African Crop Science Journal African Crop Science Society ISSN: 1021-9730 EISSN: 2072-6589 Vol. 9, Num. 1, 2001, pp. 67-76

African Crop Science Journal, Vol. 9, No. 1, March 2001, pp. 67-76

Code Number: CS01036

ABSTRACT

An experiment was conducted in 1995 and 1996 to determine optimum spacing for potato cultivars Awash, Menagesha and Tolcha that differ in canopy morphology. There were significant varietal and spacing effects on seed tuber size, average tuber weight (ATW) and number (ATN) per square metre. Highest yields of 38.5, 62.6 and 46.5 t ha^-1 were obtained for Awash, Menagesha and Tolcha, respectively, from a 45 cm between-row spacing with either 25 or 30 cm in-row spacing. However, in Menagesha tuber size exceeding 40 mm constituted >80% of the total yield thus showing the need for a narrower in-row distance for seed size tuber production. In-row spacing regulated tuber size more than yield. Varieties showed different requirements for spacing for the development of optimum leaf area and maximum tuber number and yield.

Key Words: Awash, canopy morphology, Ethiopia, Menagesha, Solanum tuberosum, spacing, Tolcha

RÉSUMÉ

Un essai a été conduit en 1995 et 1996 pour déterminer l' espacement optimal pour les cultivars Awash, Menagesha et Tolcha de pomme de terre qui diffèrent dans leur morphologie et architecture. Il y avaient des différences variétales significatives et d'effets d'espacement sur la taille de semence de tubercules, le poids moyen de tubercules (ATW) et le nombre de tubercules (ATN) par mètre carre. Les rendementds les plus élevés de 38.5, 62.6 et 46.5 t ha^-1 ont été obtenus pour Awash, Menagesha et Tolcha respectivemet à partir d'un arrangement de 45 cm entre les lignes avec soit 25 ou 30 cm sur la ligne. Cependant les tubercules chez Menagesha dépassant la taille de 40 mm constituaient plus de 80% du rendement total montrant ainsi un besoin de réduire la distance dans la ligne pour les semences de tubercules de production. L' espacement sur la ligne contrôle la taille du tubercule plus que le rendement. Les variétés ont montré des conditions d' espacement pour le développement d'une surface foliaire optimale et le nombre maximum de tubercules et de production

Mots Clés: Awash, morphologie de l'architecture, Ethiopie, Menagesha, Solanum tuberosum, espacement, Tolcha

INTRODUCTION

The potato (Solanum tuberosum) is one of the most important food crops in Ethiopia. It is estimated that about one hundred thousand hectares of land is cultivated with potato each year. Despite conducive edaphic and climatic factors, the national average yield per hectare is estimated to to range between 7-9 t ha^-1 (EARO, 1999). However, the potato hectarage is rapidly expanding due to its high yield potential and for its suitability as a security crop in times of reduced rainfall.

The low national average yield of potato is attributed to many factors that include sub-optimal agronomic techniques and lack of disease tolerant cultivars. Farmers who grow potatoes frequently give less regard to optimal plant population (spacing). The habit of irregular planting that farmers adapted probably from the broadcasting habit in cereals, is common in most potato growing areas. The possibility of securing high yield depends much upon a proper consideration of optimum number of plants per unit area and the pattern in which the given quantity of seed/plant population is arranged in the field at planting (spatial arrangement). The quantity of solar radiation which penetrates a crop canopy greatly depends on planting patterns or spacing and individual plant morphology (Jerry et al., 1980). Optimum spacing on the other hand, depends upon a number of factors such as variety, soil type, fertiliser rate, and irrigation as well as weather conditions. Closer spacing of a vigorous variety creates mutual shading of leaves in a crowded canopy resulting in a very high leaf area index and reducing the total radiation intercepted and the net assimilation (Burton, 1989). Spacing has to be regulated for higher yields depending on the purpose of production, i.e., either for ware or seed potato. Thus, a knowledge of the relationship between spatial arrangement and yield is helpful to optimise the potato yield through effective use of land in both monocropping and multiple cropping systems that are common in many potato growing areas in Ethiopia.

Berga et al. (1994a, b) reported that wider spacing gave increased average tuber weight while closer spacing increased seed-sized tubers. In a separate study at Alemaya (eastern highlands) to determine optimum row-width and in-row distance using variety AL-624, it was found out that the widest spacing used, 80 x 20 cm, gave the highest yield (34.1 t ha^-1) and lowest yield (22.2 t ha^-1) from the 60 x 20 cm (Teressa, 1997). Allen and Wurr (1992) observed that the determinate varieties that produce fixed numbers of leaves per main stem were less suited to wider rows than indeterminate ones. Such determinate types become vulnerable to any restriction of leaf expansion.

At present many high yielding, good quality varieties with high field resistance to late blight released from research in the last eight years are being widely grown in Ethiopia. The cutivars are morphologically variable and belong to different maturity types. However, their optimum spacing requirement for maximum seed and tuber yield have not been determined. Thus, in this experiment, three released cultivars namely Awash, Menagesha and Tolcha having contrasting morphological growth and maturity dates were used to determine optimum within row and between row spacing.

MATERIALS AND METHODS

The experiment was conducted in 1995 and 1996 at Holetta Agricultural Research Centre (2400 m.a.s.l) on nitosol with a pH (H2O) of 5.2, a total N (%) 0.2, OM (%) 2.9 and OC (%) 1.72. Three released cultivars representing different morphological groups, i.e., Awash (short early), Menagesha (intermediate) and Tolcha (vigorous late maturing types) and having maturity periods of 90-100, 100-115 and 120-130 days, respectively, were used in the study. Medium sized (35-45 mm) pre-sprouted tubers from the same harvest were planted at four different row- width (45, 60, 75, 90 cm) and in-row (20, 25, 30, 35 cm) spacings. Sprouted tubers were planted in ridges and fertiliser was side dressed at planting at a recommended rate 300 kg DAP ha-1 in the first week of June each year. The experimental design was a split plot in a factorial arrangement. All possible in-row and between row combinations (4 x 4) of spacing were made and the 16 treatments were randomly assigned to each main plot (cultivar) and block. All cultural operations such as weeding and ridging were done according to previous recommendations. Data were recorded for emergence, plant height, leaf area, flowering, above ground stem and tuber yield (tuber number, weight and size grades). At maturity equal area was harvested from each treatment. Whenever necessary, plants were protected against late blight and aphids. A double border row was used to eliminate boarder effects. The data were analysed separately for each year and combined analysis of variance for an unchanged location was done using MSTATC.

RESULT AND DISCUSSION

Mean squares for the measured crop parameters revealed significant effects of spacing (spatial arrangement) on plant height, stem number, yield of the different tuber size grades, tuber weight and tuber number. In 1995 yield was generally depressed compared with 1996 because of a hail storm that affected the leaf area and subsequent crop growth. In 1996, more rainfall was recorded for the months of July and September (Table 1). Thus, the differences between mean values of same treatments in the two years were treated with this understanding.

In this paper row-width refers to between rows (inter-row ) and in-row refers to within a row (intra-row) spacing. The results indicated that row-width and in-row spacings when varied significantly affected tuber yield. In all varieties the highest total yield was obtained from the in-row distance of 20 cm and row-width of 75 cm (Table 2). Up to 30 cm in-row spacing yield was significantly (P< 0.05) improved due to increase in row-width from 45 and 60 cm to 75 cm. Further increase in both ways resulted in yield decline and the rate was higher with increasing distance in both at the same time (Table 2, Figs 1 and 2) . This was found to be true for all the three cultivars considered. All peak mean yields, i.e., 26.9, 47.0 and 33.7 t ha^-1 were obtained, respectively, in cvs. Awash, Menagesha and Tolcha, all at the spacing of 75 x 20 cm. Little difference in yield was observed between consecutive in-row distances of 25 and 30 cm for all varieties for a fixed row-width. This result supports earlier findings by Allen and Wurr (1992) who found little variability in total and ware (40-65 mm) yields due to in-row spacing under moderate planting (tuber placement) down the row. The rate of change in yield within a given in-row distance was variable for each cultivar. However, the quantity of total tuber yield can change for same spacing but different seed tuber size (Kleingeld et al., 1997).

Yield distribution in seed tuber size showed highly significant (P<0.01) variation among cultivars and spatial arrangement (Table 3). Most (71.4%) tubers of cv. Awash were of good seed size (30-50 mm) while in Menagesha the highest share of yield came from tubers >40 mm that accounted for 82.8 percent of the total yield, and in Tolcha the yield from tubers >30 mm accounted for 88 percent of total yield (Table 3, Fig 3). In cvs. Menagesha and Tolcha the higher percent (55.6 and 37.0, respectively) yield for tubers of size >50 mm seems to favour the possibility for further intensification of planting density with little yield decline. At 20 cm in-row spacing, tubers >30 mm accounted for 87.4 percent and tubers >40 mm accounted for 61.8 percent of the total yield. However, the in-row distance considered in this study was found to have little effect on ware potato yield compared to that of the effect of row width. Ware yield (>40 mm) was maximised at 75 cm for all the three cultivars (Table 3). Saleable tubers yield was increased at and beyond 75 cm in case of cv. Awash and at 60 cm and above in cv. Tolcha. Much of the decline in yield at wider spacing for the early cultivar Awash was due to significantly fewer number of larger size tubers (>40 mm) produced (Fig 4). In cv. Menagesha, such yield for larger tubers was already attained at the lowest in-row and between row spacing (Table 3) that gave up to 15 - 16 t ha^-1 of >40 mm size tubers ; this accounted for 61.9 per cent of the total yield (data not shown). In general, the widest row-width reduced tuber yield in all the cultivars but the variation tended to be lower for yield from higher tuber size classes. Highly significant reduction in tuber number occurred at the widest (90 cm) low-width (Table 4). Such an effect is mostly because of less competition in growth and faster and more bulking of the few tubers formed. Similar results were reported by Ifenkely (1975), Rex et al. (1987) and Berga et al. (1994).

Decreasing row-width below 60 cm can bring in cultural problems in addition to almost doubling the seed rate (cost). The later problem can be compensated to a degree by using smaller sized seed tubers. However, problems (difficulties in field operations) can still be a challenge for narrow spacing particularly on heavy soils and in high rainfall areas.

Average tuber weight was significantly improved by increasing row-width in all cultivars. In Awash and Tolcha , average tuber weight was promoted mostly when in-row distance was increased from 20 to 35cm (Table 3). However, in most cases increasing row-width significantly (P<0.05) reduced number of tubers except for 75 cm that consistently gave the highest mean tuber number (Table 3). The increase in yield for tubers >40 mm in the two cvs. Menagesha and Tolcha when advancing from 60 to 75 cm row-width (Fig. 6) seems to have resulted from a similar magnitude increase in tuber number between the two spacings. When tuber size increased, tuber number of Awash and Tolcha significantly reduced while in Menagesha there was an exhibited increase at a decreasing rate (Fig. 4). Such varietal differences clearly indicate that optimum spacing for any purpose requires to take into account the maturity type and vegetative growth (vigour) of the crop in addition to other factors such as soil fertility and water availability.

CONCLUSION

The optimum spacing (spatial arrangement) for ware and seed as well as total yield can vary considerably. In this experiment total yield was maximised at closer spacing (75 x 20 cm) and with the exception of cv. Awash ware yield was increased at wider spacing (75 x 30 cm). For the late maturing cv. Menagesha seed size (30-50 mm) yield could not be significantly maximised even at closer spacing. This variety appeared to require a more reduced in-row distance or use of alternative cultural methods such as dehalming to control seed size. Maximising ware yield in an early cv. Awash seems to be restricted because of the low number of large sized tubers at any spacing. Supplementary cultural strategy is required to optimise ware yield and increase its acceptability. The result also showed that absence of optimal spacing practice could significantly reduce ware or total tuber yield-up to 50 per cent, and this also is dependent on the type of cultivar and its growth habit.

ACKNOWLEDGEMENT

We would like to gratefully acknowledge Dr. Berga Lemaga whose technical advice was important at the proposal development stage. We also thank PRAPACE and African Potato Association (APA) which made possible our participation at the Fifth Triennial Conference of APA.

REFERENCES

Allen, E. J. and Wurr, D. C. E. 1992. Plant density. In: The potato crop, the scientific basis for improvement. 2nd ed. Harris, P.M. (Ed.), pp. 292-330. Champan and Hall, London.

Berga L., Gebremedhin, W., Teresa, J. and Bereke, T.T. 1994. Potato agronomy research in Ethiopia. In: Horticulture Research & Development in Ethiopia. Proceedings of the 2nd National Horticultural workshop. Herath, E. and Dessalegn, L. (Eds.), pp. 101-119.

Berga Lemaga and Gebremedhin, W. Giorgis. 1994a. Prospects of seed potato production in Ethiopia.In: Horticulture Research and Development in Ethiopia. Proceedings of the 2nd National Horticulture Workshop, 1-3 December, 1992, Addis Ababa, Ethiopia. Herath, E. and Lemma D. (Eds.), pp. 254-275. IAR/FAO, Addis Ababa.

Berga Lemaga, Medhin, G., Giorgis, W. Teressa Jeleta and Bereke Tuku, T. 1994b. Potato agronomy research in Ethiopia. In: Horti-culture Research and Development in Ethiopia. Proceedings of the 2nd National Horticulture Workshop, 1-3 December 1992, Addis Ababa, Ethiopia. Herath, E. and Lemma Dessalgne (Eds.), pp. 101-119. IAR/FAO, Addis Ababa.

Burton, W. G. 1989. The Potato. 3rd ed. Longman Publisher Ltd., Singapore.

Ebwongu, M., Adipala, E., Ssekabembe, C.K., Kyamanywa, S. and Bhagsari, A.S. 2001. Effect of intercropping maize and solanum potato on yield of the component crops in central Uganda. African Crop Science Journal 9:83-96.

Ethiopian Agricultural Research Organization (EARO), 1999. Strategies and priorities for potato research. July 2000. Addis Ababa.

Ifenkely, O.P. 1975. Effect of row width and plant density on growth and development or two main crop potato varieties. PhD. Thesis. University College of Wales.

Jerry, E.M., Curry, L.G., Demichele, W.D., Beker, N.D. 1980. Light penetration in row-crop with random plant spacing. Agronomy Journal 72:1431-1439.

Kleingeld, F.C., Hammes, S.P. and Beyers, A.E. 1997. The influence of tuber size and plant density on the yield potential of mini-tubers in South Africa. Proceedings of the 4th Triennial Congress of the African Potato Association. 23-28 January, 1999. Pretoria, South Africa. pp. 32-35.

Rex, L.B., Russell, A.W. and Wolfe, R.H. 1987. The effect of spacing of seed pieces on yield, quality and economic value for processing of Shepody potatoes in Manitoba. American Potato Journal 64:177-189.

TABLE 1. Climatic and weather data for the year 1995-96 and average of 27 years at Holetta

	May		June		July		August		September		October
	95	96	95	96	95	96	95	96	95	96	95	96
Rainfall (mm)	81.3	55.4	91.6	83.8	197.1	249.6	262.7	226.6	82.2	120.7	15.5	5.3
Min . T (°C)	7.6	7.3	6.5	8.2	8.6	8.3	8.8	8.3	6.6	7.1	3.4	7.1
Max. T (°C)	23.9	23.5	23.6	20.6	19.4	19.4	19.6	19.4	20.6	20.4	22.6	20.4
Average of 27 years
Rainfall (mm)	20.7		112.2		246.2		268.8		137.6		20.8
Min. T (°C)	7.7		7.4		8.7		9.2		7.7		4.5
Max. T (°C)	23.8		22.2		19.4		19.2		20.1		21.6

TABLE 2. Combined effect of in-row distance and row-width on tuber yield (t ha^-1) of three potato cultivars

	In - row (cm) (t ha-1)
Row-width(cm)	20	25	30	35
	Pooled data
45	30.5	22.3	24.3	23.3
60	31.3	23.3	24.5	23.5
75	35.9	30.6	30.7	26.6
90	26.2	23.9	23.8	18.5
LSD 0.05	5.44
Cv (%)	7.18
	Awash
45	26.0	18.3	18.7	18.1
60	24.3	19.0	19.5	18.2
75	26.9	24.8	24.0	19.9
90	18.4	16.6	19.2	13.1
	Menagesha
45	41.0	28.4	32.5	31.6
60	41.5	34.0	33.4	31.8
75	47.0	37.4	39.8	36.8
90	35.6	33.1	30.4	26.5
	Tolcha
45	24.5	20.2	21.7	20.2
60	28.1	17.0	20.6	20.5
75	33.7	29.5	28.3	23.0
90	24.7	21.8	21.8	16.0
LSD0.05	9.42

TABLE 3. Yield in q ha -1 for different tuber sizes (mm), average tuber weight (ATW) and average tuber number (ATN) as affected by spacing and cultivar

Cultivar and Spacing	<20 g		20-30g		30-40g		40-50g		>50g		ATW (g)	ATN m-2
Awash	6.4	(3.5)*	30.8	(17.5)	67.9	(36.5)	64.9	(34.8)	16.2	(8.1)	37.9	55.5
Menagesha	2.2	(0.7)	12.3	(4.1)	35.3	(12.0)	84.2	(27.2)	196.5	(55.6)	94.6	54.2
Tolcha	1.78	(1.0)	12.0	(6.2)	44.8	(22.0)	74.2	(29.2)	82.4	(37.0)	50.9	47.0
LSD 0.05	0.56		2.02		4.93		6.13		9.52		2.1	2.84
Row-width (cm)
45	4.3	(2.4)	21.4	(11.8)	50.2	(26.5)	65.5	(31.4)	73.6	(27.9)	43.4	58.8
60	3.4	(1.9)	17.5	(10.0)	46.5	(24.8)	66.4	(31.7)	84.0	(31.5)	47.4	53.6
75	3.9	(1.4)	21.6	(7.8)	65.6	(22.8)	104.2	(33.0)	137.3	(34.8)	53.7	58.6
90	2.3	(1.4)	12.5	(7.5)	35.1	(19.4)	61.7	(31.6)	98.8	(40.1)	60.2	37.9
In row
20	3.5	(1.8)	20.6	(10.8)	53.5	(25.6)	74.1	(31.6)	91.5	(30.0)	47.7	64.9
25	3.6	(1.8)	18.2	(9.3)	50.6	(23.7)	74.0	(31.4)	100.3	(33.7)	51.1	49.7
30	3.6	(1.8)	18.0	(8.9)	49.2	(22.7)	75.2	(31.5)	101.8	(35.1)	52.0	50.5
35	3.2	(1.7)	16.2	(8.1)	44.1	(21.6)	74.5	(33.6)	99.9	(35.2)	53.4	43.8
LSD0.01	NS		2.33		5.69		7.07		10.68		2.43	3.28

TABLE 4.Effect of row-width and in-row distance (cm) on average tuber weight (g) and tuber number (in parenthesis) for three potato cultivars

Row-width	In-Row
	20	25	30	35
45	44.0(52.4)	42.9(52.7)	41.9(53.0)	47.6(44.7)
60	44.3(45.8)	46.4(45.6)	50.0(59.0)	49.0(44.5)
75	48.5(72.6)	56.5(58.9)	55.0(59.5)	54.8(57.0)
90	56.8(32.7)	58.6(36.9)	63.3(36.1)	62.1(33.2)
LSD0.05=4.85(6.56)
	Awash
45	30.4(57.0)	25.3(69.5)	31.2(56.5)	34.6(49.2)
60	33.1(46.1)	35.3(52.2)	34.6(50.5)	38.4(44.4)
75	37.5(70.6)	46.3(56.8)	42.7(60.6)	44.0(53.2)
90	42.5(32.8)	44.0(34.6)	39.2(46.3)	48.4(30.7)
	Menagesha
45	55.7(52.0)	59.6(46.1)	55.2(51.9)	62.7(45.0)
60	58.5(51.3)	58.9(49.7)	64.3(50.2)	62.1(47.2)
75	62.1(75.1)	72.3(58.7)	69.1(60.6)	62.6(70.6)
90	68.9(36.7)	73.2(42.7)	78.7(35.2)	70.0(42.1)
	Tolcha
45	37.0(48.3	43.7(42.6	39.4(50.5)	45.5(39.4)
60	41.3(39.9)	44.9(34.9)	57.0(36.2)	46.6(41.8)
75	45.7(72.1)	51.0(61.1)	53.2(57.2)	57.1(47.1)
90	59.0(28.6)	58.6(33.4)	72.0(27.0)	68.0(26.8)
LSD0.05=4.41(11.36)

Figure 1. Effect of in-row-distance on tuber mean yield of cvs. Awash, Menagesha and Tolcha over two years.

Figure 2. Effect of row-width and in-row distance on tuber mean yield of cvs. Menagesha, Tolcha and Awash over two years.

Figure 3. Mean yield for the different tuber size categories for cvs. Awash, Menagesha and Tolcha over two years.

Figure 4. Relationship between tuber size and tuber number for a combination of four row width and four in-row distance in three potato cultivars.

Figure 5. Comparison between row-width and average tuber weight (ATW), number (ATN) and yield t ha^-1 for cultivars Menagesha and Awash.

Figure 6. Relationship between row width and tuber size yields for cultivars Menagesha, Tolcha and Awash.

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