Impact of Nitrogen and Sulphur Fertilisation on Phosphorus and Silicon Content and Uptake by Biomass of Spring Wheat

Nitrogen and sulphur are among the most important plant nutrients (along with C, H, and O) and the main elements comprising the organic substance of plants. In this study, it is assumed that light soils (Cambisols) do not naturally meet the nitrogen and sulphur needs of spring wheat and, consequently, impact the phosphorus and silicon content in the plant biomass. Therefore, to determine the effect of N and S on the content and uptake of these elements at specific growth stages (BBCH 30–31: in leaves, BBCH 55–59: in whole plants, BBCH 89–90: in grain and straw), a three-year field experiment was conducted using different doses of nitrogen (0, 40, 80, and 120 kg ha−1) and sulphur (0, 50 kg ha−1). The results show that fertilisation with N and S had a significant effect on increasing the content and uptake of P and Si by phytomass in the phenostages studied. In general, as the N fertilisation dose increased, the yields of phytomass and grain increased. A beneficial effect of S on increases in green weight, straw, and spring wheat grain was found. A significant effect of N and S fertilisation on the growth of the Si:P ratio in individual parts of plants in the studied stages was also observed. A significant positive correlation between P and Si content was proven, indicating that the two elements do not act antagonistically towards each other. In contrast, a negative correlation was observed between the P content in plants and their Si uptake. Si is taken up more strongly by plants under conditions of N and S fertilisation, as evidenced by the increase in the Si:P ratio and the fact that plants accumulated on average 3.5 times more Si than P. The highest Si content was found in the green parts of plants in the BBCH 30–31 and BBCH 55–59 stages, while in BBCH 89–92, straw had nearly half that amount and grain contained a thousand times less silicon.