Magnesium Fertilizer Efficiency Evaluation For Tieguanyin (Camellia Sinensis(L.)O.Kuntze) And Special Magnesium Fertilizer Applicated Assessment

Magnesium（Mg）,as an essential element,plays an important nutritional and physiological role in tea plants growth and development.Magnesium deficiency in Tieguanyin tea gardens soil has become a limiting factor for tea production.Based on the effect of magnesium fertilizer in Tieguanyin tea garden,a special fertilizer containing magnesium was developed.It is of great theoretical and practical value for improving the magnesium nutritional status of Tieguanyin tea garden and realizing the fertilizer reduction,and finally achieving sustainable development of Tieguanyin tea industry.In the present study,four different magnesium gradient levels（Mg0（0）,Mg1（17.5 kg Mg O/ha）,Mg2（35 kg Mg O/ha）,Mg3（70 kg Mg O/ha））were performed to study the effects of Mg application on the tea yield,quality,nutrient absorption and economic benefit.Specifically,we used Tieguanyin,（Camellia sinensis（L.）O.Kuntze）as materials,and try to clarify its impact on the apparent balance of magnesium and the soil exchangeable magnesium concentration.In addition,according to the regional nutrient characteristics and expert experience of Tieguanyin tea garden in southern Fujian,special fertilizer of tea（Mg-containing）was designed and field validation was also carried out.The main results obtained were as follows:（1）Magnesium fertilizer input in Mg-deficient tea plantations significantly increased tea yield.Compared to Mg0 treatment（0 kg Mg O/ha supply）,the yield of magnesium treatment（Mg1,Mg2,Mg3）increased by 5.6%～17.6%for spring,and 5.5%～20.8%for autumn,respectively.Yield components analysis further showed that the yield increase was mainly caused by the tea buds density increment.The magnesium concentration and the magnesium taken away from the young shoots increased by 3.2%～7.6%and 12.8%～24.8%,respectively,indicating that the application of magnesium fertilizer significantly improved the magnesium nutrition of tea trees.Meanwhile,the nitrogen,phosphorus,potassium and calcium taken away from tea trees increased significantly,and the amount of nutrient taken away by young shoots in spring was higher than that in autumn,and the partial productivity of nitrogen,phosphorus and potassium fertilizers also increased with increasing of the application amount of magnesium fertilizer.（2）Magnesium fertilizer application significantly increased the soil exchangeable Mg concentration,and showed a linear upward trend with the increase of magnesium fertilizer input.After four seasons Mg application,the soil exchangeable Mg concentration in surface soil of Mg1,Mg2,and Mg3 treatments were 26.6,39.6,and 77.3 mg/kg,respectively.The apparent surplus of magnesium increased significantly with the increase of magnesium application,and soil exchangeable Mg concentration in surface and sub-surface soils was positively correlated with the apparent surplus of Mg.The linear with plateau model was best for modeling the relationship between relative yield and soil exchangeable Mg after harvest,the minimum soil exchangeable Mg needed to achieve maximum grain yield was 35.9 mg/kg for spring,21.2mg/kg for autumn.（3）Compared to the farmers’practice（FP）,the treatment of Specific Fertilizer（SF）optimized the input of fertilizer amount,and the input of N,P₂O₅,and K₂O were reduced by 43%,58%,and 64%,respectively.Whereas there was no significant difference between the yield,quality and the nutrient concentration of N,P and K in young shoots.Correspondingly,the partial productivity of nitrogen,phosphorus and potassium fertilizers increased by 72.3%,123.3%,and 117.3%,respectively,while the apparent surplus of N,P,and K decreased by48.8%,58.0%,and 65.8%,respectively.Meanwhile,the environmental impacts were also significantly reduced,and the yield-based on mean potentials for reactive N loss,global warming,acidification,and eutrophication decreased by 42.4%,41.0%,42.3%,and 42.5%,respectively.