Agronomic Evaluation of Liquid Humus Derived From Earthworm Humic Substances

Carbon (C), commonly expressed as organic matter (OM), is of vital importance in soil productivity. Liquid humus is an alkaline suspension containing humic and fulvic acids, which can facilitate C addition to the soil through the irrigation system to increase OM and soil fertility levels. Two liquid humus products were formulated from earthworm humic substances and the effects of these and other commercial products derived from leonardite, on soil and ryegrass were evaluated in a pot experiment under greenhouse conditions. On average, C application, regardless of source, increased the aerial and root dry matter, plant greenness, nitrogen (N), phosphorus (P), and potassium (K) uptake, and nutrient use efficiency. Carbon effects on plant production were larger when added over fertilized plants. Residual soil N was lowered by the application of liquid humus. No significant effect of C rate was observed on soil pH or electrical conductivity (EC) at the end of the experiment. Optimal C rates found in this study were higher than the recommended commercial ones. No major differences among earthworm liquid humus and leonardite-based products were observed; therefore the former would constitute a more sustainable alternative for organic matter additions as they are made from a renewable resource.