Residual effect of superphosphate on the sulphur status of soil and plants in a long-term NPK fertilisation experiment on a Chernozem in Hungary

Abstract

Recently, plant-available sulphur (S) in the soil is decreasing due to the limited use of S containing fertilisers and the reduction of atmospheric S deposition. The aim of this work was to evaluate the S status in a long-term fertilisation experiment on a Chernozem in Hungary, with control and 2 NPK rate treatments, considering that after 27 years of superphosphate (SP) use, SP was replaced by monoammonium phosphate in 2010. Plant and soil sampling were performed in 2017 at three different development stages of winter wheat. To assess the S status, the S balance was estimated (for 34 years), KCl soluble soil sulphate, S as well as nitrogen (N) concentration and some amino acids in wheat grain were measured. N/S ratios, S and N uptake of wheat were calculated. The residual effect of SP could be measured only in terms of KCl soluble SO₄^2–-S in soil. According to the wheat grain S concentration (0.08–0.10%) and N/S ratio (14.9–22.0), wheat was S deficient, despite the positive S balance in the fertilised plots. In this experiment, where S fertiliser was applied with 84 kg S/ha dose in 1983–2010, followed by a 7-year period without S fertilisation, S supply is necessary for achieving adequate wheat quality.