Effects of organic farming practices and salinity on yield and greenhouse gas emissions from a common bean crop

A field experiment was conducted at Agrinio, West Greece, to compare the impacts of organic vs. conven-tional farming practices on yield, N nutrition and greenhouse gas emissions in common bean (Phaseolusvulgaris cv. ‘contender’). In both farming systems, irrigation water containing 0.5 or 10 mM NaCl wasused. The conventionally treated plots were fertilized with an inorganic fertilizer, whereas the organi-cally treated plots received organic compost. Conventional farming resulted in significantly higher freshweight of green bean pods than organic farming (5.50 kg m−2vs. 3.67 kg m−2, respectively). However, thecropping system had no impact on dry pod biomass, because the dry matter content of the organicallyproduced bean pods was higher than that of pods originating from conventional farming (9.88% vs. 7.20%,respectively). The presence of 10 mM NaCl in the irrigation water restricted significantly the total plantbiomass and fresh pod yield (−22.8%), without any interaction with the farming system. The decrease infresh pod yield by organic farming was due to a shortage in soil mineral N (NO3−and NH4+) at the earlygrowth stage, which reduced the tissue N levels. Organic farming increased significantly the number orroot nodules at the stage of early pod filling in comparison with conventional farming. However, at bothsystems the total soil N increased appreciably at this developmental stage, although no N was suppliedto the crop, thereby pointing to intensive symbiotic N2-fixation by bean. Organic farming resulted insignificantly lower N2O emissions than conventional farming in terms of the overall Global WarmingPotential of the treatments (363 kg ha−1vs. 455 kg ha−1, respectively). However, the N2O emission inten-sities did not differ significantly between organic and conventional systems, highlighting the importanceof maximizing yield within organic systems in order to reduce their environmental impact.© 2014 Elsevier B.V. All rights reserved.