Abstract

Slurry can be acidified to reduce ammonia emissions during slurry application. As considerable quantities of sulfuric acid are required, a lot of S is applied to the soil. The aim of this study was to investigate whether the additional S supply from sulfuric acid has a positive effect on plant growth by comparing sulfuric acid with citric acid. Furthermore, the fate of the S supplied in excess to the plant requirement was investigated.

A field experiment was set up with slurry acidified with sulfuric and citric acid. Yield, N and S concentrations of plant and soil samples on three dates during the growing season were measured. At harvest, grain yield was determined, and the harvested crop was analyzed for N and S concentration. After harvest, soil samples were taken on two further dates and soil mineral N (N_min) and S (S_min) concentrations were measured.

At harvest grain yield and N and S uptake by the grain were the same for the sulfuric and citric acid treatments, but the sulfuric acid treatment had significantly higher S_min levels on all dates. After harvest, S_min was then leached via the 30-60 cm layer into the 60-90 cm layer.

The very high S supply from the sulfuric acid used to acidify the slurry did not affect the yield nor the N and S uptake of the wheat. S that enters the soil in excess of the plant requirements is transferred with the leachate to deeper soil layers.

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