ABSTRACT

 Laboratory, greenhouse and field experiments were conducted between 1997 and 1999 to evaluate the yield performance, N2fixation and fertilizer requirements of soybean in the humid forest zone of southeastern Nigeria. The soils for the green house study were collected from representative locations in the zone to represent the major soil types. The green house experiment was laid out in a randomized complete block design with ten replications while the field experiments located at Umudike and 0kigwe were laid out on the field in split-split plot design with four replications. The results obtained showed that the soils were acidic with p1-i values ranging from 4.30 — 5.60. They were sandy and generally low in nutrients except the soils df the Sombrairo-Warri Deltaic Plain. N2 fixations were low with values ranging from 5.53kg/ha N in Akwete to 30.62kg/ha N in Ahoada. The average N-fixed by the soybean cultivars was 21.25kg/ha N with TGX 1829 fixing the highest (34.50kg/ha N). Grain yield of soybean in the green house varied with locations in the order: - Ahaoda> lsiala-Ngwa> Elele> Okigwe> Uyo> Ohafia> Bende> Umudike> Akwete> Owerri. Exchangeable potassuim and total nitrogen correlated significantly with grain yield (r = 0.71 and 0.57 respectively). The results of the field study indicated that NPK fertilizer rate of 100kg/ha (equivalent to 20kg N, 44kg P and 83 kg k ha1) optimum was for soybean production and N fixation in the zone. Soybean cultivar TGX 1829-IE performed best inlhe two locations with grain yield of 1.12 — 1.25 tonnes per hectares and had the best yield stability and adaptability to the soils of the zone. It also had the highest nodule number and hence N2— fixation. The cultivar was, therefore, recommended for the zone. Phosphorus at the rate of 50 kg/ha P gave the optimum yield in terms of grain yield and nodulation and was recommended for the zone.