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

Addition of fertilisers increased significantly the levels of NH 4 ‐N and NO 3 ‐N in nursery potting media, and the effect of fertiliser form on NH 4 ‐N and NO 3 ‐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), (NH 4 ) 2 SO 4 , 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.