Fig. 1 shows an irrigated cotton field in a dry part of Uzbekistan. Water is brought in an open channel from a river, but the hot climate causes rapid evapo...
Question 1 Report
Fig. 1 shows an irrigated cotton field in a dry part of Uzbekistan. Water is brought in an open channel from a river, but the hot climate causes rapid evaporation. White crusts have appeared in several low areas of the field. An agricultural investigation is comparing this farm with a nearby field where drip irrigation and drainage pipes have been installed. Cotton is an important export resource for the rural community.
(a) Identify the crop shown in the cap figure. [1]
(b) State the process that removes water from the soil into the atmosphere. [1]
(c) Describe two reasons why salts may build up near the surface of this field. [4]
(d) Explain how salinisation can reduce cotton yields. [6]
(e) Describe three advantages of drip irrigation compared with the open channel system. [6]
(f) Which field measurement would best show whether salinity is falling after improvements? Explain your choice. [7]
Answer Details
(a) The crop is cotton. [1]
(b) Water leaving soil for the atmosphere does so by evaporation. [1]
(c) Irrigation water contains dissolved salts. Water remains near, or rises towards, the surface; heat evaporates this water but leaves the salts behind. Poor drainage prevents salts being washed away. Any two developed reasons. [4]
(d) Salinity increases the concentration of salts in soil water, lowering its water potential. Roots cannot take up enough water, so plants become water-stressed or wilt. Growth and photosynthesis decrease, leading to fewer or smaller cotton bolls and lower yields. [6]
(e) Drip irrigation delivers water directly to roots, reducing evaporation and waste. It reduces surface salt accumulation, uses less river water and avoids land being occupied by open channels. Any three developed advantages. [6]
(f) Measure soil electrical conductivity at fixed depths and locations. Higher conductivity indicates more dissolved salts. Repeat measurements before and after the changes, take several samples and calculate a mean, then compare with the untreated field. This gives quantitative, comparable evidence of whether salinity is falling. [7]
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