Abstract
The Ultisols are a major soil order found in the Indonesian archipelago and predominate in Sumatra where concentrated efforts are being made to increase agricultural production. The Ultisols are frequently referred to as problem soils and shifting cultivation is the normal cropping pattern followed. Three sites were located on the clayey, kaolinitic, isohyperthermic Typic Paleudult, a family in this order, in Lampung, South Sumatra, by the Benchmark Soils Project. Experiments were installed to obtain information on the response of maize to P and N application and to determine the contribution of residual P to grain yield. This information will be of assistance to developing countries in the tropics to increase the quantity and quality of maize production as well as the economic returns from fertilizer application. Two crops of maize were grown with one application of P fertilizer and produced a cumulative yield of 8-10 metric tonnes of grain ha-1. Grain yields from applied P were 5-6 t ha-1 while yields from residual P were 3-4 tha-1 (?65 per cent. of yields with applied P). P fertilizer applied to this Typic Paleudult was able to supply P for two crops of maize thereby increasing the return on the cost of P. The three sites of this soil family gave similar responses to applied P and residual P which indicates that similar management is applicable to members of the same soil family. The yield plateau was reached with 80-120 kg Pha-1 in this soil depending on previous cropping history of the field. Response to N was variable in these first crops because of residual N remaining in the soil from leguminous weeds before the area was cleared. The NPK requirements for this Typic Paleudult appear to be ?80kg N, 120 kg P, and 50 kg K ha-1 with application of 1000 kg lime plus 50 kg Mg, 15 kg Zn, and 2 kg B ha-1.
