Factors and Mechanism of Magnesium Bioavailability Reduction in Calcareous Soil in Greenhouse Cultivation
|School||Northwest University of Science and Technology|
|Keywords||sunlight greenhouse tomato deficient with magnesium ion content ionactivity nutrient absorption|
Sunlight greenhouse was one of the main modes of vegetable cultivation in northernChina. It developed rapidly in recent years. Farmers usually obtained high production byexcessive application of fertilizers and organic manures. Nutrients that had been inputtedwere much more than the crop demanded, and it led to many negative effects, such as theaccumulation of soil salinity, the low utilization rate of nutrient and the degradation of soilproperties. The phenomenon of magnesium deficiency which appeared frequently ontomatoes, cucumbers and other crops in the sunlight greenhouse of Guanzhong region was atypical manifestation of soil degradation. Magnesium deficiency had serious impacts on thesustainable development of the industry. This study researched from the angle of field surveyanalysis and bio-pot experiment about the relationships among soil salt content andcomposition, ion activity, ion ratio and magnesium deficiency of tomato, as well as the effectsof nitrogen and potassium application on soil salt content, ion activity, ion ratio, the growthand nutrient absorption of tomato, The main conclusions from the study were as follows:（1）The field survey and soil analysis results showed that as the severe of themagnesium deficiency of tomato, the contents of Ca2+, K+, NO3-ions, total salts, and moleratios of Ca2+/Mg2+, K+/Mg2+in soil significantly increased. When the tomato was severedeficient of magnesium, the soil also had the saline problem; As the severe of the magnesiumdeficiency of tomato, the activities of Ca2+and Mg2+ions decreased, and K+activityincreased. As the accumulation of salts in soil, the activities of Ca2+and Mg2+ions decreasedexponentially, and there was no significant relationships between K+activity and total salts insoil; The activity ratios of K+/Mg2+, Ca2+/Mg2+, and K+/Ca2+increased significantly as thesevere of tomato magnesium deficiency. The K+activity was higher than Mg2+activity insoils which were found magnesium deficiency of tomato.（2）Apot experiment showed that as the increase of nitrogen and potassium applicationrate, soil total salt and salt ions increased gradually, such as K+, Na+, Ca2+, Mg2+, NO3-andSO42-content. There was extremely significant positive correlation between nitrogenapplication rate and total salt, and significant positive correlation between potassiumapplication rate and total salt. As the increase of nitrogen and potassium application rate, soilK+, Ca2+and Mg2+activity showed a decreasing trend while K+/Mg2+and K+/Ca2+activity ratio increased gradually. As the increase of nitrogen and potassium application rate, tomatoplant height and stem diameter showed a decreasing trend while chlorophyll SPAD had nodifference. The biomass of tomato were significantly reduced by excessive application ofnitrogen fertilizer. Increasing potassium fertilizer had no significant impacts on plant biomassin the same nitrogen application rate. There were no significant effects of nitrogen andpotassium fertilizer on calcium and magnesium absorption of tomato in seedling andflowering stage. Excessive application of nitrogen fertilizer significantly inhibited calciumand magnesium absorption of tomato in expanding and fruiting stage.（3）There were significant positive correlations among soil K+, Ca2+, Mg2+activity andK, Ca, Mg absorption of tomato. There were significant negative correlations among soilK+/Mg2+, K+/Ca2+activity ratio and Ca, Mg absorption of tomato in expanding and fruitingstage. The increase of K+/Mg2+, K+/Ca2+activity ratio inhibited calcium and magnesiumabsorption of tomato.Through the comprehensive analyses of the relationships among soil salt composition,ion activity and ratio, the degree of tomato magnesium deficiency as well as the magnesiumand calcium absorption of tomato, the results showed that excessive application of nitrogenand potassium, especially nitrogen, led to the accumulation of soil salinity, and soil Mg2+activity dropped significantly. Because of the cation-anion balance and ion exchange, the soilsolution Ca2+, K+content increased. The ion antagonistic effects that caused by high K+/Mg2+,K+/Ca2+activity ratio were the main factors of magnesium bioavailability reduction incalcareous soil.