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

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.

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 24^th 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/P₂O₅kg/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.

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
Variety	Boot	Head	Milk	Soft dough	Grain maturity
79 Ab 382 (TX) (80 SA 94)	60.1^ab	17.5^fghi	13.0^f	15.6^defgh	14.7^bcde
79 Ab 384 (TX) (80 SA 95)	53.3^bcdef	18.6^defgh	13.9^f	13.3^gh	12.6^de
CI – 8251	48.3^defg	21.1^abc	18.1^abc	21.5^ab	19.1^abc
Jasari	51.3^cdefg	22.1^a	19.1^ab	17.7^bcdef	21.9^a
SRCP X 80 Ab 2806	60.3^ab	19.4^bcdef	17.6^bcd	15.4^efgh	11.5^e
Lampton	47.7^efg	21.7^ab	18.3^abc	15.1^fgh	15.0^bcde
SRCP X 80 Ab 2252	61.3^a	17.9^efgh	13.9^f	17.4^cdef	11.4^e
CI – 8235	49.3^cdefg	21.0^abc	13.5^f	16.6^cdefg	16.1^abcde
CI – 8237	46.0^fg	21.2^abc	18.2^abc	12.3^h	14.2^bcde
Grayalgeris	44.4^g	19.1^cdefg	18.4^abc	20.5^abc	19.9^ab
SRCP X 80 Ab 2291	56.6^abc	19.9^abcde	14.9^ef	16.4^defg	14.3^bcde
Coker SR res 80 SA 130	55.5^abcd	17.2^fghi	13.8^f	14.3^fgh	11.5^e
SRCP X 80 Ab 2764	51.5^cdefg	16. 9^ghi	14.5^ef	13.0^gh	16.6^abcde
SRCP X 80 Ab 2767	54.2^abcde	18.5^defgh	13.5^f	13.9^fgh	12.2^de
Clintland 60 MN 16016	59.3^ab	16.3^hi	13.5^f	13.9^fgh	16.2^abcde
PI – 338517	46.0^fg	19.0^cdefg	16.5^cde	19.5^abcd	19.9^ab
PI – 244475	47.4^efg	20.8^abcd	17.5^bcd	19.4^abcde	18.4^abcd
PI - 5800	45.9^fg	20.5^abcd	20.5^a	23.2^a	19.8^ab
PI – 244480	49.3^cdefg	15.5ⁱ	14.6^ef	15.3^fgh	12.6^de
Ky to 78394 Canada	56.5^abc	17.2^fghi	14.5^ef	14.8^fgh	13.3^cde
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
Variety	Boot	Head	Milk	Soft dough	Grain maturity
79 Ab 382 (TX) (80 SA 94)	29.3^abcd	23.1^defg	17.9^def	16.4^def^g	27.0^ab
79 Ab 384 (TX) (80 SA 95)	28.4^bcde	23.9^cdefg	18.9^cdef	16.4^defg	26.4^ab
CI – 8251	26.2^cde	21.9^fg	18.0^def	19.2^bcde	27.1^ab
Jasari	27.0^bcde	22.2^efg	17.2^f	16.0^efg	25.6^b
SRCP X 80 Ab 2806	25.1^de	24.8^bcd	19.4^cdef	16.1^defg	24.9^b
Lampton	29.6^abc	24.5^bcde	20.0^bcd	15.5^fg	26.3^ab
SRCP X 80 Ab 2252	24.7^e	28.4^a	19.6^cde	19.0^bcdef	27.58^ab
CI – 8235	29.4^abcd	23.9^cdef	17.6^ef	21.5^ab	27.9^ab
CI – 8237	30.0^abc	24.1^cdef	20.6^bc	17.1^cdefg	26.6^ab
Grayalgeris	26.7^cde	21.5^g	17.9^def	16.6^cdefg	26.5^ab
SRCP X 80 Ab 2291	26.8^bcde	24.1^cdef	18.6^cdef	15.5^fg	25.7^b
Coker SR res 80 SA 130	27.7^bcde	27.0^ab	20.6^bc	19.6^bcd	27.5^ab
SRCP X 80 Ab 2764	31.2^ab	24.3^cdef	19.4^cdef	15.7^efg	26.7^ab
SRCP X 80 Ab 2767	33.3^a	26.0^abc	18.7^cdef	15.1^g	26.4^ab
Clintland 60 MN 16016	29.9^abc	24.2^cdef	23.6^a	23.4^a	30.3^a
PI – 338517	28.2^bcde	22.5^defg	19. 5^cdef	17.4^cdefg	27.9^ab
PI – 244475	28.6^bcde	22.3^efg	20.5^bc	21.1^ab	26.1^ab
PI - 5800	29.6^abc	24.2^cdef	22.3^ab	20.0^abc	27.0^ab
PI – 244480	25.9^cde	28.1^a	23.2^a	20.9^ab	24.6^b
Ky to 78394 Canada	30.2^abc	22.9^defg	18.4^cdef	18.6^bcdefg	28.6^ab
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
Variety	Boot	Head	Milk	Soft dough	Grain maturity
79 Ab 382 (TX) (80 SA 94)	10.6^h	31.9^ef	38.2^bcdef	36.7^bcde	58.3^abcde
79 Ab 384 (TX) (80 SA 95)	18.3^cdef	33.3^cdef	40.3^bc	39.3^abcd	61.0^abc
CI – 8251	25. 6^ab	35.6^bc	40.1^bc	38.3^bcde	53.8^de
Jasari	21.7^bcde	32.4^cdef	37.0^defg	37.9^bcde	52.5^e
SRCP X 80 Ab 2806	14.7^fgh	32.6^cdef	37.5^cdefg	39.8^abc	63.5^a
Lampton	22.7^bcd	32.4^cdef	37.1^defg	36.3^bcde	58.8^abcd
SRCP X 80 Ab 2252	14.0^fgh	30.3^fg	39.5^bcd	36.8^bcde	61.0^abc
CI – 8235	21.3^bcde	32.7^cdef	38.4^bcdef	38.8^abcd	56.0^cde
CI – 8237	24.1^abc	33.4^cdef	39.4^bcde	36.7^bcde	59.3^abcd
Grayalgeris	28.8^a	37.1^ab	38.1^bcdef	36.4^bcde	53.6^de
SRCP X 80 Ab 2291	16.5^efgh	31.3^ef	40. 9^ab	41.2^ab	60.0^abc
Coker SR res 80 SA 130	16.8^defg	32.3^cdef	39.2^bcde	37.5^bcde	61.0^abc
SRCP X 80 Ab 2764	17.2^def	31.4^ef	36.6^efg	38.1^bcde	56.7^bcde
SRCP X 80 Ab 2767	12.5^fgh	27.0^g	36.7^defg	33.3^e	61.4^abc
Clintland 60 MN 16016	10.8^gh	32.7^cdef	36.1^fg	37.0^bcde	53.4^de
PI – 338517	25.8^ab	35.6^bcd	36.5^efg	34.6^de	52.2^e
PI – 244475	24.1^abc	34.3^bcde	38.8^bcdef	36.4^bcde	55.5^cde
PI - 5800	24.5^ab	33.4^cdef	34.9^g	34.8^cde	53.2^de
PI – 244480	24.8^ab	39.4^a	43.4^a	43.7^a	62.8^ab
Ky to 78394 Canada	13.3^fgh	32.3^def	38.0^bcdef	36.8^bcde	58.1^abcde
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
Variety	Head	Milk	Soft dough
79 Ab 382 (TX) (80 SA 94)	27.6^a	30.9^ab	31.3^abcd
79 Ab 384 (TX) (80 SA 95)	24.3^c^de	27.0^cdef	31.0^abcd
CI – 8251	21.4^f	23.7^fghi	21.0^hi
Jasari	23.4^def	26.7^cdefg	28.4^bcdefg
SRCP X 80 Ab 2806	23.2^def	25.6^defgh	28.6^bcdefg
Lampton	21. 5^f	24.6^efghi	33.1^abc
SRCP X 80 Ab 2252	23.4^def	27.0^cdef	26.9^cdefgh
CI – 8235	22.3^def	30.6^ab	23.2^fghi
CI – 8237	21.3^ef	21.9^ij	33.9^ab
Grayalgeris	22.4^def	25.6^efgh	26.6^defgh
SRCP X 80 Ab 2291	24.7^bcd	25.6^efgh	26.9^cdefgh
Coker SR res 80 SA 130	23.5^def	26.4^cdefg	28.6^bcdefg
SRCP X 80 Ab 2764	27.4^ab	29. 6^abc	33.2^abc
SRCP X 80 Ab 2767	28.5^a	31.2^a	37.6^a
Clintland 60 MN 16016	26.8^abc	24.9^efghi	24.4^efghi
PI – 338517	22.9^def	27.6^bcde	28.6^bcdef
PI – 244475	22.6^def	23.32^hi	23.1^fghi
PI - 5800	22.0^def	22.3^hi	22.2^ghi
PI – 244480	17.0^g	18.8^j	20.1ⁱ
Ky to 78394 Canada	27.6^ab	29.1^abcd	29.8^bcde
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
Variety	Boot	Head	Milk	Soft dough	Grain maturity
79 Ab 382 (TX) (80 SA 94)	9.4^ab	1.3^cde	0.8^e	0.9^bcd	0.7^bcdefgh
79 Ab 384 (TX) (80 SA 95)	4.6^de	1.3^cde	0.8^e	0.8^d	0.7^fgh
CI – 8251	3.0^de	1.2^cde	0.9^cde	1.1^abc	0.9^abcde
Jasari	3.7^de	1.4^bcd	1.0^bcd	0.9^bcd	0.9^ab
SRCP X 80 Ab 2806	6.0^bcd	1.4^bcd	1.0^bcd	0.8^d	0.6^h
Lampton	3.4^de	1.4^bcd	1.0^bcd	0.8^d	0.7^cdefgh
SRCP X 80 Ab 2252	6.2^bcd	1.5^ab	0.9^de	1.0^bcd	0.6^fgh
CI – 8235	4.4^de	1.4^bcd	0.8^e	1.0^bcd	0.8^abcdefg
CI – 8237	3.3^de	1.4^bcd	1.0^bcd	0.8^d	0.7^defgh
Grayalgeris	2.5^e	1.1^e	1.0^bcd	1.0^bcd	0.9^abcde
SRCP X 80 Ab 2291	5.4^cde	1.4^bcd	0.8^e	0.8^d	0.7^efgh
Coker SR res 80 SA 130	5.0^de	1.4^bcd	0.9^cde	0.9^bcd	0.7^fgh
SRCP X 80 Ab 2764	5.4^cde	1.3^bcde	0.9^cde	0.8^d	0.8^abcdefgh
SRCP X 80 Ab 2767	8.7^abc	1.7^a	0.9^cde	0.9^bcd	0.6^fgh
Clintland 60 MN 16016	9.8^a	1.2^cde	1.1^ab	1.1^abc	0.9^abcd
PI – 338517	3.0^de	1.2^cde	1.0^bcd	1.1^abc	1.0^a
PI – 244475	3.2^de	1.3^cde	1.0^bcd	1.1^abc	0.8^abcdef
PI - 5800	3.1^de	1.4^bcd	1.2^a	1.3^a	0.9^abc
PI – 244480	3.1^de	1.1^e	0.9^cde	0.8^d	0.6^gh
Ky to 78394 Canada	8.7^abc	1.3^cde	0.9^cde	0.9^bcd	0.7^bcdefgh
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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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

Introduction

Materials and methods

Experimental site

Oats varieties

Sowing, data collection and measurements

Statistical analysis

Results

Proportion of leaf blade

Proportion of leaf sheath

Proportion of stem

Proportion of panicle

Leaf to stem ratio

Discussion

Conclusion

Acknowledgements

References

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

Introduction

Materials and methods

Experimental site

Oats varieties

Sowing, data collection and measurements

Statistical analysis

Results

Proportion of leaf blade

Proportion of leaf sheath

Proportion of stem

Proportion of panicle

Leaf to stem ratio

Discussion

Conclusion

Acknowledgements

References

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