Climate smart agriculture and global food-crop production

(Rule 1), the reduction in GHG emissions is estimated to be equivalent to 44 Mt CO2 e yr-1 (9– 77 Mt CO2 e yr-1). The reduction of emissions is significantly higher with Rule 2, 101 Mt CO2 e yr-1 (84–124 Mt CO2 e yr-1). This shows that there is a substantial amount of area in which CSA practices can increase yields but do not reduce GHG emissions. The higher levels of emis- sions abatement come at the cost of production. On average across climate scenarios, under Rule 2 total cumulative production for the three crops is reduced by 21 Mt yr-1 (1 and 53) of fresh matter harvest compared to Rule 1. This is equivalent to 1% (0.1 and 2%) of total yearly global production of maize, wheat and rice. It is important to note that the effects on emissions vary from country to country and that we find instances in which an increase in emissions occurs in some countries (Fig 3 and Sup- plementary Table S11 in S1 File). Emissions can increase because of the potentially large changes in countries’ crop harvested areas and yields. Total emissions can increase even when a reduction of emission intensity is achieved if the reduction in emissions per unit of output is offset by increases in yields or in areas (Supplementary Discussion S10 with Supplementary Table S11 in S1 File). 3.3 Other effects related to emissions Interestingly, part of the reduction in emissions is due to the effects on soil organic carbon concentration, which is estimated to grow compared to BAU by 0.11 t ha-1 yr-1 (0–0.49 t ha-1

yr-1) over the area that adopts the alternative practices based on Rule 1, and by 0.14 t ha-1 yr-1 (0.01–0.53 t ha-1 yr-1) based on Rule 2. These changes are beneficial for sustainable production and resilience since higher soil organic carbon concentrations increase soils nutrient availabil- ity and soils water retention. Some potentially important effects on land use must be noted. The combination of higher yields and lower prices reduces producers’ incentives to expand production onto additional land as the demand for wheat and rice can be satisfied with less harvested area (Supplementary Table S12 in S1 File). Even though global harvested area for maize is projected to expand by 1 million hectares in 2050, on average across Rule 1 and 2 the net effect is a decrease in total har- vested areas for the three crops estimated at 10 million hectares (3–27 million hectares) Fig 2. Percent change in production (total output) and prices comparing years 2010 and 2050 for BAU and CSA adoption scenarios. Columns indicate the average tailoring of CSA practices; whisker bars identify results for the poor and optimal tailoring. Source: Authors. BAU = business as usual scenario. https://doi.org/10.1371/journal.pone.0231764.g002 PLOS ONE Climate smart agriculture and global food-crop production PLOS ONE | https://doi.org/10.1371/journal.pone.0231764 April 29, 2020 9 / 19