Fig. 1 is a cross-section drawn for farmers beside the Aral Sea basin in Central Asia. Water from a river is diverted along an unlined irrigation canal to c...
Question 1 Report
Fig. 1 is a cross-section drawn for farmers beside the Aral Sea basin in Central Asia. Water from a river is diverted along an unlined irrigation canal to cotton fields. In the fields, high temperatures cause rapid evaporation. The farmers have noticed a white crust on the soil and falling crop yields. Their agricultural adviser is preparing an enquiry into how water resource use can turn productive land into a desertified area. Use the study figure and your knowledge of soil processes.
(a) Name the process that leaves salt at the soil surface in Fig. 1. [3]
(b) Describe how water can be lost from the irrigation canal and fields. [5]
(c) State three effects of soil salinisation on the local farming community. [7]
(d) Explain how an improved irrigation scheme could reduce desertification without stopping cotton production. [10]
Answer Details
(a) The process is evaporation. Heat changes irrigation water into water vapour; the dissolved salts do not evaporate, so they are left behind at the soil surface as a white crust. [3]
(b) Water can seep through the unlined canal into surrounding ground. Irrigation and seepage raise the water table; salty groundwater then moves upwards through soil by capillary action. High temperatures evaporate the water from the field surface, again leaving salt behind. [5]
(c) Salinisation reduces soil fertility, so crop growth becomes poor and yields fall. This reduces farmers’ income and may reduce local food supplies, forcing families to buy more food. Severely salinised land may be abandoned; bare soil is then vulnerable to wind erosion. Any seven valid linked effects gain credit. [7]
(d) An improved scheme should keep cotton production but reduce water waste and salt build-up. Line canals or use pipes to reduce seepage. Use drip irrigation or carefully timed watering so only the amount needed by plant roots is applied. Install drainage channels: these lower the water table and allow salts to be flushed below the root zone or removed in drainage water. Salt-tolerant crops can be used where necessary. Maintaining vegetation cover retains soil fertility and yields, while reducing bare ground and wind erosion. Together, these actions interrupt the process by which irrigated land becomes desertified. [10]
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