Influence of Chemical Fertilizer Applications on Water Quality in Paddy Fields in Nong Harn, Sakon Nakhon Province, Thailand

Abstract

This study investigated the effect of chemical fertilizer on water quality in paddy fields. Six experiments were conducted using chemical fertilizer (formula 16-16-8; N-P-K) and urea fertilizer (460-0) using two different fertilizer applications at varied concentrations in Nong Harn, Sakon Nakhon province, Thailand: 1) 218.75 kg.ha-1 of 16-16-8 at 30 d after planting and 93.75 kg.ha-1 of 46-0-0 at 60 d and 90 d after planting by broadcasting (T1), deep placement at 10 cm (T2) and at 20 cm (T3); and 2) 437.50 kg.ha-1 of 16-16-8 at 30 d after planting and 187.50 kg.ha-1 of 46-0-0 at 60 d and 90 d after planting by broadcasting (T4), deep placement at 10 cm (T5) and at 20 cm (T6). The results showed that at 90 d, the lowest dissolved oxygen level was 3.21 mg.L-1 in T4. The NH4+-N levels decreased with time. The highest and lowest levels of NH4+-N were in T4 (60 d) and T3 (90 d), respectively, whereas the highest and lowest levels of NO3--N were in T4 and T1 (90 d), respectively. The levels of NO3--N in T4, T5 and T6 were higher than those in T1, T2 and T3. Additionally, the level of PO43--P decreased due to the growing season of rice. The concentrations of phosphate by broadcasting were higher than those of deep placement at 10 and 20 cm. The rice yield was higher (P < 0.05) in T4, T5 and T6 than in T1, T2 and T3 and the rice yields using deep placement at 10 cm were higher than those at 20 cm and by broadcasting. Nitrogen fertilizer application affected the utilization efficiency, influencing the rice yields and nitrogen loss. However, the recommendation of an appropriate nitrogen fertilizer application was deep placement at 10 cm based on the rice yield and the levels of NH4+-N, and NO3- -N. Furthermore, water should be retained in the rice field, leading to reduced nutrients escaping and interfering with the environment.