Biological Nitrogen Fixation and Pod Yield of Groundnut (Arachis hypogaea L.) as Influenced by a Salt-affected Alfisol at Kadawa, Nigeria

The cost of nitrogen (N) fertilizers continues to rise besides the fertilizer’s role as a potential pollutant. Amelioration and/or improvement in the fertility of poor soils using such inorganic fertilizers prove less feasible as such. The rhizobium-legume symbiosis is, therefore, suggested as an alternative to solving the soil N fertility problem. Biological nitrogen fixation (BNF) can be an important means for a continued and sustainable productivity of N-demanding agricultural crops. Most legumes are very sensitive to saline condition yet the rhizobia they house, due to adaptation of some strains to saline conditions, are not. Assessment of groundnut for BNF on saline soils cannot be overestimated, especially as more farmers are coming into irrigated agriculture. Besides, there is little to no reported work on the subject, particularly on the groundnut genotypes under study. A screen house trial was conducted in 2012 at the Department of Soil Science, Ahmadu Bello University, Zaria, Nigeria. The study aimed at determining the symbiotic nitrogen fixation of some groundnut genotypes grown on a salt-affected soil. The treatments consisted of six groundnut genotypes (SAMNUT 10, 11, 21, 22, 23 and 24) and two soil types (saline and non-saline). A non-nodulating groundnut genotype (ICGL-5) was used as a reference crop. The treatments were laid in a completely randomized design (CRD) with three replications. Indices of nitrogen fixation and yield were recorded. Effective and total nodule numbers were highest in SAMNUT 24 (19 plant-1) and 22 (34 plant-1). Although there was no statistical difference between the genotypes in terms of N2-fixed, highest amount of dinitrogen fixed was recorded for SAMNUT 21 (2, 500 mg N plant-1) and the least for SAMNUT 11 (930 mg N plant-1). SAMNUT 23 had the highest pod yield and SAMNUT 11 the least. Soil salinity did not affect N2 fixation statistically although the normal (non-saline) soil tends to positively influence most other parameters. Further studies on roles of other biochemical factors would assist in understanding the phenomena more.