Impact of sulphur, a plant protection agent in organic apple production, on nutrient and heavy metal mobility in the soil
Sulphur (S) is a widely used plant protection agent (mainly against apple scab) in organic apple production in temperate regions. Current attempts of reducing the use of copper (Cu) to avoid heavy metal accumulation in the soil lead to an increased application of S. In Germany, the amounts of S range from 30 to 90 kg ha-1 year-1 in intensive, organic apple production systems. S is washed into the soil through rainfall events and is transformed to sulphate by bacteria (Thiobacillus), which promotes soil acidification and thus increases the availability and mobility of nutrients and heavy metals. The aim of the project was to analyse the effect of S on soil-chemical changes and the leaching of nutrients and pollutants. A pot trial was conducted from November 2019 until May 2020, simulating long term S-input and leaching. Five top soils from two German fruit growing regions (Lake Constance and Altes Land near Hamburg) with differing cultivation history and differing history of S, Cu and nutrient application were chosen. Every five weeks, S was applied (as H2SO4) in three levels in order to simulate annual S input of 0, 40 and 80 kg ha-1, followed by a leaching event after two weeks. This was repeated six times during the 7 months of the trial. Nutrient and heavy metal content (N, P, K, Ca, Mg, S, Cu, Zn) were analysed in soil and eluate. S input decreased soil pH and leached K, Ca, Mg and S. Its severity varied depending on the soil type, being highest in the soil with low pH and lowest Ca content, in combination with lowest clay and highest sand content, indicating a low cation exchange capacity. S input showed no clear effect on Cu and Zn leaching. Depending on the soil, high S input poses a risk for nutrient supply of the apple trees if not compensated by liming and fertilization in the long-term.
Birgit Lepp won the ISHS Young Minds Award for the best poster presentation at the III International Organic Fruit Symposium and I International Organic Vegetable Symposium, which was held virtually in Italy in December 2021.
Birgit Lepp, Center for Organic Farming, University of Hohenheim, Stuttgart, Germany, e-mail: email@example.com
The article is available in Chronica Horticulturae