Effects Of Greenhouse Cultivation Years On Soil Ion Balance And Applying Magnesium Fertilizer On Tomato

Greenhouse cultivation is one of the most important ways of growing vegetables in northwestern region of China. The trend of utilizing greenhouse for vegetable cultivation increased rapidly in recent years. Greenhouse provide a protective environment for vegetable cultivation under which improved and better quality vegetables are produced which not only improve the farmer’s income but also play a great role in the development of rural economy. However, for getting higher yield, over-fertilization is a very common practice under greenhouse cultivations. It results in the low yield and poor quality of the crops, and also the low soil quality, especially the imbalance of nutrients in soil. Imbalanced could affect availability of other nutrients like Mg, the Mg deficiency symptom of tomato becomes common in calcareous soil under solar greenhouse in North China in recent years. It significantly affects the fruit yields and quality of these vegetable crops. Previous study showed that, when greenhouse tomato Mg deficiency appeared, correspondingly soil cation was imbalanced rather than Mg content decreased in calcareous soil. Therefore, This research analyzed soil cation content and composition with different greenhouse cultivation years by monitoring fixed-point greenhouse; and study the effect of applying Mg fertilizer on tomato yield, uptake and distribution of K, Mg, Ca by tomato, as well as the soil cation composition by field and pot experiments, so as to provide theoretical basis for the effective regulation of ion balance of soil nutrients. The following are main conclusions:( 1) There were extremely significant positive correlations between greenhouse cultivation years and concentrations of soil water soluble K+, soil water soluble Mg2+, soil exchangeable K+, soil exchangeable Mg2+, saturation of soil exchangeable K+, soil exchangeable Mg2+ and soil exchangeable K/Mg, respectively, and there was a significant negative correlation between soil exchangeable Ca2+ content and the greenhouse cultivation years. The analysis of soil exchangeable cation composition showed that the ratio of soil exchangeable K/Mg>0.7 with 3, 4 and 5 years history, which indicated a serious nutrient imbalance in soil. The rapid increase of soil K+ concentration due to excessive potassium fertilizer input was one of the principal influential factors to change soil cation composition and proportion.(2)The concentrations of magnesium and potassium in autumn-winter season tomato leaves decreased with time while the reduction in calcium concentration was very rapid in start which then became stable. spraying magnesium fertilizer increased the magnesium concentration and nutrient uptake in tomato leaves, The improvement in tomato yield at both Mg concentrations(0.2 and 0.4%) of MgSO4.7H2 O and at Mg concentrations 0.2% of Mg(NO3)2.6H2 O was 8.0, 8.9 and 5.3% respectively compared with CK.(p>0.05). The analysis of soil exchangeable cations showed that the exchangeable K/Mg ratio exceeded 0.5, which indicated a serious nutrient imbalance in soil. Even under magnesium spray, some of the leaves remained yellow which might be because of imbalanced ratio of exchangeable K/Mg in calcareous soil which might have prevented the transportation of magnesium from leaves to other organs of tomato, so there is a need to do further research on how imbalanced exchangeable cations affect magnesium adsorption and transportation within tomato.(3)Compared with conventional fertilization treatment, recommended fertilization significantly improved the saturation of soil exchangeable Mg2+, meanwhile significantly reduced the ratio of exchangeable K/Mg and Ca/Mg, so the effectiveness of soil magnesium had been improved; however, There was no significant difference in soil exchangeable nutrient composition and proportion after applying Mg fertilizer. Compared with conventional fertilization treatment, recommended fertilization significantly increase the tomato dry weight accumulation, increasing amplitude was 22.1%, enhanced magnesium uptake by tomato. Therefore, reducing K input is the key point to regulate the disorder of soil K/Mg, K/Ca, which could decrease exchangeable K/Mg, and then improve soil Mg availability, finally it will reduce the risk of Mg deficiency in crops.