EFFECT of digestates derived from the fermentation of maize-legume intercropped culture and maize monoculture application on soil properties and plant biomass production

Background The use of maize-legume mixed culture to produce renewable energy and fertilizers by anaerobic fermentation (AD), while respecting soil quality is a favourable approach in sustainable farming. This paper investigates how the substrate (silage) composition affects the quality of digestate and thus its effect on selected soil parameters (respiration, content of carbon and nitrogen). The high content of remaining nutrients (mainly N) in the AD residual biomass of digestate may increase the biomass of amended plants. One objective of this study was to determine the composition of different digestates produced by anaerobic fermentation of the biomass of intercropped (mixed) cultures. Other objectives focused the digestate impact on soil properties and yield of tested plant (lettuce) in a pot experiment, carried out under controlled conditions in the growth chamber for 6 weeks. Variants tested in the pot experiment included negative control, maize ( Zea mays L.) digestate, broad bean ( Vicia faba L.) digestate, white lupine ( Lupinus albus L.) digestate, maize + broad bean digestate, maize + white lupine digestate. Results As compared to maize, silage from the mixed culture (or legumes) positively affected the properties of digestate (content of N, P, K, Acid Detergent Fibre (ADF), Neutral Detergent Fibre (NDF), Acid Detergent Lignin (ADL). The effect of digestate application on soil parameters depended on the digestate composition: the highest basal respiration was induced by digestates with the increased content of dry matter and ADF – maize + broad bean and white lupine. The broad bean variant showed glucose-induced respiration 0.75 (μg CO 2 ·g -1 h -1 ), while the lowest value was in the maize variant (0.45 μg CO 2 ·g -1 h -1 ). The application of digestate derived from the mixed culture increased the plant biomass more than that of single maize silage digestate (+ 14% in the maize + broad bean variant and + 33% in the maize + white lupine variant). Conclusions A potential was found of silage made of leguminous plants to increase the digestate N content. Nevertheless, it is desirable to increase the C/N ratio by raising the amount of C containing substances. Fertilization with digestate showed a potential to increase the plant biomass (compared to the unfertilized control); however, differences among the individual digestates were not observed. The benefit of legume added to the maize-based silage was proven, especially the contribution of nutrien