EFFECT OF NPK FERTILIZER ON THE GROWTH AND YIELD PERFORMANCE OF YAM (Dioscorea spp.) AND EGUSI-MELON (Citrullus colocynthis) IN A SOLE AND INTERCROPPING SYSTEM

ABSTRACT

Sustainable crop production in tropical farming systems increasingly depends on efficient nutrient management and appropriate cropping practices capable of improving productivity while maintaining soil fertility. This study evaluated the influence of varying rates of NPK fertilizer on the growth and yield performance of yam (Dioscorea spp.) and egusi-melon (Citrullus colocynthis) cultivated under sole and intercrop production systems. The experiment was conducted during the 2013 early cropping season under rain-fed conditions at the Faculty of Agriculture Experimental Farm, University of Benin, Benin City, Nigeria.

The experiment was arranged in a Randomized Complete Block Design (RCBD) with three replications. Four fertilizer levels of NPK 20:10:10 (0, 200, 400, and 600 kg ha?¹) were evaluated across sole and intercrop combinations of yam and egusi-melon. Data collected included vine length, stem girth, number of tubers, pod number, pod size, seed yield, and tuber yield. The results revealed that fertilizer application significantly enhanced the vegetative growth and yield components of both crops compared with the unfertilized control. Yam cultivated as a sole crop generally produced higher tuber yield than yam grown in association with egusi-melon. However, the intercrop system demonstrated efficient land utilization and improved overall productivity.

Application of NPK fertilizer at 400 kg ha?¹ produced the highest tuber yield in yam and significantly improved egusi-melon pod development and seed yield. The 600 kg ha?¹ fertilizer treatment enhanced vegetative parameters such as vine length and stem girth in both crops. Intercropping also contributed to improved weed suppression and better soil surface coverage due to the spreading growth habit of egusi-melon.

The findings indicate that moderate fertilizer application combined with yam–egusi relay or mixed intercropping can enhance crop productivity and optimize resource utilization in humid tropical environments. The study therefore recommends the application of 400 kg ha?¹ NPK 20:10:10 fertilizer for sustainable production of yam and egusi-melon intercrop systems in southern Nigeria.

CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

Agricultural production systems in sub-Saharan Africa are increasingly confronted with declining soil fertility, land degradation, low crop productivity, and rising pressure on available arable land. These challenges have compelled researchers and farmers to explore sustainable cropping systems capable of improving productivity while conserving environmental resources. Among such systems, intercropping has remained one of the most widely adopted indigenous agricultural practices in tropical farming communities due to its economic, ecological, and agronomic advantages (Lithourgidis et al., 2011).

Intercropping refers to the cultivation of two or more crops simultaneously on the same piece of land during a growing season with the objective of maximizing resource utilization and increasing total productivity per unit area (Ofori and Stern, 1987). In traditional African farming systems, intercropping is commonly practiced because it enhances yield stability, reduces weed infestation, minimizes soil erosion, and improves efficient utilization of sunlight, water, nutrients, and space (Agegnehu et al., 2006). The system is particularly important for smallholder farmers who operate under limited land resources and low-input conditions.

Yam (Dioscorea spp.) is one of the most important root and tuber crops cultivated in West Africa and serves as a major staple food for millions of people. Nigeria remains the world’s largest producer of yam, accounting for more than 65% of global production (FAOSTAT, 2022). The crop contributes significantly to food security, rural income generation, and socio-cultural activities in many Nigerian communities. Yam tubers are rich in carbohydrates, vitamins, and minerals, making them an essential energy source in tropical diets. However, yam production is highly nutrient demanding due to the large quantity of biomass and tuber yield produced during growth (Aighewi et al., 2015). Continuous cultivation without adequate nutrient replenishment has therefore resulted in declining soil fertility and reduced productivity in many yam-producing regions.

Egusi-melon (Citrullus colocynthis), on the other hand, is an economically important cucurbit widely cultivated in West Africa for its nutrient-rich seeds. The seeds are highly valued because of their protein and oil content and are extensively used in soup preparation and food processing industries. Egusi-melon also serves important ecological functions in mixed cropping systems because its creeping growth habit provides effective ground cover that suppresses weeds, reduces moisture loss, and minimizes soil erosion (Achigan-Dako et al., 2008). In many traditional farming systems in Nigeria, egusi-melon is commonly intercropped with yam, cassava, and maize as a companion crop.

Despite the importance of yam and egusi-melon in food systems and household economies, productivity of both crops remains relatively low in many parts of Nigeria due to poor soil fertility management, continuous land cultivation, and inadequate agronomic practices. Among the essential nutrients required for crop growth, nitrogen (N), phosphorus (P), and potassium (K) play critical roles in vegetative growth, root development, flowering, and yield formation. Consequently, the application of NPK fertilizer has become a major strategy for improving crop productivity in nutrient-depleted tropical soils (Marschner, 2012).

The response of crops to fertilizer application is influenced not only by the quantity of nutrients supplied but also by the cropping system employed. In intercropping systems, nutrient competition and complementarity among component crops may alter nutrient uptake efficiency and yield performance. While excessive fertilizer application may stimulate vegetative growth at the expense of yield, inadequate application may result in nutrient deficiency and poor crop performance. Determining the optimum fertilizer rate suitable for yam and egusi-melon intercrop systems is therefore essential for sustainable crop production.

Recent concerns about sustainable agriculture and climate-resilient food systems have renewed interest in integrated nutrient management and diversified cropping systems that can simultaneously improve productivity, soil health, and environmental sustainability. Understanding how NPK fertilizer influences growth and yield components in yam–egusi intercrop systems will provide valuable information for developing efficient agronomic recommendations for farmers in the humid tropics.

1.2 Statement of the Problem

Declining soil fertility remains one of the major constraints limiting crop productivity in tropical farming systems, particularly in Nigeria where continuous cultivation and shortened fallow periods have reduced soil nutrient reserves. Yam cultivation is highly exhaustive on soil nutrients, especially nitrogen and potassium, while egusi-melon also requires adequate nutrient supply for optimum seed development. Most smallholder farmers rely on traditional cropping systems without sufficient fertilizer input, resulting in low yields and poor economic returns.

Although intercropping yam with egusi-melon is widely practiced because of its weed suppression and land-use advantages, there is limited scientific information on the appropriate fertilizer rates that optimize the productivity of both crops when grown together. Farmers often apply fertilizer indiscriminately without understanding the nutrient requirements of the intercrop system, leading to inefficient nutrient use, increased production costs, and environmental degradation.

Furthermore, excessive fertilizer application may increase vegetative growth while reducing tuber and seed yield, whereas insufficient fertilizer may limit crop development and reduce productivity. There is therefore a need to evaluate the response of yam and egusi-melon to different rates of NPK fertilizer under sole and intercrop conditions in order to identify suitable nutrient management strategies for sustainable production.

1.3 Aim of the Study

The aim of this study is to evaluate the effect of NPK fertilizer on the growth and yield performance of yam (Dioscorea spp.) and egusi-melon (Citrullus colocynthis) under sole and intercropping systems.

1.4 Objectives of the Study

The specific objectives of the study are to:

1. determine the effect of different rates of NPK fertilizer on the vegetative growth of yam and egusi-melon;
2. evaluate the influence of NPK fertilizer on the yield components of yam and egusi-melon under sole cropping conditions;
3. assess the growth and yield performance of yam and egusi-melon under intercropping systems;
4. compare the productivity of sole cropping and intercropping systems using different fertilizer rates; and
5. identify the optimum NPK fertilizer rate suitable for sustainable yam–egusi production in the humid rainforest zone of Nigeria.

1.5 Research Questions

The study seeks to provide answers to the following questions:

1. How does NPK fertilizer affect the vegetative growth of yam and egusi-melon?
2. What influence does fertilizer application have on tuber and seed yield of the crops?
3. Does intercropping yam with egusi-melon improve land productivity compared with sole cropping?
4. Which fertilizer rate produces the highest yield under sole and intercrop systems?
5. What agronomic advantages are associated with yam–egusi intercropping?

1.6 Research Hypotheses

The following hypotheses were tested in the study:

H??:

NPK fertilizer application has no significant effect on the growth parameters of yam and egusi-melon.

H??:

There is no significant difference in yield performance between sole and intercropped yam and egusi-melon.

H??:

Different rates of NPK fertilizer do not significantly influence the productivity of yam and egusi-melon intercrop systems.

1.7 Significance of the Study

This study is important because it contributes to sustainable crop production strategies suitable for tropical farming systems. The findings will provide practical information to farmers on the appropriate fertilizer rates required to improve yam and egusi-melon productivity under sole and intercrop conditions.

The study will also benefit agricultural extension agents by providing evidence-based recommendations that can be disseminated to rural farmers for improved crop management practices. Researchers and scholars will equally benefit from the study as it contributes to existing knowledge on intercropping systems, nutrient management, and sustainable agriculture.

Additionally, the study supports current global efforts toward climate-smart agriculture by promoting efficient land utilization, soil conservation, and integrated crop production systems capable of enhancing food security and rural livelihoods.

1.8 Scope of the Study

The study focused on evaluating the effect of NPK 20:10:10 fertilizer on the growth and yield components of yam and egusi-melon cultivated under sole and intercropping systems. The experiment was conducted under rain-fed conditions at the Faculty of Agriculture Research Farm, University of Benin, Benin City, Nigeria. Parameters evaluated included vine length, stem girth, tuber yield, pod number, pod size, and seed yield.

1.9 Justification of the Study

With increasing pressure on land resources and declining soil fertility, there is a growing need for sustainable production systems capable of maximizing yield while conserving soil resources. Intercropping yam with egusi-melon presents an opportunity for efficient land use, improved weed suppression, and enhanced productivity. However, optimal fertilizer management remains a critical challenge. This study is therefore justified because it seeks to establish appropriate fertilizer recommendations that can improve productivity, profitability, and sustainability of yam-based cropping systems in Nigeria.

1.10 Definition of Terms

Intercropping

The cultivation of two or more crops simultaneously on the same piece of land during the same growing season.

Sole Cropping

The practice of cultivating a single crop species on a piece of land without association with another crop.

NPK Fertilizer

A compound fertilizer containing nitrogen (N), phosphorus (P), and potassium (K), which are essential nutrients for plant growth.

Yield Components

Agronomic characteristics that contribute directly to crop yield, such as tuber number, pod size, seed yield, and biomass production.

Yam

A tropical tuber crop belonging to the genus Dioscorea, widely cultivated for its edible underground tubers.

Egusi-Melon

A cucurbit crop cultivated mainly for its edible seeds rich in oil and protein.

References

Achigan-Dako, E. G., Fagbemissi, R., Avohou, H., Vodouhe, R., Coulibaly, O., & Ahanchede, A. (2008). Importance and practices of egusi crops in sub-Saharan Africa. African Journal of Agricultural Research, 3(1), 86–92.

Agegnehu, G., Ghizaw, A., & Sinebo, W. (2006). Yield performance and land-use efficiency of barley and faba bean mixed cropping in Ethiopian highlands. European Journal of Agronomy, 25(3), 202–207.

Aighewi, B. A., Maroya, N., & Asiedu, R. (2015). Seed yam production from minisetts. International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria.

Akobundu, I. O. (1987). Weed Science in the Tropics: Principles and Practices. Wiley, New York.

FAOSTAT. (2022). Food and Agriculture Organization Statistical Database. Rome, Italy.

Lithourgidis, A. S., Dordas, C. A., Damalas, C. A., & Vlachostergios, D. N. (2011). Annual intercrops: An alternative pathway for sustainable agriculture. Australian Journal of Crop Science, 5(4), 396–410.

Marschner, P. (2012). Marschner’s Mineral Nutrition of Higher Plants (3rd ed.). Academic Press, London.

Ofori, F., & Stern, W. R. (1987). Cereal-legume intercropping systems. Advances in Agronomy, 41, 41–90.

Onwueme, I. C. (1978). The Tropical Tuber Crops: Yams, Cassava, Sweet Potato and Cocoyams. John Wiley and Sons, New York.