Evaluation of potting media for commercial nursery production of container-grown plants

Abstract

Effects of isobutylidene diurea (IBDU), osmocote, ammonium sulphate ((NH₄)₂SO₄), and urea fertilisers in the presence or absence of a nitrification inhibitor, 2-chloro-6-(trichloromethyl)-pyridinie (‘N-serve’) on the dry matter yield and nitrogen uptake of Callistephus chinensis (L.) Nees (aster) in three New Zealand commercial nursery potting media were determined. The three media were: peat-sand (P-S), peat-sand-sawdust (P-S-saw), and peatsand-soil (P-S-soil). Dipton peat was used in the main experiment and Mataura peat in the split-application experiment. In the main experiment, generally, in P-S and P-S-saw, IBDU, osmocote, osmocote and N-serve, (NH₄)₂SO₄, and urea produced significantly higher yields than did IBDU and N-serve, urea and N-serve, and (NH₄)₂SO₄ and N-serve, which contained higher concentrations of nitrogen. The reduced growth of plants was probably because of ammonium toxicity. All fertiliser treatments, including the N-serve treatment, gave similar results in the soil medium. This was attributed to high amounts of NO₃-N present, reducing the toxic effect of high NH₄-N regimes. Results also showed that asters could be grown equally well in all three media, provided adequate water and nutrients were present. There were, however, indications that the P-S-saw medium encouraged better root growth particularly when the fertilisers were applied as split dressings. The split application of (NH_{4 2}SO₄ and also that of urea reduced growth substantially in the P-S-saw medium by rapid immobilisation of applied N. Root growth in the first 49 days was greater in the Mataura peat-based media than in the Dipton peat-based media.