The main problems of peatland include low pH, low levels of N, P, K, Ca, Mg elements, and low base saturation. The purpose of this research is to determine whether there is an influence and the best treatment of cow manure fertilizer on soil pH, Base Saturation, and the growth of mustard greens (Brassica Juncea L.).This research was conducted in Sukamaju Village, North Landasan Ulin Sub-District, Liang Anggang District, Banjarbaru City. The study utilized a Completely Randomized Design with one factor, which was the application of cow manure fertilizer. The doses used were 0 tonsha^-1 or control, 10 tonsha^-1, 15 tonsha^-1, 20 tonsha^-1, and 25 tonsha^-1. The results of this study showed that the application of cow manure fertilizer affected pH, base saturation, Cation Exchange Capacity (CEC), and plant dry weight. The effectiveness of cow manure fertilizer application on plant growth was observed at a dose of 20 tons/ha, and the optimal dose to improve pH, base saturation, and Cation Exchange Capacity was 25 tons/ha.