Assessment and utilization of soil water resources

Based on the analyses of water interactions and water balance, this paper discusses the issues on the assessment and regulation of soil water resources, which lays the scientific basis for limited irrigation and water-saving agriculture.

Soil and Water Resources and Land Sustainable Productivity in the Catchment Area with Intensive Management in Hilly Red Soil Regions,China

Taking an example of Majiayu Catchment Area (14.15 ha) in Taoyuan County of HunanProvince, the soil and water resources dynamics, fertility evolution characteristics andland productivity changing situation were studied. Fixed observation results from 1993to 2002 showed that pools covering about 15% of total area could store up 10% of surfacerunoff, keep 78.1% of eroded soil and 65.4% of lost nutrients. The yearly ratio ofinterception and evapotranspiration in land, storage in pools and drainage was 7:2:1,which ensured the resources and nutrients equilibrium and a benign recycle in thecatchment area system, and benefited the aquatic culture and helped to resist seasonaldrought. Moreover, the results showed that soil erosion modulus decreased significantly,equal to or lower than soil loss tolerance (≤500 tkm-2) in reddish yellow soil regions.Soil organic matter, total and available N content in sloping land, dryland and paddyfield increased steadily (>10%); water storage enhanced by more than 20% in sloping landand dryland in drought season; crop production increased by more than 20%; and productionof trees, fruits, tea and fish as well as land productivity increased yearly.

Effects of land use patterns on slope soil water in the semiarid Loess Plateau,China

Land use patterns(LUPs)are the form in which various land use types are combined spatially,evidently impacting soil water.However,the influence mechanism by which LUPs form remains unclear.In this study,the soil water content(SWC)in the 0–160-cm soil depth was observed in shrubland(SL),mature forestland(MF),grassland(GL)and young forestland(YF)sites on four slopes with different LUPs in the Yangjuangou catchment of the Chinese Loess Plateau.The SWC in SL-YF-SL(13.28%)was significantly greater than that in YF-MF(9.93%),MF-GL-YF(10.38%)and SL-MF(10.83%)and was temporally stable during the study period.The spatial distribution of SWC along the slope differed among the four LUPs.Vegetation characteristics and soil texture mainly determined the spatial variations in SWC in the shallow soil layers(0–40 cm),while topographic factors were the determinants in the deep soil layers(60–160 cm)as well as in the entire soil profile(0–160 cm).The significance of SWC differences among the various land use patterns increased with decreasing precipitation during the growing seasons.YF-MF(77.8 mm)and SL-YF-GL(73.9 mm)required more rainwater than SL-MF(68.2 mm)and MF-GL-MF(67.5 mm)to compensate for the loss of soil water on the monthly scale during the rainy season.Therefore,vegetation restoration should consider land use patterns on hillslopes for soil water conservation.

Effects of climate and land use changes on runoff,sediment,nitrogen and phosphorus losses in the Haihe River Basin

Investigating the impacts of climate and land use changes on the hydrological cycle and water environment at the basin scale is important for providing scientific evidence to manage the trade-offs and synergies among water resources,agricultural production and environmental protection.We used the Soil and Water Assessment Tool(SWAT)with various spatiotemporal data to quantify the contributions of climate and land use changes to runoff,sediment,nitrogen(N)and phosphorus(P)losses in the Haihe River Basin since the 1980s.The results showed that 1)climate and land use changes significantly increased evapotranspiration(ET),transport loss,sediment input and output,and organic N and P production,with ET,sediment input and organic N affected the most;2)runoff,sediment and ammonia N were most affected by climate and land use changes in the Daqing River Basin(217.3 mm),Nanyun River Basin(3917.3 tons)and Chaobai River Basin(87.6 kg/ha),respectively;3)the impacts of climate and land use changes showed explicit spatiotemporal patterns.In the Daqing,Yongding and Nanyun River Basins,the contribution of climate change to runoff and sediment kept increasing,reaching 88.6%-98.2%and 63%-77.2%,respectively.In the Ziya and Chaobai River Basins,the contribution of land use was larger,reaching 88.6%-92.8%and 59.8%-92.7%,respectively.In the Yongding,Chaobai,Ziya and Daqing River Basins,the contribution of land use to N and P losses showed an increasing trend over the past 40 years(maximum 89.7%).By contrast,in Nanyun and Luanhe River Basins,the contribution of climate change to N and P losses increased more(maximum 92.1%).Our evaluation of the impacts of climate and land use changes on runoff,sediment,and N and P losses will help to support the optimization of land and water resources in the Haihe River Basin.