Evidence map of the benefits of enhanced-efficiency fertilisers for the environment, nutrient use efficiency, soil fertility, and crop production

The identification of sustainable fertilisation practices is essential to reduce agriculture’s impact on the environment while insuring sufficient crop production. The use of enhanced efficiency fertilisers (EEFs) is thought to improve nitrogen (N)-fertiliser uptake by crops while reducing nutrient losses to the environment. EEFs’ performance has been assessed in several meta-analyses and systematic reviews, which are heterogeneous in content and quality of reporting. This provides fragmented information and makes it difficult to conclude about their ability to provide more sustainable fertilisation. Here we synthetise evidence from 26 meta-analyses and reviews selected by a systematic literature search to describe the separate effects of four commonly used EEFs—nitrification inhibitors, urease inhibitors, double inhibitors, or controlled-release fertilisers—on the environment, nutrient use efficiency, soil fertility, and crop production. A unique contribution of this review is the assessment of the quality of the selected papers and the synthesis of their results through a systematic framework. Results showed that compared to conventional fertilisers, EEFs generally increased soil nutrients, crop yield, and N use efficiency, and reduced N leaching, emissions of greenhouse gases and air pollutants. Some differences were found between the different EEFs; while urease inhibitors, double inhibitors, and controlled-released fertilisers decreased ammonia emission compared to conventional fertilisers, nitrification inhibitors increased these emissions or did not affect them. The results were consistent when excluding low-quality studies from the analyses. Overall, this global synthesis indicates that EEFs could maintain crop yields while reducing some of the negative environmental impacts of conventional N-fertilisers. Attention should be paid to the potential increase of ammonia emissions by nitrification inhibitors and additional evidence is needed on the potential side effects on soil health, biodiversity, and water quality.