Fluorescence Spectroscopy Characteristics of Dissolved Organic Matter Analysis of Straw-Cow Dung Fermentation in Different Proportion: LI Yan 1,2, WEI Dan 1, 2*, WANG Wei 3, JIN Liang 2, DING Jian-li 2, CAI Shan-shan 4, HU Yu 1, BAI Yang 1: 1. College of Resources and Environment, Northeast Agricultural University, Harbin 150030, China 2.