Simulation Of The Yellow River Water Threshold Based On Limiting Factor Of Farmland Soil And Water Environment In Inner Mongolia Hetao Irrigation District

Hetao irrigation district in Inner Mongolia is facing a substantial reduction in the amount of water from the Yellow River. The stabilized environment of farmland on soil and water formed in long-term, to a certain extent, is bound to change. The regional environmental prediction method on farmland area of soil and water would be sought. The threshold of Yellow River water to the limiting factor of the farmland environment of water and soil were objectively proposed. It would be scientifically and practically significant to the sustainable development of ecological agriculture and the sustainable use of water resources.In this research, Hetao irrigation district in Inner Mongolia was as the background. Longsheng demonstration area in Yongji irrigation system was as the typical study area. The corn crops which water consumption was iarge and moderately sensitive to salt was as the representative crop. Combined with laboratory experiments and related research conclusions, the threshold (corn in normal growth) of farmland environment of soil and water limiting factor(soil moisture and salinity, groundwater depth and salinity) was comprehensively identified. Through systematic observation of field tests, we conducted the classical statistical analysis and temporal dynamics analysis on various limiting factors of farmland soil and water environment. On the basis of field observation experiments, we established a distributed unsaturated-saturated coupling model of water and salt transport. Based on the study of the threshold of farmland soil and water environment, the amount of irrigation water in growth period and autumn period were simulated. The regression relationship was established by using irrigation amount of typical research area and5irrigation districts. Combined the regression equation, the threshold of irrigation amount in typical research area was used to calculate the thresholds of irrigation amount in5irrigation districts, then that of intake from Yellow River was got.The main results of this paper were as follows:The experiments of wilting coefficient to different soil textures and the crop emergence rate to different soil salinity were carried out. Combined the related research results about suitable soil moisture, the threshold of crop salt tolerance and suitable groundwater depth, the thresholds of each limiting factor to the maize in planting stage, seeding-jointing stage, jointing-tasseling stage, tasseling-pustulation stage, after auntumn irrigation and before freeze-up were comprehensively identified. The thresholds of soil moisture were10%～15%、15%～20%、8%～25%、18%～25%、20%～24%. The thresholds of soil salinity were0.5mS/cm、0.8mS/cm、1.5mS/cm、1.7mS/cm、0.45mS/cm. The thresholds of groundwater depth were1.8～2.2m、1.6～2.0m、1.6～1.8m、1.6～2.0m、1.8～2.0m. The thresholds of groundwater mineralization were3g/l、1.7g/l、1.8g/l、2g/l、3g/l.The results of classical statistical analysis method been applied to the limit factors related experimental observation values showed that, the soil moisture content, soil salt content, groundwater depth and mineralization of groundwater associated observations pepicts a moderate variability during the corresponding time slot, herein, the soil surface salt content and groundwater mineralization related coefficients of variation are significantly higher than the soil moisture content and groundwater depth related ones, which is a strong moderate variability one. The soil moisture content, groundwater depth within the time slot and the logarithmic transformated soil salt content and groundwater mineralization associated observations are the normal distributed ones.The Kriging interpolation method of geostatistics, as well as the Surfer software was adopted to do a spatial interpolation analysis on the soil moisture content, soil salt content, groundwater depth and mineralization of groundwater of0-40cm the tillage layer depth in the typical study area. Been affeted by the boundary and terrain conditions, all the soil moisture content, soil salt content, groundwater depth and mineralization of groundwater related spatial patterns depict a decending order from northwest to southeast of the study area, which are consistent with each other. After the grey relational analysis method been applied to the water and salt related degree in different depth, results showed that, when the groundwater depth is2m, the grey correlation degree of soil moisture content, soil salt content, groundwater depth and mineralization of groundwater reach to a relative equilibrium state, indicating that the annual evaporation limitation of phreatic water in the typical study area is between2and2.5m.With the support from3S technology, the typical study area was devided into3sections with soil surface salt (0-20cm) and relative uniform texture based on the geological statistics principles. Hence, the water and salt transportation SWAP model in distributed unsaturation zone was eatablished, accompanied with the calibration and validation of the model. The transport model of groundwater and solute in the typical study area was built based on the Visual MODFLOW. With the water flux and solute flux, as well as the groundwater depth been treated as the coupled boundary in the underground water level of unsaturation zone, the model and algorithm of coupled water and salt transport in regional distributed unsaturation zone-saturation zone was eatablished, accompanied by the cyclic test been applied to the coupled model.The tested results of the coupled model meet the irrigation quatity threshold of the typical study area under conditions of agricultural soil and water environment related limitation factors threshold, the irrigation quatity threshold of the typical study area in growth period of different hydrological years are:296-308mm in dry year,197-220mm in normal flow year,118-130mm in high flow year. The average irrigation quatity threshold in autumn irrigation period is178-194mm.A regression relation was built based on the irrigation quatity in the typical study area and the ones in every irrigation field, the irrigation quatity thresholds in every irrigation field were calculated inversely based on the one in the typical study area, the direct calculation method derived annual intaken Yellow River water threshold of Hetao irrigation district is3.81389-4.18257billion m3.