Nitrogen Fixation of Sulla under Mediterranean Conditions

Abstract

Sulla coronaria (L.) B.H. Choi & H. Ohashi (=Hedysarum coronarium L.) is a Mediterranean forage legume grown extensively in rainfed Italian environments. Here we report the fi eld quantifi cation of its seasonal and annual N fi xation, using the 15 N isotopic dilution (ID) method, the infl uence of various nonfi xing reference species on these estimates, and the allocation of fi xed N between the aerial and the belowground biomass. Parallel experiments were conducted over two biennial crop cycles at two Italian locations (Sassari and Ancona), characterized by sandy-loam to heavy clay-loam calcareous soils. Th e proportion of nitrogen derived from the atmosphere (%Ndfa) present in the aerial biomass reached 78.2% at Sassari and 82.7% at Ancona, with no signifi cant eff ect of the identity of the nonfi xing reference species. At Sassari, the amount of fi xed N present in the aerial dry matter (DM) of sulla was 187 kg ha −1 in the fi rst crop cycle, and 265 kg ha −1 in the second, while the equivalent N yields at Ancona were 350 and 170 kg ha −1 . Th e relationship between the quantity of fi xed N in the aerial biomass and the aerial DM yield of sulla was signifi cant and not site-specifi c, realizing an equivalence of about 1.8 kg ha −1 of fi xed N per 100 kg ha −1 of aerial DM. Th e relative contribution of the root biomass to the amount of fi xed N was on average 4%. Th e N balance of sulla at the end of the second crop cycle was negative, but the N sparing eff ect compared with the nonfi xing species ranged from 65 to 175 kg ha −1 .

Cropping systems sustainability: Inoculation and fertilisation effect on sulla performances in a new cultivation area

“…Moreover, other inputs such as biomass residues, root turnover from both sulla crop and unsown non legumes species which benefit fixed N can, directly or indirectly, lead to positive effects on SOC (Francaviglia et al, 2014). Compared to previous estimates, the values of fixed N reported in this study are high (Sulas et al, 2009). Total absence of diseases on sulla plants, which has been observed in the new environment of cultivation, can contribute to partially explain the overall better performances.…”

“…Unfortunately, N-fixation results obtained with acetylene reduction assay by Gurfel et al are not directly comparable with our results, based on the isotopic dilution method. Few papers have focussed on sulla N-fixation (Sulas et al, 2009;Saia et al, 2016) and, to the best of our knowledge, no other information is available regarding N-fixation studies by isotopic method within field experiments dealing with the inoculation of the sulla crop with current commercial strains. Recent investigations rather deal with diversity of rhizobia nodulating sulla, selection of inoculant strains, molecular phylogenetic analysis, strain fingerprinting and species identification, extracellular polysaccharides produced by R. sullae strains (Muresu et al, 2005;Fitouri et al, 2012;Liu et al, 2012;Razika et al, 2012;Aliliche et al, 2016).…”

“…New varieties of sulla have been released in Australia, Italy and Tunisia, and several papers also documented the significant genetic potential (Yates et al, 2006;Ruisi et al, 2011;Cordoba et al, 2013;Annicchiarico et al, 2014;Issolah et al, 2014). Sulla has a valuable capacity to improve soil fertility and to fix atmospheric nitrogen (N) (Sulas et al, 2009;Saia et al, 2016). Moreover, sulla has an important role in multifunctional agriculture (Sulas, 2005), whereas interesting features of its biomass that could support the production of biofuels are recently noticed .…”

Dry matter yield, feeding value, and antioxidant activity in Mediterranean chicory (Cichorium intybus L.) germplasm

“…In Sardinia, Nieddu et al (2000) and Sulas (2004) suggested the use of chicory as a fodder crop; Sitzia et al (2006) used cultivar Spadona and sulla as forage crops in a dairy sheep system, and they concluded that both chicory and sulla, cultivated under Mediterranean conditions, can serve as high-quality pasture for sheep. According to Sulas et al (2009), the same Spadona cultivar was able to produce up to 6 t ha -1 of DM per year when harvested at a later stage (early flowering) but with a relevant contribution of stems to the total DM yield. The recorded values for Spadona leaf chemical composition, except for ADL, are quite similar to those reported by Sitzia et al (2006) and Di Grigoli et al (2012) for the same chicory cultivar grown in different grazing experiments in Sardinia and Sicily (Italy), respectively.…”

Yield and nitrogen fixation potential from white lupine grown in rainfed Mediterranean environments

“…N fertilizer application has been successfully adopted as a common protocol in previous experiments carried out in Sardinia and other Italian locations, in the framework of the Italian national research project "Physiology of production and nitrogen fixation of forage legumes in eco-compatible farming systems" (Cazzato et al, 2012;Sulas et al, 2009Sulas et al, , 2013.…”