**5. Agronomy and production of root vegetables in Nigeria**

#### **5.1 Onion (***A. cepa***)**

Onion is an important spice and one of the vegetables that is commonly consumed in Nigeria which produces underground bulb that are edible, with about two million metric tonnes of Onions produced annually in Nigeria, according to Mr. Muhammad Abubakar, the Minister of Agriculture and Rural Development, at the 4th Regional Onion annual conference held in Kano, an event organized by Regional Observatory on Onions for West and Central Africa, in conjunction with National Onion Producers, Processors and Marketers Association of Nigeria (NOPPMAN). Nigeria is part of the largest onion producers in the world with over 2,000,000 tonnes produced annually [65]; Nigeria being ranked sixth among the top 10 producers of green onion, and 11th position in dry onion production globally. Major growing ares of onion in Nigeria include Kano, Kaduna, Jigawa, Sokoto, Plateau, Bauchi and Kebbi states. Production figures in 2012 indicated about 240,000 tons of green onions and 1,350,000 tons of dry onions were produced

**Figure 1.** *Production/yield quantities of onions, dry in Nigeria.*

#### **Figure 2.**

*Production/yield quantities of onions, shallots, green in Nigeria.*

in Nigeria (**Figures 1** and **2**), with dry onion production having an increasing trend. Nigeria had a world share of 5.5% of a total 4,339,925 tons of green onions produced in 2012 and 1.6% share of a total 82,815,927 tons of dry onions produced globally in 2012 [66].

#### *5.1.1 Climate and soil*

Onions can grow in different climatic conditions. However, it requires moist soil during the early growth stages, likewise hot or dry weather during the maturity and harvesting periods. It produces flowers prematurely in very cold weather conditions (resulting in smaller bulb size). Onions require a loose soil with reasonable depth. Clay soil is not suitable as it gets waterlogged and hardens when dried up. The soil needs to be slightly acidic (pH between 6.0 and 7.0), must also be fertile with humus [67].

*Nigeria Root Vegetables: Production, Utilization, Breeding, Biotechnology and Constraints DOI: http://dx.doi.org/10.5772/intechopen.106861*

#### *5.1.2 Land preparation*

The land should be properly plowed, farm manure could be plowed into the soil. Ridges are constructed after plowing when planting is about to start.

#### *5.1.3 Planting operations*

Onions are planted either by seeds or by setts, the seeds need to be raised in the nursery for 6–8 weeks under a conducive condition. Planting is done at a spacing of 10 cm apart around November or December. It takes about 3–4 months for the crop to reach maturity.

## *5.1.4 Management*

The farm is kept weed-free because onion can not withstand weed competition. Weed should be removed regularly so as to enhance high yield as weed competition reduces yield. First weeding is done 14–21 days after transplanting. The plants are watered regularly because onion plants can not absorb water from deep layers of the soil, that is why the top soil is always kept moist. Irrigation system (either drip or surface) can be used in as much as the soil is not flooded, because onions do not thrive in soils that are flooded and poorly drained. After irrigation, mulching is used to conserve water and inhibit weed growth. Onion does not require much fertilizer in the case where the soil is fertile. However, 20 tons/ha of poultry manure should be incorporated into the soil a week before planting. Also, 75 kgN/ha can be applied at 4 and 6 weeks after transplanting [67].

### *5.1.5 Harvest and storage*

Maturity period of onions is 3–4 months, and once the leaves begin to dry off naturally, it can be harvested. Onions are harvested by uprooting the bulb and cutting off the roots and leaves. In Sokoto, it was reported that onion takes between 112 and 161 days from sowing to harvest or 15 and 8 weeks for the early and late sown onions, respectively, while the time of forming bulbs was 56 days [68]. Maximum plant height of 69 cm has been recorded and number of leaves of between 10 and 13 has also been observed. Yield of up to 48 t/ha has been recorded in the early crop but yield of less than 20 t/ha has been observed for those planted after December [68]. Thorough sun-drying after harvesting is very necessary before bagging for transportation to market or storage in a well ventilated and perfectly constructed silo. This is necessary to reduce the moisture content as much as possible thereby increasing its shelf life.
