




































Agriculture and Food 

Sciences Research 
ISSN: 2411-6653 
Vol. 3, No. 1, 1-11, 2016 
http://www.asianonlinejournals.com/index.php/AESR 
 

 
 

 

 

 

 

 

1 

 

Sweet Potato Agronomy Research in Ethiopia: Summary of 

Past Findings and Future Research Directions 

 
Daniel Markos1

   

Gobeze Loha2    

1,2
Awassa Agricultural Research Center, Awassa, 

Ethiopia 
 

( Corresponding Author) 

 
Abstract 

Sweet potato (Ipomoea batatas (L.) Lam)  is economically important food crop in Ethiopia. Since its introduction, 

numerous agronomic research activities were carried out in agricultural research centers, non-governmental 

organizations and universities. The objective of this piece of work is to document available research findings in a 

usable manner and present it to first national sweet potato workshop held between 6-7 June 2013, SARI head 

quarter, Awassa, Ethiopia. Agronomic research has been carried out on preparation of planting materials, curing 

vine cuttings, planting methods, depth of planting, plant density, planting time, cropping systems, and etc. Results 

showed that sweet potato crop has a potential of 50 to 60 t/ha in Ethiopia and the length of vines to be used for 

planting shall be 30 to 40 cm. Weeding trials elaborated that weeding twice on 30-40DAS and 70DAS regardless of 

the study sites would suffice for the crop. Planting date experiments justified early planting with the onset of 

rainfall in non irrigated fields. However, the results of population density and fertilizer regimes varied across 

locations and varieties. Thus generation and promotion of site specific recommendations are of paramount 

importance for root crops like sweet potato. 

 

Keywords: Ipomoea batatas, Ethiopia, Agronomy, Cultural practices, Varieties and research findings. 

 

Contents 
1. Introduction ...................................................................................................................................................................................2 

2. Materials and Methods .................................................................................................................................................................2 

3. Results and Discussion .................................................................................................................................................................2 

4. Conclusion .....................................................................................................................................................................................9 

5. Future Research Directions .......................................................................................................................................................10 

References ........................................................................................................................................................................................10 

 
 

Citation | Daniel Markos; Gobeze Loha (2016). Sweet Potato Agronomy Research in Ethiopia: Summary of Past Findings and Future Research Directions. 

Agriculture and Food Sciences Research, 3(1): 1-11. 

DOI: 10.20448/journal.512/2016.3.1/512.1.1.11          

ISSN(E) : 2411-6653 

ISSN(P) : 2411-6653 

Licensed:  

Contribution/Acknowledgement: 
This work is licensed under a Creative Commons Attribution 3.0 License  

All authors contributed to the conception and design of the study. Especially thanks go to Awassa, Areka, Adami tulu 

and Melkasa  research centers and Haramaya and Wolita sodo universities for giving due attention to sweet potato 

research at national level. Heart felt thanks also go to CIP for sponsoring the first sweet potato national workshop held 

on 6-7 June 2013 at SARI (Southern Agricultural Research Institute)  head quarter and also the organizing committee 

for giving us this opportunity to present the findings. 

Funding: This study received no specific financial support. 

Competing Interests: The authors declare that they have no conflict of interests. 

Transparency: The author confirms that the manuscript is an honest, accurate, and transparent account of the study was reported; that 

no vital features of the study have been omitted; and that any discrepancies from the study as planned have been 

explained. 

History: Received: 12 January 2016/ Revised: 23 January 2016/ Accepted: 29 January 2016/ Published: 4 February 2016 

Ethical: This study follows all ethical practices during writing.   

Publisher: Asian Online Journal Publishing Group 

 
 

 

 

 

 

 

 

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1. Introduction 
Sweet potato (Ipomoea batatas (L.) Lam) is a herbaceous dicotyledonous plant with creeping, perennial vines 

and adventitious roots. It belongs to family Convovulaceae (morning glory flowers) and is hexaploid, and usually 

considered the only Ipomoea species of economic importance. It has large, starchy, sweet-tasting and tuberous roots. 

It adapts tropical and warm temperate regions. It is a highly heterozygous cross pollinated crop in which many of the 

triats show continuous variation. This crop is known for its resistance to drought, vigorous early growth and low 

input requirements. It also does well in areas of high rainfall and it requires very little labor and care compared to 

other crops. Because it readily produces adventitious roots and has trailing vines, sweet potato can colonize soils 

easily. Sweet potato is grown in several agro-ecological zones and usually plays significant roles in the farming and 

food systems. Sweet potato is commonly grown by farmers in complex, mixed cropping systems where they 

normally plant several varieties with different characteristics (yield, maturity, palatability, time to maturity, root size 

and shape, root colour, storability in the ground, pest and disease tolerance, drought tolerance, and sweetness) in a 

single plot. Farmers may use the vines left in the fields to improve soil fertility, and the crop is used in crop rotation. 

Since it has a short growing period, it stores well in the soil and performs well in marginal lands. It is recognized as 

ideal crop for food security. The yellow and orange-fleshed sweet potato varieties are also known as a good source of 

vitamin A that is frequently lacking in diets of most African farming communities. However, most varieties in sub-

Saharan Africa are white-fleshed, low yielding and lacking beta-carotene, the precursor of vitamin A that was found 

vital to pregnant women and children. Also, sweet potato is widely used as animal feed (Assefa, et al. [1]; Engida, et 

al. [2]).  

Globally, sweet potato is the seventh most important food crop and second most important tuber crop in the 

world after Irish potato. It ranks seventh among all food crops worldwide, with an annual production of 124 million 

tons. Among the root and root crops, it ranks third in acreage (9.1 million ha) behind Irish potato and cassava. In 

Africa, sweet potato is the second most important root crop after cassava and production is concentrated in the East 

African countries around Lake Victoria (Dantata, et al. [3]; Ndole, et al. [4]). Sweet potato productivity is limited by 

both abiotic and biotic constraints, leading to poor yields at farm level. They include low soil fertility and drought, 

shortage of improved varieties, shortage of planting materials, pests and diseases particularly viruses, post-harvest 

problems such as storage, and market availability and demand as well as low socioeconomic status in some 

communities. As a food security crop, it can be harvested piecemeal as needed, thus offering a flexible source of 

food and income to rural households that are mostly vulnerable to crop failure and consequently fluctuating cash 

income. In addition to being drought tolerant and having a wide ecological adaptation, it has a short maturity period 

of three to five months. Sweet potato has several advantages within the context of African cropping systems: i) it 

produces food in a relatively short time, ii) it gives reliable yields in sub-optimal growth conditions, iii) it requires 

lower labor inputs (appropriate for vulnerable households) than other staples, vi) it serves as an alternative food 

source for urban populations, facing increasing prices of cereals and v) it provides a potential option to reduce 

vitamin A deficiency (Andreas, et al. [5]; Getahun and Tenaw [6]). Sweet potato has a potential of giving over and 

above 50 to 60 tons/ha in Ethiopian conditions; however, yield obtained from farmer’s field is by far lower than 6 to 

8 tons. Thus the yields are ten times lower than the potential sought. This huge variation is attributed to biotic and 

abiotic stresses, lack of improved varieties, and weak attitude of people toward sweet potato, inefficient means of 

sweet potato technology transfer, inadequate, etc set of package recommendations. 

 

1.1. Objectives 
To summarize research findings in cultural practices, cropping systems and physiology of sweet potato in 

Ethiopia. 

To recommend appropriate site specific management practices in sweet potato agronomy for future use 

To set future research directions in sweet potato management 

 

2. Materials and Methods 
Identification of major growing areas in the country was carried out initially from secondary sources. Nextly 

available published and unpublished research findings and best practices were sought from universities, research 

centers and non-governmental organizations like Farm Africa, JICA and etc. working in major sweet potato growing 

areas like Sidama, Wolaita, Harargie, Bako, etc... Personal communication with growers, seed multipliers and 

researchers who made a research in the past was carried out to confirm their findings. Available information was 

assembled into categories of cultural practices and cropping systems by pictures, tables and summary notes. 

However, by no means the results are complete and exclusive of all observations and achievements in the country. 

Finally results were summarized in usable form by providing appropriate citation for future referencing.   

 

3. Results and Discussion 
3.1. Preparation of Vines for Planting  

Results of various studies showed that sweet potatoes are propagated using seeds, vines and roots in Ethiopia. 

The use of seed is mainly for breeding purpose and not for commercial production. If the crop is to be grown from 

the root, then sets should be chosen from healthy robust marketable tubers. The most common method of planting 

sweet potatoes in commercial production is exclusively using vines mainly because vines are free from soil borne 

diseases, provide greater yield besides provision of uniform roots. The crop has a great deal of foliage; however, it 

has low multiplication rate compared to cereals. The vines are those parts of sweet potato that do not die after the 

roots are mature. However, there is shortage of preservation methods of these planting materials over the long dry 

season. Hence there is inability to meet large and regular demand for planting coming from governmental and non-

governmental organization particularly in food insecure periods of the year. Preparation of planting material involves 

http://en.wikipedia.org/wiki/Starch
http://en.wikipedia.org/wiki/Tuberous_root


Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

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removing leaves, cutting the vines to appropriate size and curing them accordingly. These reduce moisture loss and 

bulkiness (Fig 1).  

 

 

Fig-1. Preparation and packing of sweet potato planting materials 

 

To compare and evaluate the yield performance different parts of the sweet potato vines used as planting material 

(top, middle and basal parts), experiments were conducted at Awassa and Areka. Although it was not statistically 

significant, the result indicated that top vine part gave higher root yield compared to the middle and basal portion of 

the vine cuttings. However, in case of low moisture conditions, the top portion easily wilts, as it is delicate. Top part 

is relatively free from weevil and other diseases compared to basal parts (CRCT (Crop Science Research 

Department) [7]). Therefore, it was recommended to plant top and middle portion of sweet potato compared to basal 

portion.  

Vine pre rooting treatments were carried out to solve problem of establishment and yield obtained from vine 

parts. They have to be rooted under ideal condition before transferring to the field. Some farmers employ pre rooting 

to replace the dead vines in the field and minimize the time gap with the first planted crops (Geleta [8]). 

 
Table-1. Mean tuber yield (tha-1) of pre rooted vines tested for three years 

Pre rooting time (days) 1990 1991 1992 Mean  

0 4.5A 9.1B 8.8C 7.4B 

3 4.5A 15.9A 12.2B 10.8A 

6 4.2A 16.0A 15.8A 12.0A 

9 4.9A 16.6A 14.5A 12.0A 

 

Vine pre rooted for 6 and 9 days gave better root yield than 0 and 3 days. Both pre-rooting days were found to be   

consistent and better in root yield in all years (Table 1). 

 

3.2. Curing of Vine Cuttings 

An experiment was conducted at Awassa to compare establishment and root yield of sweet potato obtained from 

vine cuttings which were stored under shade for different length of time (0, 2, 4, 6, 8 and 10 days). The three years 

result of the experiment indicated that storing vines for two days could enhance better root initiation, increase vine 

establishment and root yield of sweet potato compared to others levels of vine curing. Vines stored for longer period 

dried off prior planting. Hence vine storage for two days before planting is recommended for better establishment 

and root yield (CRCT (Crop Science Research Department) [7]).  

 

3.3. Length of Vine Cuttings 
Based on the studies carried out a vine having 30 to 40 cm length with 3 to 4 buds on the cutting are preferred for 

better yield and ease of management in comparison to using whole vine. 

 

3.4. Depth of Planting 
Comparisons were made on depth of planting the vine cuttings. Results confirmed that burying two-third of the 

vine would suffice for better establishment and subsequent yield compared to other levels of burying the sweet 

potato cuttings. 

 

3.5. Vine Treatment with Insecticides 
The older sweet potato vines and roots harbor sweet potato weevil (Cylas puncticollis). Therefore it is 

recommended that all the cuttings should be dipped in the Fentain or Fentrotion insecticide solutions at the 

recommended rate just before planting in order to kill the egg or adult weevil (Endale, et al. [9]).  

 

3.6. Land Preparation for Root Production  
According to the studies carried out by national research coordination unit, land for sweet potato production 

should be ploughed thoroughly to 15-20 cm depth and could be prepared using either tractor drown implements, 

oxen drown plows or by hand tools. The land prepared could be flat as in Wolaita area and could be of ridges as in 

Hararige. In fact in research centers like that of Awassa, ridges are prepared by tractor drown implements.  Series of 

studies has been carried out to explore the comparative advantage of these land preparation methods with 

consideration of different varieties. The researchers concluded that since the varieties had no significant response to 

methods of land preparation, any of the cost effective methods could be employed (Table 2 and 3). However, flat 

planting is beneficial in areas where the amount of rainfall is sufficient and the soil is more of sandy loam.  In Areka, 

where the rainfall was higher and water-holding capacity of soil is good, flat planting produced significantly higher 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

4 

 

root yield of sweet potato. But, generally in moisture stressed areas, tie ridges are the most universally recommended 

methods of growing sweet potato (CRCT (Crop Science Research Department) [7]).  

 
Table-2. Effects of land preparation methods on root yield (t/ha) of sweet potato varieties in Awassa 

Land preparation 

methods 

Koka -6 Koka-12 

1987 1988 1989 Mean  1987 1988 1989 Mean  

Flat  15.7 16.2 12.9 14.9 17.3 14.7 7.1 13.0 

Open ridge 14.8 16.7 12.9 14.8 18.1 17.2 8.2 14.5 

Tied ridge  16.3 14.8 12.7 14.6 17.5 18.2 7.0 14.2 
                               Source: Endale, et al. [9]   

 
Table-3. Effects of land preparation methods on root yield (t/ha) of sweet potato varieties in Areka 

Land preparation 

methods 

Koka -6 Koka-12 

1987 1988 1989 Mean  1987 1988 1989 Mean  

Flat  9.5 11.2 10.4 10.4 12.4 7.0 9.1 9.5 

Open ridge 11.4 10.8 10.6 10.9 11.5 8.7 6.8 9.0 

Tied ridge  9.3 9.5 11.4 10.1 9.9 18.2 6.7 11.6 
                           Source: Endale, et al. [9]  

 

3.7. Land Preparation Methods and Production of Herbage for Animal Feed 

Research conducted at Afar (Melkaworer Agricultural Research Center) using Koka-12 variety consisted of three 

planting methods (ridge, flat, and sunken), and three vine harvesting times (45, 75 and 105 days after planting 

including one control treatment without vine harvesting). The experiment was laid out in a randomized complete 

block design in a factorial arrangement and replicated four times. The results revealed that planting sweet potato on 

ridges and harvesting the vines 105 days after planting (when about 60% of the growth phase of the plant was 

completed) led to optimum production of herbage for fodder without compromising yield of tuberous roots. Thus 

planting sweet potato on ridges and harvesting the vines when about 60% of the growth phase of the plant was 

completed enhanced the production of herbage for animal feed without compromising yield of tuberous roots to be 

used for human food. Therefore, pastoralists as well as sedentary smallholder farmers in Ethiopia who produce sweet 

potato using furrow irrigation should plant the crop on ridges and harvest the vines for animal feed at a later stage of 

growth by which time tuberous roots may have grown and bulked sufficiently. The farmers should also plant several 

adaptable cultivars having similar or different maturity times to spread vine harvests throughout the season for 

ensuring sustained availability of food for humans and fodder for animals (Mohammed, et al. [10]). 

 

3.8. Ridge Height and Furrow Width    
According to findings, ridge width and height happened to be researchable. Research recommendations showed 

that medium to high ridges (25 to 36 cm) are advantageous on poorly drained soils when there are heavy rains, and 

flat or low ridges are practiced where drainage is good and rainfall is not very high (Endale, et al. [9]). In tractor 

plown farms, furrows are spaced 75 cm apart and plants are placed 30cm away from one another.   

 

3.9. Planting Date Studies 
Planting date experiments were carried out in Awassa, Areka and Bako using varieties called Koka 6 and Koka 

12. Results indicated that planting could be carried out between June 4 to July 7 in Bako areas. This holds true to 

similar agro ecologies to that of Bako [11]. In Awassa, early planting on 13 May 1987, 4 May 1988 and 16 May 

1989 gave highest mean root yield of 28.4t/ha, 39.2t/ha and 30t/ha, respectively. Thus in Awassa and similar agro-

ecological areas the onset of rainy season particularly mid may to early June was recommended as optimum unlike 

early June planting of Bako (CRCT (Crop Science Research Department) [7]).   

 

3.10. Planting Positions 
Studies on planting positions were carried in Areka and Awassa from 1987-1989 comparing inclined (slant), 

vertical, U-shaped and horizontal planting positions in relation to different varieties. Results indicated that none of 

the varieties responded significantly (P<0.05) to varying positions of planting both in Areka and Awassa (Table 4 

and 5). At Awassa, planting cuttings at slant (inclined) position gave higher root yield compared to horizontal 

plantings. This was due to more vigorous establishment and better contact of soil and the planting material. However, 

in dry season horizontal planting is advantageous compared to slant planting. Similarly during wet seasons, slant 

planting is preferred compared to horizontal planting in Awassa. In Harargie vines are planted in inclined positions 

where plantings are done on ridges. In Wolaita, vine cuttings are buried horizontally in furrows when the land is 

prepared by oxen drown implements. In other parts of the country vertical and inclined positions predominate when 

planting is done on flat or ridges.  

 
Table-4. Effects of planting positions on root yield (t/ha) of sweet potato varieties in Awassa 

Planting Positions Koka -6 Koka-12 

1987 1988 1989 Mean  1987 1988 1989 Mean  

Inclined  22.2 18.7 15.9 18.9 28.3 15.5 15.9 16.6 

Vertical  19.2 15.3 15.5 16.6 23.0 18.1 6.8 16.6 

U-shaped 21.3 19.2 11.3 17.2 25.2 15.1 10.1 16.9 

Horizontal  24.9 9.9 7.3 14.0 15.3 11.5 6.3 11.1 
                                       Source: Endale, et al. [9] 

 

 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

5 

 

Table-5. Effects of planting positions on root yield (t/ha) of sweet potato varieties in Areka 

Planting Positions Koka -6 Koka-12 

1987 1988 1989 Mean  1987 1988 1989 Mean  

Inclined  9.2 6.4 9.0 8.2 13.2 5.5 9.3 9.3 

Vertical  10.3 6.0 7.6 7.9 12.4 6.8 8.8 9.3 

U-shaped 9.7 6.0 9.7 8.5 13.3 5.1 9.5 9.3 

Horizontal  7.5 5.8 6.6 6.6 15.5 1.3 6.8 7.8 
                                       Source: Endale, et al. [9] 

 

3.11. Plant Density Experiments in Jido Combolcha 
As shown in the table below (Table 6) values of total tuber yield of Balella variety with spacing 20 cm x 80 cm 

performed better (644 ± 105 q ha
-1

) than the rest of the treatments 20 cm x 60 cm and 50 cm x 60 cm, with the yield 

value of 590 ± 104 q ha
-1

 and 522 ± 137 q ha
-1

, respectively. But the net marketable yield obtained at spacing 

combination of 20 cm x 60 cm (590 ± 104 q ha
-1

) was by far better followed by 20 cm x 80 cm and 50 cm x 60 cm 

that gave average yield of 583 ± 82 q ha
-1

and 463±93 q ha
-1

, respectively.  

 
Table-6. Result of mean and standard error comparison of Balella variety on farm in Jido Combolcha 

Variable  Root 

Diameter (cm) 

Root Length 

(cm) 

Green Top 

(Kg) 

Marketable 

Root (q/ha) 

Unmarketable 

Root (q/h) 

Total Yield 

(q/ha) 

DF  2 2 2 2 2 2 

20 x 100 7. 2±.66a 15±3.4ab 3E4±8E3ab 438±110abc 42±21a 479±116abc 

20 x 60 5.5±.25bcd 13±.62ab 2E4±1E4ab 590±104a 0±0 a 590±104a 

20 x 80 4.9±.1d 14±2.2ab 3E4±2E4ab 583±82a 61±54 a 644±105a 

30 x 100 6.1±.25abcd 15±2.2ab 4E4±4E4a 384±221bcd 65±89 a 449±309abc 

30 x 60 5±1.1d 12±2.6ab 2E4±9E3ab 332±74bcd 12±21 a 344±63bc 

30 x 80 5.6±.63bcd 14±2.2ab 2E4±1E3ab 288±1.3cd 12±21 a 300±110bc 

40 x 100 7±1.5ab 15±1.4ab 1E4±5E3ab 285±43cd 57±81 a 323±68bc 

40 x 60 5.3±.5d 14±1.2ab 1E4±5E3ab 324±36bcd 12±20 a 336±27bc 

40 x 80 6±1.4abcd 14±1.8ab 1E4±5E3ab 278±54cd 22±20 a 299±57bc 

50 x 100 5.4±0.29cd 16±3.6a 4E4±4E4ab 294±77bcd 28±17 a 322±83bc 

50 x 60 6.9±.17abc  13±2.8ab 2E4±1E4ab 463±93ab 88±124 a 522±137ab 

50 x 80  6.1±1.3abcd 15±.91ab 1E4±8E3ab 233±47d 28±32 a 260±38c 

CV% 13.51 15.13 66.55 24.3 136.9 28.12 
              *Mean of the same letter across the column indicates non-significant difference among the treatments (p<0.05) (Teshome, et al. [12]) 
 

It is clear form Table 7 that the general yield performance of the Bareda (tubers horizontal vines spreading) 

variety was much lower than that of yield obtained by Balella (tubers vertical vines erect) in Jido Combolcha area. In 

general 20 cm x 60 cm spacing gave total yield of 409±257 q/ha followed by 20 cm x 100 cm and 30 cm x 60 cm 

that gave 347±139 q/ha and 294 ± 63 q/ha, respectively. Among all the treatments 40 cm x100 cm gave the lowest 

performance (129±69 q/ha) followed by 50 cm x 100 cm (144 ±34 q/ha) and 30 cm x 80 cm (185±111 q/ha). It is 

indicative of the fact that if spacing between plant and rows increases beyond provision of enough nutrients, the net 

number of vine decreases resulting into lower yield, since the net number of vine is positively correlated with yield 

obtained at the end of the day.  Therefore, 20 cm x 60 cm between two consecutive plants and rows should be 

adopted regardless of tuber and vine orientation for those farmers involved in sweet potato production in Jido 

Combolcha and similar agro-ecologies (FRG [13]).  

 
Table-7. Result of mean and standard error comparison of Bareda variety on farm in Jido Combolcha 

Variable  Root Diameter  

(cm)  

Root Length 

(cm) 

Green Top 

(kg) 

Marketable 

Root (q/ha) 

Unmarketable 

Root (q/h) 

Total Yield 

(q/ha) 

DF  3 3 3 3 3 3 

20 x 100 4.3±1a 19±1.3 a 3E4±3E3bcd 322±115ab 25±27a 347±139ab 

20 x 60 4.2±0.91a 19±1.9 a 3E4±2E4ab 396±267a 13±11 a 409±257a 

20 x 80 4.4±102a 17±2.6 a 4E4±1E4a 220±3.7abc 41±50 a 188±167ab 

30 x 100 4.8±1.4a 20±2.0 a 3E4±2E4bcd 270±164abc 17±4.9 a 281±160ab 

30 x 60 3.6±1.2a 19±3.2 a 2E4±3E3bcd 290±71abc 4.6±8 a 294±63ab 

30 x 80 4±1.4a 21±1.2a 2E4±1E4bcd 176±103bc 8.3±12 a 185±111ab 

40 x 100 5.5±1.2a 20±5.2 a 2E4±1E4d 110±40c 19±29 a 129±69b 

40 x 60 5.3±0.66a 21±309a 3E4±2E4abc 323±136ab 6.9±12 a 330±132ab 

40 x 80 5.1±1.4a 19±2.6 a 2E4±1E4dc 220±131abc 13±12 a 233±130ab 

50 x 100 5.7±1.4a 17±0.81 a 1E4±7E3d 130±36bc 14±4.1 a 144±34b 

50 x 60 4±0.85a 20±4.6 a 2E4±4E3d 170±74bc 3.7±6.4 a 174±71ab 

50 x 80  5±2.2a 19±0.6 a 9 1E4±9E3d 154±93bc 27±19 a 181±109ab 

CV% 14.2 12.81 31.9 42.86 138.16 50.14 
 (Teshome, et al. [14]) 

 

3.12. Plant Density Experiments in Bako Areas 
The population study at Bako was carried out during 1978 to 1982 using a cultivar white star (Table 8). The row 

spacing employed were 80, 100 and 120 cm whereas plant spacing included 30, 40 and 50 cm with population 

ranging from 41, 700 to 16,700 in a hectare of land. The results indicated that marketable and total yield increased as 

plant densities were decreased where as unmarketable yield was higher due to either higher or lower plant densities. 

Unmarketablity was mainly due to oversized and undersized roots. Undersized roots increased as spacing between 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

6 

 

rows and plants decreases. An increase in oversized roots was observed with wider spacing. 100cm x 30 cm was 

recommended for the cultivar white star around Bako and similar area. 

 
Table-8. Effects of plant density in mean root yield (q/ha) at Bako, 1978- 1982 

Row x plant spacing  

(cm
2
) 

Number of plants/ha 

(1000) 

Marketable root 

yield (kg/ha) 

Total root yield 

 (kg/ha) 

 80 x 30 41.7 206.28 319.54 

 80 x 40 31.3 193.15 309.19 

 80 x 50  25.0 187.70 299.16 

100 x 30 33.3 209.80 322.12 

100 x 40 25.0 174.59 289.94 

100 x 50 20.0 157.39 272.62 

120 x 30 28.6 188.79 302.25 

120 x 40 21.4 158.81 269.28 

120 x 50 16.7 157.84 265.53 

 

3.13. Plant Density Experiments in Awassa and Areka Areas 

Plant density recommendations varied in SARI mandate areas with variety and location (Table 9). In Areka, 

different varieties responded differently as shown in table below. However, at Awassa 60 cm x 30 cm 

recommendation was adopted after a three-year plant population experiment for a white fleshed variety called 

Awassa-83.  

 
Table-9. Recommendations of plant density in SARI mandate areas 

Variety  Location  Results  

SP-1499 Areka 100 cm x 25 cm 

SP-Koka 12 Areka  70 cm x 20 cm 

SP-2498 Areka 100 cm x 20cm 

Awassa-83 Awassa  60cm x 30 cm 
                               Source: CRCT (Crop Science Research Department) [7]  

 

3.14. Weeding 
Weeding trials revealed that the crop is highly susceptible to weeds at early stage of growth as most other root 

and tuber crops. So a grower shall induce a weeding practice staring the 7
th
 day after planting. However, the crop 

starts suppressing annual broadleaved weeds starting 45
th
 day of planting. That is because the crop is known for its 

allelophatic effects at full growth. There was an increase in yield per unit area as plant density was increased from 5 

to 10 plants m
-2

. However, there was not significant variation in yield (kg/ha) due to 7 and 10, and 7 to 12.5 plants m
-

2
 in Tis 1499 and Koka 6 (intermediate), respectively (Table 10). The yield of Tis 2498 did not show significant 

variation among plant densities despite the high yield from 10 plants m
-2

. The results showed that a population of 10 

plants m
-2

 produced significantly high tuber yield although it was not significantly different from 7 plants m
-2

. Effect 

of weeding on tuber yield was dictated by variation in variety and plant density. Weeding of Tis 1499 (erect and 

early) and Koka 6 twice increased the yield by 22.5 and 23.9%, respectively, while weeding practice did not have a 

significant effect on tuber yield of Tis 2498 (long vine, spreading and early). Although weeding once and twice 

produced more as plant density was increased (up to 10 plants m
2
), further increase reduced the yield. However, 

weeding twice increased tuber yield by 23.6, 18.2, 15.4, and 5.1% for the 5, 7, 10 and 12.5 plants m
-2

, respectively, 

compared with weeding once. The variation in root yield was not statistically significant in both weeding practices 

due to the range of 7 to 12.5 plants m
-2

. Generally speaking plant density of 25X10
3
 or less revealed poor ground 

cover percentages; Thus lower stand densities are of less value to the producers. Varieties with erect and intermediate 

growth habits can be weeded twice if high population is maintained. Growth with spreading canopy structure and 

plant density could be used as means to reduce weed infestation. This will save farmers time and labor and thus, 

breeders should focus in developing cultivars with spreading canopy structure with high yield. 

 
Table-10. Weeding frequency x variety x plant density on tuber yield of sweet potato (tons/ha) at Areka 

Variable Weeding frequency 

One time  (30 - 40 DAS) Two times (30 - 40 and 70 DAS) 

Variety   

Tis 1499  16.96bc  20.78a  

Koka - 12 6 15.45cd  19.15ab  

Tis 2498  12.53de  11.82e 

Plant density (no.ha-1 )  

50 × 103  11.60c  14.34bc 

70 × 103  16.19ab  19.14a  

100 × 103  17.16ab  19.81a  

125 × 103  14.96bc  15.72ab 
                         (Source: Tenaw, et al. [15]) 

 

DAS = days after sprouting, same letter across a column and row for each factor shows no significant difference 

at 5% probability level  

Sweet potato used to be grown without any fertilizer amendment despite its requirement and mining from the 

soil. However studies confirmed that use of either FYM or chemical fertilizers or both would increase yield. 

Fertilizer studies were carried out in sandy loam soils of Adami Tulu consisting of five levels of FYM (0, 5, 10, 15, 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

7 

 

20 t ha
-1

) and three levels of P (0, 90,180 kg P2O5 ha
-1

). It was laid out as a Randomized Complete Block Design in a 

factorial arrangement, and replicated three times (Table 10). A sweet potato cultivar known in the area called Balella 

was used for the study. The result indicated that the main effect of FYM significantly (P < 0.05) affected total 

tuberous root yield, tuberous root dry weight, fresh total biomass and dry harvest index. However, the main effect of 

P had no significant influence on all parameters studied (Table 11). Moreover, the interaction effects of FYM and P 

significantly (P< 0.05) affected marketable root yield, specific gravity and total dry biomass yield. Combined 

application of 20 t farmyard manure ha
-1

 and 180 kg ha
-1

 P2O5 resulted in production of highest marketable yield 

(32.56 t ha
-1

). The lowest marketable yield (8.8 t ha
-1

) was obtained at the application of 0 t ha
-1

 FYM combined with 

180 kg P2O5 ha
-1

. Thus, most of the yield and yield estimate parameters were enhanced in response to the application 

of FYM. For the two commonly used sweet potato quality parameters (dry matter and specific gravity), dry matter 

was not significantly responsive to both FYM and P while the highest specific gravity (1.09) was obtained at the 

combined application of 10 t FYM ha
-1

 and 0 kg P2O5 ha
-1

. Tuberous root dry weight was correlated negatively (r = -

0.32*) with shoot dry weight and was statistically significant (P < 0.05). But it was correlated positively with yield 

and yield estimate parameters like tuberous root fresh weight (r=0.965**), marketable tuberous root weight (r = 

0.842**), unmarketable tuberous root weight (r = 0.639**), average tuberous root number per plant (r = 0.582**) 

and average tuberous root length (r = 0.492**) at (P<0.01) indicating the existence of close associations among those 

parameters. Therefore, it could be concluded that tuberous root yield of sweet potato was significantly enhanced in 

response to the application of farmyard manure, indicating that enriching the soil of the area with organic matter 

through use of organic fertilizers holds the key for maximizing the yield of the sweet potato crop in the study area. 

These studies showed that higher nitrogen application would increase vine growth and suppress root growth.  

 
Table-11. Farmyard manure x phosphorus effect on marketable tuberous 

root weight (t ha-1) of sweet potato 

FYM ( t ha
-1

 ) P2O5 (kg ha
-1

) 

0 90 180 

0  15.89 12.41 8.80 

5   19.01 22.65 9.72  

10  18.67 9.01 32.04 

15  14.20 11.17 12.47 

20  24.72 22.07 32.56 

F-test  * 

LSD (P*FYM)  15.41 

CV (%)  32.70 
                                           *= Significant at P < 0.05probablity level; CV = Coefficient of Variation 
 

According to sweet potato without FYM was not foreseeable around  sandy loam soils of Adami tulu with 

chemical fertilizers alone. If a grower can have FYM as high as 5t/ha or 10t/ha then 90 kg ha
-1 

or 180 kg ha
-1 

would 

suffice to obtain agronomic optimum sweet potato root yield of 22.65 tha
-1

 and 32.04 tha
-1

 respectively (Table 11 and 

12). 

 
Table-12. Unmarketable and total root yield of sweet potato as affected by FYM and P application 

Treatment  Unmarketable Tuberous Root Yield (tha
-1

) Total Tuberous Root Yield (tha
-1

) 

FYM( t ha-1)   

0  10.00 22.37b 

5  9.70  26.83b  

10  9.39  29.30b  

15  10.75  23.30b  

20  15.91  42.89a  

F-test  NS  * 

LSD  6.54  12.48  

P2O5(kg ha-1)   

0  9.59 28.09 

90  11.49 26.94 

180  12.39  31.48  

F-test  NS  NS 

LSD  5.05 9.67 

CV (%) 31.13 23.25 
                         *=significant at p<0.05 probability levels; NS= non-significant; CV= Coefficient of variation; FYM=Farmyard manure 

 

A study was undertaken to assess the effects of combined application of inorganic (NP) and organic (FYM) 

fertilizers on root and biomass yield of Sweet potato (Ipomoea batatas (L.) Lam). The field experiment was 

conducted from June-Dec. 2008 at Delbo Watershed, two N levels (23 and 46 kg/ha) and two P levels (20 and 40 

kg/ha) were considered as inorganic fertilizers along with one unfertilized control treatment. The findings of this 

study clearly showed that yield and yield components of sweet potato at Delbo watershed can be enhanced by 

combining FYM and inorganic fertilizers. In this study the highest yield (24.12t/ha) was achieved using 46kg/ha N 

and 5t/ha FYM. Accordingly, the economic analysis showed that the highest net benefit of 37,880 Birr was obtained 

from 46kg/ha N and 5t/ha FYM. Considering the scarcity associated with inorganic fertilizer and limited amount of 

FYM, 23 N kg/ha and 2.5 t/ha FYM with a net benefit of 29,635 birr, could also alternatively be recommended for 

use by sweet potato producers in the area. Poor farmers who cannot afford fertilizer would be encouraged to use 

2.5t/ha FYM (Gezahegn and Andergachew [16]). In fact, Horticulture development department of Ministry of 

Agriculture  [17] recommended use of 100-200kg/ha DAP or equivalent animal manure in previous years. If ridges 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

8 

 

are to be made, it is recommended to apply farmyard manure prior ridging. In fact, at the level of Awassa 

Agricultural research center 50q FYM/ha was applied during ridging, 25kg /ha DAP was applied during planting and 

50kg/ha Urea applied after a month of planting.   

  

3.15. Irrigation Practices  
Even though this crop is said to be drought tolerant, research results showed needs for sufficient moisture at early 

stage especially during the first six weeks to secure healthy stand establishment. This was mainly because sweet 

potato vines are succulent and fragile, and if no sufficient moisture is supplied it dries up soon.  If there is no rain in 

early parts of planting, supplementary irrigation of 2mm of water per day is required even in the main rainy season. 

To meet this requirement, irrigating in alternative days is vital. Moisture stress during growth significantly reduces 

storage root yield. As a crop grows on, irrigating with 4-5mm water would suffice for a given week.  Because sweet 

potato crop needs sandy and well-drained soil; and if the soil has high moisture content, planting in raised bed is 

preferable (MOARD [18]). With growing interest of sweet potato as emergency food security crop in the country, 

there were increased pressure from concerned bodies to supply sweet potato cuttings in off seasons. Obviously the 

production of vines under such situations required application of irrigation water pumped from springs, rivers or 

lakes (Fig 2). There was a practice of applying water to field capacity once in a week time in such cases in majority 

of sweet potato fields.  Yield and quality of sweet potato in non-irrigated experiments were extremely low compared 

with that of irrigated experiments.   

 

 
Fig-2. Furrow irrigation practices in sweet potato seed multiplication schemes 

 

3.16. Intercropping 
Three sweet potato cultivars (Koka-12, Koka-14 and Alemaya) were grown under three sorghum varieties 

(Kobomash76, 76T1 No.23, hybrid sorghum) were tested under rainfed and irrigated conditions at Melkasa and 

Melka Werer, respectively. All pure sweet potato stands gave higher yield compared to intercrops. Sorghum grain 

yield of pure stands was lower when compared to intercrops. The results also indicated that Koka 12 and Kobomash 

76 were relatively compatible (Sirak [11]). Results further depicted that sweet potato plants are sensitive to shade 

leading to low yields. The crop should be grown under full sunlight. Tesfa, et al. [19]  also noted that maize 

intercropped with sweet potato showed reduced levels of leaf blight and common rust intensity when both crops were 

planted at the same time. 

 

3.17. Relaying and Double Cropping  
Therefore, it is only with erect leaved varieties that intercropping is recommended. However, all the varieties 

could be grown with relay crops, double crops or rotations with maize or sorghum (Table 13).  Thus the crop can 

take advantage of residual moisture and fertility. Results showed that in areas where sweet potato was grown 

previously, long season maize varieties could be grown successfully. 

 
Table-13. Double cropping of maize varieties after cereal, pulse and root crops at Awassa (1993, 1994 and 1996) 

Precursor crop Yield (q/ha) of katumani Yield (q/ha) of A - 511  

 No fertilizer 46/46kgha
-1

NP Mean  No fertilizer 46/46kgha
-1

NP Mean  

Katumani  -  - - 25.00 26.04 25.52 

A-511 5.52 5.52 5.10 - - - 

Tef  10.83 10.83 5.52 18.75 19.79 19.27 

Haricot bean (HB) 9.53 9.53 12.29 15.63 25.00 22.04 

Irish potato (IP) 14.47 14.47 13.75 18.75 26.04 22.40 

Sweet potato (SP) 7.08 7.08 6.65 17.71 26.04 21.88 

 9.49 8.66 9.08 19.17 24.58 21.88 
                       Source:  (Tesfa, et al. [19]) 

 

A double cropping experiment of maize grown after different crops in the same year was executed from 1993 to 

1996. The objective of the experiments was to properly utilize the available moisture, enhance productivity and fill 

food deficit periods. HB, IP and SP were found to be good precursors for A-511. Teff and Irish potato happened to 

be good pre cursors for Katumani under unfertilized conditions. Haricot bean would become good precursors only 

after fertilized plots. By double cropping the productivity of land was increased by 50 and 70% as compared to single 

crops under unfertilized and fertilized conditions (Table 12).  

In another study carried out in Awassa by Tolesa, et al. [20]  farmers were advised to grow either teff, haricot 

bean or sweet potato by harvesting at green ear or dry stage of maize.  The land equivalent ratio analysis revealed 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

9 

 

that the advantage of relay cropping is higher, 71% when maize was harvested green and 54.9% when maize was 

harvested at dry grain stage. The researchers obtained the highest gross return of 8912 Br./ha when maize was 

harvested at green ear stage and 5683 Br./ha when maize harvested dry grain and when sweet potato was relayed into 

maize at 50% flowering. This manifested that harvesting maize for green ears and relaying sweet potato into maize 

are economically attractive. Thus the appropriate time of relay planting sweet potato is at 50% flowering of maize for 

both harvesting systems (Table 14 and 15). 

 
Table-14. Effect of relay cropping sweet potato on maize green ear harvest and LER at Bako, 1990-1992 

Treatments Maize ears/ha Sweet potato yield (q/ha) Gross returnBr./ha LER 

Maize + 50% mf 36310.82 67.47 3911.99 1.27 

Maize +SP 15 da 50% mf 36310.82 47.13 7372.81 1.16 

Maize +SP 30 da 50% mf 40958.60 8.86 6480.39 1.07 

Sole mz - - 5967.08 1.00 
        Mz-maize, sp- sweet potato, mf-mid flowering, da-days after  
 

Table-15. Effects of relaying sweet potato after maize at Bako, 1990-1992 

Treatments Sp yield (q/ha) Sp yield reduction relative to sole (%) 

@ 50% mf 67.5 64.2 

15 da 50% mf 47.1 75.0 

 30 da 50% mf 8.9 95.3 

Sole sp 188.5 0 

LSD5% 26.6  

LSD5% 37.3  

CV (%) 27.1  

 

3.18. Rotation Cropping 
According to results of numerous year crop rotation study, maize, sweet potato and common bean coming in the 

sequence in the three year crop rotation scheme was productive compared to other cropping sequences.   

 

3.19. Growing Sweet Potato near Shrub and Tree Crops 
As leaves, barks, roots, twigs, exudates and branches release phenolic allello chemicals, eucalyptus spp. were 

generally recognized with their allelophatic effects on growth of various crops. This negative effect coupled with its 

fierce competition for sunlight, moisture and nutrients posed great threat to crop production and have been known as 

major court case in many places. However, driven by expansion of construction economy the reality of eucalyptus 

spp. expansion in most agro-ecologies of Ethiopia has become a reality. So serious studies were carried out to 

identify tolerant crops to the cumulative effect of eucalyptus and identify a mechanism for amelioration of the 

challenge. Results showed that a distance of some 5 meters should be left in lowlands to produce crops like teff, 

sweet potato and common beans; however, growing crops like wheat and barley is possible with Eucalyptus in 

highland areas where moisture is not limiting. In fact, cutting ditches was recommended to break root exudation and 

completion for moisture and nutrients (Fig 3).  

 

 
Fig-3. Ditches dug between eucalyptus hedge row and adjacent farmland  

 

There are also growing trends of growing sweet potato under other shrub crops like coffee and enset in some 

parts of the country. However, the production is maintained until canopy closure of coffee and enset, and is meant to 

fill food gaps of some forthcoming months.  

 

4. Conclusion 
Sweet potato that was once known as poor man’s crop has become a food security crop all over the country with 

numerous potentials for income generation and export. Although it required low inputs, it matured in short period of 

time and provided reliable yield in Ethiopian conditions. Consequently the crop rightly obtained national focus due 

to the various organizations in the Ethiopian agricultural research system which contributed much to the generation 

of crop management options. Sweet potato crop has a potential of 50 to 60 t/ha in Ethiopia; however, farmers are 

obtaining 6 to 8 tons/ha only. The yield is ten times lower than the potential. This yield gap would be attributed to a 

number of factors like absence of high yielding improved and virus free planting materials, appropriate insect pest 

management and use of improved crop management options. Based on research findings to date, vines taken from 



Agriculture and Food Sciences Research, 2016, 3(1):1-11 

 

 

 

 

10 

 

upper or middle portion of the plant chosen for sweet potato planting should be of 30 to 40 cm length having 3 to 4 

buds, shall be stored for two days under shade and should be buried in the soils until two-third of the cutting. The 

land prepared could be flat as in Wolaita area and could be of ridges as in Hararige depending on soil texture, 

moisture regime and tillage implements. When planting dates are considered, in Awassa and similar agro-ecological 

areas the onset of rainy season particularly mid may to early June was recommended as optimum unlike early June 

planting of Bako. Planting position study confirmed that planting cuttings at slant (inclined) position gave higher root 

yield (P<0.05) compared to horizontal plantings in areas like Awassa. In Harargie vines are planted in inclined 

positions where plantings are done on ridges. In Wolaita, vine cuttings are buried horizontally in furrows when the 

land is prepared by oxen drown implements. Plant density experiments in Jido Combolcha revealed that net 

marketable yield of Balella variety obtained at spacing combination of 20 cm x 60 cm (590 ± 104 q ha
-1

) was by far 

better followed by 20 cm x 80 cm and 50 cm x 60 cm that gave average yield of 583 ± 82 q ha
-1

and 463±93 q ha
-1

, 

respectively. According to similar studies employing cultivar Whitestar 100cm x 30 cm plant spacing was 

recommended for the Bako and similar agro-ecologies. The plant density study at Areka showed that SP-1499 should 

be grown with 100 cm x 25 cm, SP-Koka 12 with 70 cm x 20 cm, and SP-2498 with 100 cm x 20cm. However, 

similar studies employing cultivar Awassa-83 ended up in recommending 60cm x 30 cm for Awassa and similar 

agro-ecologies. For a sweet potato crop grown with recommended plant density, varieties (eg. Tis 2498) with long 

spreading vines could be weeded once on 30-40DAS but varieties with erect vines (e.g.Tis 1499) should be weeded 

twice on 30-40DAS and 70DAS regardless of the study sites. In one fertilizer study carried out in Adami tulu 

combined application of 20t farmyard manure ha
-1

 and 180 kg ha
-1

 P2O5 resulted in production of highest marketable 

yield (32.56tha
-1

). In another fertilizer study carried out at Delbo watershed, the highest root yield (24.12t/ha) was 

achieved using 46kg/ha N and 5t/ha FYM. If rains stop during early or late growth of sweet potato, supplementary 

irrigation of 2mm/day during planting (for a week or so) and 4-5mm/week during vegetative growth was 

recommended. In intercropping study carried out at Melkasa and Melka worer using three sweet potato varieties 

called Koka-12, Koka-14 and Alemaya and three sorghum varieties called Kobomash76, 76T1 No.23 and hybrid 

sorghum, sorghum grain yield of pure stands was lower when compared to intercrops and Koka 12 and Kobomash 76 

were relatively compatible. Based on relay and double cropping trial carried out at Awassa, in places where sweet 

potato was grown previously, long season maize varieties could be grown successfully and sweet potato could act as 

precursor for maize varieties. Based on green ear and dry harvest analysis, best maize and sweet potato compatibility 

was seen when sweet potato was relay cropped at 50% flowering of maize. Whenever sweet potato is grown near 

Eucalyptus tree, ditches should be cut with 60 cm depth and 40 cm width to prevent root exudates of allelophatic 

effect. Totally there is a great deal of concern on production, research and technology dissemination; however, there 

is also a need to create sustainable and site specific integrated nutrient management options, appropriate irrigation 

schedules, generation of ways of conserving planting materials in dry seasons and development of compatible 

multiple cropping options for sweet potato in the country.  

 

5. Future Research Directions 
1. As we are in the era of global climate change and soil degradation, adopting and generating eco friendly site 

specific sustainable crop production technologies through well designed research projects is necessary 

2. Information on productivity and on suitable soil fertility management practices for sustained crop production for 

the major soils of Ethiopia is still very limited. There are limited suitable options for improving soil fertility 

management (which is essential to increase crop and farm productivity) in a crop like sweet potato that is 

considered a low-input and subsistence crop and where there are few incentives to use labor and resource-

intensive technologies. Sweet potato comprehensive integrated soil fertility management (ISFM) studies for 

early, medium and late maturing varieties preferred in seed multiplication and root production schemes for 

dominant soils found in major agro-ecologies is recommended as future research strategy.  

3. Drought management is an important factor for increasing sweet potato productivity, given that sweet potato 

yields can be severely affected by limited water availability. So sweet potato irrigation studies aimed at 

economizing water use while optimizing vine and root production shall be sought in future. 

4. Design and assessment of intercropping options and crop rotations that could extend the supply period. 

5. Development of alternatives for conserving planting materials and for having planting material on a timely 

manner, particularly in drought prone areas. 

 

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