Study On Field Water Transformation Using Isotopes

Study on the rules of soil water transformation is of great importance to reasonable water resources utilization and toimprove the water use efficiency.In this paper,winter wheat and summer maize in daxing district from2013 to 2014 were taken as examples. Besides field monitoring, stable hydrogen and oxygen isotopes were used as tracers in this study.Inthis paper soil water dynamics in different seasons and distributioncharacteristics in different soil depth underdifferentirrigation and fertilization and the isotopic compositions of precipitation, soil water, irrigation water and stemswaterwere studied, besides, source of root water uptakeand its contribution proportionwasquantified and the crop water consumption rule wasclarified. All the researchcontents reveal the law of soil moisture transformation in daxing district.The main conclusions of this paper are as the following:The soil water dynamics of summer maize was greatly influenced by rainfall.Itchange significantly within 60 cm layeraffected byfrequent rainfall and high rainfall intensity in 2013, while itchanged significantly within 100 cm layerin 2014 with less rainfall. The soil water dynamics varied in different treatments, which showed that the higher the soil water content, the less obviously the water dynamics changed.The soil waterdynamicsof winter wheat changed significantly within 100 cm layer, and it changed most significantly in jointing and heading stage, in which winter wheat needs much more water. The range of the soil water dynamicsvariation in different depth gradually reduced with the increaseofirrigation.The meteoric water line is expressed as δD=7.1145δ18O+1.7407(R2=0.9298) and the soil water isotope fitting curve is expressedas δD=6.1496δ18O-9.066(R2=0.6924), which proves that precipitation and soil water evaporated obviously. The soil water isotope within 100 cm layer changessignificantly, while it is relatively stable under the 100 cm layer.The soil water isotope of summer maize varied in different treatments affected by soil water content, which showed that the higher the soil water content, the less enriched the soil water isotope, while that of winter wheat varied in differenttreatments affected by irrigation, which showed that the higher the irrigation, the less enriched the soil water isotope. The stem water isotopewasmore enriched in seedling stage than that in vigorous growth stages, and the stem water isotope of winter wheat was more depleted than that of summer maize.The summer maize in 2013 mainly used the water in 0-50 cm layer. The higher the soil water content, the lower the root water uptake depth, while the contribution proportion of shallow water was higher. The root water uptake depth of summer maize in 2014 was deeper than that in 2013. The summer maize in 2014 could use soil water from under 90 cm layer. The maximum depth of winter wheat root water uptake was 200 cm layer. The root water uptake depth varied in different treatments affected by irrigation. The winter wheat used water from relatively shallow layer. The root water uptake depth in jointing(reviving) stage was less than that in heading(tasselling) and filling stage.The higher the soil water content, the greater the water consumptionof summer maize, while the water use efficiency was lower, and the yield was thebiggest with no fertilization. The water consumptionof winter wheatwas greater under higher irrigation. And the water use efficiency was the biggest(1.74kg/m3) in T2 treatment, which was irrigated in winter, reviving andfilling stage, and the yield of this treatment wasrelatively high(6659.3kg/ha). It was suggested that the total irrigation of local winter wheat should be 220 mm.