Agricultural Science (AS)·Soil · NSSCAS 2.4
Soil salinity & crop productivity
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A farmer near the Orange River waters his lucerne every single day. The soil is damp when you press it, yet the crop is wilting, stunted and dying. How can a plant die of thirst in wet soil? In this lesson we uncover the hidden enemy — salt — how it robs a plant of water, why our hot Namibian climate makes it worse, and how a careful farmer can wash it away and keep the land productive.
What you'll learn in this lesson
By the end you should be able to (NSSCAS Agricultural Science (AS) 2.4):
- Explain what soil salinity is and how it reduces crop productivity through the osmotic effect
- Explain, in terms of osmosis, why a plant wilts in salty soil even when the soil is damp
- Describe how ion toxicity, nutrient imbalance, poor germination and reduced yield further harm a salt-affected crop
- Describe the factors that cause soil to become saline: salty irrigation water, poor drainage, high evaporation, a shallow water table, over-fertilising and seawater intrusion
- Explain why Namibia's hot, arid, high-evaporation climate makes irrigated soils especially prone to salinity
- Describe leaching and good drainage as the main strategies for overcoming salinity
- Discuss further strategies to prevent salinity: quality irrigation water, avoiding over-irrigation, mulching, gypsum for sodic soils and salt-tolerant crops
- Recognise the field signs of a saline soil and suggest suitable action for a Namibian irrigation farmer
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