Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

The demand for nitrogen (N) for crop production increased rapidly from the middle of the twentieth century and is predicted to at least double by 2050 to satisfy the on-going improvements in productivity of major food crops such as wheat, rice and maize that underpin the staple diet of most of the world's population. The increased demand will need to be fulfilled by the two main sources of N supply – biological nitrogen (gas) (N2) fixation (BNF) and fertilizer N supplied through the Haber-Bosch processes. BNF provides many functional benefits for agroecosystems. It is a vital mechanism for replenishing the reservoirs of soil organic N and improving the availability of soil N to support crop growth while also assisting in efforts to lower negative environmental externalities than fertilizer N. In cereal-based cropping systems, legumes in symbiosis with rhizobia contribute the largest BNF input; however, diazotrophs involved in non-symbiotic associations with plants or present as free-living N2-fixers are ubiquitous and also provide an additional source of fixed N. This review presents the current knowledge of BNF by free-living, non-symbiotic and symbiotic diazotrophs in the global N cycle, examines global and regional estimates of contributions of BNF, and discusses possible strategies to enhance BNF for the prospective benefit of cereal N nutrition. We conclude by considering the challenges of introducing in planta BNF into cereals and reflect on the potential for BNF in both conventional and alternative crop management systems to encourage the ecological intensification of cereal and legume production

Carbon sequestration potential, challenges, and strategies towards climate action in smallholder agricultural systems of South Asia

South Asia is a global hotspot for climate change with enormous pressure on land and water resources for feeding the burgeoning population. The agricultural production systems are highly vulnerable in the region and is primarily dominated by small and marginal farmers with intensive farming practices that had favored the loss of carbon (C) from soil. This review discusses the potential of soil and crop management practices such as minimum/reduced/no-tillage, use of organic manure, balanced and integrated plant nutrient application, precision land levelling, precision water and pest management, residue management, and cropping system optimization to maintain the C-equilibrium between soil and atmosphere and to enhance the C-sequestration in the long run. Results of meta-analysis show a potential 36% increase in soil organic C stock in the top 0–15 cm layer in this region which amounts to ∼18 Mg C stocks ha−1. Improved management practices across crops and environment may reduce methane em0ission by 12% resulting in an 8% reduction in global warming potential (GWP), while non-submerged condition led to a 51% GWP reduction in rice. Conservation agriculture and precision fertilization also reduced GWP by 11 and 14%, respectively. Although several innovative climate resilient technologies having significant potential for C-sequestration have been developed, there is an urgent need for their scaling and accelerated adoption to increase soil C-sequestration. Policies and programs need to be devised for incentivizing farmers to adopt more C-neutral or C-positive agricultural practices. The national governments and other agencies should work towards C farming together with global initiatives such as the “4 per 1000” Initiative and Global Soil Partnership, and regional public-private partnership initiatives on carbon credits for Regenerative Agriculture such as by Grow Indigo-CIMMYT-ICAR in India, in addition to research and policy changes. This will be vital for the success of soil C sequestration towards climate action in South Asia

Nitrogen Challenges and Opportunities for Agricultural and Environmental Science in India

In the last six decades, the consumption of reactive nitrogen (Nr) in the form of fertilizer in India has been growing rapidly, whilst the nitrogen use efficiency (NUE) of cropping systems has been decreasing. These trends have led to increasing environmental losses of Nr, threatening the quality of air, soils, and fresh waters, and thereby endangering climate-stability, ecosystems, and human-health. Since it has been suggested that the fertilizer consumption of India may double by 2050, there is an urgent need for scientific research to support better nitrogen management in Indian agriculture. In order to share knowledge and to develop a joint vision, experts from the UK and India came together for a conference and workshop on “Challenges and Opportunities for Agricultural Nitrogen Science in India.” The meeting concluded with three core messages: (1) Soil stewardship is essential and legumes need to be planted in rotation with cereals to increase nitrogen fixation in areas of limited Nr availability. Synthetic symbioses and plastidic nitrogen fixation are possibly disruptive technologies, but their potential and implications must be considered. (2) Genetic diversity of crops and new technologies need to be shared and exploited to reduce N losses and support productive, sustainable agriculture livelihoods. Móring et al. Nitrogen Challenges and Opportunities (3) The use of leaf color sensing shows great potential to reduce nitrogen fertilizer use (by 10–15%). This, together with the usage of urease inhibitors in neem-coated urea, and better management of manure, urine, and crop residues, could result in a 20–25% improvement in NUE of India by 2030

Developmental stages in a nonheterocystous filamentous cyanophyte

Developmental stages broadly similar to those previously reported in Nostoc have been seen in an Oscillatoria-like cyanophyte isolated from nature and grown in unialgal cultures. Apparent cell fusions and anastomoses occurred in cultures raised from single filaments