Study on calcium nutrition in Chongqing citrus orchards

Status of calcium nutrition in Chongqing citrus orchards was studied to propose comprehensive management measures for Ca nutrition of citrus orchards. Ca contents in soils and leaves of 218 citrus orchards were studied. The results show that there is abundant soil Ca in Chongqing citrus orchards with an average of 3316.7 mg/kg, and soil available Ca contents in 49.5% citrus orchards exceed 3000 mg/kg belonging to excessive range and those in 17.9% citrus orchards are less than 1000 mg/kg which are in the range of deficiency. The Ca contents in leaves of 38.3% citrus orchards are in the range of deficiency（30 g/kg）, and those of 0.3% citrus orchards exceed 70 g/kg which is in excessive range. This indicates that soils with abundant Ca do not ensure the need of citrus trees to Ca nutrition. The relationship of Ca contents in soils with those in citrus leaves is not certain because of the change of Ca contents in soils. When the content of available Ca in soils is low, Ca concentrations in leaves are increased with the increase of soil Ca contents and there is a significant positive correlation y=0.0151 x +16.459 (r=0.608**, n=39，r0.01=0.408). When soil Ca content is in high or very high range, it is not correlated with Ca contents in leaves, and leaves with both deficient and excessive contents are found. As a result, not only Ca deficiency in soils could lead Ca deficiency in leaves, but also excessive Ca in soils could cause Ca deficiency in leaves. When managing Ca nutrition in citrus orchards, every factor influencing Ca availability should be considered, which includes types and application methods of Ca fertilizers, phases, the ability of soil to supply Ca, citrus cultivars, rootstocks, the balance of main nutritional elements, and then propose rational management measures of Ca nutrition.