Impact of fertilizer application on rice field on variation in nitrogen concentration in drainage canals of the Han Quang watershed, Bac Ninh province

Abstract

    Recently, water quality has degraded seriuously in the Han Quang watershed belonging to service area of the Bac Duong irrigation system. Exceeded fertilizer application on rice fields was considered as a main cause. This paper aims to assess impact of change in fertilizer application on variation inboth NH4 and NO3 concentration in drainage canals during the period of 2000 - 2013. The results indicate that a decrease by 50% in manure together with a decrease in nitrogen fertilization by 33% in spring season and 46% in wet seasoninduced a decrease in NO3 by 38% and in NH4 by 46%. In addition, variation in both Q1 (Quartile 1) and Q2 (Median)was greater than variation in Q3(Quartile 3). IQR(Interquartile range) of NO3 ranged from 0.03 mg/l to 2.2 mg/l and IQR of NH4was in the range of 0.37 - 7 mg/l.