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African Crop Science Journal, Vol. 9, No. 1, March 2001, pp. 77-82
A. M. Khalafalla
Code Number: CS01037 ABSTRACT The effect of size of seed tuber (whole, ½ seed and farmer's seed piece) and intra-row spacing (15, 25, 35 cm) on growth and yield of potato was studied during three winter seasons in Khartoum State, Sudan at two locations, namely Shambat Research Farm and Shehainab Isand representing two soil types. Yield decreased with decrease in seed size and increase in spacing at both locations. Close spacing of 15 - 25 cm was better than wide spacing 35 cm. Seed size affected some yield parameters, i.e., marketable tubers plant-1, marketable tuber weight, number of marketable tubers per plant and number of stems plant-1. These parameters were also affected by plant spacing except number of stems. Key Words: Potato yield, spacing, Sudan, tuber size RÉSUMÉ L'effet de la taille du tubercule (entier, moitié et une partie de la semence de l'agriculteur) et l' écartement entre les lignes (15, 25 et 35cm) sur la croissance et la production de la pomme de terre a été étudié pendant trois saisons d' hiver dans l' état du Khartoum au Sudan dans deux localités, la station de recherche de Shambat et l' île de Shehainab représentant deux différents types de sols. Le rendement a diminué avec la réduction de la taille de la semence et avec l'augmentation de l' écartement dans les 2 localités. L'espacement étroit de 15 et 25 cm était le meilleur plus que l' espacement plus large de 35 cm. La taille de la semence a influencé certains sparamètres à savoir tubercules commercialisables par plante, le poids des tubercules commercialisables, et le nombre de tiges par plante. A part le nombres de tiges, les autres paramètres étaient aussi affectés par l'écartement des plants. Mots Clés: Rendement de la pomme de terre, écartement , Suidan, taille des tubercules INTRODUCTION Potato (Solanum tuberosum L.) production in Sudan is steadily increasing
and total production has tripled during the last ten years (Mohamed, 1999).
It is now considered to be a rewarding cash crop for the farmer and an important
component of the diet especially in urban areas. However, the increase in hectarage
has not been accompanied by increase in productiviy. The average yields in Khartoum
State, which is considered to be one of the most important areas for potato
production in Sudan, is estimated to be around 12 tons ha-1. Factors that influence
potato yield and quality include cultivar, soil type, weather conditions, water
management, fertilisation, plant population, seed piece size, pests and diseases.
High plant population per ha is reported to increase total yield, specific gravity
and reduce the incidence of hollow heart (Iritani et al., 1972; Nelson,
1976; Rex et al., 1987). Yield increases are attributable to more tubers
being produced at the greater plant population per hectare although average
tuber size is decreased because of increased inter-plant competition with closer
spacing (Rex et al., 1987). MATERIALS AND METHODS The experiments were conducted at two sites, namely, Shambat Research Farm and Shehainab Island 50 kilometers north of Khartoum along the River Nile. The soils at Shabat and Shehainab are heavy clay and light loamy soils, respectively. The experiment was run for three years, 1991 - 1993. Certified seed tubers imported from Holland of variety alpha were graded into medium size tubes 45/35 mm. The treatments consisted of 3 seed sizes (whole, ½ seed tuber and farmers seed size) and 3 intra-row spacings (15, 25, 35 cm). The ½ seed tuber were prepared by hand cutting medium size tubers longitudinally into two halves from the apical to the basal end leaving about 2 cm at the basal end uncut to keep the two halves intact. The intact cut tubers were put in boxes and suberised under nursery shed with a high relative humidity exposed to indirect light for four days prior to planting. The tubers to be cut into farmers seed pieces were cut by the farmer at the time of planting. The treatments were factorially combined in randomised complete block design replicated four times at both locations. Each plot consisted of 4 rows, 6 m long with rows spaced 70 cm apart. Fetiliser included 36 kg P205 ha-1 broadcasted before planting and 72 kg N ha-1 split applied after 50% emergence and at earthing up. Irrigation, weeding, pest and disease control were kept at the optimum level. At harvest, data on total yield, marketable yield, small size tuber (≤ 35 mm) and % tubers > 60 mm were taken from the two middle rows and recorded. Sub-samples of 10 plants were taken from each plot for the determination of marketable tuber yield per plant, and marketable tuber weight and number of stems per plant. All data were subjected to analysis of variance to determine significance effects. RESULTS Effect of in-row spacing on yield. Marketable and unmarketable (≤ 35 mm) yield for the three seasons (1991, 1992 and 1993) are shown in Table 1. Marketable yield increased with close spacing except in 1991 at Shehainab. At Shambat marketable yield significantly (P<0.05) increased with close spacing and out-yielded wider (35 cm) spacing by 26%. Unmarketable yield (≤35 cm) was significantly (P< 0.01) affected by seed spacing at Shehainab during 1991 and close spacing (15 and 25 cm) produced more small size tubers than 35 cm. Effect of seed size on yield. Seed size significantly affected marketable yuield in the three seasons (Table 2). Whole seed tuber maitnained higher yield than cut tuber. However, marketable yield was markedly decreased from farmer's seed piece in comparison with ½ seed tuber and whole seed tuber. At Shambat only two sizes were planted (½ seed and farmer's seed piece). The ½ seed tuber significantly (P = 0.01) out-yielded farmer's seed piece during the three seasons. Unmarketable yield was nonly significantly (P = 0.01) affected by seed size at Shehainab during the 1991 season. Whole sed tuber gave more unmarketable tubers than ½ seed and farmer's seed piece. The three years means for the marketable yuield at Shehainab and Shambat for the two factors (seed size and inter-row spacing) are shown in Table 3. The inter-row spacing effect at Shambat is the mean of one season only. Marketable yeild at Shehainab out-yielded Shambat by 119% and 53% for seed size and inter-row spacing, respectively. At both locations, the results showed decreasing yield with decreased tuber size and increased inter-row spacing. Yield attributes. Some yield attributes are shown in Table 4. Marketable yield and number of tubers per plant decreased with decrease in seed size and increase in row spacing and vice versa for market tuber weight. Number of stems per plant decreased with decerase in seed size but were not affected by inter-row spacing. Percent large tubers, i.e., those > 60 mm increased with wider spacing. The seed size - spacing interaction was significant for oversize tubers (Table 5). At the wide spacing (35 cm) yield of over size tubers with whole seed was significantly more than ½ seed and farmer's seed piece (Table 5). Also farmer's seed piece at 25 cm spacing gave more oversize tubers than½ seed tubers. DISCUSSION The study reported in this paper mainly dealt with investigating the effect of seed size and intra-row plant spacing on yield and some yield components of potato. Seed size and intra-row spacing describe plant density, which is given as number of stems/unit area since the plant could consist of two, three or more stems. Beukema (1979) indicated that the number of sprouts developing on a seed tuber and the number of seed tubers planted may give an advance indication of the stem density to be expected to affect yield and other yield components of potato. Previous studies showed that an increase in stem numbers markedly favours haulm production (Sevensson and Naglicka, 1975), stem elongation (Harris, 1972; Ifenkwe, 1975) increases tuber numbers (Hammes, 1985), total tuber yield per plant or per unit area of land (Iritani et al., 1972) but the average tuber weight was decreased (Allen, 1978). Seed cutting is practiced by many farmers in different parts of the world mainly to economise on seed cost and to stimulate sprout growth, especially when the tubers are still dormant or in the apical stage; cutting may lead to earlier emergence and development of more stems per plant. One of the major constraints in the production of potatoes in developing countries is the high cost of seed tubers which makes up 50-74% of the total cost of production (Swaminathan and Sawyer, 1983). Farmers in Sudan cut the seed into small eye-pieces that result in single plant stems, low emergence due to seed piece decay and, consequently, low plant population. It has been found that in general the % emergence is inversely related to the degree of sub-division of the seed (Beukema, 1979). The results in the present study indicated that yield decreased with increasing sub-dividison of the seed. Similar results were reported from Sagai in Khartoum State (Ali, 1988) but difference between whole and ½ seed tuber were not high enough o justify whole seed planting because of the cost of the seed. Similarly, under the Gezira conditions in heavy clay soils half big tubers produced significantly low yield than big, medium and small size tubers (Ahmed, 1989). Number of stems on whole, ½ seed tuber and farmer's seed-piece were 3.0, 2.8 and 1.7 stems/plant, respectively. Tuber yield increased with increased stem numbers. In agreement with this finding Gray (1972) found that increase in stem density markedly increased total tuber yield per plant and per unit area of land. The increased yield by high plant population can be explained by the increased number of plants/unit area and more tubers/plant. Similar results were reported by Nelson (1976) in North Dakota. He found that increased plant populations reduced average tuber weight but increased yields due to more tubers being harvested. Rex et al. (1987) also found closer seed piece spacing of Shepody increased yields and specific gravely particularly during early harvest. Ahmed (1989) found that closer spacing (20 cm) gave higher yields than wider spacing (30 cm). On the other hand, closer spacing and big seed size gave less tuber weight but more number of tubers/plant. Sharper and Dent (1968), Thompson and Taylor (1974), Collins (1977) and Allen (1978) reported similar results. The over size tubers percentage increased with spacing increase. There was a significant seed-piece size x spacing interaction for over size tubers (Table 5). The increase in yield of over size tubers was greater for whole seed tubers when the spacing was wide (35 cm). In summary, the present farmer's practice in Sudan of subdividing of seed tubers into small eye pieces is not recommended as indicated by the results of this study. In agreement with Ali (1988), our results clearly show that use of seed tuber planting is less preferable to ½ seed tuber, since the difference in yield were not significant leave alone the higher cost of whole seed. Consequently, it is advisable to cut medium size tubers into two halves and plant at a spacing of 15 - 25 cm to obtain acceptable yield and good quality tubers. REFERENCES
TABLE 1. Effect of inter-row spacing of tuber seed on marketable and unmarketable (≤35 mm) yield of potato (t ha-1) at two location in Khartoum State
TABLE 2. Effect of seed size and spacing on marketable and unmarketable tuber yield of potato (t ha-1) at two location in Khartoum State
TABLE 3. Effect of inter-row spacing and seed size on markatable yield of potato at the two location in Sudan
*Mean of 3 years
TABLE 4. Effect of seed size and plant spacing on some potato yield attributes at Shehainab, Sudan
TABLE 5. Interaction of in-row spacing and tuber size on yield of over size tubers > 60 mm. (t ha-1)
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