Influence of Native and Applied Sulphur on Yield and S Uptake by Sunflower at Different Stages of Growth

The pattern of sulphur uptake by three genotypes of sunflower (Helianthus annuus L.) at four growth stages was studied using ³⁵S-labelled sources under field conditions on sulphur deficient Vertisol and Alfisols with four doses of sulphur. In case of Alflsol while there was increase in dry matter yield up to 60 kg S ha⁻¹ level, with respect to Vertisol, the increase in yield was recorded only up to 40 kg S ha⁻¹. Sulphur content of plants increased with S application through different sources viz., gypsum, ammonium sulphate and superphosphate and decreased with progress in plant growth. Sulphur application increased S uptake by sunflower at star, bud, flowering and maturity stages. The ratio of S uptake from native to applied source indicated preferential absorption of soil sulphur at all levels of applied S. The efficiency of native source of S was high at all the growth stages.