(a) Discuss the cultivation of Citrus spp under the following headings: (i) Method of propagation (ii) Spacing in the field (iii) Nursery practices (iv) Pes...

(a) Cultivation of Citrus spp

(i) Method of propagation: Citrus is propagated both sexually (by seeds) and, more commonly for commercial orchards, vegetatively by budding (T or shield budding) onto a resistant rootstock such as rough lemon or sour orange. Budding is preferred because it keeps the desirable qualities of the parent, ensures early fruiting and gives uniform trees.

(ii) Spacing in the field: Citrus is planted at about 6 m x 6 m to 8 m x 8 m (approximately 150 to 280 trees per hectare), depending on the species and soil fertility. Wide spacing allows light penetration, air circulation and easy movement for spraying and harvesting.

(iii) Nursery practices:

• Prepare fine, well drained nursery beds and sow rootstock seeds.
• Provide partial shade and water regularly.
• Weed, and apply fertilizer to raise vigorous seedlings.
• Bud the seedlings when the stems reach pencil thickness.
• Harden off seedlings before transplanting to the field.

(iv) Pests: Aphids, citrus leaf miner, fruit flies, mealy bugs, scale insects and citrus psyllid.

(v) Diseases: Citrus canker, gummosis (foot rot caused by Phytophthora), citrus greening (HLB), tristeza virus and sooty mould.

(b) Definitions

(i) Surface irrigation: The application of water to farmland by allowing it to flow over the soil surface by gravity, for example through furrows, basins or borders, so that it infiltrates into the root zone.

(ii) Surface drainage: The removal of excess water from the top of the land surface by means of open channels, ditches or graded slopes so that waterlogging is prevented.

(c) Advantages

(i) Surface irrigation:

• It is cheap and simple, requiring little equipment or technical skill.
• It does not require pumping energy where gravity flow is available.
• It can cover large areas and helps leach out harmful salts from the soil.

(ii) Surface drainage:

• It removes excess water and prevents waterlogging, improving soil aeration.
• It reduces soil erosion and the incidence of water-borne diseases.
• It allows earlier cultivation and prevents root rot, improving crop yield.