Livestock Research for Rural Development 20 (6) 2008 Guide for preparation of papers LRRD News

Citation of this paper

Proportions of morphological fractions of oats (Avena sativa L.) as affected by variety and growth stage

Fekede Feyissa, Adugna Tolera and Solomon Melaku**

Ethiopian Institute of Agricultural Research, Holetta Research Center, Animal Feeds
and Nutrition Research Program, P.O.Box 2003, Addis Ababa, Ethiopia

*Department of Animal and Range Sciences, Hawasa University, Awassa College of

Agriculture, P.O.Box 5, Awassa, Ethiopia

**Department of Animal Sciences, Haramaya University, PO Box 138, Dire Dawa, Ethiopia

Ffeyissa@yahoo.com  or  atolera@yahoo.com

 

Abstract

 

This paper presents relative proportions of morphological fractions of 20 oats (Avena sativa L.) varieties harvested at different growth stages at Holetta, central highlands of Ethiopia. On average the proportion of leaf blade decreased from 52.2 to 15.6% with parallel increase in the proportion of stem from 19.4 to 57.6% as growth advanced from boot stage to grain maturity stage. The average proportion of leaf sheath decreased from 28.4 to 18% as growth advanced from boot stage to the soft dough stage, but it tended to regain at grain maturity stage (26.8%). The panicle proportion was found to be relatively stable increasing only by 4% units with advance in growth from heading to the soft dough stage.

 

The different varieties also exhibited considerable differences with respect to the proportion of morphological fractions over the different growth stages. Taking the physiological maturity for forage harvest of the soft dough stage as a reference, the oats varieties PI – 5800, CI – 8251 and Grayalgeris were found to contain a higher proportion of leaf in their dry matter (DM) than the other varieties, while the oats varieties PI – 244480, SRCP X 80 Ab 2291 and SRCP X 80 Ab 2806 had comparatively higher proportion of stem in their DM.  The results showed the presence of considerable varietal differences in the proportion of morphological fractions thereby suggesting the possibility of improving forage production in oats through proper exploitation of the varietal differences.

Keywords: leaf blade, leaf sheath, maturity, panicle, stem


Introduction

Oats (Avena sativa L.) is a well-adapted fodder crop grown for a long period of time in the highlands of Ethiopia. Although it was initially perceived as a fodder crop, its grain has also become part of the staple diet of human beings in some parts of the country (Lulseged 1981). Oats being an annual forage crop is highly useful for integration into the prevailing mixed crop- livestock farming systems of the Ethiopian highlands on accounts of its short-term yielding characteristics, use in overcoming seasonal feed shortages, convenience in crop rotations and its fodder conservation characteristics.

 

Different lines of oats were introduced from different parts of the world to Ethiopia in the early 1970s and mid 1980s.  However, due to lack of formal variety development and release mechanism for forage crops in the country, no significant progress has been made beyond preliminary screening and selection works. Studies conducted on oats varieties in Ethiopia were inadequate to fully describe the overall forage production potentials of the different varieties. To this effect, recommendations so far made on oats have been based on some general aspects of the varieties; mainly environmental adaptation and herbage yield regardless of morphological features and quality (Astatke 1976). On the other hand, proportion and quality of different morphological fractions as causes of differences in nutritional quality in forage crops and crop residues has been a subject of numerous experiments (Thiago and Kellaway 1982; Åman and Nordkvist 1983; Kernan et al 1984; Ohlde et al 1992; Tan et al 1995; Adugna and Sundstøl 1999). Similar studies (Ørskov 1988; Ohlde et al 1992) also showed that proportion and quality of the different morphological fractions varies considerably in temperate cereals such as wheat, oats, barley and rye. The leaf blade and leaf sheath portions have been reported to be more nutritious and digestible than stems.

 

It is generally evident that dry matter yield as a single index of productivity could not lead to conclusive remarks in forage crops. Getnet (1999) through interviewing farmers has pointed out that the varieties of oats that were recommended from earlier introductions and put under production had high stem proportion and the hay made out of them is less palatable to livestock. This clearly shows that the different varieties need to be assessed for their morphological features and nutritional quality to make concrete recommendations for forage production. Therefore, this study was designed to assess the proportion of different morphological fractions at different growth stages in 20 selected varieties.

 

Materials and methods 

Experimental site

 

The experiment was conducted at Holetta Agricultural Research Center (HARC) in the central highlands of Ethiopia. The center is located at 38° 30`E, 9° 3`N and 45 km west of Addis Ababa and lies at an elevation of 2400 m above sea level. Based on an average meteorological data of 34 years (1969 – 2003) of the HARC, the annual rainfall of the area is 1066 mm with bimodal distribution, over 70% of which occurs during the main rainy season (June to September) and 30% during the small rainy season (February to April). The average annual minimum and maximum temperatures of the area are 6° to 22°C. The area is also characterized by occasional frost that occurs in the months of October to December, where temperatures below zero are recorded for few days during these months.

 

The major soil type of the area is a red-brown clay loam nitosol, and analysis of composite soil sample taken from the upper 20 – 30 cm soil horizon of the specific experimental plot in this study indicated that the soil had a pH (1:1 H2O) of 5.1, total N content of 0.2%, P content of 12.4 ppm, OM content of 2.2% and cation exchange capacity (CEC) of 17.0 meq/100 g soil. Similarly, values for the major climatic variables during the course of the experimental period (June – December 2003) were: total rainfall (686 mm), average minimum and maximum temperatures (6.5° and 21.2°C) and relative humidity of 60.6% (HARC meteorological data).

 

Oats varieties

 

Twenty oats varieties that were selected on the basis of their adaptation to the highlands of Ethiopia from previous introduction and screening works were used for the experiment. The varieties and their respective origins are shown in Table 1.


Table 1.  Varieties of oats used in the study

Serial No

Variety

Origin

1

79 Ab 382 (TX) (80 SA 94)

CIMMYT

2

79 Ab 384 (TX) (80 SA 95)

CIMMYT

3

CI – 8251

Yugoslavia

4

Jasari    

Kenya

5

SRCP X 80 Ab 2806

CIMMYT

6

Lampton

Ethiopia

7

SRCP X 80 Ab 2252

CIMMYT

8

CI – 8235

USA

9

CI – 8237

USA

10

Grayalgeris

Algeria  

11

SRCP X 80 Ab 2291

CIMMYT

12

Coker SR res 80 SA 130

CIMMYT

13

SRCP X 80 Ab 2764

CIMMYT

14

SRCP X 80 Ab 2767

CIMMYT

15

Clintland 60 MN 16016

CIMMYT

16

PI – 338517

Not specified

17

PI – 244475

Not specified

18

PI – 5800             

Not specified

19

PI – 244480

Not specified

20

Ky to 78394 Canada

CIMMYT


Sowing, data collection and measurements

 

The varieties were sown on 24th of June 2003 in a Randomized Complete Block Design (RCBD) with four replications. Sowing was made by drilling the seeds in rows of 0.2 m wide on 4m x 3m plots spaced 0.5 m apart. A starter dose of fertilizer at the rate of 18/46 N/P2O5 kg/ha (100 kg DAP/ha) was applied to all plots at sowing. A uniform seeding rate of 100 kg/ha was used for all the varieties as per previous recommendation for pure stand of oats in the highlands of Ethiopia (Astatke 1979). All the plots were hand weeded once, a month after sowing and thereafter as required based on occurrence of weeds.

 

The varieties were closely examined beginning from the early vegetative growth and record of the different growth stages (boot, heading, milk, soft dough and grain maturity stages) was taken. To determine proportions on DM basis of the different morphological fractions, five plants were randomly clipped at ground level from each plot at the different growth stages (Habib et al 1995; Getnet 1999).  The plants were then manually fractionated into the different morphological fractions including leaf blade, leaf sheath, stem and panicle except at boot stage where panicle was not developed and at grain maturity where it was harvested along with seed. After measuring their fresh weights, the fractions were oven dried at 100°C for 24 h in order to determine their dry biomass. Proportions of each morphological fraction were then determined as the ratio of dry biomass of each fraction to total dry biomass multiplied by 100.

 

Statistical analysis

 

Analysis of variance was performed using the statistical analysis system (SAS) software (SAS 2001) and mean separation was carried out using the Duncans new multiple range test.

The following general linear model was used for the analysis:

Yijk = m + Bi + Oj+ Sk+ (OS)jk + Eijk

Where:

Y – the measured response

m  - the overall mean

Bi – effect of the ith block

Oj  – effect of the jth oats variety

Sk – effect of kth growth stage

(OS)jk – interaction effect of jth oats variety and kth growth stage

Eijk – the error term associated with each Yijk

 

Results  

Proportion of leaf blade

 

Table 2 shows the proportion of leaf blade in 20 oats varieties at different growth stages.


Table 2.  Proportion of leaf blade on dry matter basis in 20 oats varieties at different growth stages

Variety

Growth stage

Boot

Head

Milk

Soft dough

Grain maturity

79 Ab 382 (TX) (80 SA 94)

60.1ab

17.5fghi

13.0f

15.6defgh

14.7bcde

79 Ab 384 (TX) (80 SA 95)

53.3bcdef

18.6defgh

13.9f

13.3gh

12.6de

CI – 8251

48.3defg

21.1abc

18.1abc

21.5ab

19.1abc

Jasari

51.3cdefg

22.1a

19.1ab

17.7bcdef

21.9a

SRCP X 80 Ab 2806

60.3ab

19.4bcdef

17.6bcd

15.4efgh

11.5e

Lampton

47.7efg

21.7ab

18.3abc

15.1fgh

15.0bcde

SRCP X 80 Ab 2252

61.3a

17.9efgh

13.9f

17.4cdef

11.4e

CI – 8235

49.3cdefg

21.0abc

13.5f

16.6cdefg

16.1abcde

CI – 8237

46.0fg

21.2abc

18.2abc

12.3h

14.2bcde

Grayalgeris

44.4g

19.1cdefg

18.4abc

20.5abc

19.9ab

SRCP X 80 Ab 2291

56.6abc

19.9abcde

14.9ef

16.4defg

14.3bcde

Coker SR res 80 SA 130

55.5abcd

17.2fghi

13.8f

14.3fgh

11.5e

SRCP X 80 Ab 2764

51.5cdefg

16. 9ghi

14.5ef

13.0gh

16.6abcde

SRCP X 80 Ab 2767

54.2abcde

18.5defgh

13.5f

13.9fgh

12.2de

Clintland 60 MN 16016

59.3ab

16.3hi

13.5f

13.9fgh

16.2abcde

PI – 338517   

46.0fg

19.0cdefg

16.5cde

19.5abcd

19.9ab

PI – 244475

47.4efg

20.8abcd

17.5bcd

19.4abcde

18.4abcd

PI - 5800

45.9fg

20.5abcd

20.5a

23.2a

19.8ab

PI – 244480

49.3cdefg

15.5i

14.6ef

15.3fgh

12.6de

Ky to 78394 Canada

56.5abc

17.2fghi

14.5ef

14.8fgh

13.3cde

Mean

52.2

19.1

16.0

16.5

15.6

SE

2.7

0.83

0.9

1.4

2.3

abc… means with different superscripts within a column are significantly different (P<0.05)


The proportion of leaf blade ranged from 44 to 61% at boot stage, 16 to 22% at heading, 13 to 20% at milk, 12 to 23% at the soft dough and 11 to 20% at grain maturity stages. Significantly higher (P<0.05) proportion of leaf blade was obtained at boot stage than in the other stages for all the varieties. The proportion of leaf blade showed a marked reduction as growth advanced from boot to heading stage, but showed slight and non-significant (P>0.05) variation from milk stage onwards in most of the varieties. The overall average proportion of leaf blade decreased by 70% as growth advanced from boot stage to grain maturity stage.

 

Considerable and variable differences were also observed among the varieties in the proportion of leaf blade at different growth stages. SRCP X 80 Ab 2252, SRCP X 80 Ab 2806 and 79 Ab 382 (TX) (80 SA 94) had significantly higher leaf blade proportion (P<0.05) whereas Grayalgeris, PI-5800 and CI-8237 had significantly lower (P<0.05) proportion than most of the other varieties at boot stage. Jasari, Lampton, CI-8237, CI-8251 and CI-8235 had significantly higher (P<0.05) proportion of leaf blade than most of the other varieties at heading stage. At milk stage, the proportion of leaf blade was significantly higher (P<0.05) in PI-5800 followed by Jasari, Grayalgeris and Lampton. On the other hand, PI-244480, Clintland 60 MN  16016 and SRCP X 80 Ab 2764 had significantly lower (P<0.05) proportion of leaf blade at heading stage, while 79 Ab 382 (TX) (80 SA 94), SRCP X 80 Ab 2767 and CI-8235 had significantly lower (P<0.05) proportion of leaf blade than most of the other varieties at milk stage.

 

At the soft dough stage, the proportion of leaf blade was significantly higher (P<0.05) in PI-5800, CI-8251, Grayalgeris, PI-338517 and   PI- 244475, but was significantly lower (P<0.05) in CI-8237, SRCP X 80 Ab 2764, 79 Ab 384 (TX) (80 SA 95) and SRCP X 80 Ab 2767 than most of the other varieties. At grain maturity stage, Jasari, PI-338517, Grayalgeris, PI-5800 and CI-8251 had significantly higher (P<0.05) proportion of leaf blade, while SRCP X 80 Ab 2252, Coker SR res 80 SA 130 and SRCP X 80 Ab 2806 had significantly lower (P<0.05) proportion of leaf blade than most of the other varieties. It was generally shown that varieties with higher proportion of leaf blade during the early growth stage had lower proportion of leaf blade towards later stages and vice versa.

 

Proportion of leaf sheath

 

Table 3 shows the proportion of leaf sheath in 20 oats varieties at different growth stages.


Table 3.  Proportion of leaf sheath on dry matter basis in 20 oats varieties at different growth stages

Variety

Growth stage

Boot

Head

Milk

Soft dough

Grain maturity

79 Ab 382 (TX) (80 SA 94)

29.3abcd

23.1defg

17.9def

16.4defg

27.0ab

79 Ab 384 (TX) (80 SA 95)

28.4bcde

23.9cdefg

18.9cdef

16.4defg

26.4ab

CI – 8251

26.2cde

21.9fg

18.0def

19.2bcde

27.1ab

Jasari

27.0bcde

22.2efg

17.2f

16.0efg

25.6b

SRCP X 80 Ab 2806

25.1de

24.8bcd

19.4cdef

16.1defg

24.9b

Lampton

29.6abc

24.5bcde

20.0bcd

15.5fg

26.3ab

SRCP X 80 Ab 2252

24.7e

28.4a

19.6cde

19.0bcdef

27.58ab

CI – 8235

29.4abcd

23.9cdef

17.6ef

21.5ab

27.9ab

CI – 8237

30.0abc

24.1cdef

20.6bc

17.1cdefg

26.6ab

Grayalgeris

26.7cde

21.5g

17.9def

16.6cdefg

26.5ab

SRCP X 80 Ab 2291

26.8bcde

24.1cdef

18.6cdef

15.5fg

25.7b

Coker SR res 80 SA 130

27.7bcde

27.0ab

20.6bc

19.6bcd

27.5ab

SRCP X 80 Ab 2764

31.2ab

24.3cdef

19.4cdef

15.7efg

26.7ab

SRCP X 80 Ab 2767

33.3a

26.0abc

18.7cdef

15.1g

26.4ab

Clintland 60 MN 16016

29.9abc

24.2cdef

23.6a

23.4a

30.3a

PI – 338517   

28.2bcde

22.5defg

19. 5cdef

17.4cdefg

27.9ab

PI – 244475

28.6bcde

22.3efg

20.5bc

21.1ab

26.1ab

PI - 5800

29.6abc

24.2cdef

22.3ab

20.0abc

27.0ab

PI – 244480

25.9cde

28.1a

23.2a

20.9ab

24.6b

Ky to 78394 Canada

30.2abc

22.9defg

18.4cdef

18.6bcdefg

28.6ab

Mean

28.4

24.2

19.6

18.1

26.8

SE

1.6

0.9

0.8

1.2

1.6

abc… means with different superscripts within a column are significantly different (P<0.05)


The overall trend showed that the proportion of leaf sheath decreased from boot to soft dough stage but tended to regain at grain maturity. It generally ranged from 24.7 to 33.3% at boot, 21.5 to 28.4% at heading, 17.2 to 23.6% at milk, 15.1 to 23.4% at soft dough and 24.6 to 30.3% at grain maturity stages. The overall mean proportion of leaf sheath decreased from 28 to 18% with advancing growth from boot stage to the soft dough stage and increased to 27% at grain maturity stage with reduction in overall average proportion only by 5.5% as growth advanced from boot stage to grain maturity stage.

 

As in the case of leaf blade, the variation in the proportion of leaf sheath among varieties was not consistent over the different growth stages. SRCP X 80 Ab 2767, SRCP X 80 Ab 2764 and Ky to 78394 Canada in descending order had comparatively higher, while SRCP X 80 Ab 2252, SRCP X 80 Ab 2806 and PI-244480 had lower proportion of leaf sheath at boot stage than the other varieties. At heading stage, significantly higher (P<0.05) proportion of leaf sheath was recorded for SRCP X 80 Ab 2252, PI-244480 and Coker SR res 80 SA 130, whereas Grayalgeris and CI- 8251 had significantly lower (P<0.05) proportion of leaf sheath than most of the other varieties. At milk stage, the relative proportion of leaf sheath was significantly higher (P<0.05) in Clintland 60 MN 16016, PI-244480 and PI-5800, and significantly lower (P<0.05) in Jasari, CI-8235, 79 Ab 382 (TX) (80 SA 94) and Grayalgeris than most of the other varieties. Similarly, Clintland 60 MN 16016, PI-8235 and PI-244475 had higher (P<0.05), whereas SRCP X 80 Ab 2767, Lampton, and SRCP X 80 Ab 2291 had significantly lower (P<0.05) proportion of leaf sheath at the soft dough stage. The proportion of leaf sheath in the straw (at grain maturity) was comparatively higher in Clintland 60 MN 16016 and Ky to 78394 Canada in descending order and was lower in PI-244480 and SRCP X 80 Ab 2806.

 

Proportion of stem

 

The proportion of stem in 20 oats varieties at different growth stages is presented in Table 4.


Table 4.  Proportion of stem on dry matter basis in 20 oats varieties at different growth stages

Variety

Growth stage

Boot

Head

Milk

Soft dough

Grain maturity

79 Ab 382 (TX) (80 SA 94)

10.6h

31.9ef

38.2bcdef

36.7bcde

58.3abcde

79 Ab 384 (TX) (80 SA 95)

18.3cdef

33.3cdef

40.3bc

39.3abcd

61.0abc

CI – 8251

25. 6ab

35.6bc

40.1bc

38.3bcde

53.8de

Jasari

21.7bcde

32.4cdef

37.0defg

37.9bcde

52.5e

SRCP X 80 Ab 2806

14.7fgh

32.6cdef

37.5cdefg

39.8abc

63.5a

Lampton

22.7bcd

32.4cdef

37.1defg

36.3bcde

58.8abcd

SRCP X 80 Ab 2252

14.0fgh

30.3fg

39.5bcd

36.8bcde

61.0abc

CI – 8235

21.3bcde

32.7cdef

38.4bcdef

38.8abcd

56.0cde

CI – 8237

24.1abc

33.4cdef

39.4bcde

36.7bcde

59.3abcd

Grayalgeris

28.8a

37.1ab

38.1bcdef

36.4bcde

53.6de

SRCP X 80 Ab 2291

16.5efgh

31.3ef

40. 9ab

41.2ab

60.0abc

Coker SR res 80 SA 130

16.8defg

32.3cdef

39.2bcde

37.5bcde

61.0abc

SRCP X 80 Ab 2764

17.2def

31.4ef

36.6efg

38.1bcde

56.7bcde

SRCP X 80 Ab 2767

12.5fgh

27.0g

36.7defg

33.3e

61.4abc

Clintland 60 MN 16016

10.8gh

32.7cdef

36.1fg

37.0bcde

53.4de

PI – 338517   

25.8ab

35.6bcd

36.5efg

34.6de

52.2e

PI – 244475

24.1abc

34.3bcde

38.8bcdef

36.4bcde

55.5cde

PI - 5800

24.5ab

33.4cdef

34.9g

34.8cde

53.2de

PI – 244480

24.8ab

39.4a

43.4a

43.7a

62.8ab

Ky to 78394 Canada

13.3fgh

32.3def

38.0bcdef

36.8bcde

58.1abcde

Mean

19.4

32.3

38.3

37.5

57.6

SE

2.1

1.2

1.0

1.8

2.2

abc… means with different superscripts within a column are significantly different (P<0.05)


Unlike the proportion of leaf blade, the stem fraction showed an increasing trend with advancing maturity from boot stage to grain maturity stage in all the varieties. The stem proportion was significantly lower (P<0.05) at boot stage and higher (P<0.05) at grain maturity stage, but did not significantly vary (P>0.05) between milk and soft dough stages. The proportion of stem in general ranged from 10.64 to 28.83% at boot, 27.03 to 39.44% at heading, 349 to 43.4% at milk, 33.3 to 43.7% at soft dough and 52.2 to 63.5% at grain maturity stages. The overall average proportion of stem showed an increment of 196% with advancing growth from boot stage to grain maturity stage.

 

 As in the case of the other morphological fractions, there was significant but variable differences among the varieties in the proportion of stem at different growth stages.  The oats varieties Grayalgeris, PI-338517, CI-8251 and PI-244480 had significantly higher (P<0.05) proportion of stem than most other varieties at boot and heading stages. On the other hand, 79 Ab 382 (TX) (80 SA 94), Clintland 60 MN  16016, SRCP X 80 Ab 2767 and Ky to 78394 Canada had significantly lower (P<0.05) proportion of stem at boot stage, whereas SRCP X 80 Ab 2767 had lower proportion of stem followed by SRCP X 80 Ab 2252 and SRCP X 80 Ab 2291 at heading stage. The oats variety PI-244480 had still higher proportion of stem followed by SRCP X 80 Ab 2291 at both milk and soft dough stages. Likewise, the proportion of stem was relatively higher in 79 Ab 384 (TX) (80 SA 95) at both stages. The oats varieties CI- 8251 and SRCP X 80 Ab 2806 also had higher proportion of stem at milk and soft dough stage respectively. The proportion of stem was significantly lower (P<0.05) in PI-5800 followed by Clintland 60 MN 16016, PI-338517, SRCP X 80 Ab 2764 and SRCP X 80 Ab 2767 at milk stage. Similarly, SRCP X 80 Ab 2767, PI-338517 and PI- 5800 had lower proportion of stem at the soft dough stage. The proportion of stem in the straw (at grain maturity stage) was higher in SRCP X 80 Ab 2806, PI-244480, SRCP X 80 Ab 2767 and 79 Ab 384 (TX) (80 SA 95) while PI-338517, Jasari, PI- 5800, Clintland 60 MN 16016 and Grayalgeris had comparatively lower proportion of stem in the straw. In general, stem accounted for more than 50% of the straw in all the varieties.

 

Proportion of panicle

 

Table 5 shows the proportion of panicle in the 20 varieties at heading, milk and soft dough stages.


Table 5.  Proportion of panicle on dry matter basis in 20 oats varieties at different growth stages

Variety

Growth stage

Head

Milk

Soft dough

79 Ab 382 (TX) (80 SA 94)

27.6a

30.9ab

31.3abcd

79 Ab 384 (TX) (80 SA 95)

24.3cde

27.0cdef

31.0abcd

CI – 8251

21.4f

23.7fghi

21.0hi

Jasari

23.4def

26.7cdefg

28.4bcdefg

SRCP X 80 Ab 2806

23.2def

25.6defgh

28.6bcdefg

Lampton

21. 5f

24.6efghi

33.1abc

SRCP X 80 Ab 2252

23.4def

27.0cdef

26.9cdefgh

CI – 8235

22.3def

30.6ab

23.2fghi

CI – 8237

21.3ef

21.9ij

33.9ab

Grayalgeris

22.4def

25.6efgh

26.6defgh

SRCP X 80 Ab 2291

24.7bcd

25.6efgh

26.9cdefgh

Coker SR res 80 SA 130

23.5def

26.4cdefg

28.6bcdefg

SRCP X 80 Ab 2764

27.4ab

29. 6abc

33.2abc

SRCP X 80 Ab 2767

28.5a

31.2a

37.6a

Clintland 60 MN 16016

26.8abc

24.9efghi

24.4efghi

PI – 338517   

22.9def

27.6bcde

28.6bcdef

PI – 244475

22.6def

23.32hi

23.1fghi

PI - 5800

22.0def

22.3hi

22.2ghi

PI – 244480

17.0g

18.8j

20.1i

Ky to 78394 Canada

27.6ab

29.1abcd

29.8bcde

Mean

23. 7

26.1

27.9

SE

1.1

1.2

2.2

abc… means with different superscripts within a column are significantly different (P<0.05)


The proportion of panicle showed an increasing trend from heading to the soft dough stage in most varieties with few exceptions such as CI-8235 and CI- 8251 in which the panicle proportion was significantly higher (P<0.05) at milk stage than at heading and soft dough stages. In general, the proportion of panicle ranged from 17.0 to 28.5% at heading, 18.8 to 31.2% at milk and 20.1 to 37.6% at soft dough stages. The overall average proportion of panicle increased by 18% as growth advanced from heading to the soft dough stage.

 

SRCP X 80 Ab 2767 had significantly higher (P<0.05) while PI- 244480 had significantly lower (P<0.05) proportion of panicle than the other varieties at all the growth stages. Moreover, 79 Ab 382 (TX) (80 SA 94), Ky to 78394 Canada, SRCP X 80 Ab 2764 and CI-8235 had comparatively higher proportion of panicle at heading and milk stages and CI-8237 and Lampton had relatively higher proportion of panicle in addition to those mentioned above at the soft dough stage. The proportion of panicle tended to be lower in CI-8251, Lampton and CI-8237 at heading stage, in CI- 8237, PI-5800 and PI-244475 at milk stage and in CI-8251, PI-5800 and PI-244475 at the soft dough stage, all following PI-244480 which consistently had the lowest proportion of panicle over the growth stages.

 

Leaf to stem ratio

 

Leaf to stem ratio of the 20 oats varieties at different growth stages is shown in Table 6.


Table 6.  Leaf to stem ratio* of 20 oats varieties at different growth stages

Variety

Growth stage

Boot

Head

Milk

Soft dough

Grain maturity

79 Ab 382 (TX) (80 SA 94)

9.4ab

1.3cde

0.8e

0.9bcd

0.7bcdefgh

79 Ab 384 (TX) (80 SA 95)

4.6de

1.3cde

0.8e

0.8d

0.7fgh

CI – 8251

3.0de

1.2cde

0.9cde

1.1abc

0.9abcde

Jasari

3.7de

1.4bcd

1.0bcd

0.9bcd

0.9ab

SRCP X 80 Ab 2806

6.0bcd

1.4bcd

1.0bcd

0.8d

0.6h

Lampton

3.4de

1.4bcd

1.0bcd

0.8d

0.7cdefgh

SRCP X 80 Ab 2252

6.2bcd

1.5ab

0.9de

1.0bcd

0.6fgh

CI – 8235

4.4de

1.4bcd

0.8e

1.0bcd

0.8abcdefg

CI – 8237

3.3de

1.4bcd

1.0bcd

0.8d

0.7defgh

Grayalgeris

2.5e

1.1e

1.0bcd

1.0bcd

0.9abcde

SRCP X 80 Ab 2291

5.4cde

1.4bcd

0.8e

0.8d

0.7efgh

Coker SR res 80 SA 130

5.0de

1.4bcd

0.9cde

0.9bcd

0.7fgh

SRCP X 80 Ab 2764

5.4cde

1.3bcde

0.9cde

0.8d

0.8abcdefgh

SRCP X 80 Ab 2767

8.7abc

1.7a

0.9cde

0.9bcd

0.6fgh

Clintland 60 MN 16016

9.8a

1.2cde

1.1ab

1.1abc

0.9abcd

PI – 338517   

3.0de

1.2cde

1.0bcd

1.1abc

1.0a

PI – 244475

3.2de

1.3cde

1.0bcd

1.1abc

0.8abcdef

PI - 5800

3.1de

1.4bcd

1.2a

1.3a

0.9abc

PI – 244480

3.1de

1.1e

0.9cde

0.8d

0.6gh

Ky to 78394 Canada

8.7abc

1.3cde

0.9cde

0.9bcd

0.7bcdefgh

Mean

5.1

1.3

0.9

0.9

0.8

SE

1.2

0.1

0.1

0.1

0.1

* Leaf to stem ratio = Leaf blade + Leaf sheath/stem
abc… means with different superscripts within a column are significantly different (P<0.05)


The leaf to stem ratio generally showed a decreasing trend from boot to grain maturity stages, but sharply declined between boot to heading stages and the decline from heading stage onwards was low and variable. It ranged from 2.5 to 9.8, 1.1 to 1.7, 0.8 to 1.2, 0.8 to 1.3 and 0.6 to 1.0 units at boot, heading, milk, soft dough and grain maturity stages, respectively. The leaf to stem ratio was significantly higher (P<0.05) at boot stage than in the other growth stages in all the varieties, but the difference was not significant (P>0.05) from heading to grain maturity stages in most of the varieties. The overall average leaf to stem ratio of the 20 varieties was decreased by 85% as growth advanced from boot stage to grain maturity stage.

 

Considerable variability was realized among the varieties with respect to leaf to stem ratio at different growth stages. Clintland 60 MN 16016, 79 Ab 382 (TX) (80 SA 94), SRCP X 80 Ab 2767 and Ky to 78394 Canada had significantly higher (P<0.05) leaf to stem ratio than most of the other varieties whereas, Grayalgeris, CI-8251 and PI-338517 had lower (P<0.05) leaf to stem ratio at boot stage. At heading stage, leaf to stem ratio was still higher in SRCP X 80 Ab 2767 followed by SRCP X 80 Ab 2252 and Lampton while Grayalgeris, PI-244480 and PI-338517 had lower leaf to stem ratio. At milk stage, PI-5800, Clintland 60 MN 16016 and Lampton had significantly higher (P<0.05) while CI-8235, 79 Ab 382 (TX) (80 SA 94) and 79 Ab 384 (TX) (80 SA 95) had significantly lower (P<0.05) leaf to stem ratio than most of the other varieties. Similarly, the oats varieties PI-5800, PI-244475 and CI-8251 in descending order had higher leaf to stem ratio, while 79 Ab 384 (TX) (80 SA 95), SRCP X 80 Ab 2764 and SRCP X 80 Ab 2291 had comparatively lower leaf to stem ratio at the soft dough stage.  The leaf to stem ratio in the straw (at grain maturity stage) was higher in PI-338517 followed by Jasari and PI-5800 but lower in SRCP X 80 Ab 2806 followed by PI-244480 and SRCP X 80 Ab 2767.

 

Discussion 

Both variety and growth stage had considerable effects on the proportion of morphological fractions in oats. The variation among the varieties in the proportion of morphological fractions might have arisen from heritable genotypic characteristics such as differences in maturity and plant height. Capper et al (1988) reported higher proportions of leaf in the straw of shorter barley and wheat varieties. Ramazin et al (1986) also reported that shorter or late-maturing barley varieties are likely to have higher proportion of leaf and better quality straw than tall or early-maturing varieties. Similarly, Mohammed (1992) confirmed that leaf proportion was higher in late maturing wheat cultivars. Moreover, better straw quality was reported in shorter varieties of wheat, barley and oats (Colucci et al 1992). The results of the present study in oats was in agreement with the above findings as shorter varieties tended to have higher proportion of leaf and leaf to stem ratio than taller varieties. This could be due to more number of nodes from where the leaves arise and/or shorter stem inter-nodes in shorter varieties as compared to in taller varieties that are characterized by continuous elongation throughout the growing season.

 

Early maturing varieties such as SRCP X 80 Ab 2252, 79 Ab 382 (TX) (80 SA 94), SRCP X 80 Ab 2806 and Clintland 60 MN 16016 had higher proportion of leaf than stem with the corresponding higher leaf to stem ratio during the early stages of growth, while late maturing varieties such as Grayalgeris, PI-338517, CI-8251, PI-244475 and PI-5800 had comparatively higher leaf to stem ratio towards the later stages of growth. This could be attributed to the longer vegetative growth period which allowed late maturing varieties to make full use of the better growing conditions as compared to early maturing varieties that progress through different development stages at a faster rate and tend to express their potential in the earlier growth stages.

  

The tendency to shift from vegetative growth stage to the grain filling stage could explain the marked reduction in the proportions of leaf blade and leaf sheath as growth advanced from boot stage to milk stage in the oats varieties. Nelson et al (1995) illustrated that during the course of development from boot stage to heading and milk stages, nutrients stored in the lower leaves are redistributed to the upper plant, including the developing kernels, causing some of the bottom leaves to die with the consequent drop in the proportion of leaves in wheat, barley and oats. On the other hand, the proportion of leaf blade in maize stover was reported to be similar between the two early stages of maturity (30.2 and 22.5% grain moisture content), but significantly decreased as grain moisture content decreased to 12.3% (Adugna and Sundstøl 1999). Shattering loss due to brittleness and detachment from the stem was reported to be the major cause for reduction in the proportion of leaf blade in maize stover with advancing maturity (Adugna and Sundstøl 1999). The absence of much difference in the proportion of leaf blade from heading to grain maturity stages and the comparatively higher proportion of leaf sheath towards later stages could imply the ability of oats to retain more of their leaf material as compared to the coarse stemmed crops such as maize.

 

The increase in the proportion of leaf sheath at later stage could be explained with respect to the development pattern of the stem as the sheath represents the tubular portion of a grass leaf that encloses the stem. At boot stage, the stem was highly succulent and less developed while the sheath was thicker. From heading to soft dough stages, the stem showed progressive development while the sheath was getting thinner with the consequent low proportion. Hence, the increase in the proportion of leaf sheath at grain maturity stage indicates that the sheath may rebound its thickness after the termination of stem development in oats. Adugna and Sundstøl (1999) also reported that the proportion of leaf sheath decreased only by 4.5% as grain moisture content decreased from about 30 – 10% in maize.

 

The overall average proportion of stem increased by 196%, whereas, the proportions of leaf blade, leaf sheath and leaf to stem ratio decreased by 70%, 5.5% and 85%, respectively, as growth advanced from boot to grain maturity stage. The stem accounted for more than 50% of the straw in all the oats varieties. Contrary to this, Capper et al (1988) reported that leaf blade and sheath made up a higher proportion than stem in barley and wheat straws (35.5 and 43%, respectively). Similarly, a study on eight maize varieties at Awassa (Adugna et al 1999) has shown that the proportion of stem ranged from 30.6 to 49.7% with a mean of 39.1% in the stover.

 

The proportion of panicle was increased by 18% as growth advanced from heading to the soft dough stage. The milk and soft dough stages did not differ much with regard to the average proportion of morphological fractions which in turn could imply that herbage quality may not differ at these growth stages so that harvesting for hay could be made at a stage when yield is high. Besides its effect on proportion of morphological fractions, stage of maturity at harvest is the most important factor determining the yield and quality of a cereal crop when used as forage. As reported by Johnston et al (1998), forage yield increased by 90% to 110% as maturity advanced from the boot to the soft dough stage in both oats and barley. At the same time the authors reported that, CP dropped by about 40 to 50%, ADF and NDF levels increased by 15% to 25%. This indicates that maximum yield of energy per unit area will occur when the cereal is harvested at the soft dough stage whereas protein content is high in the earlier stages. Ciha (1983) also reported that forage yield increased by 37%, 68%, 73% and 137% whereas the CP decreased by 32%, 37%, 36% and 53% from heading to the soft-dough stage in oats, barley, wheat and triticale, respectively. With earlier harvest, a second cutting could be possible under good moisture conditions that promote better re-growth, and this enables to get a considerable amount of high quality forage (Ciha 1983).

 

Generally, the considerable variability among the oats varieties with respect to the proportions of morphological fractions and leaf to stem ratio at different growth stages indicates the presence of wide scopes for exploiting varietal differences for forage production. Moreover, the inconsistency of variation in the proportion of morphological fractions among the varieties at different growth stages indicates the need and possibility to select different varieties for different growth stages based on the intended quality of the forage to be produced. Owing to their high proportion of leaf blade, SRCP X 80 Ab 2252, SRCP X 80 Ab 2806, 79 Ab 382 (TX) (80 SA 94) and Clintland 60 MN 16016 could provide comparatively better quality forage than the other varieties at boot stage. On the other hand, better quality forage could be obtained from PI-5800, CI-8251 and Grayalgeris at physiological maturity for forage harvest (soft dough stage) as they had comparatively higher proportion of leaf blade at this stage.

 

Conclusion 


Acknowledgements
 

We would like to acknowledge the financial support by the Agricultural Research and Training Project (ARTP) of the Ethiopian Agricultural Research Organization (EARO). We are also grateful to the staff of Feeds and Nutrition Research Program at Holetta Agricultural Research Center for their keen cooperation during the execution of the experiment both at field and in the laboratory.

 

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Received 17 January 2008; Accepted 4 March 2008; Published 10 June 2008

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