Acidified Biogas Residues Improve Nutrient Uptake and Growth of Young Maize

Biogas residues (BGR) contain a variety of plant nutrients and are, therefore, valuable fertilizers. However, ammonia (NH3) emissions occur during slurry and BGR application. These emissions can be reduced by lowering the pH of the BGR. Acidification technology works well for slurry, but little is known about the effects on fertilizer properties of acidified BGR (ABGR). This study aimed to examine the impact of acidification on the chemical composition of BGR and its influence on plant growth of juvenile maize and the soil pH, as well as the soluble soil phosphorous (P) and manganese (Mn), after application of ABGR. The soluble amount of nutrients in BGR was compared with that in ABGR. In an outdoor pot experiment, BGR and ABGR were incorporated in soil, and maize was grown for 8 weeks. Two different BGR P levels were compared with (NH4)2HPO4 and a control treatment without additional P. BGR acidification increased dissolved amounts of P from 15% to 44%, calcium from 6% to 59%, magnesium from 7% to 37%, and Mn from 2% to 15%. The dry matter of ABGR-fertilized maize was 34%, 45% higher than that of BGR-fertilized maize. The soluble Mn content in the soil was 74% higher with the low ABGR dose and 222% higher with the higher ABGR dose than the BGR treatments. The fertilizer efficiency of ABGR was higher than that of BGR, indicating that the absolute amount of applied fertilizer could be reduced in systems using ABGR.