Nitrate (NO3) leaching was studied in an Andisol treated with four N fertilizers (SC: swine compost, CU: coated urea, AN: ammonium N, or NF: no fertilizer) for 7 years. Sweet corn (Zea mays L.) was grown in summer, followed by Chinese cabbage (Brassica rapa L. var. amplexicaulis) or cabbage (Brassica oleracea L. var. capitata) in autumn each year. In chemical fertilizer plots treated with AN or CU, NO3-N concentrations in soil water at I-m depth increased markedly in the summer of the second year and fluctuated between 30 and 60 mg l(-1). In the SC plot, NO3-N concentration started increasing in the fourth year, reaching the same level as in the AN and CU plots in the late period of the experiment. In the NF plot, NO3-N concentration was about 10 mg l(-1) for the first 4 years and decreased to 5 mg l(-1). The potential NO3-N concentrations by an N and water balance equation satisfactorily predicted NO3-N concentration in the AN and CU plots, but substantially overestimated that in the SC plot, presumably because a large portion of N from SC first accumulated in soil in the organic form. Our results indicate that, under the Japanese climate (Asian monsoon), excessive N from chemical fertilizers applied to Andisols can cause substantial NO3 leaching, while compost application is promising to establish high yields and low N leaching during a few years but would cause the same level of NO3 leaching as in chemically fertilized plots over longer periods. (C) 2002 Elsevier Science Ltd. All rights reserved.