宁夏引黄灌区稻田氮素浓度变化与迁移特征

Concentration change and migration characteristics of nitrogen in the paddy field of Ningxia Yellow River Irrigation Area

过量施氮与不合理灌水是农田面源污染加剧的主要原因。为了寻求较优的水氮管理模式以促进农业生产和减少农田退水对黄河水体的污染,在宁夏引黄灌区典型稻田中开展了不同水氮条件下稻田氮素迁移转化规律研究。结果表明:不同水氮条件下稻田田面水NH4+-N与NO3--N浓度伴随施肥出现明显峰值,NO3--N峰值出现时间较NH4+-N晚,且变化较平缓。3次追肥时期和整个生育期田面水NH4+-N平均浓度与施氮量和灌水量都呈显著相关,田面水NO3--N平均浓度与施氮量呈显著正相关,与灌水量相关性不显著。稻田30 cm与60 cm深度的直渗水NH4+-N浓度受施肥影响较大,与田面水NH4+-N浓度变化规律相似,90 cm处直渗水NH4+-N浓度峰值出现较为滞后,且浓度较上层土体低,120 cm处直渗水NH4+-N浓度大体呈现持续上升趋势,整个生育期直渗水NH4+-N平均浓度与施氮量呈显著相关,仅30 cm处NH4+-N平均浓度与灌水量呈负相关,其他土层深度不显著。30 cm与60 cm直渗水NO3--N浓度在首次灌水后急剧下降,在施肥后有较小幅度上升,90 cm与120 cm直渗水NO3--N浓度下降缓慢,仅30 cm处NO3--N平均浓度与施肥量显著正相关。总的结果表明减少施肥或灌水均可达到减少农田氮素淋失的目的。

Excessive use of nitrogen and irrational irrigation are the primary drivers of aggravated non-point farmland pollution.It is therefore urgent to develop effective coupling modes of water and nitrogen use in agricultural production in Ningxia Yellow River Irrigation Area that reduces non-point farmland pollution of the Yellow River.To that end,an experiment was conducted in typical paddy fields of the area to study the effect of irrigation and nitrogen use on non-point pollution.Based on the results,high concentra-tions of NH4＋-N and NO3--N were noted in surface water of paddy fields after fertilization.Compared with NH4＋-N,the peak con-centration of NO3--N was a little delayed and built up more slowly.During the periods of topdressing and the entire experimentation,NH4＋-N average concentration in field surface waters was obviously related with nitrogen input and irrigation amount.The average concentration of NO3--N in field surface water was significantly related with nitrogen input,and not irrigation amount.The concen-trations of NH4＋-N in seepage waters at depths of 30 cm and 60 cm were strongly influenced by fertilizer dose.The dynamics of NH4＋-N concentration in the seepage waters were similar to that of NH4＋-N in field surface water.There were larger lags in the peak concentration of NH4＋-N at 90 cm soil depth,and which was much lower than that in the upper soil layers.The concentration of NH4＋-N at 120 cm soil depth steadily increased.The average concentration of NH4＋-N in the different layers over the entire period of experimentation was significantly related with nitrogen input,and not irrigation amount except at the depth of 30 cm.The concentra-tions of NO3-N in seepage water at 30 cm and 60 cm soil depths dropped sharply after the first irrigation,but gradually increased after each fertilization.The concentrations of NO3--N at 90 cm and 120 cm soil depths slowly dropped.A significant correlation be-tween NO3--N concentration and nitrogen input was only noted in seepage water at 30 cm soil depth.The overall result suggested that deficit irrigation limited nitrogen leaching.