Previous Page Table of Contents Next Page


Poster 8.2: Effect of time of day on the WSC content of Kikuyu grass - Alan G. Kaiser, John W. Piltz, John F. Hamilton and Euie J. Havilah


Alan G. Kaiser and John W. Piltz

John F. Hamilton and Euie J. Havilah



NSW Agriculture, Wagga Wagga Agricultural Institute
PMB, Wagga Wagga
NSW, 2650, Australia
E-mail: [email protected]

NSW Agriculture, Pasture Research Unit
PO Box 63, Berry
NSW, 2535, Australia

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
(Australian Eastern Standard Time)

DM content
(g/kg)

N content
(g/kg DM)

WSC
(g/kg DM)

Starch
(g/kg DM)

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
(Australian Eastern Standard Time)

DM content
(g/kg)

Total N
(g/kg DM)

WSC
(g/kg DM)

Starch
(g/kg DM)

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.


Previous Page Top of Page Next Page