Seasonal patterns in water uptake for Medicago sativa grown along an elevation gradient with shallow groundwater table in Yanchi county of Ningxia,Northwest China

Lucerne （Medicago sativa L.） is a deep-rooted perennial leguminous forage with high evapo-transpiration rate exceeding the annual precipitation in semi-arid areas of Northwest China. Groundwater might be the potential water sources of lucerne in the area with shallow groundwater table. In this study, stable isotopic compositions of oxygen and hydrogen （6180 and 8D） of different water sources and xylem sap were analyzed to determine the seasonal （April, June, July and August） and topographic （three slope positions） variations in water sources for lucerne growing in Ningxia eastern semi-arid area adjacent to Mu Us Desert characterized by shallow groundwater table. IsoSource software was used to calculate the probable contribution of different water sources to the total plant water uptake. Stomatal conductance, stem water potential, carbon isotope discrimination （A13C） of whole plant were also determined for evaluating the water status of lucerne growing at different slope positions. The results showed that soil water content increased as the elevation decreased. Oxygen compositions of soil water in the 0-40 cm profile fluctuated considerably. Soil water 8180 values in deep profile （〉3.5 m） were similar to those in groundwater, implying the recharge of groundwater to this soil layer. Highest water utilization rate from deep soil profile （below 350 cm） was recorded for lucerne grown at the slope position 1 （groundwater table depth of 3.5-3.9 m） in April, June and July. The lucernes at slope position 2 （groundwater table depth of 5.8-6.4 m） and slope position 3 （groundwater table depth 7.1-8.3 m） mostly used water from deep soil layers （below 350 cm） during dry period, and turned to use water from superficial soil layer in wet period. Higher yield, A13C value of whole plant and stomatal conductance were observed for lucerne grown at the slope position 1 than those at other slope positions. These results indicated that groundwater is a significant water source for transpiration of lucerne grown in Ningxia semi-arid area with shallow groundwater table where lucerne grassland is suggested to be established so as to obtain better yield performance.

The integration of FAO-CropWat Model and GIS Techniques for Estimating Irrigation Water Requirement and Its Application in the Gaza Strip

In the Gaza Strip irrigation practices are only based on the farmer’s own experience, they determine when and how to irrigate crops based on the appearance of the soil and the climatic conditions. Even though FAO-CropWat model is used for many countries to estimate irrigation water requirements, it is rarely used for Gaza Strip. In the current re-search, it is the first attempt to model the historical available meteorological data to estimate the irrigation water requirements for the most common cultivated crops (citrus, almonds, date palms, grapes) and to compare the results with the farmer irrigation practices. The model results show that, the reference evapotranspiration accounts for 1451 ± 5 mm/year. Therefore the irrigation water requirements estimated to be 763, 722, 1083, 591 mm/year in average for Citrus, Almonds, Date palm, Grapes, respectively. The farmer irrigation practice exceeding the irrigation water requirement by 30%. The spatial distribution of irrigation water requirements in the entire area of Gaza Strip is shown on maps derived by GIS technique based on data from eight meteorological stations. Irrigation water quality is not optimal in the Gaza Strip, chemical analysis of irrigation wells indicate high salinity and SAR ratio. The obtained results from the model could be a good management tool for the planners and decision makers to minimize the overexploitation of the groundwater and to build fair and strict regulations to optimize the water use in agricultural sector in the Gaza Strip which characterized by semi-arid region.

Irrigation Demand VS Supply-Remote Sensing and GIS Approach

To determine the irrigation requirements of rice crop on different soils, an integrated approach is used using Remote Sensing and GIS techniques. Depending on the type of soil, climate and the crop acreage, the water requirement for paddy fields is derived. This study is focused on estimating the water demand for rice crop in Rabi season. Crop evapo-transpiration and soil percolation losses account more in rice fields especially in hot climate like Rabi season. In addition to evapo-transpiration and percolation losses, the conveyance losses are also accountable in the case of unlined canals. Satellite data is used to estimate the rice and fallow lands. In conjunction to satellite interpreted data, climate and soil data are also integrated in GIS platform. CROPWAT model is used to determine the crop evapo-transpiration (ETc). There are 11 Water User’s Associations (WUA) in the command area and under which 13 canal blocks are delineated. These blocks are again delineated in to 212 sub blocks. This study indicates that there exists a 5% to 20% of water deficiency in some WUAs and also water surplus in some WUAs varying from 15% to 40%.

Driving mechanisms of desertification process in the Horqin Sandy Land—a case study in Zhalute Banner,Inner Mongolia of China

Both natural and human factors contributing to desertification were examined to understand the driving mechanisms of the desertification process in Zhalute Banner,Inner Mongolia of China.The coefficient of variation(CV)and climate departure index(Z)were calculated to examine the fluctuations and trends of interannual variations of temperature and precipitation;TM remote sensing data was extracted to obtain the sandy land area;linear regression analysis was used to analyze climate changes and the socio-economic evolution over the years,and it was also used to standardize the variables,which included annual temperature,annual precipitation,human population,and livestock number,in order to measure the difference in the rate of change between climate and anthropogenic factors.The results showed that there was a rise of about 1.6uC in temperature but no significant change in precipitation from 1961 to 2000,which indicated a short-term climatic trend toward aridity in this area,a condition necessary for desertification.The fraction of precipitation in spring tended to increase whilst the fraction in autumn and winter decreased.Both the human population and livestock population had tripled and the cultivated area had doubled from 1961 to 2000,suggesting that socio-economic factors might have contributed more significantly to the desertification.Between 1988 and 1997,the sandy land area increased by 12.5%,nearly 2.4 times in the farming section.It could be concluded that the driving mechanisms of the desertification processes in Zhalute banner are mainly the policy of cropland expansion and the rising populations of humans and their livestock,which has affected the land use pattern in the past decades.