G.D. Sharma and S.K. Sharma, Jintu Dutta, N.K. Sankhyan, S.P. Sharma,. “Sulphur Fractions in Acid Soil Continuously Fertilized With Chemical Fertilizers and Amendments under Maize-Wheat System”. Journal of the Indian Society of Soil Science, vol. 61, no. 3, Dec. 2013, https://epubs.icar.org.in/index.php/JISSS/article/view/35618.