RESIDUAL EFFECTS OF NATURAL BUSH, CAJANUS-CAJAN AND TEPHROSIA-CANDIDA ON THE PRODUCTIVITY OF AN ACID SOIL IN SOUTHEASTERN NIGERIA

An experiment was established in 1986 to examine the contribution of Tephrosia candida and Cajanus cajan shrubs to improving the productivity of an acid soil. The main treatments were N levels (0 and 60 kg ha-1) with subplots of maize/natural bush, maize/Tephrosia candida, maize/Cajanus cajan, maize + cassava/natural bush, maize + cassava/Tephrosia candida, and maize + cassava/Cajanus cajan. In 1988, all plots were cleared and maize uniformly planted to study the residual effects of the treatments. No residual effects of N application were observed. Tephrosia candida and Cajanus cajan increased surface soil organic carbon and total N levels over the natural bush. However, only Tephrosia candida plots produced improved maize grain and stover yield. Highly significant correlations were found between maize grain yield and earleaf N (r = 0.73**), grain N (r = 0.51**), and stover N (r = 0.54**) contents. These results suggest that Tephrosia candida increased N availability in the soil. Therefore, the shrub has potential for improving the productivity of acid soils under traditional systems. where N is limiting due to the absence of N2-fixing legumes in the natural bush fallow.