Poultry litter hydrochar as an amendment for sandy soils

Abstract

The conversion of poultry litter to hydrochar has been proposed for stabilization of the soils and to eliminate pathogens. Still, research on the hydrochar's effect on soil properties as a function of production temperature, and its direct use with plants is limited in general and even less so on poultry litter. We characterized poultry litter hydrochar as an amendment for sandy soils in terms of changes to the soil's bulk density, porosity, water-retention capacity, and fertility. Soil bulk density, porosity and water-retention capacity were determined in a pneumatic tension plate system for sand with hydrochar-amendment rates of 0.5, 1 and 2%, and hydrochar-production temperature of 180, 220, and 250 °C. Soil fertility was assessed by growing lettuce seedlings in a randomized block design planter experiment, consisting of 16 blocks that were sampled every 10 days. The addition of poultry litter hydrochar resulted in decreased soil bulk density. Soil porosity increased with hydrochar generated at a temperature of up to 220 °C, and decreased with hydrochar generated at 250 °C. Soil water content increased as compared to unamended sand, but decreased with increasing hydrochar-production temperature, probably due to increasing hydrophobicity of the poultry litter hydrochar. The addition of hydrochar at concentrations of 0.5 and 1% resulted in improved plant growth despite an initial delay. While increased soil moisture due to increased soil water-retention capacity was confirmed, it did not seem to be responsible for the improved plant growth. It was also demonstrated for the first time that hydrochar decreases nitrate leaching from soils. Therefore, poultry litter-derived hydrochar seems to be an adequate amendment for sandy soils.

Keywords: Fertilizer; Hydrothermal carbonization; Plant growth; Soil fertility; Soil water-retention capacity.