Agronomic Use of Slurry from Anaerobic Digestion of Agroindustrial Residues: Effects on Crop and Soil

Abstract

In a greenhouse experiment we evaluated the application of slurry generated by a biogas reactor of agroindustrial residues. The objectives of this study were to determine the response to slurry application on dry matter production and nutrients absorption of Setaria italica (setaria), and to evaluate the effect of the slurry on soil properties. Two soils, of different texture, were mixed either with slurry or with diammonium phofsphate (DAP) at 0, 80, and160 kgN ha-1 equivalent rates. The setaria was harvested 68 days after planting, and separated into leaves plus stems, ears, and roots. Total biomass and content of N, P, K, Ca, Mg, Cu, Fe, Mn, and Zn were determined in each fraction. In the soil we determined pH, electric conductivity (EC), organic C, available P, mineral N, and exchangeable cations. Although the biomass produced and the amounts of nutrients absorbed were different in the two soils, in both of them setaria responded to the slurry application. The amounts of N absorbed from slurry and DAP were similar, indicating that the N from the slurry was readily available. The slurry application also increased the absorption of other macro and micro nutrients (P, Ca, Mg, and Zn). No significant changes in soil exchangeable cations, pH, and EC were observed at setaria harvest. In the silty soil the crop almost depleted the mineral N in all treatments, but in the sandy soil large amounts were left, especially in the treatments with slurry. This fact highlights the importance of a careful dosage of this soil amendment, to avoid the excess of mineral N, which is potential pollutant for the environment. It can be concluded that the use of slurry from the reactor had a positive effect on the nutrients availability, without negative effects on soil properties.