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United States Department of Agriculture

Agricultural Research Service

Research Project: Mitigating Agricultural Sources of Particulate Matter and Greenhouse Gas Emissions in the Pacific Northwest

Location: Northwest Sustainable Agroecosystems Research

Title: Cultivar effects on nitrogen fixation in peas and lentils

Authors
item Abi-Ghanem, Rita -
item Carpenter-Boggs, Lynne -
item Smith, Jeffrey

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 26, 2010
Publication Date: August 10, 2010
Citation: Abi-Ghanem, R., Carpenter-Boggs, L., Smith, J.L. 2010. Cultivar effects on nitrogen fixation in peas and lentils. Biology and Fertility of Soils. DOI: 10.1007/s00374-010-0492-6.

Interpretive Summary: Over 12 million tons of fertilizer N is applied annually in North America. The price of nitrogenous fertilizers have more than tripled over the last four years primarily due to increased price of natural gas. Several billion dollars in producer profit has been lost because of natural gas price increases. In 1975, nearly half of the N needed in agriculture, 44 to 66 million tons annually, was provided through legume-rhizobial symbiosis. By 2005, synthetic N provided three times as much N to agriculture as biological N fixation (BNF) on a global basis. Biological N fixation presents economic, environmental, and agronomic benefits and could be used to a larger degree as an alternative to synthetic fertilizers. We found that the percent of N fixed was significantly affected by crop variety and significantly correlated with number of nodules in both lentils and peas. This implies that one strategy for enhancing crop N fixation is developing varieties that have higher rhizobium infection rates. Total N fixation in lentils was significantly influenced by both crop variety and rhizobial strain. These findings suggest that N fixation improvement in lentils and peas may be addressed most effectively by breeding crops for greater N fixation hosting capacity. This research clearly shows that simply breeding legumes for yield potential may be a flawed strategy for the best environmental use of nitrogen. Breeding plants for increased N fixation will decrease N fertilizer use that effects climate change and environmental quality. This research will benefit legume breeders and legume growers.

Technical Abstract: Increasing nitrogen fixation in legume crops could increase cropping productivity and reduce nitrogen fertilizer use. Studies have found that crop genotype, rhizobial strain, and occasionally genotype-specific interactions affect N fixation, but this knowledge has not yet been used to evaluate or breed for greater N-fixation in U.S. crops. In this study five USDA varieties of lentils (Lens culinaris Medik.) and five varieties of peas (Pisum sativum L.) were tested with 13 to 15 commercially available strains of Rhizobium leguminoserum bv. viciae to identify the better N-fixing rhizobial strains, crop varieties, and specific pairings. Peas and lentils inoculated with individual strains were grown in growth chambers for 6 weeks. Plants received (15NH4)2 SO4 (5 atom %) starter fertilizer to measure N fixation by isotope dilution. Below and above-ground biomass, numbers of nodules, and the proportion of plant N supplied by fixation (PNF) were determined. The percent of N fixed was significantly affected by crop variety and significantly correlated with number of nodules in both lentils and peas. This implies that one strategy for enhancing crop N fixation is developing varieties that have higher rhizobium infection rates. Total N fixation in lentils was significantly influenced by both crop variety and rhizobial strain. Eston variety lentil and Shawnee variety pea had the highest PNF of 80.8% and 91.3% respectively. The different strains of R. leguminoserum affected PNF in lentils but not in peas. These findings suggest that N fixation improvement in lentils and peas may be addressed most effectively by breeding crops for greater N fixation hosting capacity.

Last Modified: 12/18/2014
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