100 100
80 80
~ ~:>I<~
<ll 60
cl> 60 Cl
Cl "'
J!l<: C
~ 40
<ll 40
~ cl>
<ll
a. a.
20 20
0
0 0 1000 2000 3000 0
Exchangeable Ca (mg/kg)
_ _ Ryegrass
1000 2000 Excha ngeableCa(mg/kg)
Ryegrass
Ryegrass
o 60 120
Totalexchangeable cations (m moIc/kg)
o
100
80·
~<llCl 60
E
e~ 40
<ll
a.
20 100
80
~ClCl 60 J!lc
<ll 40
~<ll
a.
20 0
0 200 400
ExchangeableMg (rug/kg)
Ryegrass
100
80 ~--- _.
~
cl> 60
~Clcl>
40 ·
<ll~
a.
20 0
0 100 300
ExchangeableK(mg/kg)
-- - - -
L . . . - _
K ikuyu
K ikuyu
200 400 600
ExchangeableMg(mg/kg)
- -- - - - - - -- -- - 80 ~---_j
100
Kikuyu
100· - - - -- - - - - --- - --- -
20
o o
20+ - -- -
lOO 300 500
Exchangeable K (mg/kg)
60 120 18 24
Totalexchangeablecations(mmole/kg) 80~---~~---___j
~
~
Cl 60 +-- -- - - -
aCl
<:
~ 40 ~---_:_:c__---_j
rf
l
Cl 60 .-- --- --- - -
~Cl
~ 40+---==-- - - , rf
100 80
~
~~
Cl 60
Cl
.l!l<:
Cl 40
~Cl
a.
20 0
-- - - _ .._-- - -_ ._- - - _._-- -- -- -
gure5.3Frequency distribution (%)ofexchangeableCa,Mg,K and total exchangeable cation iluesin soils under kikuyu and ryegrasspastures in the Tsitsikamma region.
80 - ----- -- --- --- --------- -- - ---
Ryegrass
o
10 20 30ExtractableZn(mg/kg)
-- - - _..-
='. :::
f....
:j~:~:::::::~:
:~100
80 ::R~
Q) 60
Cl
....
ellc::Q) 40
...
oQ)
n,
20 0
Kikuyu
l ll iIlL~,~ ~
o
10 20 30 40 50 60 70 80ExtractableZn(mg/kg) 100
;R~
Q) 60
Cl
....
ellc::Q) 40
o
...
Q)
n,
20 0
._---_.~~--
- - - - --_ .._~_._---
15
ExtractableMn(mg/k g)
Ryegrass
- -- -- -- - ..._-- ~
I
o 5
o
-- - - _._ - -
100 80 ::R0
Q) 60
Cl
-
ellc::Q) 40~Q)
a,
20 -
35 45 25
_L-_J!I!!!!'!!L-~_""":'_ _.
55
Kikuyu
15
ExtractableMn(mg/kg)
o 5
o
20
80 -- - ---- -
100 ~---...::.._---
~ 60
....
ellc::Q) 40
~Q)
n,
gure5.4Frequency distribution(%)ofextractableZn and Mn values in soils under kikuyu and egrass pastures in the Tsitsikamma region.
5.3.2 Herbage properties
There were no clear differences in herbage nutrient contents between the three regions (Table 5.2). Ingeneral,in kikuyu herbage concentrations of tissue P and Cu were higher and those for Ca and Na lower than in ryegrass herbage.
The frequency distribution of herbage nutrient concentrations for data pooled from the three regions is presented in Figures 5.5, 5.6, 5.7 and 5.8. As noted above, in general the Ca concentration was lower for kikuyu than ryegrass herbage (Figure 5.5). The critical leaf Ca concentration is considered to be 0.11and 0.25 %for kikuyu and ryegrass respectively (Miles, 1998). Thus, tissue Ca concentrations are adequate for pasture growth since less than 2% and 1
% are below the required level for kikuyu and ryegrass respectively. If, however, the animal nutritional requirement of 0.43 - 0.66%(National Research Council, 1988; Miles et al., 1995), is considered, then much ofthe pasture herbage is deficient in Ca. That is, 55%ofthe kikuyu and 41 % of the ryegrass fields had herbage Ca concentrations of below 0.4 %.
Phosphorus concentrations (Figure 5.5) were higher for kikuyu than ryegrass herbage and this is illustrated by thefact that only 33 % of the ryegrass samples were above 0.4 %,whilst 53 % of the kikuyu samples were above that concentration. The critical P content ofgrass herbage is 0.22- 0.24%(Miles, 1998), so few fields had low tissue P concentrations. The dietary P requirements for lactating dairy cows is generally reported to be between 0.28 and 0.41 % (National Research Council, 1988; Miles et al., 1995). Most of the herbage P concentrations in both kikuyu and ryegrass samples were above 0.28%and P supply to grazing livestock should,therefore, inmost cases be adequate.
The critical K concentration in pasture herbage is approximately 2.0 - 2.2% (Miles, 1998). Most ofthe herbage samples for both kikuyu (89 %) and ryegrass (82 %) were above 2.0 % (Figure 5.5) and K was not generally a limiting nutrient for pasture production. In terms of animal nutritional requirements, the K concentration required is only 0.5 - 0.8 % (Grunes and Welch, 1989), so concentrations in the herbage were well in excess of animal requirements. Excess K (i.e. above 3 %; Mileset al.,1995) can,however, be problematic due to its effect on the absorption of other minerals particularly Ca and Mg. Kikuyu herbage generally had a higher K content than ryegrass with 60 % of kikuyu but only 30 % of ryegrass samples having concentrations above 3 %.
l'a ble 5.2 Mean herbage nutrient content, standard error and range of values for kikuyu and yegrass pasture inthe three regions ofthe Tsisikamma.
Region1 Kikuyu Annual
Plant Nutrient Mean Std Error Min Max Me an StdError Min Max
Calcium(%) 0.386 0.023 0.270 0.570 0.426 0.032 0.260 0.660
Phosphorus(%) 0.369 0.033 0.200 0.580 0.386 0.025 0.260 0.560
Potassium(%) 2.741 0.255 0.720 4.160 2.691 0.195 1.760 4.470
Magnesium(%) 0.329 0.018 0.220 0.520 0.314 0.018 0.240 0.480
Sodium(%) 0.400 0.059 0.200 1.080 0.630 0.050 0.420 1.140
Nitrogen(%) 3.014 0.208 1.850 4.150 3.349 0.139 1.890 3.950
Sulphur(%) 0.273 0.022 0.160 0.480 .3.7 0.015 0.250 0.430
Zinc (mglkg) 55.071 6.207 22.000 107.000 70.071 8.274 34.000 142.000 Manganese (mglkg) 58.500 4.273 39.000 89.000 80.429 5.865 37.000 122.000
Copper(mglkg) 6.214 0.909 2.000 13.000 3.929 0.588 0.000 9.000
Boron (mg/kg) 12.571 0.830 6.000 18.000 13.357 1.036 6.000 20.000
no.=15 no.=14
Region 2 Kiku yu Annual
PlantNutrient Mean Std Error Min Max Mean StdError Min Max
Calcium(%) 0.391 0.033 0.100 0.720 0.425 0.031 0.260 0.590
Phosphorus(%) 0.453 0.032 0.100 0.630 0.375 0.034 0.220 0.570
Potassium(%) 3.358 0.239 0.940 4.670 2.811 0.339 0.930 5.150
Magnesium(%) 0.317 0.021 0.100 0.440 0.292 0.012 0.250 0.350
Sodium(%) 0.295 0.024 0.120 0.470 0.415 0.052 0.120 0.600
Nitrogen(%) 3.465 0.115 2.520 4.100 2.967 0.218 1.360 4.090
Sulphur(%) 0.329 0.015 0.220 0.410 0.304 0.022 0.160 0.400
Zinc(mg/kg) 66.467 6.878 14.000 120.000 59.364 5.672 25.000 89.000 Manganese (mg/kg) 81.800 7.920 16.000 140.000 90.818 7.908 31.000 134.000
Copper(mglkg) 7.533 0.584 2.000 11.000 6.545 0.813 2.000 11.000
Boron (mglkg) 8.067 0.733 2.000 14.000 7.273 0.449 6.000 9.000
no.=15 no.=11
Region 3 Kikuyu Annual
Plant Nutrient Me an StdError Min Max Mean Std Error Min Max
Calcium(%) 0.389 0.026 0.270 0.500 0.453 0.034 0.310 0.610
Phosphorus(%) 0.456 0.031 0.350 0.660 0.413 0.015 0.360 0.480
Potassium(%) 2.942 0.379 1.690 5.000 2.954 0.265 1.640 4.230
Magnesium(%) 0.311 0.019 0.210 0.400 0.279 0.016 0.210 0.360
Sodium(%) 0.378 0.062 0.120 0.720 0.476 0.053 0.330 0.800
Nitrogen(%) 3.147 0.243 1.650 4.010 3.169 0.116 2.750 3.800
Sulphur(%) 0.034 0.031 0.240 0.520 0.349 0.020 0.280' 0.460
Zinc (mg/kg) 47.444 2.977 36.000 61.000 44.000 1.427 39.000 49.000
Manganese(mg/kg) 48.444 7.509 23.000 95.000 70.375 13.608 36.000 135.000
Copper(mglkg) 5.333 0.928 2.000 9.000 4.500 0.627 2.000 8.000
Boron (mg/kg) 7.556 0.709 4.000 11.000 7.625 0.498 6.000 9.000
no.=9 no.=8
117
100 100
80 80
~ ~
Q) 60
Q) 60
Cl
Cl ~
~~Q) 40 ~Q) 40
a. a.
20 20
0 0
0 0.2 0.4 0.6 0.8 0.2 0.4 0.6
Caconcentration(%) Ca concentration(%)
Ryegrass
11.
~j~1~~~j
100 80
l
Q) 60Clca 1:~Q) 40 a.
20
0 0.2 0.4 0.6
P concentration(%)
Ryegrass
100
~ 80
Q) 60
~Cl
~ 40 a.Q)
20
0 0.5 1.5 2.5 3.5 4.5 5.5
K concentration(%)
100
Ryegrass
~ 80
Q) 60
~Cl
~ 40 a.Q)
20 0
0.2 0.4
Mg concentration(%)
Kikuyu
-I'lL
100 80
~Q)Cl 60
~Q)
~ 40 a.Q)
20 0
0 0.2 0.4 0.6
P concentration(%)
Kikuyu
100 80
~Q)Cl 60
~~Q) 40 a.
20 0
0.5 1.5 2.5 3.5 4.5
K concentration(%)
Kikuyu
100 80
l
Q) 60Clca 1:~Q) 40 a. 20
0
0 0.2 0.4 0.6
Mg concentration(%)
Figure 5.5 Frequencydistribution(%)ofCa,P,K and Mg concentrations in herbage from kikuyu and ryegrasspasturesin the Tsitsikammaregion.
The Mg concentration in pasture herbage considered to be critical for growth is approximately 0.10% (Mil;s, 1998). As can be seen from Figure 5.5 all the concentrations in ryegrass and 97
% in the kikuyu were above this level. A nutritional Mg requirement in forage for high producing dairy cows of0.2 % is considered sufficient (Grunes and Welch, 1989) and again all the ryegrass and 97 % ofthe kikuyu herbage samples were above this level. High K levels can,however, have inhibitory effects on Mg absorption.
The Na concentrations (Figure 5.6)were considerably higher in ryegrass than kikuyu herbage, with only 26 % ofkikuyu samples above 0.4 % whilst 78 % ofthe ryegrass samples were above that same concentration. The recommended concentration ofNa in feed for grazing animals is approximately 0.12 % (Holmes and Wilson, 1987) and both kikuyu (90 %) and ryegrass (95 %) were well in excess of this requirement, accordingly no apparent Na problems should exist.
The critical N concentration for pasture growth is approximately 2.7 - 3.5 % (Miles, 1998) and the nutritional requirement for lactating dairy cows is between 1.9 and 3.0 % (Whitehead, 2000).
Seventy percent ofkikuyu and 73 % of ryegrass values were above 3.0 % (Figure 5.6), reflecting the heavy rates of fertilizer N used in the region. Most of the herbage samples had an S concentration ofbetween 0.2 and 0.4 % (Figure 5.6). The critical concentration for pasture growth is approximately 0.12- 0.20 % (Miles, 1998); the nutritional S requirement is very similar and about 0.16 - 0.2 % (Whitehead, 2000) Less than 8 % ofthe kikuyu and 3 % ofthe ryegrass were below 0.2 %, consequently there is little or no expected problem with the S concentrations for pasture growth or animal nutrition.
The Ca : P ratio in feed is consideredimportant in terms ofanimal nutrition and results are shown in Figure 5.7. This ratio should ideally not be below 1:1 (Bredon, 1980),but 65%of the kikuyu and 42 % of ryegrass samples were below this value. The K : Ca+Mg is another ratio that is important and is often used as anindicator ofthe potential for grass tetany (Holmes and Wilson, 1987).The ratio is recommended not to be above 2.2 (Mileset al., 1995), but from the results (Figure 5.7) it can be seen that 30%of the kikuyu and 21%ofthe ryegrass samples had ratios above 2.0. The N : S ratio in herbage(Figure 5.7)was higher in the kikuyu herbage samples than in the ryegrass samples, with 61 % ofthe kikuyu herbage samples having values> 10, whilst only 50 % of the ryegrass herbage samples were> 10.