Ionic balance and composition of perennial ryegrass (Lolium perenne L.) as influenced by nitrogen and sulphur fertilisation

Abstract

Perennial ryegrass (Lotium perenne L. cv. ‘Grasslands Ruanui’) plants were grown in a sulphur-responsive soil in a glasshouse with five rates of fertiliser nitrogen (N) Ca (NO₃) ₂·4H₂O) and three rates of sulphur (S) (CaSO₄.2H₂O). Compared with control, N fertilisation significantly increased sodium (Na) concentration in both tops and roots, but decreased potassium (K) concentration. However, S fertilisation increased K but decreased Na content of tops only at low N levels. The effect on roots was not consistent. Increasing N applied generally decreased the sum of inorganic anions (∑A = CI⁻ + NO₃ ⁻ + H₂ PO₄ ⁻ + SO₄ ²⁻), mainly due to decreases in CI⁻, SO₄ ², and H₂PO₄ ⁻ concentrations. Nitrate concentration increased with N applications and showed an inverse relationship to cr concentration in plant tops. The organic acid content (C - A) of herbage was not directly related to levels of N applied. Nitrogen fertilisation decreased the cation/anion ratios and S applications increased the ratios. The EB/N ratios were also decreased by N fertilisation, and S fertilisation, particularly at low N levels, increased EB/N ratios.