SYMBIOTIC NITROGEN FIXATION AND CONTRIBUTION TO SOIL NITROGEN BY GROUNDNUT (ARACHIS HYPOGAEA L) GENOTYPES IN THE NORTHERN GUINEA SAVANNA OF NIGERIA

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SYMBIOTIC NITROGEN FIXATION AND CONTRIBUTION TO SOIL NITROGEN BY GROUNDNUT (ARACHIS HYPOGAEA L) GENOTYPES IN THE NORTHERN GUINEA SAVANNA OF NIGERIA

Abstract:

Evaluation of existing groundnut genotypes for nitrogen fixation may be useful as selection criteria for high nitrogen fixation thereby minimizing the high cost of inorganic fertilizer and its associated environmental consequences. The objectives of this study were to determine symbiotic nitrogen fixation and contribution to soil nitrogen by groundnut (Arachis hypogaea L). The treatments consisting ten groundnut genotypes(SAMNUT 24, SAMNUT 22,ARRORSICGX-SM 00017/5/P15/P2, SAMNUT 10, ICIAR 7B, ARRORSICGX 000201/5/P4P10, SAMNUT 21, SAMNUT 23 and SAMNUT 14) and two rates of nitrogen fertilizer (0 and 30 kg/ha) were laid out in a split plot design with three replications under rain-fed conditions in 2011 and 2012. Nitrogen fixation parameters were measured/calculated as nodule number, nodule dry weight, plant total nitrogen, biologically fixed N, nitrogen derived from atmosphere (Ndfa) and soil nitrogen balance while agronomic data determined were shoot and root dry weights, 100-seed weight, pod and haulm yield, harvest index (HI) and nitrogen harvest index (NHI). The difference between years was significant for most variables with 2011 statistically out-performing 2012 except for HI, pod yield and 100-seed weight which maintained similar trend in both years. ARRORS-ICGX 000201/5/P4P10 (29.11 kg N/ha) and SAMNUT 23 (22.27 kg N/ha) were the best genotypes in terms of biological nitrogen fixation, nodule number, nodule dry weight, HI and NHI. SAMNUT 14 and 6AT which fixed relatively lower amount of N2; 17.10 and 19.95 kg/ha respectively, impacted positively on the soil N balance than all other genotypes in 2011. These genotypes had lower NHI than the highest N2 fixers which mean that most of the N derived from BNF was not translocated to the seeds but retained in other plant parts such as shoot and root. 9 Application of 30 kg N ha-1 significantly increased the agronomic and nitrogen fixation parameters. Wide variations exist in the pod yield across the genotypes. ARRORSICGX 000201/5/P4P10 with an average pod yield of 2670 kg/ha was the best genotype in our recent finding. The result of the interaction between nitrogen rates and groundnut genotypes indicates that ARRORS-ICGX 000201/5/P4P10 (2739 kg/ha) and SAMNUT 22 (3346 kg/ha) performed best even without the addition of the starter dose of nitrogen fertilizer signifying their ability to reduce the cost of production by saving cost on inorganic fertilizer. However, the N starter dose would be necessary to prevent soil N mining in view of the overall negative soil N balance obtained despite application of 30 kg N ha-1 to all genotypes. In conclusion, groundnut genotypes used in this study could be grouped into three distinct categories based on the amount of biologically fixed nitrogen and pod yield. ARROS-ICGX000201/5/P4P10 and SAMNUT 22 are both high fixing and high yielding; 6AT was high fixing and low yielding; but contributing positively to the soil nitrogen balance; while SAMNUT 21 and ICAR 7B are low fixing. The remaining genotypes could not be classified into any of these groups. Similarly, the results of principal component analysis conducted in the measured parameters suggest that future breeding effort should be targeted at improving the efficiency

SYMBIOTIC NITROGEN FIXATION AND CONTRIBUTION TO SOIL NITROGEN BY GROUNDNUT (ARACHIS HYPOGAEA L) GENOTYPES IN THE NORTHERN GUINEA SAVANNA OF NIGERIA

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