Biological nitrogen fixation by common beans (Phaseolus vulgaris L.) increases with bio-char additions

Biological nitrogen fixation by common beans(Phaseolus vulgaris L.) increases with bio-char additions
Marco A. Rondon & Johannes Lehmann & Juan Ramírez & Maria Hurtado

Abstract
This study examines the potential, magnitude, and causes of enhanced biological N2 fixation (BNF) by common beans (Phaseolus vulgaris L.) through bio-char additions (charcoal, biomass-derived black carbon). Biochar was added at 0, 30, 60, and 90 g kg−1 soil, and BNF was determined using the isotope dilution method after adding 15N-enriched ammonium sulfate to a Typic Haplustox cropped to a potentially nodulating bean variety (CIAT BAT 477) in comparison to its non-nodulating isoline (BAT 477NN), both inoculated with effective Rhizobium strains. The proportion of fixed N increased from 50% without biochar additions to 72% with 90 g kg−1 bio-char added. While total N derived from the atmosphere (NdfA) significantly increased by 49 and 78% with 30 and 60 g kg−1 bio-char added to soil, respectively, NdfA decreased to 30% above the control with 90 g kg−1 due to low total biomass production and N uptake. The primary reason for the higher BNF with bio-char additions was the greater B and Mo availability, whereas greater K, Ca, and P availability, as well as higher pH and lower N availability and Al saturation, may have contributed to a lesser extent.

Enhanced mycorrhizal infections of roots were not found to contribute to better nutrient uptake and BNF. Bean yield increased by 46% and biomass production by 39% over the control at 90 and 60 g kg−1 bio-char, respectively. However, biomass production and total N uptake decreased when biochar applications were increased to 90 g kg−1. Soil N uptake by N-fixing beans decreased by 14, 17, and 50% when 30, 60, and 90 g kg−1 bio-char were added to soil, whereas the C/N ratios increased from 16 to 23.7, 28, and 35, respectively. Results demonstrate the potential of biochar applications to improve N input into agroecosystems while pointing out the needs for long-term field studies to better understand the effects of bio-char on BNF.

Keywords Biological N fixation . Boron . Charcoal . Molybdenum . Mycorrhiza . 15N

Received: 14 December 2005 / Revised: 28 September 2006 / Accepted: 29 September 2006
# Springer-Verlag 2006

M. A. Rondon : J. Ramírez : M. Hurtado
Centro Internacional de Agricultura Tropical (CIAT),
A.A 6713, Cali, Colombia
J. Lehmann
Department of Crop and Soil Sciences, Cornell University,
Ithaca, NY 14853, USA

M. A. Rondon (*)
International Development Research Centre,
250 Albert Street, P.O. Box 8500, Ottawa, ON, Canada K1G 3H9
e-mail: mrondon@idrc.ca