Soil–wheat nutrient interactions following fertilization with digestate from one- and two-stage molasses anaerobic digestion: a field study

Sustainable soil management besides ecologically friendly alternatives to mineral fertilizers, requires also bioconversion technologies capable of generating soil amendments with targeted agronomic functions. Two-stage system of anaerobic digestion with spatial separation of processes into two bioreactors allows to obtain two-stage digestate (2-SD), which possibly differs from conventional one-stage digestate (1-SD). This study evaluated whether these process-derived differences translate into fertilizing properties of digestates, altered soil functioning and plant responses. A field experiment with wheat comparing 2-SD digestate with 1-SD digestate, synthetic fertilization (SF), reffered to unfertilized control (NF) was performed. Soil physicochemical properties, plant nutrient status, digestate chemistry and microbial consortia were analyzed. Soil–plant interactions were assessed through root nutrient transporters genes expression and finally crop yield was determinated. Compared with 1-SD, 2-SD digestate exhibited a higher mineralization degree and distinct microbial diversity, indicating different chemical and microbiological functionality. Only bioavailable phosphorus was increased in soil treated with 1-SD digestate. Both digestates treatments enhanced root TaAMT1.2 gene expression, altering nitrogen acquisition pattern. 2-SD digestate treatment caused stronger yield response than 1-SD (2.8 t ha −1 vs 2.1 t ha −1 ), while both maintained soil pH stability unlike SF. Crop performance was slightly associated with soil pH and TaPHT1.10 gene expression. Findings demonstrate that 2-SD digestate is a functionally distinct, more mineralized, biologically active soil amendment from 1-SD digestate. Both with specific effects on soil chemistry, plant nutrient uptake patterns and enhanced productivity, highlighting two-stage anaerobic digestion as a promising source for circular nutrient management in cereal tillage.