Impact of residual sulphur on mulberry ( Morus alba L.) nutrition and soil reaction

The principal contributors for sulphur deficiency in soil are continuous use of high analysis sulphur-free fertilizers, enhanced exhaustion of sulphur from soil by high-yielding mulberry varieties, increased cropping intensity and wide-spread lack of organic matter in tropical soil under mulberry farming (Bose and Kar, 2007; Kar et al., 2008). Recently, Bose et al. (2010a) has reported the direct effect of fertilizer sulphur on growth, yield and nutrient uptake of mulberry on a sulphur-deficient sandy clay loam soil under irrigated condition. The increasing surface activity of the adsorbed sulphate ion with an increase in its activity in the soil solution (Dolui et al., 1993) and preponderance of carbon-bonded sulphur in soil (Bhogal et al., 1996) indicates formation of its stable as well as reserve pool under sulphur fertilization. This exerts special significance of sulphur fertilizer in terms of its carry-over effect. Higher soil efficiency factor of sulphur over its fertilizer efficiency factor (Bose et al., 2010b) further substantiates the earlier postulation. Therefore, an investigation was undertaken to study the residual effect of sulphur on the performance of mulberry in terms of productivity as well as sulphur uptake and also on soil reaction as well as availability of sulphur in soil. The field experiment was conducted at Central Sericultural Research and Training Institute, Berhampore, West Bengal during 2009-10 to 2010-11 on a sandy clay loam soil under irrigated condition. It was previously treated with varying levels of sulphur and uniform levels of nitrogen, phosphorus, potassium and FYM for three years (2006-07 to 2009-10) as per the recommended doses of mulberry for irrigated condition. The experiment under Gangetic alluvial soil comprised four levels of sulphur (0, 20, 30 and 40 kg ha year in five equal split doses corresponding to five crops) through two sources, namely elemental sulphur (ES) and ammonium sulphate (AS). All the treatments including control received recommended doses of N, P2O5 and K2O @ 336, 180 and 112 kg ha -1 year , respectively and were applied in five equal split doses along with 20 mt FYM ha year applied in single dose. The experiment was laid out in a randomized block design with three replications for mulberry (Morus alba L.) variety S-1635 planted at 60 cm x 60 cm spacing. The treatments were applied in the preceding mulberry crops for three years along with other inputs as mentioned. Mulberry crops of the succeeding year received only other inputs at the same doses but no sulphur treatment to find out the residual effect of the respective treatment. Mulberry leaf and shoot yields were recorded for five crops of the succeeding year, pooled and presented on annual basis. For computation of sulphur uptake, leaf and shoot samples were digested in di-acid mixture (HNO3 : HClO4 :: 4 : 1) and sulphur content of the digested material was analyzed by turbidimetric method. Soil samples, drawn from each plot after completion of the crop schedule in the succeeding year, were extracted with 0.15% CaCl2 and available sulphur in the clear extract was estimated by the method as described by Chesnin and Yien (1951).