| The ongnen lain in northeast China is among the nation’s most importantcommodity grain production bases where much of the rice crop is cultivated. Soilsalinization, water scarcity and unreasonable use are major threats to sustainabledevelopment of agriculture. Irrigated rice culture is an effective low-cost ameliorationapproach to prevent and/or reduce soil salinization. But few studies focused on theeffects of water discharge on saline-sodic salt improving, rice yield and effectiveutilization of water resource. The study area was the typical saline-sodic irrigationarea of the Songnen Plain (i.e., Qianguo irrigation district). A field experimentconsisting of a low, a moderate and a high saline-sodic soil and six irrigationschedules was carried out to investigate changes in root-zone soil salt content, riceyield and irrigation water use efficiency on saline-sodic soils across a salinity gradientunder different irrigation schedules. The irrigation and discharge schedules were:(1)30-mm irrigation with9-time discharge (I-30-9);(2)30-mm irrigation with6-timedischarge (I-30-6);(3)30-mm irrigation with3-time discharge (I-30-3);(4)50-mmirrigation with6-time discharge (I-50-6);(5)50-mm irrigation with3-time discharge(I-50-3);(6)80-mm irrigation with2-time discharge (local traditional irrigation anddischarge, I-80-2). In addition, salt balance of the Qianguo Irrigation Area was carriedout. On this basis, we put forward comparatively good management options forreclamation the saline-sodic soil, increase rice yield and saving water. This study hasimportant theoretical significance and practical value for long-term, sustainable development and food security in the saline-sodic irrigation area of the Songnen Plain.Through the above research, we mainly obtained the following conclusion:(1) Reductions in soil salt under different irrgaiton and discharge schedules com-bined with different initial salinity were analysised. While all six treatments reducedroot zone salt content, the reduction increased with increasing discharge frequency:reduction in soil salt under I-30-9treatment was about5.3times than that underI-80-2, reduction in soil salt under I-30-6treatment was about3.5~4.3times than thatunder I-80-2, whereas reduction in soil salt under I-30-6treatment was about1.1~1.7times than that under I-80-2; the reduction increased with increasing salinity as well:reduction in soil salt in the high saline-sodic soil was about6.9~8.9times than that inthe low saline-sodic soil, whereas reduction in soil salt in the moderate saline-sodicsoil was about2.8~6.0times than that in the low saline-sodic soil.(2) Rice yield under different irrgaiton and discharge schedules combined withdifferent initial salinity were analysised. Irrigation water depth and dischargefrequency have a major impact on the rice yield. Rice yield increased with increasingirrigation water depth; Rice yield increased with increasing discharge frequency underall30-mm irrigation on the low saline-sodic soil; Rice yield decreased with increasingdischarge frequency under50-mm irrigation with6-time discharge and50-mmirrigation with3-time discharge on the low, moderate and high saline-sodic soils,whereas no significant difference among the rice yields mentioned above and yieldunder local traditional irrigation and discharge schedule were found; Rice yielddecreased with increasing salinity.(3) Water balance components, irrigation water use efficiency and water useefficiency under different irrgaiton and discharge schedules combined with differentinitial salinity were analysised. During the5-month rice growth period, total rainfallwas recorded466mm. Irrigation water during the same period was530mm for I-30-9,440mm for I-30-6,320mm for I-30-3,520mm for I-50-6,320mm for I-50-3, and340mm for I-80-2. The irrigation water use efficiency decreased with increasingdischarge frequency; Discharge frequency has small impact on the water useefficiency; both the irrigation water use efficiency and the water use efficiency decreased with increasing salinity.(4) The present situation of water and salt balance of the Qianguo irrigationdistrict was estimationed. The Qianguo Irrigation Area is in the desalinization state.Salt removed through drainage was4.8times as salt input through irrigation in theQianguo irrigation district. Net salt losses (salt input through irrigation minus saltremoved through drainage) was3.5×108kg in2012.(5) Considering reduction of soil salt, maintain and increase rice yield and watersaving and efficient water utilization as a whole, and in view of the Qianguo IrrigationArea salt balance situation, we put forward that the main regulating targets of thesaline-sodic irrigation areas on the Songnen Plain is the moderate and highsaline-sodic soils and the comparatively good option of irrigation and dischargeschedule for the two kind of soils are50mm irrigation with6-time discharge; thesecondary regulating targets of the saline-sodic irrigation areas on the Songnen Plainis the low saline-sodic soils and the comparatively good option of irrigation anddischarge schedule for this soil is the local traditional irrigation and dischargeschedule. |
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