Potassium and iron are both considered essential nutrients for plant growth. Mineral weathering and the release of potassium and iron are the major sources supplying these nutrient elements in many soils, particularly, the soils of arid and semiarid regions. Carbonates are among the most common soil components in arid and semiarid regions and profoundly influence the soil physical and chemical characteristics including the release rate of nutrient elements from soil minerals. Too many investigations have so far been carried out on the factors controlling potassium and iron release from soil minerals. However, no research has yet been conducted on the role of organic matter to alleviate the adverse effects of carbonates on the release of K and Fe from micaceous minerals. In this research, the effect of carbonates and organic matter and their interaction on the release of K and Fe from phlogopite and their uptake by alfalfa were studied under greenhouse conditions. Treatments included 5 levels of carbonate content (0, 2, 5, 12, and 25%) and 4 levels of organic matter content (0, 0.25, 0.5, and 1%) with factorial arrangement using a completely randomized design with 3 replications. A total of 60 pots were used. Pots were irrigated with Fe- and K-free nutrient solution during the growing period and the release of Fe and from phlogopite was the sole source of these elements for plants. Shoots and roots were harvested after a period of 210 days. Shoot and root dry weight as well as the concentration of K, Fe, and Ca were measured. The results indicated that as the rate of carbonate addition to the plant growth medium increases, the mean concentration of K and Fe in shoot and root decreases. It seems that with increase in carbonate percentage and the hydrolysis of calcium carbonate, the concentration of Ca increases in soil solution, which in turn, changes the ratios of K/Ca and Fe/Ca in plant growth medium. Therefore, the uptake rate of K and Fe by plants decreases and the yield and quality of plant also decrease. As organic matter and its decomposition rate in growth medium and organic acids production increase, the conditions of plant growth medium improve in terms of mineral weathering and K and Fe release. In other words, as the organic matter content increases in carbonatic plant growth media, the ratios of K/Ca and Fe/Ca improve as such that the uptake of both nutrients by plant greatly improves. This indicates that organic matter can, to some extent, compensate the adverse effects of carbonates on plant yield and quality. Keywords: Potassium and iron release, Phlogopite, Carbonates, Organic matter