The Multifactorial Effect of Digestate on the Availability of Soil Elements and Grain Yield and Its Mineral Profile—The Case of Maize

Abstract

The fertilizer value of digestate (a biogas plant byproduct) depends on its impact on the availability of soil nutrients and on the concentration of minerals, including heavy metals, in the edible crop parts. This hypothesis was verified in field experiments with maize conducted in the years 2014, 2015, and 2016 in Brody, Poland. The two-factorial experiment consisted of the digestate application method and its rate: 0.2, 0.4, and 0.8 t ha−1. Maize yield in consecutive years fitted the quadratic regression model, reaching a maximum grain yield of 11.5, 10.8, and 9.2 t ha−1 for an optimum digestate rate of 0.56, 0.66, and 0.62 t ha−1, respectively. The supply of N-NO3 to maize, concomitant with a shortage of magnesium and iron, was the key factor limiting the grain yield. Cadmium concentration in maize grain exceeded its threshold content in plants fertilized with digestate. An excessive concentration of lead in grain was recorded in the dry season 2015. Cadmium concentration in grain was controlled by the availability of soil Fe and Pb by a shortage of N-NO3, zinc, and copper. The negative relationship of Pb with K, Na, Zn, and Fe contents in grain suggests their usefulness as agents to reduce the accumulation of heavy metals.