THE EFFECT OF PLANTING METHODS ON THE GROWTH AND YIELD OF SWEET POTATO (A CASE STUDY OF SWEET POTATO FARMERS IN NSUKKA LOCAL GOVERNMENT AREA, ENUGU STATE)

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Sweet potato (Ipomoea batatas L.) is a trailing, warm-season root crop grown mainly for its starchy storage roots. According to Orji and Ikeokwu (2022), the crop originated in South America and was carried to Spain by Christopher Columbus in 1492; its cultivation in Africa began in São Tomé in 1520, and it reached Nigeria through Portuguese traders between 1694 and 1894. It belongs to the family Convolvulaceae, which has more than 1,000 species, of which Ipomoea batatas is the most important. The leaves vary in shape, colour and size according to variety, and the storage roots may be cream, yellow, purple, red or white fleshed.

The crop is attractive to smallholder farmers because of its short duration and modest requirements. Orji and Ikeokwu (2022) report that it matures within three to five months after planting, thrives at temperatures of about 20 to 28 °C and annual rainfall of about 500 to 1,250 mm, and is rich in vitamin A and other minerals needed for proper body function, with a low glycemic index. These qualities make it a useful food security crop, especially in households that depend on rainfed farming. Beyond the roots, the vines and leaves are also used as vegetable and livestock feed in many farming communities, and the crop has been proposed as a source of biofuel and for food fortification (Orji & Ikeokwu, 2022). In Nigeria, eleven varieties have been isolated and released to farmers by the National Root Crop Research Institute, Umudike (Orji & Ikeokwu, 2022).

In terms of production, a value chain review based on FAOSTAT data placed Nigeria as the third largest sweet potato producer in the world, after China and Uganda, at the time of the review, while noting that production continued to show significant yield gaps and stagnant productivity (Bergh et al., 2012). Only a small share of the crop is exported. Production in Nigeria is further constrained by factors such as poor funding and outbreaks of sweet potato virus disease (Orji & Ikeokwu, 2022). Although these constraints are important, the way the crop is planted is one of the few factors that is entirely within the control of the farmer and costs little to change, which makes it a practical entry point for improving yield.

Sweet potato is propagated from vine cuttings rather than seed, and its storage roots develop from adventitious roots formed at the buried nodes. The condition of the soil around those nodes, including its looseness, aeration, depth and drainage, therefore influences how much root growth and bulking can occur. Farmers prepare this environment in different ways. The crop may be planted on ridges, on individual mounds or on the flat, and the cuttings may be set upright, horizontally, or folded and looped. Chagonda et al. (2014) observed that smallholders in Zimbabwe use different tillage methods and vine orientations because of their belief that these give different yields, although evidence for choosing among them was limited. In their trial, ridges and mounds did not differ significantly in yield, but ridges produced longer storage roots (134.2 mm against 115.9 mm), and horizontal and looped vines produced about 34.8 and 35.5 t/ha respectively, compared with 28.7 t/ha for folded vines.

Recent work from other environments shows that the results are not consistent. In a two-season trial with the Beauregard variety in Hungary, Balázs et al. (2024) found that ridge cultivation combined with twin-row planting gave the highest yield (up to 40.87 t/ha in 2020) while flat cultivation in single rows gave the lowest; they also reported that plant density affected yield and carotenoid content more strongly than the choice between ridge and flat, and they noted that earlier work had found flat planting to out-yield ridges. In North Carolina, Woodard et al. (2024) reported that horizontal planting orientation raised marketable yield by 16% in one season in an organic system, but that the difference was absent in the following season. Taken together, these studies show that the effect of planting method varies with soil, season, cultivar and management.

Evidence from Nigeria is more limited. Anene-Okeakwa et al. (2024) compared ridge, zero, mound and flat tillage on sweet potato at Asaba, Delta State, measuring growth at four, six and eight weeks after planting and final yield, and reported that tillage practice had a significant effect on growth and yield. Nsukka Local Government Area, in Enugu State, lies in the derived-savannah belt of south-eastern Nigeria, where researchers at the University of Nigeria, Nsukka have described the soils as droughty (Obi et al., 2024). Soil conditions of this kind may favour one seedbed form over another, which is why results from Asaba or from other countries cannot be assumed to apply. It is against this background that the present study was designed to determine the effect of planting methods on the growth and yield of sweet potato among farmers in Nsukka Local Government Area.

1.2 Statement of the Problem

Sweet potato is widely grown in Nigeria and is recognised as a food security crop, yet its productivity remains below what is achievable. A value chain review noted significant yield gaps and stagnant productivity in the Nigerian sweet potato sector (Bergh et al., 2012), and other reviews list poor funding and sweet potato virus disease among the constraints (Orji & Ikeokwu, 2022). Part of the yield gap is attributable to agronomic practices, including how the crop is planted.

Sweet potato farmers in Nsukka Local Government Area plant mainly according to personal experience, family practice and the labour available. Ridging, mounding and flat planting are all in use, but the differences in vine growth, root number, root size and yield associated with each method have not been measured under local soil and rainfall conditions. The studies reviewed for this work were conducted in Zimbabwe, Hungary, the United States and Asaba in Delta State; they report conflicting outcomes (Balázs et al., 2024; Chagonda et al., 2014; Woodard et al., 2024) and the literature consulted did not reveal a comparison of planting methods carried out with farmers in Nsukka.

The consequence is that farmers do not know whether the extra labour required to make ridges or mounds is repaid by better growth and higher yield, or whether flat planting gives equally good results at lower cost. Extension agents face the same difficulty because they have no local figures on which to base recommendations. Without this information, farmers may continue to use methods that give low or inconsistent yields, and the potential of the crop as a source of food and income in the area may not be fully realised. This study was therefore undertaken to provide locally generated evidence on the effect of planting methods on the growth and yield of sweet potato.

1.3 Objectives of the Study

The main objective of the study was to determine the effect of planting methods on the growth and yield of sweet potato among farmers in Nsukka Local Government Area, Enugu State. The specific objectives were to:

(i) identify the planting methods currently used by sweet potato farmers in the study area;

(ii) compare the effect of ridge, mound and flat planting on the growth of sweet potato (vine length and number of leaves);

(iii) compare the effect of the three planting methods on storage root number, size and yield; and

(iv) determine the planting method that gives the most dependable growth and yield.

1.4 Research Questions

The following research questions guided the study:

(i) What planting methods are used by sweet potato farmers in Nsukka Local Government Area?

(ii) How do ridge, mound and flat planting affect the growth of sweet potato?

(iii) How do the planting methods affect the yield of sweet potato?

(iv) Which planting method is most suitable for sweet potato production in the study area?

1.5 Research Hypotheses

The following null hypotheses were tested at the 0.05 level of significance:

H01: Planting method has no significant effect on the growth of sweet potato.

H02: Planting method has no significant effect on the yield of sweet potato.

1.6 Significance of the Study

The findings will help sweet potato farmers in Nsukka to choose planting methods supported by local evidence, which may reduce unnecessary labour and improve yield. Extension agents will have local data to support their recommendations.

The study will also add to the literature on sweet potato production in south-eastern Nigeria and provide a reference for students and researchers carrying out related work.

1.7 Scope and Limitations of the Study

The study covers sweet potato farmers in Nsukka Local Government Area, Enugu State. It is limited to the effect of planting method (ridge, mound and flat) on growth and yield, and does not include variety, fertilizer or pest effects.

Limitations include the short duration of the study (one growing season), the limited number of farms covered, and dependence on weather conditions during the season. The findings should therefore be applied with care to areas whose soils and climate differ from those of the study area.

1.8 Definition of Terms

Planting method: the form of seedbed on which sweet potato cuttings are set, namely ridge, mound or flat.

Growth: measurable development of the plant, such as vine length and number of leaves.

Yield: the weight of marketable storage roots harvested per plant or per unit area.

Ridge: a long raised strip of soil on which crops are planted.

Mound: an individual heap of soil on which one or a few cuttings are planted.

Vine cutting: a portion of sweet potato stem used as planting material.

REFERENCES

Anene-Okeakwa, J. E., Chukwukelu, I. S., & Oyana, V. N. (2024). Effect of different tillage practices on the growth and yield of sweet potatoes (Ipomoeo batata L) in Asaba, Delta State Nigeria. International Journal of Research and Innovation in Social Science, 8(1), 2079–2084. https://www.rsisinternational.org/journals/ijriss/Digital-Library/volume-8-issue-1/2079-2084.pdf

Balázs, V., Helyes, L., Daood, H. G., Pék, Z., Ilahy, R., Neményi, A., Égei, M., & Takács, S. (2024). Cultivation technology and plant density affecting the yield and carotenoid content of Beauregard sweet potato. Agronomy, 14(11), 2485. https://doi.org/10.3390/agronomy14112485

Bergh, K., Orozco, P., Anderson, C. L., & Gugerty, M. K. (2012). Crop value chains: Sweet potatoes in Nigeria (EPAR Technical Report No. 220). Evans School Policy Analysis and Research, University of Washington. https://epar.evans.uw.edu/crop-value-chains-sweet-potatoes-in-nigeria

Chagonda, I., Mapfeka, R. F., & Chitata, T. (2014). Effect of tillage systems and vine orientation on yield of sweet potato (Ipomoea batatas L.). American Journal of Plant Sciences, 5(21), 3159–3164. https://doi.org/10.4236/ajps.2014.521332

Obi, J. O., Onah, C. J., Nnadi, A. L., Osadebe, V. O., Akubue, J. C., Amuji, C. F., & Obalum, S. E. (2024). Sensitivity of rainfed okra (Abelmoschus esculentus L. Moench) to mulch material and plant spacing in drought-prone tropical soils. Agroindustrial Science, 14(2), 97–106. https://doi.org/10.17268/agroind.sci.2024.02.02

Orji, K. O., & Ikeokwu, C. (2022). Sweet potato (Ipomoea batatas L.) production in Nigeria: A synoptic review of its importance, problems and prospects. Nigerian Journal of Scientific Research. https://journals.abu.edu.ng/index.php/njsr/article/view/313

Woodard, A., Schultheis, J., Jennings, K., Woodley, A., & Suchoff, D. (2024). Horizontal planting orientation can improve yield in organically grown sweetpotato. HortScience, 59(1), 36–42. https://doi.org/10.21273/HORTSCI17352-23