Sulphur stocks in 'Sindhri' mango soils in Sindh, Pakistan, in relation to leaf tissue analysis

Sulphur is an essential nutrient required for growth and development of plants. It increases the yield and quality of produce. As a constituent of three amino acids, cysteine, cystine and methionine, it plays a vital role in chlorophyll synthesis and is also required for enzyme activation. Studies related to sulphur contents of mango in Sindh, Pakistan, are not on the record. This study was carried out with the main aims of generating a baseline of soil and 'Sindhri' mango leaf sulphur contents and determining the relationship between them. Soil and leaf tissue samples were collected from 25- to 30-year-old 'Sindhri' mango orchards in the districts Mirpurkhas, Naushahroferoze, Shaheed Benazir Abad, Sanghar and Umerkot, Sindh province, during December 2012. Twenty-five recently matured leaves (third leaf from the top) were collected from fruiting branches of each tree and combined. Available sulphur in soil was extracted by using 0.001 M CaCl2 (1:2 soil/CaCl2) and leaf samples were digested in acid mixture (HClO4/HNO3; 1:5). Sulphur was quantified in clarified extracts in both cases by a turbidimetric method using BaCl2. Physical and chemical properties of soil showed silt loam to silty lay loam texture, electrical conductivity 0.33-0.83 dS m-1, pH 7.33-7.77 and organic matter content 0.88-1.54%. Available sulphur contents of all soils in the study varied from 11 to 550 (0-15 cm soil) and 4 to 632 (15-30 cm soil) mg kg-1, with only 3% of samples being low (KLEINERDAN10 mg kg-1). Leaf tissue sulphur contents were between 0.25 and 0.97%, with 34% of samples being low (‹0.5% S) in Umerkot, Naushahroferoze and Sanghar. The correlation coefficient between organic matter content and sulphur in leaf tissue show a linear and positive relationship (r=0.54), with significant quantities of sulphur coming from the organic pool. In the light of soil testing and leaf tissue analysis data, it is concluded that, although all the mango orchard soils ranked high to very high in sulphur contents, three (Umerkot, Naushahroferoze and Sanghar) of the five districts were low in leaf tissue sulphur.