In this study, farmland soils with two different degrees of Cd contaminated in southern China were used to study the changes of soil fertility and Cd availability during crop growth by applying different organic manures (pig manure, commercial organic manure, rice straw and biochar), and the correlations between soil Cd availability and nutrients. The results showed that the application of organic materials significantly increased the contents and availability of soil nitrogen, phosphorus and potassium, commercial organic manure increased soil total nitrogen content, pig manure significantly increased the contents of soil total and available phosphorus, and commercial organic manure and rice straw biochar significantly increased the contents of soil total and available potassium. Soil organic matter contents of the lightly-contaminated soil treated with rice straw and biochar increased to level 1 (>40 g/kg). Compared with the treatment without fertilizer, the effects of organic materials on the contents of available Cd in lightly-contaminated soil were not significant, but the contents of available Cd in moderately-contaminated soil decreased significantly, with a maximum reduction of 20.00%. The content of available Cd was negatively correlated with the contents of total nitrogen, phosphorus and potassium as well as available phosphorus. Cd contents in the aboveground of Brassica chinensis L. treated with pig manure and biochar were lower than 0.20 mg/kg. Soil nutrient index treated with commercial organic manure was the highest, which was 1.50–3.18 times of other treatments, but Cd content in the aboveground of Brassica chinensis L. had a higher risk. Therefore, the application of pig manure can be considered for the cultivation and safe utilization of Cd contaminated farmlands in southern China.