Black chalk with humus — how to retain water in the soil during drought?

Black chalk with humus is an innovative organic-mineral fertiliser that combines rapid deacidification with humus rebuilding. Thanks to its content of humic acids and highly reactive lime, it increases the soil's water capacity, which is crucial in the face of ever more frequent droughts in Poland. Increasing humus content by 1% can raise the soil's storage capacity by as much as around 150 m³ of water per hectare (about 15 l/m²).

Why do Polish soils lose water so quickly?

Agriculture in Poland is grappling with progressing climate change and drastic rainfall deficits. IUNG reports for 2025 indicate that agricultural drought affected as many as 16 provinces, hitting spring and winter cereals and strawberries the hardest.

The main problem is the prevalence of light, sandy soils with a low organic-matter content. In such conditions, rainwater seeps through the soil profile by gravity, giving plants no chance to take it up. Low retention goes hand in hand with acidification, which further restricts root development.

The role of humus, calcium and soil structure

The solution is to use Bluebird black chalk with humus — an organic fertiliser made from unique lake chalk. Its mechanism of action rests on two pillars:

• Rapid pH regulation — highly reactive calcium carbonate (CaCO₃ above 92%) enables a quick reaction in the soil and reduces aluminium (Al³⁺) toxicity.
• Building the sorption complex — up to 15% organic carbon compounds and humic acids bind fine particles into aggregates, creating a crumb structure that retains water.

Benefits for soil and plants

• Maximum water retention — every percent of humus means an additional 150,000 litres of water per 1 hectare.
• Intensive root development — eliminating aluminium opens the way to deeper layers.
• Biological revival — humus provides food for microorganisms, speeding up straw mineralisation.
• Reduced pathogen pressure — raising the pH creates more favourable conditions for a healthy crop start.

How to apply black chalk with humus

• The 3–6 mm granule fraction allows stable, even spreading with modern disc spreaders.
• Granulation makes it possible to use it in a starter system (band applicator for maize).
• The best results come from post-harvest application onto stubble; doses of 0.6–2.4 t/ha depending on pH and soil category.