The significance of magnesium for crop quality

From the review “The significance of magnesium for crop quality“, of Jóska Gerendás and Hendrik Führs, published in Plant Soil

The importance of magnesium (Mg) as an essential plant nutrient is well established, the impact of Mg nutrition on quality parameters has only been rarely addressed.
Photosynthesis as the central process for crop production depends on the plant’s Mg status in several respect. Due to the complex roles of Mg in chlorophyll and protein biosynthesis severe Mg deficiency results in interveinal chlorosis of older and fully mature leaves as Mg is highly mobile within the plant.
This review aims at evaluating the available knowledge on the influence of Mg on produce quality. The question whether Mg application beyond yield optimum further improves crop quality is specifically addressed.
Increasing Mg supply on Mg-deficient sites tends to increase the quality of agricultural crops, particularly when the formation of quality traits is dependent on Mg-driven photosynthesis and assimilate translocation within the plant. In fruits and vegetables, ratios of Mg to other nutrients like Ca and K were shown to be a more reliable indicator of the quality response than the Mg status alone.
Decisive quality parameters important for horticultural crops like TSS and acidity are often more closely correlated with cation ratios, e.g. Ca/Mg and K/Mg rather than with Mg concentrations alone. Since Mg is capable of replacing Ca from binding sites, imbalanced Ca/Mg ratios in the tissue often negatively affect product quality.
It is concluded that Mg doses beyond those required for maximum yield rarely induce a further improvement of produce quality.