This study assessed the balance of N, P, K, Si, Ca, Mg, and Na in a lowland sawah (rice fields) in the Citarum Watershed, Java, Indonesia. The soil properties at sites studied were not significantly different (P>0.05) in terms of pH, available P, available Si, and exchangeable Ca, K and Na, while TC, TN, and exchangeable Mg showed different levels. The nutrient balances were estimated as an average of total input minus total output at four study sites. Input parameters were nutrient content derived from fertilizer, irrigation water, and nitrogen fixation, and output parameters were nutrient loss through harvest, drainage water, and denitrification. The results showed a positive balance for N, P, Ca, Mg, and Na; however, K and Si showed a negative balance. The balance values were estimated at 5, 8, 387, 65, 281, -198 and -21 for N, P, Ca, Mg, Na, Si and K, respectively. The decrease in Si and K observed in this study is likely due to the substantial uptake of these nutrients without adequate replenishment through fertilizer.
Key words: intensive rice-farming system, nutrient balance, rice productivity, sawah
Paper published at Journal of Agricultural, Food, and Environmental Science. Volume 4, Issue 1, 2010. ISSN: 1934-7235.