Concentrated Humus Improves Nutrient Utilization Note: John & Bob's Soil Optimizer consists of the concentrated humus used for this study along with three other organic ingredients to maximize benefits by blending calcium, iron, and soluble concentrated humus. This chart summarizes the results of 24 published studies of concentrated humus and nutrient uptake. Of all these nutrients uptake was increased consistently except for sulfate and manganese. Chart adapted from page 375 of S. Nardi, 1996 .