The efficiency of phosphorus (P) use in agriculture needs to be improved, with farmers being increasingly forced by law to reduce P soil fertilization. Thus, P foliar application might become more important in agriculture. The effect of foliar P fertilization has not been widely studied in maize, despite it being a crop with high P demand during juvenile development. Our aim was to investigate the effect of P foliar application during juvenile development on maize crop growth and yield. We conducted outdoor pot experiments to investigate the effect on P uptake, translocation, and dry matter following three applications of foliar fertilizer of various P formulations and with additional P soil fertilization between the 4th and 6th leaf stage during two growing seasons. To determine direct and possible long-term effects, plants were harvested at various developmental stages. P foliar application resulted in a significant increase in P concentration in all plant parts ten days after the last application, regardless of P form, nutritional status, or year. P concentration remained high only in those parts of the plant that were present during foliar application. Biomass effects were sporadically visible until flowering, but not at maturity. We conclude that foliar P fertilization during juvenile development does not increase yield but might nevertheless be a useful remedy for short-term P deficits.

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.