Effect of gypsum on potassium and iron release from phlogopite to alfalfa

This study evaluated the effects of gypsum on the release rate of potassium (K) and iron (Fe) from phlogopite to alfalfa under greenhouse conditions. The medium was a mixture of quartz sand as filling material, K- and Fe-bearing micaceous mineral (phlogopite) and different levels of gypsum (0%, 2%, 5%, 12% and 25%). During the 6-month cultivation period, the pots were irrigated and/or fed with distilled water and four different nutrient solutions. The results showed statistically significant effects of different levels of gypsum on dry weight and K and Fe concentration of shoots and roots. It seems that an increase in calcium (Ca) concentration, due to the addition of gypsum, changes the equilibrium of K and Fe in the root zone and plant tissues. The results of this study show that the rate of K and Fe release from micaceous minerals is extremely reduced in the presence of gypsum.