• Energy Research

This working paper explores a generic method that can be used to benchmark nitrogen (N) input requirements for crop production and the efficiency by which inputs are used. Two types of N benchmarks are introduced: one for short-term and another for long-term assessments. We explain the underlying assumptions, data requirements and types of applications. Both benchmarking methods are especially suitable for regional, national or global analyses. The proposed methodology is illustrated for cereal production (maize, wheat, rice, millet and sorghum) in ten countries in sub-Saharan Africa, under current and optimal nutrient management, for today and towards 2050. We show that agronomic nitrogen-use efficiency (NUE) can be two to four times larger than currently observed in on-farm trials for the long- term benchmark. Potential improvements in N input requirements are related to greenhouse gas (GHG) emission mitigation potentials, using scenarios that include population increase and dietary change, potential yield increase and avoided land reclamation. Here, we show that when following the current trajectory of yield trends while maintaining the low current nitrogen-use efficiency, GHG emissions from cereal production will be three times larger than sustainable intensification of cereals in sub-Saharan Africa. The proposed N benchmarking method is most useful for regional or larger scale analyses and less useful for field assessments. Nonetheless, this might fill a gap in higher scale analyses, especially for estimating potential improvements in NUE and reducing GHG emissions. This working paper presents work in progress. In the future, we will test the proposed methodology on different case studies to evaluate its potential and finetune its operation.

As global anthropogenic emissions of greenhouse gases keep rising, there is increased pressure to utilise so-called natural climate solutions. Sequestration of additional organic carbon in agricultural soils is one such approach but it continues to provoke much debate. Published estimates for the potential magnitude of soil carbon sequestration (SCS) vary dramatically, from very modest to very substantial (Moinet et al., 2023). The estimations recently published by Almaraz et al. (2023) are of the latter category and we question here the validity and realism of their claims. This article is a Response to the Letter by McClelland et al, https://doi.org/10.1111/gcb.17012 & Moinet et al, https://doi.org/10.1111/gcb.17010, which was related to the paper of Almaraz et al., https://doi.org/10.1111/gcb.16884 Letter to the Editor

To increase productivity and profitability, while limiting nutrient losses and related GHG-emissions, African smallholders need more tailored fertilizer advice. Yet, such advice critically hinges upon – largely lacking – field-level management data, as management is key to efficient fertilizer use. The Maize- Nutrient-Manager (MNM) mobile phone application enables collection of such data at scale, and directly converts this data into actionable advice for the farmer. Focusing on field-level management data, MNM can identify those management practices that are currently imperative for enhancing smallholder farmers’ efficient use of fertilizers in their locality, thereby increasing productivity while reducing greenhouse gas (GHG) emissions. This document describes the background, design principles and development process of then MNM mobile phone application, as well as its pilot use in advisory practice in the Mbozi and Momba districts of Songwe region, Tanzania.

The provision of more tailored fertilizer management advice to smallholder farmers critically hinges upon – largely lacking – field-level management data, as management is key to efficient fertilizer use. The Maize-Nutrient-Manager (MNM) mobile phone application collects of such data at scale, and directly converts this data into actionable advice for the farmer. This data document describes the data collected with the MNM application (n=1038 records) in the Songwe region in Tanzania in the 2019-2020 season. In addition, this report provides information on the data collected through farmer Advice Forms (AF) one which the MNM advice was written. As these forms were simultaneously used by farmers as Field Records (FR) of in-season management practices, these forms constitute another source of data (n=723). This report presents some descriptive statistics on MNM use and management practices in the 2019- 20 season, but due to an incomplete data collection process (partially caused by COVID-19 travel restrictions), cannot present extensive analyses of the data collected. Analyses that can identify major yield determining factors and impacts of MNM use will be conducted in 2021, when 2019-20 yield data has been collected through the deployment of MNM (in November and December 2020) just before the start of the 2020-2021 season.

To mitigate climate change, greenhouse gas emissions from the agricultural sector need to decrease. In this light, increasing agronomic use efficiency of nitrogen (N) application (i.e., additional grain yield per kg of N applied) is a promising avenue to attain similar yields with less inputs in regions such as Europe (with high N inputs). In contrast, on the African continent, N inputs need to increase to raise yields, which may contribute to improved food security and prevent land use change. In such case, increasing agronomic N use efficiency (N-AE) and simultaneously increasing N inputs can also be a mitigation strategy by decreasing losses to the environment and improving profitability. In both contexts, it is relevant to understand how much N-AE can be increased in a certain location, compared to the current status, and which N source (organic and/or mineral fertilizer) will be most efficient. In this working paper we present ongoing work on N benchmarking from the crop nutrient gap project (full name: Bringing Climate Smart Agriculture practices to scale: assessing their contributions to narrow nutrient and yield gaps). First, we compare current observed N-AE to the values they could potentially reach under optimal agronomic management. For this, we propose a new benchmarking method based on recent insights on the shape of N response curves and introduce the related ‘degree of good agronomy’. Second, we compare the performance of mineral versus organic fertilizers for cereal cultivation on two continents (Europe and sub-Saharan Africa) based on large number of field experiments. Finally, we assess whether and how N-AE of mineral N fertilizer can be improved when combined with organic amendments. Preliminary findings show that the proposed benchmarking method can work but relies on availability of data on soil N supply, potential yield and attainable yields. Currently, this information is sparsely available which might be a barrier for uptake of the method. We show that N supplied by mineral fertilizers is taken up more efficiently than from organic sources, with variation depending on the type of organic amendment. Variation was larger for sites in Africa than Europe, which makes targeted fertilizer strategies less straightforward. Based on European experimental data, we show that organic amendments do not increase the N-AE of mineral fertilizer N application, most likely due to the increased total N availability. In future research, we hope to improve the data requirements for the proposed benchmarking method, assess drivers of variation for nitrogen fertilizer replacement values of organic amendments and disentangle effects of organic amendments on the efficiency of mineral fertilizer N use, while extending our analysis to tropical regions.

In many places on earth, livestock and feed production are decoupled, as feed is grown in one region and fed to livestock in another. This disrupts nutrient cycles by depleting resources in feed producing regions and accumulating resources in livestock areas, which leads to environmental degradation. One solution is to recouple livestock and feed production at a more local level, which enhances nutrient circularity. Recoupling livestock and feed production creates a natural ceiling for livestock numbers based on the feed producing capacity of a region. In this study we assess the consequences of recoupling livestock and feed production (i.e., by avoiding the import and export of animal feed) on ammonia and greenhouse gas (GHG) emissions, with and without feed-food competition. To this end, we used FOODSOM, an agro-ecological food system optimisation model representing the Dutch food system in this study. The Netherlands is one example of a region with high livestock densities and resource accumulation. We found that recoupling decreased livestock numbers (beef cattle: -100 %; dairy cattle: -29 %; broiler chickens: -57 %; laying hens: -67 %; pigs: -62 %; sheep -100 %) and animal-sourced food exports (-59 %) while still meeting the current human diet in the Netherlands. Consequently, ammonia emissions and GHG emissions decreased, and the nitrogen use efficiency increased from 31 % to 38 % at the food systems level. Recoupling alone was almost sufficient to meet national emission targets. Fully meeting these targets required further small changes in livestock numbers. Avoiding feed-food competition decreased livestock productivity and GHG emissions but did not improve nitrogen use efficiency. Total meat production could not meet domestic consumption levels while avoiding feed-food competition, and resulted in additional beef cattle. We show that recoupling livestock and feed production is a promising next step to enhance circularity while decreasing agricultures environmental impact.

Considering projected population trends, food requirements in East Africa will drastically increase in the coming decades (van Ittersum et al., 2016). One way to ensure supply will meet demand is by raising crop yields in the region. In East Africa, agricultural yields still have large potential to increase due to the large gaps between actual and potential yields. A recent study has shown that intensification of agriculture in regions with low current yields (such as in East Africa) is an option to reduce greenhouse gas emissions by avoiding or reducing agricultural land expansion into forests and/or grasslands, thus preserving carbon stocks (Van Loon, Hijbeek, ten Berge and Van Ittersum 2018, in prep). This is however only valid if higher yields are obtained with highly efficient use of fertilisers. For a successful implementation of such climate smart agricultural intensification, improved nutrient management options need to be economically viable for farmers in East Africa. It is however often unclear under which conditions agricultural intensification is beneficial for farmers’ income in sub saharan Africa (Marenya and Barrett, 2009; Place et al., 2003; Sheahan et al., 2013). Besides a number of good agricultural practices (such as improving planting densities and sound crop protection measures), farmers need to apply more nutrients to intensify production. The amounts of additional nutrients required represents the ‘nutrient gap’ between current nutrient applications and the total amount of nutrients removed from fields with increased yields (de Vries et al., 2017). Farmers can use several nutrient management options to close the nutrient gap (e.g. use mineral or organic fertilisers, split application of fertilisers, combine with local or hybrid seeds). The nutrient management option a farmer chooses not only affects his or her nutrient use efficiency (how much of the applied nutrients are recovered by the crop), but also his or her income generation and the contribution to greenhouse gas emissions. Some practices might be most beneficial for farmers’ income, but have a larger contribution to greenhouse gas emissions. Others might have the reversed effect. So far, trade-offs and/or synergies between farmers’ income and greenhouse gas mitigation as a function of nutrient management options have not been systematically assessed. Additionally, it is uncertain how such trade-offs or synergies might evolve over time, in cases where soil carbon and nutrient pools respond over longer time frames to the management exposed. We therefore address the following question: Can certain nutrient management practices be identified which are beneficial for both climate change mitigation and for farmers’ income in East Africa? The aim of this report is to develop a running prototype of a bio-economic model which can be used to assess trade-offs between yields, farmers ‘income and greenhouse gas emissions in function of different nutrient management options, both on the short and the long term. The proposed model will focus on nitrogen (N) as the main limiting nutrient, which is also highly relevant for greenhouse gas emissions (i.e. N2O). The model will be useful for R&D investors, agri-business (including fertiliser companies) and government agencies for ex ante assessment of specific nutrient management options.

Current initiatives to store carbon in soils as a measure to mitigate climate change are gaining momentum. Agriculture plays an important role in soil carbon initiatives, as almost 40% of the world's soils are currently used as cropland and grassland. Thus, a major research and policy question is how different agricultural management practices affect soil carbon sequestration. This working paper focuses on the impact of mineral fertiliser use on soil carbon sequestration, including synergies with the use of organic inputs (for example crop residues, animal manure) and trade-offs with greenhouse gas (GHG) emissions. Findings from scientific literature show that fertiliser use contributes to soil carbon sequestration in agriculture by increasing biomass production and by improving carbon:nitrogen (C:N) ratios of residues returned to the field. The use of mineral fertiliser can also support the maintenance of carbon stocks in non-agricultural land if improved fertility on agricultural land reduces demand for land conversion. Combining organic inputs with mineral fertiliser seems most promising to sequester carbon in agricultural soils. Increasing nutrient inputs (either organic or mineral fertilisers) may however lead to trade-offs with GHG emissions such as N2O. Improving the agronomic nitrogen use efficiency of nutrient inputs (i.e., additional grain yield per kg N applied) can alleviate this trade-off. While soil carbon sequestration can benefit soil fertility under some conditions and compensate for some GHG emissions related to agriculture (first assessments indicate up to 25% of the emissions related to crop production, depending on region and cropping system), it seems unlikely it can compensate for GHG emissions from other economic sectors. If soil carbon sequestration is a policy objective, priorities should be areas with higher storage potential (wetter and colder climates) and/or regions where synergies with soil fertility and food security are likely to occur (for example farming systems in tr! opical regions, on sandy soils and/or when cultivating more specialized crops). However, regions with the highest storage potential most likely do not overlap with regions where the largest benefits for soil fertility and food security occur.