Polysulphate Improves Lettuce Growth in Acidic Soils

Research Background

In acidic soils, calcium ions are leached much more easily, causing severe deficiency symptoms in crops and damage to soil structure. Previous studies found that 27-34% of soil calcium is leached, in quantities of 275-1,045 kg per hectare per year.

Research Objectives

The study examined the agronomic effects of different calcium fertilizer types and application levels, focusing on the fate of calcium in the soil-crop system in acidic soils under simulated leaching conditions.

Research Method

A two-year, two-stage pot experiment was conducted, growing lettuce under simulated rainfall conditions. The research compared three types of calcium fertilizers:

• Calcium chloride (CC) – fast-release fertilizer
• Gypsum (GS) – slow-release fertilizer
• Polysulphate (polyhalite) (PH) – water-soluble fertilizer with slow-release characteristics

The fertilizers were tested at five levels: 0, 20, 40, 80, and 160 kg calcium per hectare.

Main Results

Improvement in Yield and Biomass

In both growing seasons, lettuce yield and biomass increased significantly by 5-25% and 2-60% respectively, across all fertilizer types and levels.

Polysulphate (polyhalite) showed particularly excellent performance:

• Polysulphate (polyhalite) increased lettuce yield by 13-25% in the in-season experiment and by 10-20% in the residual effect experiment
• Polysulphate (polyhalite) showed significantly better performance than gypsum across all growing seasons

Enhanced Calcium Uptake

Calcium uptake by lettuce increased by 7-55% in the in-season experiment and by 25-117% in the residual effect experiment, depending on fertilizer type. Polysulphate (polyhalite)  contributed to significant improvement in calcium uptake, especially at higher application rates.

Significant Reduction in Calcium Leaching

One of the study’s key findings: Polysulphate (polyhalite) reduced calcium leaching by 3-26% compared to other fertilizers.

Polysulphate (polyhalite) reduced calcium leaching by 5-26% compared to calcium chloride and by 3-25% compared to gypsum, thanks to its complex molecular structure and slow-release characteristics.

Calcium Retention in Soil

Polysulphate (polyhalite) successfully retained larger amounts of calcium in the soil over time. Compared to calcium chloride, Polysulphate (polyhalite) retained approximately 5-6% more calcium at 7-15 cm depth and approximately 10-26% more at 0-7 cm depth.

The Mechanism Behind the Success

Polysulphate (polyhalite) is a water-soluble fertilizer with a slower and more sustained calcium release characteristic, allowing more calcium to be steadily available to the plant under leaching events.

Calcium deficiency caused visual symptoms in lettuce, especially at lower levels (0 and 20 kg per hectare), leading to decreased yield. Calcium is essential for regulating cell wall formation, cell membrane stabilization, cell elongation, and stomatal conductance, thus affecting photosynthesis and phytohormone synthesis.

Practical Implications for Agriculture

The research emphasizes the importance of applying calcium fertilizers in acidic soils, especially in areas with heavy rainfall or excessive irrigation.

Advantages of Polysulphate (polyhalite):

• Continuous and stable supply of calcium to the plant
• Significant reduction in leaching losses
• Improved nutrient utilization
• Increased yield and crop quality
• Contribution to sustainable development goals in agriculture

Conclusions

The research confirms the necessity of applying calcium fertilizers to improve crop production and nutrient uptake in acidic soils under intensive leaching conditions.

Stable calcium supply, such as that provided by Polysulphate (polyhalite), helps meet crop calcium requirements while reducing leaching, thereby achieving green and sustainable development goals by increasing yield and nutrient use efficiency.

The findings indicate that Polysulphate (polyhalite) represents an advanced and particularly effective fertilizer solution for modern agriculture, balancing plant nutritional needs with soil and environmental quality preservation.