Digestate Not Only Affects Nutrient Availability but Also Soil Quality Indicators

Digestate contains many essential nutrients for crops, including nitrogen (N) and phosphorus (P), and it can alter the biogeochemical cycle of nutrients and soil functionality. This work aimed to assess the fertilizing effects of digestate on chemical and biological soil properties in a field experiment in eastern Portugal with two horticultural crops involving nine treatments: control without fertilization; mineral N fertilization with 85 kg ha(-1); fertilization with digestate (DG) with increasing N rates (85, 170, 255, or 340 kg N ha(-1)); and fertilization with different combinations of digestate plus mineral N (DG at 85 or 170 kg N plus 60 kg mineral N ha(-1) or DG at 170 kg N plus 25 kg mineral N ha(-1)). In addition to N, digestate supplied significant amounts of P, Ca, K, and Mg and significantly increased soil Olsen P, mineral N, and organic C. At high doses, it decreased phosphatase and beta-glucosidase activities, as well as fungi and bacterial biomass, compared to the control or mineral N fertilization, and it also negatively affected soil P and C cycling capacity and microbial biomass. The organic to total N ratio and the N to P ratio in digestate are crucial properties for evaluating its agronomic management as fertilizer.

Automated summary

This study aimed to assess the fertilizing effects of digestate on soil properties. The results showed that digestate not only contains essential nutrients for crops but also can alter the biogeochemical cycle of nutrients and soil functionality. However, at high doses, digestate application negatively affected soil enzyme activities, microbial biomass, and soil P and C cycling capacity.