Appraisal of the 15N-isotope dilution and 15N natural abundance methods for quantifying nitrogen fixation by flood-tolerant green manure legumes

Quantification of biological nitrogen fixation (BNF) is fundamental to identifying potential green manure legumes for their enhanced nitrogen contribution to sustained crop production. A screenhouse experiment compared BNF by Aeschynomene afraspera L. as affected by phosphorus, using the 15Nisotope dilution and the 15N methods. Rice (Oryza sativa L.) was grown as a non-fixing plant. Phosphorus significantly increased the percent N derived from the atmosphere (% Ndfa), whereby the 15N method tended to overestimate BNF contribution on average by 20% compared to the15 N dilution. Data confirmed rice as a non-fixing plant for estimation of BNF by flood-tolerant legume

Comparative studies of drying methods on the seed quality of interspecific NERICA rice varieties (Oryza glaberrima x Oryza sativa) and their parents

Seed moisture content (MC) is a key component that determines storability of germplasm conserved in seed genebanks. The purpose of this research was to compare the efficiency of sun-, shade-, silica geland conventional room drying in terms of rice seed MC and viability using seeds of two interspecific progenies (NERICA 1 and NERICA 3) and their parents Oryza glaberrima and O. sativa varietiesharvested 15 days before, at and 15 days after mass maturity. Sun drying most significantly reduced MC (4-5%) and was comparable with silica gel drying regardless of the variety tested and the maturity stageat harvest. Likewise, sun drying gave the best germination percentages followed by silica gel. Shade and room drying did not significantly lower MC and led to poor germination, especially when rice washarvested prematurely. Except for the sativa variety, harvesting prematurely resulted in no germination. In contrast, the initial germination percentages in all tested varieties improved as rice was harvested at or after mass maturity rather than 15 days earlier. Though comparable to sun drying, silica gel may not be readily available and affordable for resource-limited seed storage facilities. In this case sun drying was found an effective and affordable method for short-term storage, especially farm-saved seeds

Appraisal of 15N enrichment and 15N natural abundance methods for estimating N2 fixation by understorey Acacia leiocalyx and A. disparimma in a native forest of subtropical Australia

It is anticipated that global climate change will increase the frequency of wildfires in native forests of eastern Australia. Understorey legumes such as Acacia species play an important role in maintaining ecosystem nitrogen (N) balance through biological N fixation (BNF). This is particularly important in Australian native forests with soils of low nutrient status and frequent disturbance of the nutrient cycles by fires. This study aimed to examine 15N enrichment and 15N natural abundance techniques in terms of their utilisation for evaluation of N2 fixation of understorey acacias and determine the relationship between species ecophysiological traits and N2 fixation