Evaluating sulphur nutrition to improve the yield and quality of aggregatum onion (Allium cepa var. aggregatum) grown in Sulphur deficient soil

A field experiment was conducted to assess the impact of sulphur fertilisation on the yield and quality of aggregatum onion (CO (On) 5) grown in S deficient black soil (Typic Ustropept) which was sandy loam in texture with available S content of 7 mg kg-1. Ammonium sulphate and Single super phosphate were the two sources of sulphur applied along with recommended doses of N, P and K at the levels of 0, 20 and 40 kg S ha-1 with and without VAM. The bulb yield increased significantly both with the application of ammonium sulphate (with VAM - 4.70 t ha-1, without VAM - 4.68 t ha-1) and Single super phosphate (with VAM - 4.65 t ha-1, without VAM - 4.63 t ha-1) with recommended dose of fertilizers and at the higher level of 40 kg S ha-1 which were 26.6 and 26.3% increase over RDF alone application incase of application of Ammonium sulphate + RDF with and without VAM, respectively; and 25.8 and 25.5% increase over RDF alone application incase of single super phosphate + RDF application with and without VAM, respectively. Thus, application of VAM with ammonium sulphate and RDF at higher levels was also statistically on par with the same combination without VAM. The highest sulphur content (0.444%) and sulphur uptake in bulbs (6.23 kg ha-1) were higher with application of ammonium sulphate @ 40 kg S ha-1 + RDF which was on par with the same combination without VAM and Single super phosphate @ 40 kg S ha-1 + RDF with and without VAM. The quality parameters of aggregatum onion like ascorbic acid and pyruvic acid were also higher with the application of ammonium sulphate and recommended dose of fertilizers @ 40 kg S ha-1 which was on par with the same combination without VAM and Single super phosphate @ 40 kg S ha-1 + RDF with and without VAM.