Continuous growing cassava on dry land reduces soil quality and fertility, and decreases cassava yield. Returning the crop residues is expected to reduce the rate of decline in soil fertility. This study was aimed to determine the effect of returning groundnut residues and maize stover on improving soil fertility and soil quality of dry land. Laboratory and greenhouse studies were conducted at Iletri Malang in 2012. Laboratory study was to determine the N mineralization. The treatments were combination of crop residues and soil status. The crop residues consisted of groundnut residue; maize stover; 50% of groundnut + 50% of maize; 66% of groundnut + 34% of maize; 34% of groundnut + 66% of maize; and no application of crop residue. The soil status were soil planted to cassava in less than 10 years; and soil planted to cassava in more than 30 years. The twelve treatment combinations were arranged in a completely randomized design in three replicates. The soil treatments were incubated for 14 to 84 days. N mineralization was estimated using the first order equation. Similar twelve soil treatments were tested in the green house, using 15 kg treated soil, and were arranged in a randomized block design in three replicates. Treatments were incubated for twelve days before planted with cassava, which was harvested after the crop was three mounth old. In greenhouse experiment data were collected for pH, N and C in total, NH4+, NO3-, N labile fractions, C labile fractions and uptake of N, P, K. Results showed that application of groundnut + maize residues of 2 to 1 ratio, increased the rate of K mineralization by 27-32% and increased the amount of mineralized N by 171-222%, as compared with that of no residues application. Application of groundnut maize + residues of 1 to 1 ratio or groundnut maize residues of 2 to 1 ratio was able to improve soil fertility as indicated by the increases of the availability of total N, C-organic, NH4+ and NO3-. Soil quality improved with the increasing of the soil quality variables namely N and C labile fractions. The treatments also increased the uptake of N, P and K by cassava plant. Returning the crop residues of groundnut mixed with that of maize had restored the soil fertility of dry land continuously planted to cassava.