Manganese functions primarily as a part of enzyme systems in plants. It activates several important metabolic reactions and plays a direct role in photosynthesis. Manganese accelerates germination and maturity, while increasing the availability of phosphate and calcium. Deficiency symptoms first appear on the younger leaves with yellowing between the veins – and sometimes brownish-black specks. Deficiencies occur most often on high organic matter soils, and on those soils with neutral to alkaline pH. Symptoms are most severe during cool spring months when soils are sometimes water logged.