The cycles and apparent balances (ABs) of N, P, K, Ca and Mg were studied in two kinds of normal paddy field ecosystems with the crop rotations in both the wheat-rice sequence and the barleyrice-rice sequence. The research was based upon field experiments on three critical types of paddy soils in the Tai Lake region, The transportation of concern was inputs through fertilization, irrigation, precipitation, sowing and transplantation, and outputs by crop removal, surface drainage and leaching. Nitrogen outpu...