Table 13.

Agronomic practices with potential to enhance BNF inputs in cereal-based farming systems.

Practice	Likely mechanism for enhancement of BNF inputs	References
Zero or reduced tillage	Positive changes in diversity and heterogeneity of rhizosphere diazotrohphic community Higher organic matter and substrate inputs in rhizosphere Lower soil nitrate from reduced disturbance of soil organic matter reduces risk of inhibition of BNF	Li et al. (2021) Zhou et al. (2020) Peoples et al., 1995b, Torabian et al., 2019
Crop residue retention	Availability of a wide range of C compounds as source of C and energy substrates by diazotrophs Residue mulch creates conducive microenvironment (i.e., moisture conservation, lower O2 environment, steady supply of C) for diazotrophs Crop residue of high C:N (i.e., cereal straw) immobilizes inorganic N result in stimulation of BNF	Roper and Ladha (1995) Fan et al. (2020) Palm et al. (2014)
Smart synthetic N management	Optimal rate and timely application of synthetic N to cereals improves N use efficiency and reduces risk of unutilized fertilizer N inhibiting BNF by diazotrophs during cereal phase	Ladha et al., 1998
Application of biochar	Biochar enriches soil and stores organic C in a form that provides C and energy source for diazotrophs Biochar immobilizes inorganic N so BNF less likely to be suppressed Increases P bioavailability which stimulates BNF	Laird (2008) Nelson et al. (2011) Thies and Rilling (2009)
Use of manure with or without inorganic fertilizer.	Enhances soil C storage and nutrient availability after decomposition which will serve as C and energy source for diazotrophs Supports more diverse soil microbial communities and increases microbial biomass contributing to increase in BNF	Ladha et al. (2011)
Increased water availability Controlled water application	Drought suppresses BNF process Adequate plant-available water via rainfall or irrigation increases BNF by stimulating plant growth and microbial activity ‘Saturated soil culture’ (long-term flooding) enhances nodulation and BNF by soybean	Peoples et al., 1995b, Santachiara et al., 2019
Integration of legume in fallow or in rotation as part of diversification and intensification	Increased frequency of use of legumes in cropping system results in increased inputs of BNF Supply of in situ high quality residues with high N concentration and a low C:N ratio improves soil N status	Franke et al. (2018)
Green or brown legume manurea	Increased frequency of use of legumes in cropping system results in increased inputs of BNF Supply of in situ legume residue with high N concentration and a low C:N ratio improves soil N status Green manure mulch and brown manuring assist the management of weeds	Becker et al., 1995, Singh et al., 2009 Peoples et al. (2017)
Intercropping legumes within cereals	Increased frequency of use of legumes in cropping system results in increased inputs of BNF Intercropped legume has higher %Ndfa than legume sole crop Increased yield stability and yield per unit area, reduced pest problems and lower requirements for agrochemicals and N fertilizer to support cereal yield	Lithourgidis et al. (2011) Bedoussac et al. (2015) Fletcher et al. (2016) Jensen et al. (2020)

^aGreen manure = slashing/mulching live legume crop; Brown manure = legume crop killed with knock-down herbicide prior to see-filling (an emerging farmer practice to manage herbicide-resistent weeds and improve soil mineral N for following cereal crop).