| Pinghe county is the main honey pomelo production areas in China. Planting area,output and exports are the first in the nation. In recent years, Calcium deficiency leading to fruit granulation,magnesium deficiency causing leaf abnormally shed and chlorosis have become honey pomelo production problems which received widespread attention. Calcium,magnesium and sulfur nutrition research reports in honey pomelo is less.In this papper, soil and leaf samples from more than 300 pomelo orchards in 10 villages and towns of Pinghe County were analysed to study the nutrition status of calcium,magnesium and sulfur. Field experiment aimed to remediate the problem of honey pomelo magnesium deficiency was carried out. The main conclusions wree as follows:1 Pomelo calcium nutrition status1.1 Exchangeable calcium content in orchard soilSoil exchangeable calcium content in pomelo orchards of Pinghe county ranged from 98.27mg/kg to 2084.03mg/kg, the average was 495.98±317.97 mg/kg. Soil excchangeable calcium content of 0.32% soil samples was enrichment(>2000mg/kg), 34.39% soil samples was in the suitable range(500mg/kg-2000 mg/kg),65.29% soil samples was lower than critical value of 500mg/kg.Correlation analysis showed that soil excchangeable calcium content significantly positively correlated with soil pH,CEC and significantly positively correlated with soil organic matter content.1.2 Leaf blade calcium content of pomeloLeaf blade calcium content of pomelo ranged from 1.03% to 5.63%, the average was 3.10±0.71%.Leaf calcium content of 4.8% leaf samples was enrichment(>3.8%), 78.8% leaf samples was in the suitable range(2%-3.8%),16.3% leaf samples was lower than critical value of 2%. Correlation analysis showed that leaf calcium content very significantly positively correlated with soil excchangeable calcium and very significantly negatively correlated with Mg/Ca ratio and Potassium content of leafs.2 Pomelo magnesium nutrition status2.1 Excchangeable magnesium content in orchard soilSoil excchangeable magnesium content in pomelo orchards of Pinghe County ranged from 3.23mg/kg to 204.01 mg/kg, the average was 56.67±47.53mg/kg. Soil excchangeable magnesium content of 8.7% soil samples was enrichment(>125mg/kg), 14.2% soil samples was in the suitable range(80mg/kg-125 mg/kg),77.1% soil samples was lower than critical value of 80mg/kg. Correlation analysis showed that soil excchangeable magnesium content very significantly positively correlated with soil pH,CEC.2.2 Leaf blade magnesium content of pomeloLeaf blade magnesium content of pomelo ranged from 0.17% to 0.72%, the average was 0.35±0.08%.Leaf magnesium content of 9.6% leaf samples was enrichment((>0.47%),52.6% leaf samples was in the suitable range(0.32%-0.47%), 37.8% leaf samples was lower than critical value of 0.32%. Correlation analysis showed that leaf magnesium content very significantly positively correlated with soil excchangeable magnesium content and very significantly negatively correlated with K/Mg ratio and Ca/Mg ratio of leafs.3 Sulfur nutrition status of pomelo orchard3.1 Orchard soil available sulfur contentSoil available sulfur content in pomelo orchards of Pinghe county ranged from 10.98mg/kg to 116.65mg/kg, the average was 55.75±24.50mg/kg. Soil available sulfur content of 83.6% soil samples was enrichment(>30mg/kg),12.9% soil samples was in the suitable range(16mg/kg-30mg/kg),3.5% soil samples was lower than critical value of 16mg/kg.Correlation analysis showed that soil available sulfur content very significantly positively correlated with soil CEC and<0.002mm particle content,but,very significantly negatively correlated with soil pH,2-0.02mm particle content.3.2 Leaf blade sulfur content of pomeloLeaf blade sulfur content of pomelo ranged from 0.24%to 0.53%, the average was 0.34±0.04%.Leaf sulfur content of 12.2% leaf samples was enrichment(>0.4%), 87.8% leaf samples was in the suitable range(0.2%-0.4%).Correlation analysis showed that leaf sulfur content significantly positively correlated with soil available sulfur content and very significantly positively correlated with the total nitrogen content of leafs.4 Rectification of pomelo magnesium deficiency4.1 Effect of different magnesium deficiency rectification measuresLeaf blade magnesium contents of 5 magnesium deficiency rectification treatments in harvest stage was used as evaluation measurement.The result showed that the effect of Spraying 1%Mg(NO3)2·6H2O was better than 1%MgSO4·7H2O treatment; the effect of soil application 1 kg/plant agricultural magnesium hydroxide was better than 2kg/plant agricultural magnesium sulfate.The best measure of magnesium deficiency rectification was 1 kg/plant agricultural magnesium hydroxide used as base fertilizer combining with 1%Mg(NO3)2·6H2O spraying.4.2 Effect of Mg application on photosynthetic physiology of pomelo under Mg deficiencyThe results showed that magnesium fertilizer application increased the contents of Chlorophyll a,chlorophyll b and chlorophyll (a+b), leaf transpiration rate, stomatal conductance and net photosynthetic rate of magnesium deficiency pomelo. Adding magnesium fertilizer increased Fv/Fm, electron transfer rate, performance index (PIABS and PICS) of reaction center significantly, but decreased inactivation rate of PS Ⅱ reaction center significantly, indicating magnesium fertilizer could alleviate the damage of PS Ⅱ under the stress of magnesium deficiency. |
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