The Long-Term (13 years) Effect of Rice Based Organic Farming on Soil Sulphur Dynamics in a Typic Ustochrept Soil of Indo Gangetic Plain of India

Scarce information is available on long-term organic nutrient management practices on soil sulphur (S) fractions, their relationship with various soil physico-chemical properties and crop yield, and sulphur availability indices. Hence, the leading objectives of the present investigation were to assess long-term (13 years) organic nutrient fertilization on: (i) different soil S fractions in surface soil and (ii) relationship of S fractions with different soil properties along with S availability index. Treatments were control (no organic manures applied), farmyard manure (FYM), vermicompost (VC), FYM + crop residue (CR), VC + CR, FYM + CR + biofertilizers (BF), and VC + CR + BF applied in rice-wheat-mungbean (RWMCS) and rice-wheat (RWCS) cropping systems. The experiment was executed in strip plot design with three replications. The available S, water soluble S, heat soluble S, adsorbed S, organic S, and total S fractions were analyzed in 0-15 cm soil layer. In addition, correlation and regression equations of soil S fractions with different soil properties and rice yield were developed. Results affirmed that treatments receiving vermicompost (VC) either alone or in combination with crop residues and biofertilizers (VC + CR and VC + CR + BF) recorded 44%, 70%, and 73% higher available S over the control in RWMCS, respectively. Further, integrated application of organic amendments in FYM + CR, VC + CR, FYM + CR + BF, and VC + CR + BF treatments found superior in respect of water soluble S (WSS), organic S (OS), total S (TS), and sulphur availability index (SAI) over the unfertilized control plots as well as FYM and VC alone treated plots in both the cropping systems. The adsorbed S (NaHCO3 extractable S) ranged from 43.59 to 51.58 mg kg(-1) and 39.84 to 48.34 mg kg(-1) in RWMCS and RWCS, respectively. Plots treated with FYM + CR and VC + CR treatments recorded significant highest (153.6 and 155.7 mg pNP g(-1) soil h(-1)) arylsulfatase activity in RWMCS and RWCS, respectively. The soil organic carbon (SOC) and clay content had significant positive correlation with all the sulphur fractions and rice yield in both the cropping systems. Treatments with integrated application of organic nutrient sources had higher SOC: OS and SOC: TS ratio than control plots. Overall, the integrated application of organic nutrient sources in FYM + CR + BF and VC + CR + BF treatments not only had higher sulphur fractions and SAI in surface soil but also had better rice yield than manures alone treatments and hence should be adopted under organic farming.