**1. Introduction**

Vegetable is one of the important sources of vitamins and minerals [1] and dietary fiber [2] and are essential in prevention of diseases [3]. Vegetable production is of great economic importance in the agricultural sector [4]. Its value chain can provide income and reduces poverty and unemployment [1]. Vegetable production has the potential to increase food security and create employment [5]. Smallholders' farmers made up large number of vegetable producers in Nigeria [6].

Insufficient intake of fruit and vegetables is estimated to cause around 14% of gastrointestinal cancer deaths, about 11% of ischemic heart disease deaths and about 9% of stroke deaths [7]. The World Health Organization recommended consumption of 400 g of fruits and vegetables daily to maintain good health. Vegetables production is profitable, and the actors will require adequate knowledge, capital, and new methods [8].

Tomato, pepper, and onion are important vegetables in the global economy due to their high consumption [1]. Tomato is one of the foremost, essential vegetables in Nigeria [9], virtually consumed by every tribe [10], and grown all over Nigeria [11]. Tomato stands out as one of the important vegetables considering the scale of production and level of consumption [12]. It is beneficial for the maintenance of good health and disease prevention [13]. Tomato production presents an opportunity for increasing rural incomes particularly among peri-urban smallholder farmers due to the high demand in urban centers [14]. Farmers are willing to cultivate tomato more than any other vegetable because of its high demand, multiple harvests produced [15]. Tomato is produced across Nigeria and smallholder farmers cultivating between 0.5 and 4 hectares of land account for 90% of production [16]. Tomato is mainly produced by resource poor small farmers with small farm holdings and they are responsible for the tomato consumed in the nation [17].

Tomato production is profitable in Nigeria, and average profit of tomato production under irrigation was N128,750 (\$ = N350) in Kogi and Benue State [18], while the rate of naira on naira invested on tomato production in Kano was 1.5 indicating profitability of the enterprise [19].

Pepper is a rich source of vitamins A, C, and E [20]. It is a high value crop [21] and has economic significance in the world market. It has potentials to generate foreign exchange and can be utilized in confectionary, medicinal, and culinary purpose [22]. Pepper production is an important source of foreign exchange and its exportation in Nigeria has been reported to be lucrative [23]. The northern part of Nigeria is the major areas of production [20, 22], and it is mostly produced by smallholder farmers [24].

Onion is an important vegetable and is of commercial importance throughout the world [25]. Onion production in Nigeria is profitable with rate of returns on investment of 91.89 and 119.78% in Sokoto and Kebbi state [26]. Onion consumption and demand is throughout the year [27]. Onion is used as spice, vegetable, salad, and dressing [28]. The production of onion can improve economic status and welfare of farmers [29]. In Nigeria, bulk of onion is produced under irrigation in the Northern states [30].

Despite the importance of vegetable in the daily diet and the competitive and comparative advantage the country has in the production, vegetable production is fluctuating [6]. For instance, the average yield of tomato is far below the potential of the crop. For instance, the average yield of about of 6 tones is much lower than 7 tones and 6.48 tones reported for Tanzania and Uganda, respectively [31]. Agricultural production can be sustained through efficient resource use [32]. Efficiency is the ability to produce maximum output from the least input combination during the production process [33, 34]. Efficiency is crucial in resource saving [35]. Factors influencing efficiency of farmers can be categorized into agent and structural facts [36]. Agents' factors are educational level, age, and social capital, while structural factors include farm size, fertility, and among other [37].

Analyzing efficiency levels provides understanding of constituent of efficiency system and strategies to improve efficiency [38]. It is worthy of note that efficient utilization of resources leads to improvement in production [38]. Improvement in technical efficiency of farmers will lead to better yield, food security, and better standards of living [39].

A series of studies have been carried out to assess and compiled factors affecting agricultural productivity and its drivers in Nigeria, which include [40–44]. They have focused on commodities such as rice, maize, and tuber crops. None of the aforementioned studies, however, has compiled factors affecting efficiency of vegetable production in Nigeria. This paper intends to identify and collate factors affecting efficiency of vegetable production in Nigeria.
