Study On The Magnesium Nutrition Diagnosis Of 'Shatangju' And The Effect Of Magnesium Application In 'Shatangju' Orchard

‘Shatangju' is the main cultivated variety of citrus and the production of‘Shatangju' is an important pillar of the farmer's economy in the countryside.‘Shatangju' is grown mainly in South China,red soil is the main type of soil and Salt-based ions are easily lost due to weathering and leaching which caused magnesium defficiency and yellowing in orchards,seriously hinder the sustainable development of the citrus industry.In order to master the nutritional status of the ‘Shatangju' orchard,the present study collecting soil and leave samples to examine and analyze the mineral elements.In addition,the physiological changes in the leaves of magnesium deficiency under hydroponic culture were explored to find the indicators for the early diagnosis of magnesium deficiency in ‘Shatangju'.At the same time,a field experiment was carried out to compare the effect of magnesium fertilizers applied under different weight,The main results are as follows:1.The nutrient content of 130 soil and leaf samples in ‘Shatangju' orchard of Guangdong province was analyzed,The results showed that the soil of ‘Shatangju' orchard was generally acid with averager pH 4.52.The content of soil organic matter was 18.06g/kg at suitable level.The available N and K in soil was at low level and the proportions of soil sample below optimum were 76.16% and 56.15%,respectively.The available P was at higher level with 55.38% of soil samples at a high level.The exchange Ca and Mg were in serious shortage and the proportions in extreme deficiency status were 52.31% and 93.08%.The content of available Zn and B in the optimum level account for 53.85% and 42.31%,respectively.The content of N element was at lower level,accounting for 83.08% of leaf samples.K and B content is basically normal and the proportions in optimum were 79.23%and 81.54%.P is mainly in the optimum or low level,the proportion is 53.08% and 40.77%.Ca,Mg and Zn are extremely deficient with leaf samples below the normal level accounting for 96.92%,87.69% and 80.77%,respectively.The results of the DRIS diagnosis alsoshowed that the Ca,Mg and Zn elements need a lot of supplements.2.The results of the hydroponic cultivation showed that there was no significant difference in the contents of chlorophyll,sucrose and starch in the leaves among different treatments in the first 40 days of the experiment,after that,the accumulation of chlorophyll,sucrose and starch appeared in the leaves of magnesium deficiency.Different treatments had no significant effect on the activity of pyruvate kinase in ‘Shatangju' leaves.The content of soluble sugar in magnesium deficiency leaves increased gradually and short-term accumulation phenomenon appeared in the later period of the experiment.At the beginning of the experiment,the activity of acid invertase in magnesium deficiency leaves began to decline and decreased significantly after 20 days.In addition,the activity of enzymes in magnesium deficiency leaves was significantly lower than the control in later experiments.Therefore,the activity of acid invertase is sensitive to the change of magnesium concentration and can be used as an indicator for early diagnosis of magnesium deficiency in ‘Shatangju'.3.The effect of magnesium fertilizers application found that the length of spring shoots and summer shoots can be significantly increased when MgO 320 g was applied,which was 48.81% and 36.31% higher than that of control respectively.When MgO 640 g was applied,the autumn shoot length and chlorophyll content were significantly higher than the control,increased by 43.34% and 26.99%.the content of P and Mg in the leaves was the highest and the yield,vertical,vitamin C,reducing sugar content of ‘Shatangju' were significantly higher than the control too,increased by 237.84%,9.87%,22.44% and29.35% respectively,At the same time,the content of magnesium in the leaves is the highest and it's at the optimum level for citrus growth;.Different weights of MgO can increase the pH value of the soil and they are all in the optimum range for the growth of citrus.N and K contents in soil and leaves were not significantly different from those in the control.The content of exchangeable Mg in soil increase with the increase of fertilizer weight.In a word,applying MgO 640 g has the best effect.