Crop Production: Propagation and Husbandry

What you need to know

• Crops are classified by life cycle into annuals that complete their cycle within one season, such as maize, rice, cowpea and tomato; biennials that need two seasons, such as carrot, onion and cabbage grown for seed; and perennials that live and bear for many years, such as cocoa, oil palm, citrus, rubber and mango.
• Crops are classified by use into cereals such as maize, rice, sorghum and millet; legumes or pulses such as cowpea, groundnut and soya bean; roots and tubers such as yam, cassava, cocoyam and sweet potato; vegetables such as tomato, okra, pepper and amaranth; fruits such as citrus, mango and pineapple; beverages such as cocoa, coffee and tea; oil crops such as oil palm, groundnut and melon; fibres such as cotton, jute and kenaf; spices such as ginger and pepper; and latex crops such as rubber.
• Sexual propagation uses seed, which is cheap, easy to store and transport, allows deep taproot development and permits breeding of new varieties, but gives plants that vary from the parent and take longer to mature. Maize, rice, cowpea, tomato and okra are grown from seed.
• Asexual or vegetative propagation uses a part of the parent plant, so the offspring is genetically identical and comes into bearing sooner, but it carries any disease of the parent and the planting material is bulky. Cassava and sugarcane are grown from stem cuttings, plantain, banana and pineapple from suckers, yam and Irish potato from tubers or setts, ginger and turmeric from rhizomes, onion from bulbs and cocoyam from corms.
• Specialised vegetative methods include budding, where a single bud of the desired variety is inserted under the bark of a rootstock, used on citrus and mango; grafting, where a scion shoot is joined to a rootstock, used on cocoa and rubber; layering and marcotting, where a shoot is induced to root while still attached to the parent; and tissue culture for disease-free planting material.
• Nursery practice matters for small-seeded crops. Prepare a fine, weed-free seed bed or use polythene bags, shade the bed, water morning and evening, prick out crowded seedlings, harden off by gradually removing the shade before transplanting, and transplant in the evening or just after rain with soil around the roots to limit transplanting shock.
• Land preparation follows a sequence: clearing the vegetation, stumping to remove roots and stumps, ploughing to cut and invert the soil, harrowing to break clods into a fine tilth, and ridging or bed making for root crops and for drainage. Zero tillage with herbicide is used where erosion is a risk.
• Standard spacings to memorise are maize 75 cm by 25 cm with one plant per stand, cowpea 60 cm by 20 cm, yam 1 m by 1 m, cassava 1 m by 1 m, tomato 60 cm by 45 cm, cocoa 3 m by 3 m, and oil palm 9 m triangular giving about 143 palms to the hectare.
• Supplying is the replacement of seeds that failed to germinate, done early so the replacements are not shaded out. Thinning is the removal of surplus seedlings to leave the correct number per stand, and it prevents competition for light, water and nutrients.
• Weeds reduce yield by competing for water, nutrients, light and space, harbouring pests and diseases, and contaminating produce at harvest. They are controlled by hand pulling, hoe weeding, slashing, mulching, cover cropping, crop rotation, close spacing, flooding in rice, and herbicides such as glyphosate before planting and atrazine or paraquat as directed.
• Fertiliser is applied by broadcasting over the whole field for close-growing crops, by band or row placement beside the row, by ring application around tree crops at the drip line, by side dressing beside established plants, and by foliar spray for quick correction of deficiency. Nitrogen fertiliser on maize is usually split, part at planting and part about four weeks later, to reduce leaching loss.
• Other husbandry operations are mulching to conserve moisture and suppress weeds, staking of yam and tomato to lift vines off the ground, pruning of cocoa and citrus to open the canopy to light and air, irrigation in the dry season, and pest and disease control.
• Harvesting must be at the correct maturity index: maize when the husk is dry and the grain hard with a black layer at the base; cassava from nine to eighteen months when the leaves yellow and the soil cracks; yam when the vines wither; tomato at the turning to red stage for market; cowpea when the pods are dry and brown; and oil palm when a few loose fruits drop from the bunch.
• Post-harvest handling decides how much of the crop survives. Grains must be dried to about 12 to 13 per cent moisture before storage, stored in cribs, silos, jute bags on pallets or hermetic bags, and protected with dust or fumigant where permitted; yams go into a shaded barn; and perishables such as tomato need rapid sale, cool storage or processing, because Nigeria loses a large share of fruit and vegetable output after harvest.