Runoff loss of nitrogen and phosphorus from a rice paddy field in the east of China: Effects of long-term chemical N fertilizer and organic manure applications
Naxin Cui, Min Cai, Xu Zhang, Ahmed A. Abdelhafez, Li Zhou, Huifeng Sun, Guifa Chen, Guoyan Zou, Sheng Zhou
Abstract
Agrochemicals, e.g., nitrogen (N) and phosphorus (P) fertilizers are being used extensively to increase the agricultural production; however, considerable losses of these fertilizers find their way to the surrounding surface water bodies causing severe pollution and eutrophication. Such non-point source of pollution seemed to be more pronounced in the rice fields. Accordingly, a two-year (2018–2019) field study was conducted at a rice paddy field under long-term N fertilizer management practices in the rural suburb of Shanghai, China. N and P losses through the surface runoff in the paddy field were measured. Six N fertilizer practices were performed since 2011 as follows: no N treatment (N0), chemical N treatment (urea, N 46%) applied at the rates of 100 (N100), 200 (N200), 300 (N300) kg N ha−1 and combinations of chemical and organic N fertilizers (30% organic manure) at the rates of 200 (ON200) and 300 kg N ha−1 (ON300). Results showed that the highest runoff losses of TN (20.5 kg ha−1) and TP (1.66 kg ha−1) were respectively produced by N300 and ON300 practices during the rice growing season. TN runoff loss significantly decreased by reducing the rate of N fertilizer (P < 0.05). Comparing with N300 treatment, ON300, ON200 and N200 treatments reduced N loss by 2.4%, 27.0%, and 13.9% in 2018 and by 24.0%, 49.0% and 37.5% in 2019, respectively. Organic manure substitute decreased N loss but increased P loss from the surface runoff. The time period after fertilizer application significantly impacted N and P loss from surface runoff. The surface runoff occurring during the early stage after fertilizer applications contributed mostly to the total N loss. Consequently, the control of initial surface runoff events might be an effective strategy to attenuate the surrounding water pollution due to N surface runoff in the paddy fields.