Influence of anaerobic digestate type on nitrogen dynamics and leaching losses across two soils

Abstract

To enhance soil fertility and subsequent crop yields, digestate, byproduct of anaerobic digestion, can serve as a supplement or potential alternative to chemical fertilizers when sensibly utilized. This study assessed the impact of two types of digestates on two distinct soils for the perspective of agriculture (affecting pH, EC, organic carbon and mineral nitrogen) and environment (mineral nitrogen leaching under two rainfall patterns). Both soils mainly differed in silt and sand contents: 32% silt and 47% sand for soil-1 and 42% silt and 39% sand for soil-2. Two sets of controlled experiments served the purpose, in which first set involved a soil incubation experiment, applying two digestates to two soil types at 28°C for 60 days. The second set comprised reconstituted soil columns to collect soil solutions at depths of 2.5 cm and 7.5 cm after rainfall application under two patterns for 45 days. Results indicated that application of both digestates in test soils initially increased pH at day 15, followed by a decrease at days 30 and 60. Both digestates significantly elevated soil electrical conductivity compared to control treatments in both soils. Organic carbon content displayed variable impacts, with a slight decrease for solid digestate (12%) and higher decrease for liquid-amended soil (43%) for soil-1. While a significant decrease was observed for soil-2 throughout the incubation period for both amendments (34% and 36% for solid and liquid amended soils respectively). Rapid nitrification occurred with the application of both digestates in both soils, albeit at different rates. Soil-2 exhibited 1.2 to 2 folds higher net nitrification rate (depending upon digestate type and days of incubation) compared to soil-1. Liquid digestate induced more mineral nitrogen compared to solid digestate in both soils. Interestingly, rainfall frequency, digestate type, and soil type influenced the leaching of ammonium and nitrates, with nitrates recording higher levels in both soils, at both depths, and under both rainfall patterns.