The Effect of an Organic Soil Amendment on Soil Microbial Activity and Corn Performance.

Soil microbial activity is often used as a biological indicator since microbes are sensitive and respond rapidly to soil alteration. A soil amendment product that increases microbial activity could be beneficial to the soil’s overall health. In 2013 we studied the effect of inorganic fertilizer and organic soil amendments on soil microbial activity and field corn yield. The organic amendment, GreatGrow (GG), is a proprietary mixture of microorganisms, fermented chicken manure, plus oyster and crab shells. The study was conducted at two field sites (one irrigated; one non-irrigated) on Maryland’s Eastern Shore. Each site contained six soil treatments in a randomized complete block design with four replications. The treatments were control (no amendment or fertilizer), ½ strength GG (100 lbs acre^-1), full strength GG (200 lbs acre^-1), 2x strength GG (400 lbs acre^-1), full strength inorganic (based on soil test), and a mixture of ½ strength GG and ½ strength inorganic.  The soil treatments were applied in the spring prior to corn planting, and all samples were collected in the fall at or near harvest.  Seven microbial activity measurements were carried out on the soil samples: substrate induced respiration (SIR), sediment basal respiration, community level physiological profiling, biomass carbon, nitrogen mineralization, dehydrogenase activity, and fluorescein diacetate (FDA) hydrolysis. We also measured corn height, yield, and several soil physical and chemical properties. SIR, FDA hydrolysis, and dehydrogenase activity appear to be more sensitive measurements of soil microbial activity. The inorganic amendment resulted in the highest corn yield and height. GG did not increase corn height or yield over the control. We are repeating this experiment in 2014 with some modification.