Bioassays of the influence of Eucalyptus saligna and Albizia falcataria on soil nutrient supply and limitation

Replicated plantations of Eucalyptus saligna (Sm.) and Albizia falcataria (L.) Fosberg [= Paraserianthes falcataria (L.) Nielsen] in Hawaii allowed an assessment of 12 years of influence of each species on soil fertility. Bioassays with Eucalyptus and Albizia seedlings showed that each species of seedling grew better in soil from the plantations with the other species. The nutrient content of seedlings showed that soils under the influence of Albizia had higher supplies of available N, but lower supplies of available P. Albizia seedlings were strongly limited by P supply in the soils from either species, whereas the growth of Eucalyptus seedlings was limited by both N and P. Albizia seedlings fixed > 95% of the N they used, and took up less soil N than did Eucalyptus seedlings. The overall pattern indicated that Albizia increased soil N supply and growth of Eucalyptus seedlings, although the higher supply of N was not enough to remove N limitation on growth. Albizia also reduced the P supply of the soil, and Albizia seedlings were strongly P-limited regardless of the plantation species. The long-term productivity of tropical plantations depends on continued supplies of nutrients, and these supplies may be strongly influenced by the species selected for plantation use.