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Abstract
The effects of climatic conditions and plant nutrition on the appearance of Mg deficiency in tomatoes (Lycopersicon esculentum Mill.) grown in rockwool were studied. Humid conditions as a consequence of double glass layers and thermal screens aggravated Mg deficiency symptoms. Raising the temperature in the root environment from 19 to 24C lessened the symptoms.
High EC‐values in the root environment, obtained by increased nutrient concentrations, strongly increased Mg deficiency symptoms. High as well as low K/Ca ratios reduced the symptoms. With respect to cation ratios, however, the most striking effect was found with the relative Mg content. In nutrient solutions, the supplied Mg appears to be at least 9% of the cations and in the root environment at least 16%.
Yields were not affected by slight and moderate Mg deficiency symptoms. Severe deficiencies hampered fruit setting and reduced yields.
Magnesium concentration of leaf tissues usually displayed a close relationship with the extent of the symptoms. However, prediction of Mg deficiency symptoms by means of tissue analyses was somewhat dependent on plant age and tissue sampled. A concentration of about 150 mmol Mg per kg dry matter was sufficient to prevent severe deficiencies.