Transforming waste to wealth: Impact of food waste-derived soil amendments and synthetic nitrogen fertilizer on soil dynamics

Approximately one-third of all food produced globally goes to waste, highlight-ing the need for sustainable waste management technologies like composting and anaerobic digestion. These technologies convert food waste into soil amend-ment products such as compost, liquid digestate (LD) and solid digestate (SD).However, these food waste-derived soil amendments have relatively low nu-trient contents compared with synthetic nitrogen (N) fertilizers such as urea,making their agricultural use challenging. Despite this, food waste-derived soil amendments can enhance the physical and biological properties of soil, poten-tially creating synergistic effects when combined with synthetic N fertilizers. This study aimed to investigate effects of food waste-derived amendments in soilapplied at 50 kg ha −1 total N (compost, LD or SD) and synthetic N fertilizer [ureaammonium nitrate (UAN)] at 50 and 100 kg ha −1 total N. Over 56 days of soilincubation, greenhouse gases (CO 2 , N 2 O), soil chemistry (NH+4 –N, NO−3 –N, pH)and microbial biomass C (MBC) were measured. Results showed that LD + UAN50 reduced cumulative N 2 O emissions by 23% compared with UAN 100, despitehaving the same total N and similar available N rate applied to soil. ReplacingUAN with LD in farming practices can supply equivalent available N whilelowering N 2 O emissions, offering a sustainable nutrient strategy. Moreover, ap-plying food waste-derived soil amendments can enhance N retention in soils,reducing the need for increased applications of synthetic N fertilizers to com-pensate for N deficits in farming. Food waste-derived soil amendments can alsoact as a slower N release compared with UAN, reducing nitrogen run-off. SD hadthe highest CO 2 emissions, followed by LD and compost. SD + UAN 50 increasedMBC levels because of higher carbon content and labile carbon, and available Nbecause of the application of UAN. The major drawback of using SD comparedwith LD is that the process of evaporating LD to form SD causes high ammonia