Nutrient balances of wetland rice fields for the semarang district (Indonesia)

Data from 1978 to 2003 were analyzed to evaluate the history of rice yields, rice-producing area, and total rice production for the Semarang District of Indonesia. The data were grouped according to the 5-year development plans executed in Indonesia, called PELITA (Pembangunan Lima Tahun). Nitrogen, phosphorus and potassium balances of the wetland rice fields were assessed for the same period. The highest average rice yield, about 5.10 t ha-1, was reached during the PELITA V and the economic crisis era. In general, the N, P, and K balances were found to be negative, which points towards nutrient mining from the rice fields. When a high production level is targeted, nutrient mining can only be avoided by recycling rice straw and applying fertilizers at high rates