Publications

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.