(Kanter et al., 2019; Singh et al., 2018).<sup>21</sup> With increased availability and affordability, data from satellite sensors such as the European Space Agency’s SENTINEL-2 Multi Spectral Imager and the series of sensors from Planet’s Dove satellites are being explored to bring satellite monitoring to the individual-field level. Recent research has shown that data from low-cost satellite sensors can help predict crop yields at the individual-field scale, which can serve as crucial information for farmers to inform their agriculturalmanagement practices and help them make decisions about where and when to apply fertilizer (Jain et al., 2019). Building the capacity of local agricultural-extension officers to appreciate the usefulness of these datasets and apply them in practice will be critical (Dash, 2019).

Other initiatives and technologies, such as nitrogen-fixing bacteria, efficiency enhancing fertilizers or fertilizer deep placement that targets fertilizer right at the source also show promise. At the same time, even as countries focus attention on best management practices on-farm, there is an increasing need to extend attention to off-farm actors across the agricultural value chain that are capable of influencing farmlevel nitrogen management (Kanter et al., 2020a).

For example, since 2015, the Government of India has made efforts to improve nitrogen use efficiency in agriculture and has mandated manufactures of urea, a type of nitrogen fertilizer that is commonly applied in India, to produce neem-coated urea. Neem-coating helps to reduce leakages by making it more difficult for black marketers to divert urea to industrial consumers (Government of India, 2016). At the same time, it has the potential to benefit farmers. Since neem acts as a nitrification inhibitor, it allows a more gradual release of nitrogen into the soil, thereby improving nitrogen use efficiency. Neem, however, is one of many possible compounds and the responses of different crops under different conditions can be highly variable (Searchinger et al., 2020).

Another technique developed by the International Fertilizer Development Center is using fertilizer deep placement that enhances the efficiency of nutrient delivery to crops. The method buries nitrogen fertilizer into the soil, which feeds nitrogen directly into a plant and reduces losses. However, the potential to scale such technology in regions like Africa may be more limited due to the nature of the soils that can hinder the pathways of nutrient distribution (Cox et al., 2015). Expanding frontier agricultural technologies such as insect and hydroponic farming that have minimal land and water footprints and employ circular economy principles is increasingly being seen as an attractive option to enhance food security and livelihood opportunities, especially in Africa and countries affected by fragility, conflict, and violence. Waste from insects can also be fed back into the food system as organic fertilizers to help improve soil health (Verner et al., 2021). More research on these new technologies and initiatives is needed to better understand their efficacy across different locales, and to quantify the environmental and economic consequences of such measures.

Several countries have taken steps to reduce problems related to fertilizer use using a mix of instruments. For instance, since the early 1990s, Denmark has reduced its nitrogen balance by 56 percent, although its agricultural productivity has continued to increase over this period. Policy makers used a portfolio of strategies, including targets for reductions of nitrogen discharges, fertilizer accounting systems, nitrogen quota systems to regulate use, bans on manure application on bare fields, fertilizer taxes for nonagricultural uses, as well as agricultural environmental schemes and advisory services (OECD, 2021).

Ultimately, there is no easy solution for curbing nitrogen waste, given the diversity of agricultural, climatic and political systems across the world. Nevertheless, as the challenge mounts and world population grow, it is urgent to close efficiency gaps, and explore policy options on and off-farm that make it possible to

> 21 For example, UjuziKilimo, a Kenyan company, uses simple ground sensors to provide nitrogen recommendations via text messaging. A Nigerian company, Hello Tractor, connects farmers with tractor services via apps and text messaging (Kanter et al., 2019).

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