Alan G. Kaiser and John W. Piltz |
John F. Hamilton and Euie J. Havilah |
|
|
NSW Agriculture, Wagga Wagga Agricultural Institute |
NSW Agriculture, Pasture Research Unit |
INTRODUCTION
In studies with temperate forage species WSC content has been observed to increase during the day due to photosynthetic activity within the plant. With warm and sunny conditions, the content of WSC in the plant is higher in the afternoon than early morning. It has been suggested that cutting of forages for silage should be delayed until the afternoon to maximize the amount of WSC available for fermentation. There are few data available on variation in WSC content of tropical grasses, so the current study was conducted to monitor changes during the day in the composition of Kikuyu grass (Pennisetum clandestinum).
MATERIALS AND METHODS
Two studies were conducted in which nitrogen (N) fertilized Kikuyu grass was sampled to monitor changes in WSC during the day. The first study was conducted over 3 days in March, with 30-day Kikuyu regrowth, and in adjoining plots over 3 days in April, with 30- and 45-day Kikuyu regrowths. A second study in April investigated the change in WSC content of 30- and 45-day regrowth Kikuyu mown for silage production at three times during one day. The two studies were conducted at different sites within the same paddock. The forage samples were analysed for DM, N, WSC, and starch content, and for in vitro organic matter digestibility (OMD).
RESULTS AND DISCUSSION
In the first study, weather conditions over the three days during the March sampling ranged from warm and sunny through to overcast. Warm and sunny weather was experienced on all days during the April sampling. No significant differences were observed between days in forage composition at either sampling (Table 1).
During the second study, warm and sunny weather conditions prevailed until just prior to the last mowing. Rainfall from local storms commenced during mowing and continued to fall during the collection of samples. This resulted in a decline in DM content but no differences in the composition of the DM (Table 2).
These study results confirm that sugar levels are higher in Kikuyu grass in the middle of the day and afternoon (60.6 g/kg DM), than in the morning (47.2 g/kg DM). Despite this increase in sugar content (to 12.0 g/kg fresh forage), the level was still well below the critical value (25-30 g/kg fresh forage) for low-risk preservation of unwilted forage (Wilkinson, 1990). Other effects of changing the time of cut to the afternoon were a small increase in forage DM content, a small reduction in N concentration, an increase in starch content, but no effect on digestibility.
Table 1. Effect of time of day on the composition of Kikuyu grass in Study 1
Sampling time |
DM content |
N content |
WSC |
Starch |
OMD |
|
March - 30-day regrowth |
||||
07:35 |
167 |
34.6 |
50.2 |
42.3 |
0.698 |
11:45 |
167 |
34.9 |
68.4 |
51.4 |
0.710 |
15:55 |
171 |
33.6 |
66.1 |
57.8 |
0.726 |
Time of day |
ns |
P0.10 |
P0.01 |
P0.01 |
P0.01 |
s.e.d. |
5.5 |
1.07 |
2.66 |
4.17 |
0.0073 |
|
April - 30-day regrowth |
||||
08:20 |
191 |
24.4 |
48.1 |
40.4 |
0.668 |
14:00 |
203 |
23.6 |
60.2 |
50.6 |
0.674 |
17:00 |
202 |
23.2 |
63.2 |
53.3 |
0.673 |
|
April - 45-day regrowth |
||||
08:20 |
193 |
24.4 |
48.0 |
39.0 |
0.672 |
14:00 |
196 |
23.6 |
61.0 |
52.0 |
0.681 |
17:00 |
202 |
22.9 |
63.8 |
51.7 |
0.674 |
Regrowth |
ns |
ns |
ns |
ns |
ns |
Time of day |
P0.01 |
P0.01 |
P0.01 |
P0.01 |
ns |
Regrowth time |
P0.10 |
ns |
ns |
ns |
ns |
Notes: ns = not significant. s.e.d. = significat difference. OMD = organic matter digestibility
Table 2. Effects of regrowth intervals and time of day on composition of Kikuyu grass in Study 2
Sampling time |
DM content |
Total N |
WSC |
Starch |
OMD |
|
30-day regrowth |
||||
10:30 |
221 |
19.8 |
43.8 |
39.6 |
0.720 |
14:15 |
231 |
20.4 |
59.2 |
53.7 |
0.675 |
16:15 |
204 |
19.9 |
53.6 |
45.4 |
0.714 |
|
45-day regrowth |
||||
10:30 |
208 |
19.8 |
46.0 |
37.6 |
0.640 |
14:15 |
214 |
18.6 |
55.3 |
54.9 |
0.647 |
16:15 |
191 |
17.4 |
54.7 |
49.4 |
0.621 |
Regrowth |
P<0.05 |
P<0.10 |
ns |
ns |
P<0.10 |
Time of day |
P<0.01 |
ns |
P<0.01 |
P<0.05 |
P<0.05 |
Interaction |
ns |
ns |
ns |
ns |
P<0.01 |
s.e.d. |
7.3 |
0.86 |
1.92 |
5.20 |
0.0197 |
Notes: ns = not significant. s.e.d. = significat difference. OMD = organic matter digestibility
CONCLUSIONS
The benefits of higher WSC content obtained by delaying cutting to the afternoon are small, as WSC levels were still well below the critical value required to ensure a good silage fermentation. In addition, cutting in the afternoon could have a negative effect on the ensiling process by slowing wilting. A slow wilt has been shown to adversely affect the fermentation quality of Kikuyu grass.
ACKNOWLEDGEMENTS
We are greatly indebted to the Australian Dairy Research and Development Corporation and NSW Agriculture for funding this research, and for assistance from local dairy producers who provided access to land and equipment.
REFERENCE
Wilkinson, M. 1990. Silage UK. 6th edition. Marlow, UK: Chalcombe Publications.