Crop Water requirement (mm per season) Cost of irrigation per hectare ($) Tomatoes 620 185 Cabbage 440 130 Onions 510 155 (a) Table 1.1 shows the water requ...

(a)(i) From the table, tomatoes have the highest water requirement at 620 mm per season. [1]

(a)(ii) The cost of irrigating 5 hectares of tomatoes:

\[ \text{Total cost} = \text{cost per hectare} \times \text{number of hectares} = \$185 \times 5 = \$925 \] [2]

(b)(i) In furrow irrigation, water is released at the top of a gently sloping field and flows by gravity along shallow furrows (trenches) dug between the crop rows. [1] As the water moves along each furrow it soaks laterally (sideways) through the soil into the raised ridges or beds where the crop roots are growing. [1]

(b)(ii) Two advantages of drip irrigation over furrow irrigation for vegetable production:

1. Higher water-use efficiency - drip delivers water directly to the root zone of each plant through small emitters, so very little is lost to evaporation or surface run-off. In a semi-arid setting or where water is costly, this can substantially reduce total water consumption. [1]
2. Reduced foliar disease risk - because drip irrigation does not wet the leaves, the moist microclimate that favours fungal diseases (such as downy mildew or blight on tomatoes) is avoided. Furrow irrigation can splash soil onto lower leaves, and sprinkler systems wet the entire canopy. [1]

(c) Over-irrigation in semi-arid regions causes soil salination through a two-step process:

1. All irrigation water contains some dissolved salts. When water is applied generously, it carries these salts into the soil. [1]
2. In a semi-arid climate, high temperatures and low humidity drive intense evaporation. Water is drawn upward through the soil by capillary action and evaporates at or near the surface, but the salts it carried cannot evaporate. They accumulate in the upper soil layers. Repeated irrigation cycles without adequate drainage concentrate these salts to toxic levels, forming a visible white crust and poisoning plant roots. [1]