A test kit for determining the “volatile ammonia content” of biological samples comprising any wet or dry compost, manure, plasma or soil sample. The kit includes a transparent container for holding the sample, and a reactant chemistry gel system, located within the container in the space not occupied by the sample. The reactant mass includes an acidic pH reactant material, and a color change indicator material, responsive to pH changes in the reactant material. Ammonia vapors diffuse into the reactant material, reacting chemically with the acidic pH reactant material so as to produce a color change. The nature of the color change is an indication of the quantity of NH3 in the test-jar atmosphere, which in combination with the known pH of the sample, indicates the total ammonium in the biological sample.