SUKRISTIYONUBOWO1, GIJS DU LAING2, and MARC G. VERLOO2
1Soil Research Institute, Bogor, Indonesia
2Department of Applied Analytical and Physical Chemistry, Laboratory of Analytical Chemistry and Applied Ecochemistry, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
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.
KEYWORDS nutrient balance, wetland rice, nitrogen, phosphorus, potassium.