Nitrogen Contribution by Groundnut (Arachis hypogaea L) Genotypes in the Northern Guinea Savanna of Nigeria

Most grain legumes irrespective of their ability to fix substantial amount of nitrogen to the soil, could impact negatively on the soil nitrogen balance, particularly if the fix nitrogen is exported from the field with harvested biomass (Shoot, root, grain/kernel). Thus, for agronomic purposes, it is important to quantify the potential amount of nitrogen from this source that will become available to the soil for subsequent crop uptake and/or ecosystem balance. The field trial was undertaken at the teaching and research field of the Institute for Agricultural Research (IAR) Samaru Zaria in the wet planting season of 2011 and 2012. The treatments consist of ten groundnut genotypes (SAMNUT 24, SAMNUT 22, ARRORSICGX-SM 00017/5/P15/P2, SAMNUT 10, ICIAR 7B, ARRORSICGX 000201/5/P4P10, SAMNUT 21, 6AT, SAMNUT 23 and SAMNUT 14), and two rates (0 and 30 kg N ha-1) of nitrogen (urea) fertilizer arrange in a split plot design. Nitrogen balance was estimated as the difference in nitrogen fix by the plant and nitrogen content of kernels/haulms. Results of the analysis of variance indicate that there was significant variation among the selected groundnut genotypes in their net contribution of nitrogen in both 2011 and 2012 at instances where both the groundnut kernel and haulms were exported from the field. Nitrogen contributions by the genotypes were not consistence in both years. In 2011, while SAMNUT 14 left the highest value of 9.79 kg N ha-1, ICIAR 7B returned the highest value in 2012. ICGX-SM 00017/5/P15/P2 (-16.55 kg N ha-1) and SAMNUT 22 (-56.07 kg N ha-1) contributed the least amount of nitrogen in 2011 and 2012 respectively when the kernel were removed from the field. On the other hand, 6AT was relatively stable in both years, and contributed close to 1 kg N ha-1. Even though negative nitrogen balances were reported at instances where the kernels were exported from the field, a more severe N depleting effect was observed when both haulms and kernels were removed from the field. Although, negative N balance was predominant at both rates (0 and 30 kg N ha-1) of N application, but the average nitrogen contribution was significantly higher (-1.10 kg N ha-1) with the application of starter nitrogen than the control (-13.23 kg N ha-1). In view of these findings, groundnut genotypes 6 AT, SAMNUT 14 and ICIAR 7B could be elite genotypes if building a resilience sustainable ecosystem is a priority due to their high biological nitrogen fixing abilities and nitrogen contributing potential.