Deficiency diseases are diseases caused by a lack of essential vitamins or mineral ions. Scurvy is a deficiency disease historically found in sailors who did not have enough fresh fruit or vegetables, so were deficient in Vitamin C. Plants suffer from deficiency diseases when they do not have enough mineral ions.
Plants use nitrates as a supply of nitrogen, which is needed to make proteins for healthy growth. Plants absorb nitrates in water through their roots. Nitrates are present in high levels in plant fertilisers.
Without nitrates, the amount of chlorophyll in leaves reduces. This means leaves turn a pale green or yellow colour. This reduces the plant's ability to photosynthesise and grow properly, which reduces the farmers' crop yield. Farmers or gardeners can add chemical or natural fertilisers, such as manure to increase nitrate levels.
Plants use magnesium ions to make chlorophyll in their leaves. Like in nitrate deficiency, the plant is limited in terms of its photosynthetic ability and the plant growth is compromised. Magnesium is a limiting factor in healthy plant growth.