Nitrogen-fixing (c2h2-reducing) activity and plant growth characters of 16 wetland rice varieties

Abstract

Nitrogen fixation associated with 16 rice (Oryza saliva) varieties or lines of short and long durations, grown in a flooded field, during the 1984 wet season and 1985 dry season was measured by a simple and rapid acetylene reduction assay. Assaying the plants at heading stage for 3 consecutive days was found suitable for determining varietal differences in associative N2fixation. Significant differences in acetylene-reducing activity (ARA) per plant and unit plant dry weight among short- and long-duration varieties were found. Plant ARA significantly correlated with root dry weight, and total plant dry weight at heading, and total plant dry weight at harvest during both dry and wet seasons. Plant ARA also showed significant partial correlation coefficients with root dry weight, keeping the shoot dry weight constant which indicates that the root biomass (dry weight) is an important plant character affecting ARA. Generally, ARA per plant was proportional to plant biomass. Although IR50, a short-duration variety had a lower biomass, ARA was similar to that of some long-duration varieties with a high biomass. On the other hand, Peta and Rodjolele, which are tall varieties produced a high biomass but low ARA. IR42, a long-duration variety. had the highest ARA per plant and per unit weight of plant. Harvest index (HI), nitrogen harvest index (NHI), and nitrogen remobilization efficiency (NRE) of the varieties were also determined in the wet season. NHI was significantly different among long- and short-duration varieties and NRE differed among the short duration varieties. No correlations between ARA per plant and HI, NHI, and NRE were found. The possibility of using rice plant characters as criteria for screening varieties for their ability to stimulate biological N2fixation is discussed. © Taylor & Francis Group, LLC.