【作者】 张爱平；

【导师】 杨正礼；

【作者基本信息】 中国农业科学院 ， 作物生态学， 2009， 博士

【摘要】 以农田为核心的灌区退水污染正在成为影响黄河水质的主要污染源,控制灌区农田退水污染对保障黄河水质安全与整个黄河流域社会经济的可持续发展,具有现实迫切性与长远的战略意义。针对黄河上游灌区农田退水中氮、磷等典型污染物对水质的影响,在宁夏黄灌区吴忠国家科技园区选择灌区典型作物-水稻开展田间试验,通过蒸渗仪测定蒸散量和垂直退水量,采用侧渗液收集仪收集侧向退水量,运用土壤溶液提取仪分层提取0-200cm处土壤溶液,利用田间定位通量法计算农田退水过程中氮磷的流失量,分析探讨了水稻生育过程中农田退水规律,揭示了不同水肥管理下退水过程中氮、磷的迁移和污染特征,结合灌区宏观调研资料,计算了宁夏黄灌区水稻生育期内农田退水的氮、磷负荷量。主要研究结果如下:(1)分析了农田退水量的组成及其影响因素,揭示了影响农田退水量的主要控制因素和作用变量,提出水稻抽穗开花前是调控农田退水量的主要时段。研究结果表明农田退水量主要受灌溉量和地下水位的影响,与二者的相关系数分别为0.88和-0.61,受降雨量和蒸散量的影响较小;在水稻生育期内控制灌溉量可以显著降低退水量,在常规灌溉(W3)、节水20%(W1)和节水40%(W2)三个灌溉量下退水量的差异达到极显著水平,退水量分别占相应灌溉量的38%、35%和30%;传统灌溉量下退水量分别是优化灌溉处理的1.46和2.19倍。在水稻的整个生育过程中,农田退水主要发生在抽穗开花前,此阶段的退水量占各处理全部退水量的80%左右,调控农田退水量应主要在一阶段进行;根据退水量和其影响因素之间相关关系比较明显的特点,利用统计方法建立了稻田退水量与其影响因素的多元回归模型。(2)分析了影响地表退水过程中氮磷的流失量的主要因素,发现田面水中氮磷浓度和退水量是影响地表退水过程中氮磷流失量和潜在污染风险的主控因子。通过对田面水中氮磷的相互转化和衰减情况等动态变化规律进行分析,结果表明:田面水中氮磷浓度与灌溉量和施肥量有关,同一施氮水平下,灌溉量大时田面水中氮磷的浓度相对低,同一灌溉水平下,施肥量大时田面水中氮磷浓度相对高。田面水中氮磷浓度随时间在总体上逐渐降低,受追肥的影响,追肥后有峰值出现,但出现时间不同,总氮和总磷在施肥当天浓度达到最大,铵态氮一般要到施肥后的1-2天,硝态氮要到3-4天。受施肥量和作物生长状况的影响,施基肥后田面水中氮磷的浓度最高。据此动态变化特征可知地表退水发生的时间直接关系到地表退水携带氮磷的状况,地表退水距离施肥时间越近,地表退水过程中氮磷的流失量越大,污染风险越高。(3)垂直退水过程中氮磷污染特征和直渗水中氮磷动态紧密相关,水稻抽穗前的水肥管理是降低农田退水污染的关键时期。定时对0-200cm的土壤溶液进行时空分析表明,在时间上,直渗液中三氮和总磷浓度随时间下降,追肥后有峰值出现。垂直退水污染发生的关键时期是插秧后80天内,即抽穗前,这一阶段由于大量的施肥和长时间的泡田,各层直渗液中氮磷浓度是整个生育期中同层土壤溶液中氮磷浓度最高的时候,也是垂直退水量最多的时候,导致农田退水携带的污染物量最大。常规灌溉量下这一阶段总氮、铵态氮、硝态氮和总磷在垂直退水中的流失量分别占水稻整个生育期垂直退水氮磷流失量的81.4%、73.6%、87.2%和70%,其他水肥处理下流失比例基本相同。水稻抽穗前的水肥管理是降低农田退水污染的关键时期。在深度上,三氮和总磷的浓度基本上都是随深度加深而浓度下降,但在80cm左右浓度回升,是一浓度转折界面,120cm以下浓度变化不大。直渗液中氮磷的浓度受灌溉量的影响,经相关分析,灌溉量和80cm处直渗液中总氮、铵态氮、硝态氮以及总磷平均浓度的相关系数分别为:0.76、0.48、0.74和0.37。农田退水作用的驱动下,铵态氮和总磷向下迁移的距离加长,污染风险加大。(4)垂直退水中氮磷流失量受灌溉量和施肥量的显著影响。传统施氮量下通过降低灌溉量可以明显降低稻田生育期内垂直退水过程中氮磷的流失量,传统灌溉量(W3)下农田退水带走的总氮、铵态氮、硝态氮和总磷分别比节水20%(W1)和节水40%(W2)高出1.29、1.20、1.35、0.79和1.70、1.59、1.73、1.14倍。降低灌溉量同样可以减少退水过程中氮磷的流失量,与N0、N1和N2相比,常规灌溉量下N3处理总氮高出14.11、5.42、2.35,铵态氮高出14.1、5.27、2.31,硝态氮高出16.34、5.74、2.45,总磷流失量高出0.82、0.50、0.65倍。所有处理中常规水肥条件(W3N3)下的流失量最大,其次是W1N3和W2N3,这表明农田退水污染负荷受灌溉量和施肥量的双重影响,二者的交互作用明显,但是起决定作用的是施肥量。(5)侧向退水间歇发生,最先出现在40cm和80cm的土层,以硝态氮的流失最为严重,受降雨量和灌溉量显著影响。4个施肥水平下侧渗液中总氮、铵态氮、硝态氮和总磷的浓度在时间上表现出相同的变化趋势,插秧后20天内各层土壤溶液中的浓度最高,随后下降,在追肥后有小幅回升;在深度上,三氮和总磷整体上随深度下降,水稻全生育期总氮、铵态氮、硝态氮和总磷的浓度变化范围分别是:0.84-17.99、0.03-1.28、0.3-13.21和0.001-0.14mg/L,侧渗液中三氮的浓度波动范围较大,总磷变幅很小,侧向退水过程中氮磷的流失量同样受施肥量的影响,常规灌溉条件N3处理下总氮、铵态氮和硝氮的流失量分别比N2、N1和N0高出1.08、1.34、2,1.17、1.46、2.11和1.21、1.40、2.43倍。(6)计算了不同水肥处理下农田退水中氮磷的比负荷量,结果发现:灌溉量和施氮量对农田退水中总氮和硝态氮的比负荷量有着显著的影响,二者之间存在显著的交互作用。农田退水中氮素的流失以硝态氮为主,占总氮的70%左右。在所有处理中常规灌溉和常规施氮(W3N3)情况下氮磷的比负荷量最大,地表退水中总氮的比负荷量为12.84kg/hm2,铵态氮、硝态氮和总磷的比负荷量分别为7.59、0.57和017 kg/hm2,垂直退水中总氮、铵态氮、硝态氮和总磷的比负荷量分别为84.66、13.54、61.80和0.73 kg/hm2,侧向退水中分别为17.95、2.55、12.65和0.047 kg/hm2。农田退水中总氮和总磷的比负荷量与灌溉量的相关系数分别为0.91和0.88。(7)2008年宁夏黄灌区稻田退水总氮负荷达到0.81万吨,铵态氮为0.16万吨,硝态氮为0.52万吨,总磷为0.0066万吨。更多还原

【Abstract】 The return flow widely existing in many irrigation regions is becoming a major pollutant deteriorating the quality of the Yellow River; agricultural return flow plays a contributory role. To ensure the water quality of the Yellow River as well as the social and economic sustainability of the Yellow River region, controlling agricultural return flow is urgent and strategically meaningful. Focusing on the effect on water quality of such typical pollutants like nitrogen (N) and phosphorusus (P) from the irrigated areas in the upper reaches of the Yellow River, a study was carried out at WuZhong National Science and Technology Park in Ningxia irrigation region, with rice being selected as a typical crop. Through the determination of the amounts of evapotranspiration and vertical leachate using lysimeter, the collection of lateral return flow and soil solution of 0-200 cm soil profile and lateral leachate of 0-80 cm profile, and the calculation of N and P loss during the process of agricultural return flow, this study has investigated the patterns of agricultural return flow during rice growing season as well as the pollution characteristics of nitrogen and phosphorusus during the process of drainage, and revealed the movement and polluting characteristics of N and P under the effect of different irrigation and fertilizer regimes. At last, the research calculated the load of N and P in the agricultural return flow. The major findings are as follows:(1) The composition of agricultural return flow and its factors were analyzed. Results indicated that the quantities of agricultural return flow are mainly affected by the amount of irrigation and groundwater level, with the corresponding correlation coefficient being 0.88 and -0.61, respectively. The impact of the amounts of precipitation and evapotranspiration was relatively little. Reducing irrigation during rice growth period obviously decreased agricultural return flow quantity. The volume of return flow was significantly different among the three irrigation levels, accounting for38%, 35% and 30% of the irrigation amount, respectively. The volume of return flow of traditional irrigation treatment was 1.46 times and 2.19 times of the W1 and W2. Return flow mainly occurred before tassel during the whole growth period of rice accounting for 80% of the total return flow volume. This is the appropriate time to modulate the agricultural return flow. Based on the rather obvious relation between the return flow volume and its factors, a multivariate regression model was built.(2) The main factors that impact the loss of N and P in surface return flow was examined; the concentrations of N and P as well as the return flow volume were found to be two major factors. The dynamic curve showed the concentration of N and P in surface water were affected by the quantities of irrigation and fertilizer applied. Under the same N treatment, the concentrations of N and P were much lower at a high irrigation level. Under the same irrigation level, the concentrations of N and P were much higher at a high application rate of fertilizer. The concentrations of N and P in surface water decreased with time. When fertilizer was further applied, a peak was observed, but the occurrence time was different. The amount of total N (TN) and total P(TP) peaked on the first day after fertilizer application, but 1-2 days and 3-4 days for ammonium (NH4+-N) and nitrate (NO3--N), respectively. Under the impact of fertilization amount and crop growth conditions, the concentrations of N and P were highest after the application of basal fertilizer. The characteristics of such dynamics reflected that the occurrence time of surface return flow was directly related to the amount of N and P carried in the flow. The nearer the surface flow was to the time of fertilizer application, the greater the loss of N and P.(3) The vertical return flow and the concentrations of N and P in the vertical leachate were closely related. The critical period to reduce agricultural return flow pollution is before the heading stage of rice. The regular analysis of the soil solution in 0-200 cm showed that the concentrations of N and P decreased with time and peaked after further application of fertilizer. The critical occurrence time of vertical flow pollution is within 80 days after sowing, i.e. before heading. At this period, the concentrations of N and P were the highest within the growing period as a result of the high fertilizer application rate and continual flooding condition. Under traditional irrigation level, the losses of TN, NH4+-N, NO3--N and TP in return flow accounted for 81.4%, 73.6%, 87.2% and 70% of the total amount of loss, respectively, and the corresponding percentages were basically the same under other irrigation treatments. The concentrations of TN、NH4+-N、NO3--N and TP decreased with depth, but there was a turning point at the interface at 80 cm, after which their concentrations increased. The concentrations of TN, NH4+-N, NO3--N and TP did not alter much below 120 cm. The concentrations of N and P in vertical leachate were affected by the amount of irrigation. The correlation coefficient between irrigation volume and the mean concentration of TN, NH4+-N, NO3--N and TP was 0.76, 0.48, 0.74, and 0.37, respectively. The further the travel distance of NH4+-N and TP driven by agricultural return flow,. the higher the risk of pollution.(4) The loss of N and P were affected by the amount of irrigation and fertilizer applied. Under the traditional N application rate, reducing irrigation during paddy growth period obviously reduced the loss of N and P. The amount of loss of TN, NH4+-N, NO3--N and TP under W3 is respectively 1.29, 1.20, 1.35 and 0.79 times, and 1.70, 1.59,1.73 and 1.14 times higher than under W1 and W2. Decreasing the amount of N-fertilizer applied can substantially reduce the loss of N and P. While the loss of TN in N3 was 14.11, 5.42 and 2.35 times higher than N0, N1 and N2, respectively, that of NH4+-N was 14.1, 5.27 and 2.31 times, NO3--N was 16.34, 5.74 and 2.45, and TP was 0.82, 0.50 and 0.65 times, respectively. The greatest loss of N and P among all treatments was observed under W3N3, followed by W1N3 and W2N3. This suggests that the pollution load of N and P was impacted by both the amount of irrigation and fertilizer applied with a significant interaction. Nonetheless, the amount of fertilizer played a more important role.(5) The lateral return flow occurred intermittently and first appeared in the 40 cm and 80 cm of soil profile, with the loss of NO3--N being the most serious. Lateral return flow is impacted by the quantities of irrigation and rainfall. The concentrations of TN, NH4+-N, NO3--N and TP in lateral return flow followed the same trend with time, and were the highest in soil solution 20 days after sowing. The concentrations declined subsequently and increased slightly again when fertilizer was further applied. The concentrations of TN, NH4+-N, NO3--N and TP decreased with depth. The concentrations TN, NH4+-N, NO3--N and TP during the growth period of paddy averaged 0.84-17.99, 0.03-1.28, 0.3-13.21 and 0.001-0.14mg/L, respectively. The concentrations of TN, NH4+-N and NO3--N covered a wider range than TP. The amounts of N and P in lateral return flow were impacted by the irrigation volume and fertilizer application rate. Under the traditional irrigation level in N3, the loss amount of TN, NH4+-N, NO3--N and TP was higher than in N2, N1 and N0 by 1.08, 1.34 and2 times,1.17, 1.46 and 2.11 times, and 1.21, 1.40 and2.43 times.(6) The load of N and P was estimated in different water and fertilizer treatments. Results indicated that the effect of irrigation and N application levels on the amount of TN and NO3--N in agricultural return flow was remarkable. There was a significant interaction between irrigation norm and N application level. Nitrate N, which accounted for about 70% of the TN, was mainly drained in the agricultural return flow. Among all treatments, the load of N and P per unit area was the greatest under traditional irrigation and N application. The load of TN per unit area was 12.84kg/hm2 in surface return water, while that of TN, NH4+-N, NO3--N and TP per unit area was respectively 7.59, 0.57 and 0.17 kg/hm2. The load of TN, NH4+-N, NO3--N and TP in vertical return water and lateral return water was respectively 84.66, 13.54, 61.80 and 0.73 kg/hm2,and 17.95, 2.55, 12.65 and 0.047 kg/hm2 .The correlation coefficient between irrigation and the load of TN in agriculture return water and that with TP was 0.91 and 0.88, respectively.(7) The load of TN in rice return water from rice paddy reached 8100 tons in 2008 in Ningxia irrigation region, while that of NH4+-N, NO3--N and TP was1600, 5200 and 66 tones, respectively.更多还原