Mechanism Of Magnesium Deficiency And The Effects Of Magnesium On Tomato In Greenhouse That Built On Calcareous Soil

Greenhouse culture is one of the main vegetable facility cultivation in North China and nutrient input is always excess. Problems such as salt accumulation, nutrient imbalance, environment problems appear as a result and have attracted wide attention except Mg deficiency. This study focus on Mg deficiency which badly affects yield and quality is more and more outstanding in greenhouse built on calcareous soil. Analyzing soil properties of greenhouse with different tomato Mg deficiencies and correlation with Mg deficiency,nutrient uptake,yield through investigation and sampling. Studying the effect of Mg input on nutrient balance(K, Ca, Mg), tomato yield and nutrient uptake. Causes of Mg deficiency and effect of Mg input was evaluated and provided an important theoretical and practical guidance for nutrient comprehensive management. We got the main conclusions as follows:(1) Soil properties were significantly different with each other among greenhouse with different Mg deficiencies. Soil EC, NO3--N, readily available potassium, exchangeable K, potassium saturation, Ca2+/Mg2+ and K+/Mg2+ significantly increased in greenhouse with severe Mg deficiency. Soil organic matter, exchangeable Mg,magnesium saturation and were significantly lower in greenhouse with severe Mg deficiency than that in greenhouse without deficiency. Magnesium was abundant in calcareous soil with or without Mg deficiency. But Mg saturation were less than 10%(critical value of Mg deficiency) and Ca2+/Mg2+ and K+/Mg2+ ratios were imbalanced according to some scholars in soil with Mg deficiency.(2) Tomato yields decreased with Mg deficiency aggravated. Tomato yields were 38.02% and 59.53% lower in Moderate and Serious Mg deficiency treatments than control. Mg concentration of tomato leaf and tomato yield were positive correlation with readily available potassium,Ca2+/Mg2+ ratio(p<0.05 or p<0.01). It indicated that increasing of potassium was the main course of Mg deficiency and yield drop.(3)Tomato yield increased with Mg input increased,but the differences were not significantly. There was not obviously change on color of tomato leaves when Mg was put into soil where tomato showed Mg deficiency. Analyzing of cation composition in soil solid and liquid phase indicated that Mg input made potassium transferred from soil solid phase to soil liquid phase and potassium concentration decreased in liquid phase. But there were no significant differences among K+/Mg2+ ratios in soil liquid phase. In addition, farmers used to apply excess and imbalanced N, P, K fertility to soil every stubble tomato comes out. That coursed more and more serious K+/Mg2+imbalance which was the main cause of tomato Mg deficiency bad correction from flowering stage to fruit swelling period. These all indicated that potassium input must be controlled and nutrient must provided balanced in case to preventing Mg deficiency in greenhouse built on calcareous soil.