NITROGEN-SUPPLYING CAPACITY OF LEAVES OF DACTYLADENIA-BARTERI (HOOK EX OLW) AND LEUCAENA-LEUCOCEPHALA (LAM) DEWIT IN 2 SOILS OF DIFFERENT ACIDITY FROM SOUTHERN NIGERIA

The evolution of mineral and hydrosoluble organic N released from two soils differing in pH and treated with leaves of Leucaena leucocephala (0, 8.3, 16.7, and 33. g kg-1 soil), Dactyladenia barteri (syn. Acioa barteri; 0 and 16.7 g), and their mixtures was studied in the laboratory using the aerobic incubation-leaching method. N mineralization in untreated soils and in soils supplemented with 8.3 g leucaena leaves was 41 - 53% higher in the soil from Onne (pH 4.7) than in the soil from lbadan (pH 6.2), but the organic N content was similar with these treatments in the leachates of the soils from both locations. The application of 16.7 or 33.3 g of either or both type of leaves reduced the rate of mineral N production during the first 4 weeks, particularly in soils treated with dactyladenia leaves (C:N = 36). After this lag period, N mineralization proceeded at a faster rate in the soil from lbadan treated with 16.7 or 33.3 g of leucaena leaves (C:N = 12), even in the presence of dactyladenia leaves. In lbadan soil, after 12 weeks, mineral N apparently derived from leaves of both dactyladenia and leucaena averaged 6.3% of the N applied, and organic N from leaves averaged 9.5%. The addition of dactyladenia and leucaena leaves did not increases the mineral N content in the acid soil from Onne but leaching of soluble organic N with addition of 16.7 or 33.3 g of leaves contributed an N-mineralizable pool of 5.9% of the N applied.