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Accueil du site → Doctorat → Chine → 2016 → Effects of Reclaimed Water Irrigation on Salt Transportation and C/N Transformation in Deep Soils

Université de l’Agriculture de Chine (2016)

Effects of Reclaimed Water Irrigation on Salt Transportation and C/N Transformation in Deep Soils

商放泽

Titre : Effects of Reclaimed Water Irrigation on Salt Transportation and C/N Transformation in Deep Soils

Auteur : 商放泽

Grade : Doctoral Dissertation 2016

Université : Université de l’Agriculture de Chine

Résumé
Reclaimed water irrigation is an important way to alleviate water resource shortages in agriculture. Compared with ground water, reclaimed water has higher salt, nutrients, and dissolved organic matter (DOM). Its application could thus increase the salt ion in deep soils, increase the risk of salt for pollution the groundwater, and enhance greenhouse gas emission potential in farmland soils. Therefore, based on the field plot experiments in summer maize/winter wheat crop rotation, the effects of different chemical N application rates and irrigation levels on nitrate, and reclaimed water irrigation levels on salt ion migration and accumulation in deep soils were studied, respectively. Then the reliability of the soil water and salt movement parameters under reclaimed water irrigation were calibrated and validated, and a regional simulation model and evaluation model were established to predict salt pollution risk to groundwater under long-term reclaimed water irrigation. Finally, one kind of incubation experiments were conducted to study the effects of irrigation water types (ground water and reclaimed water), N fertilization types (K15NO3 and (15NH4)2SO4) and soil moisture contents (40%,60% and 90% WFPS) on N2O emissions and N fertilizer transformations, the other kind of incubation experiments were conducted to study the effects of irrigation water types (ground water and reclaimed water), N fertilization types (urea, ammonium sulfate and slow-release urea) on soil C and N mineralization. The main results include :(1) In deep loam soils,3 chemical N application rates (142.5,285.0 and 427.5 kg N hm"2) and 80 mm irrigation quota caused NCV-N, NH+-N and TN mainly changed in 0-145 cm soil layer, while the influence depth was 440 cm. In deep heterogeneous soils, the soil texture and structure had a significant influence on soil moisture, NO3-N and TN migration, and the soil structure had a significant effect on soil NH+-N migration.4 chemical N application rates (0,130,260 and 390 kg N hm-2) and 2 irrigation quota (52.5 and 105 mm) caused NO3-N, NH++-N and TN mainly changed in 0-400,0~200 and 0~120 cm soil layer, respectively, while the influence depth was 400 cm for all. In deep heterogeneous soils,380~450 cm clay loam layer blocked the migration of nitrogen.(2) In deep heterogeneous soils, the soil texture and structure had a significant influence on salt ion content and migration.3 irrigation treatments (ground water irrigation with a quota of 52.5 mm, reclaimed water irrigation with a quota of 52.5 and 105 mm, respectively) caused Na+, Mg2+, SO42-and HCO3- mainly migration and accumulation in 0-120 cm soil layer.380-450 cm clay loam soil layer played a role as block layer for soil salt leaching and reduced the risk of the salt pollution groundwater. Compared with ground water irrigation treatment, soluble K+、Ca2+ and Cl= in reclaimed water irrigation treatment had a strong leaching and migration ability, and these 3 salt ion mainly changed in 0~450,0~250 and 0~120 cm soil layer, respectively, and the influence depth was 450,450 and 380 cm, respectively.(3) In deep heterogeneous soils, soil water content and electrical conductivity (ECe) were simulated, and the soil water and salt movement parameters were calibrated and validated. A regional soil water and salt movement simulation model was established, and the results showed that the average soil ECe at the bottom of vadose zone in the Tongzhou and Daxing Districts under the reclaimed water irrigation were 0.70 and 0.85 dS m-1, which was 1.40 and 1.09 times higher, respectively, than the corresponding soil ECe under the ground water irrigation over the next 50 years. A regional evaluation model based on 5 risk indicators was established, the results showed that in the Tongzhou and Daxing Districts, the risk scores of reclaimed water irrigation for polluting groundwater were on average 1.06 and 1.08 times, respectively, higher than the scores under the ground water irrigation. The risk scores of ground water or reclaimed water irrigation for polluting groundwater in the Tongzhou District was average 1.75 or 1.72 times, respectively, higher than that in the Daxing District. Long-term reclaimed water irrigation needs taking salt concentration in reclaimed water and the characteristics of vadose zone structure into account.(4) The cumulative N2O emissions were 3.78-36.30 mg N m-2, and fertilizer derived N2O losses account for 0.14%-2.44% of N fertilizers, while fertilizer derived N residues account for 10.16%-26.95% of N fertilizers from intact soil cores in a 216 h incubation, which added K15NO3 or (15NH4)2SO4) under different soil moisture contents. Compared with ground water irrigation, reclaimed water irrigation significantly enhanced N2O emissions at 40% WFPS by 10.98%, and increased fertilizer derived N residues at 60% WFPS by 20.95%. Irrigation water types and soil moisture contents had significant interaction effect on N2O emission, and irrigation water types and N fertilization types had significant interaction effect on fertilizer derived N residues. These results indicated that reclaimed water irrigation affected N2O emissions and N fertilizer transformations in some special conditions. N fertilizer types and soil moisture contents are the two important factors for N2O emissions and N fertilizer transformations. Control soil moisture contents between 41% and 60% WFPS (the optimum value was 45.5% WFPS), and fertilizer with KNO3 under reclaimed water drip irrigation can reduce N2O emissions and fertilizer derived N2O losses, and correspondingly increase fertilizer derived N residues.(5) The average cumulative mineralization of soil C (incubation 20 days) and N (incubation 14 weeks) in different treatments were 73.50-91.37 mg kg-1 and 52.65~64.04 mg kg-1, respectively. Compared with ground water, reclaimed water irrigation did not significantly increased DOC, DON, soil organic carbon and soil organic nitrogen, while enhanced the mineralization of C by 3.33% and N by 1.01%. Compared with soils without N fertilizer application, N fertilization significantly enhanced the mineralization of C by 14.14~21.22% and N by 15.81%~22.16%. The cumulative mineralization of C and N in soils after DOM removal average significantly decreased 9.83% and 14.83%, respectively. N fertilization and DOM are the two important factors for C and N mineralization.(6) Considering the effects of ground water and reclaimed water irrigation on soil-groundwater-greenhouse gases, we recommend when irrigation with reclaimed water, using drip irrigation, fertilization with NO3" form of chemical N less than 150 kg N hm"2 in a single season, and controlling soil moisture contents between 41%and 60%WFPS in Beijing and other similar sub-humid areas

Mots clés : Reclaimed water; Deep soils; Nitrate; Salt ion; N2O; C and N mineralization;

Présentation (CNKI)

Page publiée le 23 janvier 2017, mise à jour le 11 septembre 2017