Critical Concentrations

Tissue Magnesium Concentration Associations with Crop Yields

The magnesium concentration of tissues considered as deficient, sufficient, or toxic depends on what growth parameter is being measured in the crops. In many food crops, classification of nutrient sufficiency is based on harvestable yields and quality of the edible plant parts (198). In ornamental plants, sufficiency values are based on plant growth rate and visual quality of the vegetative and reproductive organs. In forestry, ratings are based on rate of growth and wood quantity and quality. For example, in birch (Betula pendula Roth.) seedlings, magnesium sufficiency levels in leaves were correlated with relative growth rate (36). Based on their studies, maximum growth rate was correlated with a mature healthy leaf magnesium concentration of 0.14%, a concentration that was considered deficient for rough lemon (Citrus jambhiri Lush.) production (28).

Austin et al. (199) reported that magnesium concentrations in taro (Colocasia esculenta Schott) varied from 0.07 to 0.42% with hydroponically grown plants and noted that growth parameters (biomass, leaf area, nutrient concentrations) did not vary as the magnesium in solution varied from 1.20 to 19.2 mg L^-1. In corn, optimal leaf magnesium concentrations were determined to range between 0.13 and 0.18% for maximum corn yields (198). With peach (Prunus persica Batsch.), the critical concentration or marginal level of magnesium in leaves was determined to be about 0.2% of the dry mass based on the appearance of symptoms of deficiency but with no growth suppression at this concentration (200).

Tabulated Data of Concentrations by Crops

In most commercially grown crops, magnesium concentrations average between 0.1 and 0.5% on a dry weight basis (29). However, total magnesium concentration may vary considerably between different plant families. The legumes (Leguminosae or Fabaceae) can have nearly double the magnesium concentration as most cereal crops (201). Likewise, oil seed crops and root crops can also contain high concentrations of magnesium (201). A tabulated description of magnesium concentrations for different crops is presented in Table 6.1.

TABLE 6.1

Ranges of Magnesium Concentrations in Different Crops, Which Were Considered Deficient, Sufficient, or Excessive, Depending on the Crop and the Crop Yield Component Being Considered

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