Research On Farmland Water And Soil Environment Response To Water Saving In Qingtongxia Irrigation District

Influenced by the extensive agricultural irrigation mode and a sharp growth of fertilizer amount, a series of agricultural water and soil environment problems occurred in Ningxia irrigation district, such as agricultural non-point source pollution, high groundwaterlevel, soil salinization, water pollution in the Yellow River etc.However,Ningxia goverment began to implement water-saving irrigation since 1999, and as a result, the proportion of agricultural water consumption declined gradually and extensive irrigation mode has been improved. Thus in order to exploreinfluence of water-saving irrigation on water and soil environment problems above, Qingtongxia Irrigation District taken as the research object, evolution characteristics of agricultural non-point source pollution, groundwater level with soil salinizationand the water environment in the Yellow River were analysed.At the same time the pollution control measures forwater pollution in the Yellow Riverwere proposed.The main research results are summarized as follows:Irrigation mode gradually improved since water-saving irrigation was carried out. The average annual water diversion quantitywas reduced by 20.2% and farmland drainage dropped by 29.7% in recent 10 years; fertilizer growth has slowed and nitrogen per unit area was lower than before; planting structure changed greatlyand the planting proportion of crops decreased by 11%.The wheat sown ratio reduced from 30% to 16% and corn planting ratio increased from 25% to 32%.The fruits and vegetables remained the biggest increase; grain yield was affected obviously by water saving irrigation, fluctuating with irrigation area.And per unit area yield of grain increasedby 15.9% within 11 years.Based on evolution analysis ofirrigation return water pollution in the typical drainage ditches such as Yinxin and Fifth drainageditches,the effect of water-saving irrigation on agricultural non-point source pollution abatement were concluded. First, water in the drainage ditch decreased during the process of water-saving agriculture, and irrigation return water quality has improved.For the Yinxin drainageditch ammonia concentrationin July tended toward a dynamic stability and total phosphorus showed a decreasing trend, whilebothconcentrations declined for Fifth drainageditch.Furthermore farmland pollution load decreased significantly.For example, compared with early stage of water-saving agiculture, ammonia nitrogen and phosphorus reduced by 35.3% and 41.7%separately in the Yinxin drainageditchand correspondingly 71.2% and 63.7% for Fifth drainageditch.It wasproven later thatfarmland pollution load and relative farmland water existed significant positive correlation,thus the implementation of agricultural water-saving contributes toagricultural non-point source pollution prevention and control.Irrigation diversion was the main reason for the change of groundwater level. The groundwater depth gradually increased in the irrigation area after water saving. Small depth (<1.5m, heavy salinized area) area ratio decreased from 55% in 2000 to 37% in 2013. Meanwhile agricultural water saving also brought a significant impact to soil salinization in the irrigated area and on the wholethe situation of soil salinization made some improvement, althoughsome areadeteriorated somewhat.At last through the salt balance analysis in the irrigation district,it was concluded thatdrainage engineering management should be strengthened wih the implementation of water saving in agriculture.Through the spatial and temporal characteristics analysis of runoff, water quality and pollution load in Yellow River Stations,it was found thatdiversion and drainagein Qingtongxia Irrigation Districtcaused significant influence for water environment of drainage receiver.The Yellow River water quality influencing factors model of principal component analysis showed that water quality influencing factors of the Yellow River were complex,and agricultural non-point source pollution contributed more to the water quality of the Yellow River,while industrial wastewater pollution showed a weakening influence. Furthermore the Yellow River pollution load multiple regression prediction model showed that the total phosphorus load came mainly from fertilizer runoff pollution, and chemical fertilizer and livestock pollution contributedlarger to the COD emission load in the Yellow River, and to cut ammonia nitrogen pollution load in the Yellow River, the measures focus was to reduce the drainage amount. Finanlly, in order to improve water environmentof the Yellow River, to reduce fertilizer use, developing agriculture water-saving technology andto strengthen prevention and control of animal husbandry pollution and the irrigation drainage water quality monitoring and governance were proposed in this paper.