In the first greenhouse experiment, the requirements for all the essential nutrients were studied in a subtractive design using PG. Significant growth reductions were obtained with the singular elimination of all nutrients except B. Growth on the two FGDG materials was poor due to the presence of high levels of soluble salts. These materials were leached before being studied in the second experiment in which only N, P, and K were varied at constant basal rates of the other essential elements. The 100N-50P-150K (mg kg⁻¹) treatment proved to be the best for total plant growth on all three gypsum materials. The results indicate that providing the proper nutrient balance is important in obtaining good growth on by-product gypsum materials.

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