Magnesium Deficiency of Tomato in Calcareous Soil Under Solar Greenhouse.

Magnesium deficiency of tomato in calcareous soil under solar greenhouse Zhujun Chen*, Huimin Wang, Wenyan Zhao, Jianbin Zhou College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Yangling, Shaanxi 712100, China Email of the corresponding author: zjchen@nwsuaf.edu.cn Key words: Magnesium deficiency; K and Mg ratio; soil salinization; solar greenhouse Magnesium (Mg) deficiency is usually common in plants growing on coarse-texture acidic soils. However, Mg deficiency becomes common in recent years for tomato grown in solar greenhouse in Loess Plateau, China, where the soil is calcareous one. To find the reasons of tomato Mg deficiency, we had determined the concentrations and activities of soluble ions, especially Mg2+, Ca2+, K+ ions in soils with the different ages and the different degrees of Mg deficiency of tomato in different solar greenhouses. It indicated that the concentrations of Ca2+, K+, NO3- ions in soil increased linearly as the aging of solar greenhouse. Ca2+ ion was the dominate cation ions in the soluble salt, and NO3- ion became the dominate anion ions after 5-year cultivating. There were significant relationships between Ca2+ and NO3- ions, and total salts and NO3- ions in soil, indicating that NO3- ion was the main reason for soil salinization. The contents of Ca2+, K+, NO3- ions, total salts, and mole ratios of Ca2+/Mg2+, K+/Mg2+ in soil significantly increased as the severity of the Mg deficiency of tomato. When the tomato was severe deficient of Mg, the soil salinization was also very high. And as the accumulation of salts in soil, the activities of Ca2+ and Mg2+ ions decreased exponentially. Compared to the tomato without Mg deficient symptom, the activities of Ca2+ and Mg2+ ions in soil solution of tomato deficient in Mg were significantly lower; for the activity ratios of (K+)/(Mg2+), (Ca2+)/(Mg2+), the situation was different. The activity ratios of (K+)/(Mg2+), (Ca2+)/(Mg2+), and(K+)/(Ca2+) increased significantly as the severity of tomato Mg deficiency. When the activity ratio of (K+)/(Mg2+) in soil solution was higher than 1, tomato showed Mg deficiency. We concluded that the low Mg2+ activity due to the salt accumulation in soil and the antagonistic interaction between Mg2+ and K+ ion were the main reasons for tomato Mg deficiency in calcareous soil under solar greenhouse.