Addendum: Global mean nitrogen recovery efficiency in croplands can be enhanced by optimal nutrient, crop and soil management practices

In our recent publication titled "Global mean nitrogen recovery efficiency in croplands can be enhanced by optimal nutrient, crop and soil management practices" 1 , we presented a comprehensive analysis of the potential for improving nitrogen recovery efficiency (NUEr) in croplands worldwide through the adoption of optimized management practices.In the published version of the study, we assumed that current management practices across global croplands were entirely conventional.This assumption implied that the identified improvements from enhanced management practices would apply across all cropland areas.The approach did not consider the existing adoption of improved management practices in various regions, which may have caused an overestimation of the potential for enhancing NUEr globally. Estimation of the current adoption rates of improved management practicesTo assess whether this assumption has significantly influenced the potential for further enhancements in NUE, we have now incorporated an estimate of the current adoption rates of improved agronomic measures.This involved creating detailed maps of current agronomic measures using methodologies outlined by Lessmann et al. 2 .The datasets utilized included Kppen-Geiger climate classification map 3 , SPAM for land use 4 , maps of nitrogen fertilizer application rates 5 , nitrogen manure production and application rates 6 , global tillage system dataset 7 , FAO databases on cropping systems 8 , crop residue retention 9 , and crop residue burning 10 .These datasets facilitated a more accurate representation of current agronomic measures and their spatial distribution.The assessment of agronomic measures covered various practices related to (i) nutrient management, including enhanced efficiency fertilizer, combined fertilizer, organic fertilizer, fertilizer placement, timing and rate, (ii) crop management, including crop residue retention, cover cropping and crop rotation, and (iii) soil management, including zero and reduced tillage.Combined and organic fertilizers were applied only in regions where part of the manure was not yet utilized.Enhanced efficiency fertilizer and optimized fertilizer placement and timing were only applied in low-technology cropland areas, used SPAM data 4 to identify those areas (>50% of cropland), assuming that in high-technology areas these practices are already applied.Adjusting fertilizer rates focused on areas with low nitrogen use efficiency (NUE <0.5), based on the global NUE map derived with the IMAGE model as used by Schulte-Uebbing et al. 11 .Increased crop residue retention was assumed applicable in regions where burning of crop residues was common (>25% cropland), while cover cropping was applied in areas where in less than 25% of the area catch crops were used.Cover cropping was applied in regions (grid cells) with a cropping intensity of less than one harvest per year, as defined in the GCI (Global Cropping Intensity) dataset 12 , indicating fallow or partially cropped areas.Both zero and reduced tillage (conservation agriculture) were applied in regions with high or intermediate tillage (<50% cropland). Revised estimation of potential increase in nitrogen recovery efficiency by improved managementConsidering the areas where it is likely that improved measures are already applied, the potential for further improvement in NUEr is substantially lower than initially estimated.This impact on the results is reflected in the updated maps presented in this Addendum as Figs. 1, 2, replacing the original Figs. 4 and 5 in ref. 1. Figure 1 presents the spatial variation in the mean,