Effects of Lignite Addition on the Spectral Characteristics of Dissolved Organic Matter During Fermentation of Sheep Manure Organic Fertilizer: DONG Li-chao 1, WANG Xiao-xia 1, MA Li-tong 1,2*, WANG Ya-xiong 1,3* 1. School of Chemistry and Chemical Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China 2.