Effects of Sulfuric and Citric Acid for Slurry Acidification on Winter Wheat Yield, N- and S-Balance

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 (Nmin) and S (Smin) 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 Smin levels on all dates. After harvest, Smin 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.