Abstract
Several experiments were conducted with leucaena in which acid Ultisol and Oxisol layers were placed below 30 cm layers of limed surface-soil in 3 cm diameter glass tubes. The surface soil associated with the Ultisol was limed at rates equivalent to 0. 1.5 and 3 times the meq of soil exchangeable Al/100 g; similarly, the soil above the Oxisol was limed with 0, 1 and 2 times the equivalent amounts of exchangeable Al. In contrast to the control, without lime in the surface soil, the limed surface-soil treatments allowed plant-root systems to develop through acid soil layers as thick as 90 cm. In other experiments, PVC bottomless pots (tubes), 12 cm diameter x 30 cm high, were filled with the Ultisol or Oxisol and limed according to the criteria used in the tube experiments; P, K, micronutrients and rhizobium were added. After development of the plants for one month, the PVC tubes were embedded in acid Spodosols in the field. Results showed that leucaena trees may be established in acid soils if all leucaena requirements are satisfied in the 30 cm surface layer of soil. Thus, the costly process of liming the entire land surface may be avoided. Long-term development of leucaena plants under these conditions remains to be determined.
