliser suggests that
palatability was maintained by the increase in K concentration, from 16 to 20 g kg~1 DM.
These experiments conÐrm that young grass swards
with low Na contents will respond in herbage Na
content more to fertiliser Na than taller, older swards. If
herbage Na content is increased to approximately
5 g kg~1 DM by Na fertiliser, cattle will prefer that
herbage to herbage with a more normal Na content and
will bite it faster, leaving a sward grazed down to a
lower height.
ACKNOWLEDGEMENTS
The authors are grateful to the University Farm technical sta† for assistance in the running of the experiment
and to Cleveland Potash Ltd for the supply of fertilisers
in Experiment 2.
REFERENCES
ARC 1980 T he Nutrient Requirements of Ruminant L ivestock.
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AOAC 1984 Official Methods of Analysis (14th edn). Association of Official Analytical Chemists, Washington, DC,
USA.
Chiy P C, Phillips C J C 1991 The e†ects of sodium chloride
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E†ects of Na and K fertiliser on cattle pasture
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Omed H M, Axford R F E, Chamberlain A G, Givens D I
1989 Development of a method for the in vitro estimation of
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Richter C P 1956 Salt appetite in mammals : its dependence
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Schneider P L, Beede D K, Wilcox C J 1986 Responses of
lactating cows to dietary Na source and quantity and potassium quantity during heat stress. J Dairy Sci, 69 99È110.
Whitehead D C, Jones L H P, Barnes R J 1978 The inÑuence
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