Fertiliser use efficiency by containerised nursery plants - 3. Effect of heavy leaching and damaged fertiliser prills on plant growth, nutrient uptake, and nutrient loss

Nutrient leaching loss, plant growth, and nutrient uptake of 4-week (transp lanting to sale) ground-cover species were investigated under a range of le aching conditions and with different sources of a controlled-release fertil iser (CRF), Osmocote NPK (3-4 month) (Osm). Osm was applied pre-planting at a rate equivalent to 800 g N/m(3) to pots containing sand, and composted p inebark and hardwood sawdust medium that had received nutrient amendment du ring formulation. Two experiments were conducted in a glasshouse over summer-autumn where irr igation treatments produced defined leachate volumes. In Expt 1, leachate v olumes of <5, 50, and 200 mL every 2 days each received an additional singl e heavy leaching event of 400 mL after 1, 2, or 3 weeks. In Expt 2, the 3 l eachate volumes were each fertilised with new Osm (a newly purchased Osm) o r old Osm (a 2-year-old source), where both of these sources contained 0.5- 1.5% visibly damaged prills; and damaged Osm, where damaged prills were use d exclusively. In both experiments, increasing leachate volume increased (P < 0.001) leach ing of N (nitrate + ammonium), P, K, Ca, and Mg. In Expt 1, leaching was hi ghest (P < 0.01) when the heavy leaching event occurred after 2 or 3 weeks for N and after 2 weeks for P When damaged Osm was used, N, P, and K loss w as 3-15 times higher (P < 0.001) than from new and old Osm (98.5-99.5% unda maged). The highest leaching loss of N, P, K, Ca, and Mg occurred in the fi rst week after potting up, with damaged prills at highest leaching volume. Increasing leachate volume (in the presence of a heavy leaching event) redu ced (P < 0.001) electrical conductivity (EC) of potting medium after 4 week s from 1.02 to 0.54 dS/m. Damaged prills reduced (P < 0.001) EC at the high leachate volume in relation to new Osm (2.38 v. 0.29 dS/m). Treatments that increased (P < 0.05) nutrient leaching generally reduced (P < 0.05) nutrient concentrations in shoots and depressed the growth of some plant species. Shoot growth of 2 of 5 species was reduced (P < 0.001) at t he highest leachate volume with an additional heavy leaching event in Week 1 or 2, and root growth of all but the slowest growing species declined wit h increasing leachate volume. Damaged prills reduced (P < 0.001) shoot grow th of 2 of the 5 ground-cover species. This study demonstrated that excessive leaching and the use of damaged pril ls for containerised nursery plants fertilised with CRF results in high nut rient loss, low residual nutrient content, reduced nutrient uptake in shoot s, and reduced shoot growth of some species.