In Spain, alkaline soils are common in regions where arid or semi-arid climatic conditions and a geology rich in calcareous materials predominate. These areas tend to have low levels of precipitation, which limits the washing of salts and carbonates, factors that contribute to soil alkalinity.
A soil is considered alkaline when its pH is above 7, generally due to an accumulation of carbonates, bicarbonates or calcium and magnesium salts. This type of soil is common in arid or semi-arid regions, where insufficient rainfall limits the washing of minerals.
Main areas with alkaline soils in Spain:
Southeast peninsular: Regions such as Murcia, Almeria and the Guadalentin Valley are known for their alkaline soils due to their dry climate and calcareous geology.
Central Plateau: Much of the Northern and Southern Plateau has soils with alkaline characteristics, especially in areas of low rainfall and where the parent materials include calcareous rocks.
Ebro Valley: In communities such as Aragon, Navarra and parts of Catalonia, the soils are usually alkaline due to the accumulation of salts and the nature of the alluvial sediments.
Balearic Islands: The Balearic Islands, especially in coastal areas, have alkaline soils due to the marine influence and the calcareous composition of the parent rocks.
Eastern Andalusia: In provinces such as Granada, Jaén and Málaga, the combination of dryness and calcareous substrates also favors the appearance of alkaline soils.
How to detect alkaline soils
How to identify them?
- pH Analysis: A laboratory analysis is recommended to determine the exact pH.
- Physical aspect: They are usually compact, light-colored soils with low permeability.
- Plant symptoms: Yellowing of leaves (chlorosis) due to deficiencies of essential nutrients such as iron, zinc and manganese.
Disadvantages of alkaline soils
- Low nutrient availability: Key nutrients such as iron, phosphorus, zinc and manganese are locked in non-soluble forms.
- Compaction: Texture can hinder drainage and root penetration.
- Salinity: In some cases, alkaline soils also have problems of excess salts.
Solutions to improve alkaline soils
1. Chemical amendments
- Elemental sulfur: Reduces pH by oxidizing and forming sulfuric acid.
- Agricultural gypsum: Improves soil structure and reduces compaction, favoring drainage.
- Iron chelates: Increase iron availability in alkaline soils, preventing iron chlorosis.
2. Use of adequate fertilizers
- Fertilizers rich in ammoniacal nitrogen (such as ammonium sulfate), which help acidify the soil.
- Organic fertilizers with high organic matter content, such as compost or manure, which improve soil structure and microbiota..
3. Cultural improvements
- Crop rotation: Combine tolerant and soil-improving crops, such as alfalfa.
- Efficient irrigation: Apply water in small, frequent amounts to avoid salt accumulation.
4. Specific organic fertilizers
- Organic fertilizers such as those produced by BH Terra are ideal because they contain nutrients in plant-available forms and improve water retention and soil structure. Providing quality organic matter can be key to balancing the chemical and physical properties of the soil.
Alkaline soils present a challenge, but with the right strategies they can be managed effectively. The selection of suitable crops, together with the application of organic fertilizers and manures, allows taking advantage of the benefits of these soils while mitigating their drawbacks. Regular soil testing and adaptation of agricultural practices are key to achieving sustainable and productive agriculture.