Spring and autumn nitrogen fertiliser effects, with and without phosphorus, potassium and sulphur, on dairy pastures: pasture nutritive value and mineral content

Experiments were conducted at three sites to examine effects of applying different nitrogen(N) fertilisers at 45kg N ha-1, with and without phosphorus (P), potassium (K) and sulphur (S) on dairy pasture nutritive value and mineral content in autumn and spring. Pasture nutritive value was assessed by measures of crude protein (CP), metabolisable energy (ME), water-soluble carbohydrates (WSC) and neutral detergent fibre (NDF)). Pasture mineral content was assessed by estimates of the major minerals phosphorus (P), potassium (K), sulphur (S), sodium (Na), calcium (Ca) and magnesium (Mg), and trace minerals manganese (Mn), iron (Fe), copper (Cu) and zinc (Zc). Apart from some exceptions, applications of N, with and without additional P, K and S generally increased pasture CP and ME content in autumn and CP content in spring. Again with some exceptions, pasture WSC content was unaffected by fertiliser application in autumn, but was decreased by some treatments (containing N and N with P, K and S) in spring. Fertiliser treatments generally had no effect on pasture NDF content at Sites 1 and 3 during autumn and spring. At Site 2, some treatments (containing N and N with P, K and S) reduced pasture NDF content in autumn while during spring some treatments (containing N and N with P, K and S) increased pasture NDF content. Different N fertilisers applied at the same rate, with and without additional P, K and S, generally produced the same effect on pasture nutritive value. The application of P, K and S in the absence of N generally had no effect on pasture nutritive value. Apart from some exceptions, pasture P content was increased by fertiliser treatments including P, K and S, but N on its own did not influence pasture P content. Pasture K content was generally not influenced by treatment. At Site 1 during autumn and spring, and at Site 3 during spring, treatments containing P, K and S increased pasture S content while applications of N had no effect. At Site 2 during autumn, P, K and S increased pasture S content relative N only, while during spring pasture S content was generally increased by all treatments. At Site 3 during autumn, applications of N decreased pasture S content while P, K and S increased pasture S content relative to no fertiliser. Pasture Na and Ca content were generally not influenced by treatment. Pasture Mg content was not influenced by treatment at Sites 2 and 3. At Site 1 during autumn and spring, however, some treatments(containing N and N with P, K and S) increased pasture Mg content. Fertiliser treatments produced no consistent patterns or differences with respect to trace minerals (Mn, Fe, Cu and Zn).Keywords: Australia; autumn; botany; carbohydrates; crude protein; dairy pastures; fertilizer; Lolium perenne; metabolisable energy; mineral content; neutral detergent fibre; nitrogen; nutritional value; pastures; phosphorus; potassium; spring; Trifolium repens; Victoria; water-soluble carbohydrates; calcium; carbohydrate; copper; cu; effects; energy; fibre; iron; magnesium; manganese; minerals; mn; na; pasture; pasture nutritive value; pattern; protein; sodium; treatment; treatments; zinc; znAfrican Journal of Range & Forage Science, Vol. 15(3), pp. 109–11