Abstract

Umeh S. I. and Mbah B. N

The measurement of the benefits of biological nitrogen (N) fixing properties of soybean in cassava and soybean intercrop was conducted at the University of Nigeria, Nsukka between 2000, 2001 and 2002. Changes in soil nutrient concentration were measured at 0 – 30 cm. The effects of N- fertilization on cassava tuber yield and soil-N were monitored for the three seasons using factorial in randomized complete block design. There was no apparent shading effect during the growth of the two crops. Soybean was harvested 110 days after planting, while cassava was harvested at 4, 8 and 12 months after planting in each year. Cassava tuber yield was highest at intercrop X 60 and intercrop X 45 kg N ha-1 (30.0 and 29.9 t. ha-1 ) x tuber yield of intercrop X 45 kg N ha-1 . The result indicates that 60 kg (90 – 30) of applied nitrogen could be spared per hectare by intercropping cassava with soybean due to soybean nitrogen fixation. Grain yield of soybean may not be compromised by intercropping with cassava. Soil - N increased from 0.042 mg kg-1 before the experiment to 0.168 mg kg-1 in sole soybean system and 0.086 mg kg-1 in intercrop system at 8 months after planting and 0.150 mg kg-1 in the sole soybean and 0.085 kg mg-1 in intercrop system in 12 months after planting. The highest land equivalent ratio (LER) of 2.3 and area × time equivalent ratio (ATER) of 1.8 were obtained at 45 kg N ha-1 in the intercrop system.