Khalid, R., K. S. Khan, G. Shabbir, M. Yousaf, and S. Y. Naz. “Status of Plant Available Sulphur and Its Relationship to Other Soil Characteristics in Pothwar Soils: Plant Available Sulphur in Soil”. Biological Sciences - PJSIR, vol. 52, no. 2, Apr. 2009, pp. 84-90, https://v2.pjsir.org/index.php/biological-sciences/article/view/521.