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

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Abstract
Addition of fertilisers increased significantly the levels of NH4-N and NO3-N in nursery potting media, and the effect of fertiliser form on NH4-N and NO3-N levels was less apparent in cropped media than in fallow media. Nitrification was only partially controlled in the soil media, and ‘N-serve’ (2-chloro-6-(ttichloromethyl)-pyridine) had less effect on nitrification in soilless media (peat-sand and peat-sand-sawdust) because of low microbial activity. If the application of fertiliser nitrogen (N) did not affect mineralisation of native soil N, estimates of N recovery showed that aster plants recovered less than 50% of the applied N. In soilless media plant recovery of N from osmocote was about 10% above those from IBDU (isobutylidene diurea), (NH4)2SO4, and urea, which in turn were higher than those from N-serye treatments of these fertilisers. In the soil medium percent N recoveries from all fertiliser treatments were similar. Total recoveries for fertiliser N were consistently higher in fallow pots than in their cropped counterparts probably because of higher leaching losses of N in cropped media. A high proportion of the applied N was immobilised, more in fallow than in cropped media. The mean percentages of immobilisation were 50 and 39 for peat-sand, 81 and 54 for peat-sand-sawdust, and 37 and 18 for peat-sand-soil in fallow and cropped soils respectively. The high degree of immobilisation in peat-sand-sawdust was because of a very high C:N ratio.