WHICH SOIL HORIZON IS RICH IN HUMUS? EXPERTS PLS ANSWER..... Share with your friends Share 1 Vaibhav T. answered this The O horizon and the A horizon are most rich in humus due to the organic material being highest in those two layers. O is higher than A, though. 0 View Full Answer Achal answered this A HORIZON -1 Jonathan answered this the o horizon and a horizon -1 Ishaan Gafoor K answered this 1 -2 Kripi Singla answered this Topsoil is rich in humus or u can say that the topmost layer -1