Biological nitrogen fixation in three long-term organic and conventional arable crop rotation experiments in Denmark

Reviews and syntheses: Review of causes and sources of N<sub>2</sub>O emissions and NO<sub>3</sub> leaching from organic arable crop rotations

“…1 and an overview of performance of selected drivers of SMN in organic and non-organic crop rotations are given in Table 1. Despite substantial inputs of N from biological nitrogen fixation (BNF;Kayser et al, 2010;Pandey et al, 2017) and from organic amendments, the N supply is often below op-timum for plant growth in arable organic farming (Berry et al, 2002;Tuomisto et al, 2012). BNF may be a more important N source than N from organic manures and fertilisers in organic arable cropping systems (Pandey et al, 2018).…”

Nitrogen fixation and productivity of winter annual legume cover crops in Upper Midwest organic cropping systems

“…However, inoculation of legumes with highly effective rhizobia often fails when transferred to the field due to competition with existing endogenous rhizobia (Streeter 1994;Triplett and Sadowsky 1992). The success of the inoculant in the field may depend on genetic specificity (Mothapo et al 2013a;Thies et al 1992), environment (Pandey et al 2017;Parr et al 2011), soil pH (Wongphatcharachai et al 2015), and competition with endogenous strains (Brockwell et al 1995;Kosslak et al 1983;Thies et al 1992). Plant available soil N in the form of nitrate is also wellknown to inhibit nodulation (Streeter 1985).…”

Transitions to greater legume inclusion in cropland: Defining opportunities and estimating benefits for the nitrogen economy

“…Without reducing cereal yield itself, there are few options for further reduction in N other than by maximizing the use of the biologically fixed residual from legume crops, yet the quantity of this residual in present crop-grass systems is highly F I G U R E 6 Examples of estimated reduction in cumulative nitrogen (N) application in crop sequences following substitution of existing crops with a grain legume, numbers to the right showing initial N input (kg/ha) averaged over the 6 years then downwards, N input and percentage of initial following increasing substitution in: (a) winter cereals, system V, initially with 188 kg/ha then replacing WOSR with legume including 50 kg/ha residual (83%), replacing WOSR and WB with legumes and same residual (70%), and as previous but omitting N fertilizer to legumes and assuming substitutions plus residual N of 75 kg/ha (50%); and (b) the same procedure for spring cereals, system III, initially with 104 kg/ha and replacing one SB (66%), two SB (73%), and finally two SB with 50 kg/h residual (43%) uncertain. The fixation rate by grain legumes in the field is well documented to lie typically between 100 and 350 kg/ ha (Kopke & Nemecek, 2010;Panday et al, 2017), but the proportion of this left as residual N has shown great variability between locations and cropping systems. Comprehensive field studies are now needed to confirm the calculations in Figure 6 that suggest mineral N could be taken to 50% of current inputs by increasing legume inclusion to one third and assuming realistic residuals are fully used.…”

“…The heavy reliance on imported food and feed protein would threaten food supply in conditions of blockade or war, high tariffs, environment disasters and increasing global demand for legumes. Strong environmental arguments for legumes center on their ability to fix their own nitrogen from the air, leave some of this as residue for the next crop and hence reduce the total mineral nitrogen input (Jensen, Peoples, & Hauggaard-Nielsen, 2010;Kopke & Nemecek, 2010;Panday, Li, Askegaard, & Olesen, 2017). Legumes have many other beneficial ramifications for ecological sustainability, including enhanced soil structure and habitat diversity and introducing breaks in the sequence of cereal crops to allow management of pests (Kopke & Nemecek, 2010;Stagnari et al, 2017).…”