To investigate the dynamic effects of biochars produced from different biomass materials on farmland soil acidity, exchangeable cations, phosphorus nutrient, and crop yield, a field experiment was performed on acid paddy soil. Five types of biochars-rice straw biochar (RSB), maize straw biochar (MSB), wheat straw biochar (WSB), rice husk biochar (RHB), and bamboo charcoal (BCB)-were applied to farmland soil at mass fraction of 0.1%. No biochar addition was used as control treatment (CK). The soil physicochemical properties and crop yields were analyzed after harvesting rice, rapeseed, and corn crops. Results indicated that the addition of biochars could effectively increase soil pH and exchangeable cations and reduce exchangeable acid content, but the effects decreased with time. The biochars increased the content of exchangeable K, Ca, and Mg and decreased the exchangeable Na content in soils. The biochars increased the contents of organic matter (SOM), available phosphorus, total phosphorus, and inorganic phosphorus (Al-P and Fe-P). Compared with the control treatment, biochars significantly (<0.05) increased the yields of rice, oil seed, and maize crops. Rice husk biochar (RHB) had the best effect in improving acid soil physicochemical properties and increasing crop yield.