Soil sulphur status and citrus sulphur application response

In order to investigate the status of soil S in citrus gardens in Hunan Province and citrus in response to S application,we carried out a survey of soil S in 81 citrus gardens,and conducted field experiments in 4 citrus gardens of Taoyuan county and Zhuzhou county of Hunan Province during 20002004.Results showed that for available S content at the surface 020 cm layer of citrus gardens soils,9.9% was lower than critical level,and 17.3% was potentially deficiency(average 47.7 mg/kg).Soil available S content increased gradually with increase in soil depth,whereas total S content decreased stepwise.Regarding the available S regional distribution,there were 10.0%75.0% citrus gardens that soil available S in 020 cm soil layer was deficient or potentially deficient in 81.3% of all the investigated counties.The citrus garden in which total S content of citrus leaves was lower than critical value accounted for 27.2%(average 2.32 g/kg).Field experiments results showed that citrus yields increased by 5.3%30.0% after continuous S fertilization for 45 years.Continuous S fertilization evidently enhanced S and N content in citrus leaves and S content in citrus fruit skin,reduced N content in citrus fruit skin,consequently improved quality of fruit.The order of yield and quality response to S fertilization was as follows: Available S deficient soilavailable S latent deficient soilavailable S medium and sufficient soil,and older tree-agesyounger tree-ages.With the years of S fertilizer application extending,the yield and quality response of S fertilization became more distinctively.