IB ESS HL 5.1.7 Soil transformations Question Bank

Practise IB ESS SL/HL 005.001.007 by applying soil transformations concepts to exam-style environmental systems questions.

[Maximum number: 4]

(a)

Figure:Impact of irrigation water salinity on crop yield potential

Figure:Fact file on agriculture in California

Figure: Fact file on agriculture in California: Fact file on agriculture in California
Over 36000 km2 of agricultural land is irrigated. During severe drought, Central Valley farmers receive no state water for irrigation. Over 50% of irrigated land is impacted by salinity. California produces 81% of the world’s almonds, its most economically valuable agricultural export. The water footprint of one almond is 12 litres. Almond samples have contained up to nine pesticide residues, some toxic to bees.

With reference to Figure: Impact of irrigation water salinity on crop yield potential, state the relationship between irrigation water salinity and crop yield potential.

[ 1 ]

(b)

Figure: Fact file on agriculture in California context — over 36 000 km² of California agricultural land is irrigated; over 50% of irrigated land is affected by salinity. California produces 81% of the world’s almonds, and one almond has a water footprint of about 12 litres.

Explain how irrigation has reduced soil fertility in the Central Valley.

[ 3 ]

a. irrigation water is often pumped up from underground/from wells;
b. groundwater contains (mineral) salts / water used for irrigation may contain salts/be saline;
c. in areas of high evaporation/dry/semi-arid climates, water evaporates from the surface, leaving salts behind;
d. the dissolved sodium ( $\mathrm{Na}^{+}$ ) and chloride ( $\mathrm{Cl}^{-}$ ) ions can displace other mineral nutrients in the soil needed for plant growth, such as potassium (K) and phosphorus (P) / minerals required for plant growth are replaced ;
e. salin(is)ation of soils/over time the salts build up, leading to levels higher than macroinvertebrates/decomposers can tolerate;
f. reduction in macroinvertebrates/decomposers may reduce nutrient cycling;
g. excessive irrigation can lead to leaching of nutrients from the soil (reducing soil fertility) / irrigation can lead to erosion of fertile top soil;
h. excessive irrigation can lead to water-logging/rise in water table and poor aeration of the soil, reducing nutrient cycling;
i. irrigation leads to an increase in plant growth that utilizes/absorbs nutrients from the soil (hence reducing soil fertility over time);

Note: do not accept just "salin(is)ation" or "leaching" as this does not explain why loss of soil fertility occurs.

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5.1.7—Soil transformations question 1

Question (a)

Question (b)