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

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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 (NH4 2SO4 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.