Relationship between Biomass Production and Nitrogen Fixation under Drought-Stress Conditions in Peanut Genotypes with Different Levels of Drought Resistance

The relationship between biomass production and N₂ fixation under drought-stress conditions in peanut genotypes with different levels of drought resistance is not well understood. The objective of this study was to determine the effect of drought on biomass production and N₂ fixation by evaluating the relative values of these two traits under well watered and water-stress conditions. Twelve peanut genotypes were tested under field conditions in the dry seasons of 2003/2004 and 2004/2005 in north-east Thailand. A split-plot design with four replications was used. Main-plot treatments were three water regimes [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW], and sub-plot treatments were 12 peanut lines. Data were recorded on biomass production and N₂ fixation under well watered and water-stress conditions. Genotypic variations in biomass production and N₂ fixation were found at all water regimes. Biomass production and N₂ fixation decreased with increasing levels of drought stress. Genotypes did not significantly differ in reductions for biomass production, but did differ for reductions in N₂ fixation. High biomass production under both mild and severe drought-stress conditions was due largely to high potential biomass production under well-watered conditions and, to a lesser extent, the ability to maintain high biomass production under drought-stress conditions. High N₂ fixation under drought stress also was due largely to high N₂ fixation under well-watered conditions with significant but lower contributions from the ability to maintain high nitrogen fixation under drought stress. N₂ fixation at FC was not correlated with the reduction in N₂ fixation at 2/3 AW and 1/3 AW. Positive relationships between N₂ fixed and biomass production of the tested peanut genotypes were found at both levels of drought stress, and the relationship was stronger the more severe the drought stress. These results suggested that the ability to maintain high N₂ fixation under drought stress could aid peanut genotypes in maintaining high yield under water-limited conditions.