Human appropriation of biogenic silicon – the increasing role of agriculture

Summary Terrestrial plants create roughly 84 Tmol biogenic silicon ( BS i) each year. This substantial uptake of dissolved silicon ( DS i) by land plants represents an important, yet often overlooked, pathway of Si on the global scale. Agricultural crops account for ~35% of BS i created by land plants globally due to a combination of large biomass and relatively high Si concentrations in the tissue of many crops. In this review, we investigate the global importance of terrestrial BS i fixation by agricultural crops. Using annual data from 1961 to 2012 of the 10 most important crops (ranked by mass produced globally), we quantify how agriculture has altered the amount of BS i created on land. Over this time period, average annual BS i production by the top 10 crops tripled globally, increasing by an additional 39 Gmol Si each year. We refer to this BS i in agricultural crops as human‐appropriated biogenic Si ( HABS i). Based on projected increases in human populations and land cover change, HABS i is projected to increase by 22–35% by 2050. Human agricultural practices are increasing the size of relatively labile plant BS i pool on land. Considering its bioavailable nature, we suggest that increasing plant BS i on land has the capacity to alter Si availability in downstream receiving waters, although this depends on the fate of harvesting and threshing losses, which varies substantially across the globe. We highlight similarities between the N, P and Si cycles in agricultural settings, such as the often unidirectional flow of Si away from croplands (similar to N) and soil BS i depletion (similar to P). We then address how changing human diets will continue to alter plant BS i cycling in future decades.