ISHS Acta Horticulturae 819: International Symposium on Growing Media 2007
NITROGEN BALANCE OF THREE ORGANIC POTTING-MEDIA IN RELATION TO THE ADDED CARBON SOURCES |
| Authors: | A. Amde Yosef, H. Bohne |
| Keywords: | cellulose, denitrification, glucose, incubation test, N-immobilization, N-mineralization |
| Abstract:
alance was investigated for white peat, substrate-compost and a mixture of white peat and substrate-compost at 3:2 [v/v] (peat-reduced) in a completely randomized design with five replications. Samples with no C-input were also included as the control treatment. The potting media were incubated aerobically for six weeks at 25°C and 80% of their maximum water capacity after adding 1000 N mg L-1 in white peat and peat-reduced, and 870 mg N L-1 in the substrate-compost in the form of NH4NO3. At the beginning of incubation (t0), and after, 1, 2, and 6 weeks samples were analyzed for mineral N (Nmin) and total N. In a parallel experiment, volatilized N was measured from airtight glass jars after 1, 2 and 6 weeks. Denitrified N was calculated as the difference of total-N between t0 and sampling intervals minus volatilized N. Immobilized or mineralized N was then computed by adding gaseous N to that of the Nmin change over the incubation period. According to the standard incubation test, the control treatments of white peat and substrate-compost showed a stable N-balance (as the change in Nmin was within ±150 mg L-1) while the peat-reduced did not. Amending each potting-medium with C decreased the amount of recovered Nmin and the higher fall observed mostly in the glucose received samples. The computed gaseous-N loss in the control treatments ranged from 53 to 68 mg L-1 over two weeks. However, ammonia volatilization accounted for ≤5.4 mg L-1 to suggest that denitrification was the major avenue for gaseous losses in the current incubation conditions. Although this was not the case in the white peat, denitrified-N in the substrate-compost and peat-reduced media increased by the added C sources. The additions of both glucose and cellulose also increased N-immobilization in the peat-reduced medium, but this only occurred in the white peat amended with glucose. The computed immobilized-N in the substrate-compost, however, was not affected by the addition of C. In general, the effects of cellulose in all potting-media became apparent later than that of glucose. | |
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