Effects of Gypsum Enhanced Composts on Yield and Mineral Composition of Broccoli.

Gypsum (CaSO₄^.2H₂O) additions during composting of dairy manure or biosolids reduced ammonia nitrogen losses and provided a new way for odor control. However, the composts produced were not tested for plant nutrients and environmental concern elements uptake by plants. A field study using broccoli was conducted to evaluate the effects of these gypsum-enhanced composts on plant growth and element composition. Gypsum composts and composts without gypsum were applied to soil at the rate of 10 Mg ha^-1. Inorganic fertilizers N, P and K and unfertilized treatments were controls. Broccoli was harvested once per week for five consecutive weeks. Compared to composts without gypsum, gypsum biosolids compost significantly increased and gypsum dairy manure compost had a strong trend to increase total yields of broccoli. Gypsum dairy manure compost increased S concentration, whereas gypsum dairy manure and biosolids composts reduced Mo in broccoli flowers. Compared to inorganic fertilizers, gypsum dairy manure compost increased Ca, S, and Fe but decreased K, Mn, and Ni, while gypsum biosolids compost increased Ni and Zn but decreased P and Mo. Environmental concern element Ba was increased and Cd was decreased by gypsum dairy manure compost in broccoli flowers.