| Popis: |
This paper elucidates nutrient dynamics in 5- to 8-year-old poplar ( Populus deltoides ) clone D 121 plantations previously investigated for dry matter dynamics. The nutrient concentration in different layers of the vegetation were in the order: tree > shrub > herb, whereas the standing state of nutrients were in the order: tree > herb > shrub. Soil, litter and vegetation, respectively, accounted for 80-89, 2-3 and 9-16% of the total nutrients in the system. Considerable reductions (trees 42-54, shrubs 31-37 and herbs 15-23%) in concentration of nutrients in leaves occurred during senescence. The uptake of nutrients by the vegetation and also by the different components, with and without adjustment for internal recycling, has been calculated separately. Annual transfer of litter nutrient to the soil by vegetation was 113·7-137·6 N, 11·6-14·6 P and 80·1-83·2 K kg ha -1 year -1 . Turnover rate and time for different nutrients ranged between 0·72-0·89 year -1 and 1·12-1·39 years, respectively. The high turnover rate of litter on the forest floor indicates the greater productivity of the stands, which was due to the higher dry matter dynamics and nutrient release for the growing vegetation. The nutrient use efficiency in poplar plantations ranged from 159-175 for N, 1405-1569 for P and 295-332 for K. Compared with Eucalyptus , there was a higher proportion of nutrient retranslocation in poplars largely because of higher tissue nutrient concentrations; this indicates lower nutrient use efficiency as compared to the eucalypt plantation. Compartment models for nutrient dynamics have been developed to represent the distribution of nutrient pools and net annual fluxes within the system. |
