Nitrogen fertilization and use efficiency in an intercrop system of cassava (Manihot esculenta Crantz) and soybean (Glycine max (L) Meril.)
Experiments were conducted at the Department of Crop Science, University of Nigeria, Nsukka Research farm during the 2008 and 2009 cropping seasons to determine the effects of intercropping cassava and soybean on cassava tuber and soybean grain yields respectively and on nitrogen use efficiency of cassava at the intercropping system. The experiment for each year was laid out in a factorial arrangement in randomized complete block design (RCBD). The treatments were the nitrogen rates, sole soybean (TGM 579), sole cassava (TMS 30572) and cassava + soy bean intercrop. Intercropping cassava with soybean showed a significant (P ≤ 0.05) yield advantage over sole cropping system in 2008. Increased fertilizer rates up to 90 kg N/ha-1 increased fresh cassava yield in sole cropping system, while in the intercrop, increased application of nitrogen at 60 kg N decreased cassava tuber yield. The cassava nitrogen use efficiency (NUE) increased with increase in applied nitrogen up to 60 kg N/ha-1 and then decreased beyond this point. Similar trend was observed in 2009, except that total harvested cassava tuber yield was significantly higher in 2009 than that obtained in 2008. This result suggests that intercropping cassava with soybean with or without application of nitrogen is beneficial but high doses of nitrogenous fertilizer in sole soybean field is uneconomical and should be avoided.
Key words: Cassava, soybean, intercrop, sole crop, nitrogen use efficiency.