Study On Management And Utilization For Water And Soil Resources Under Subsurface Pipe Drainage System In Coastal Saline-alkali Regions Of Hebei Province

Draining water and salt technology by laying subsurface pipe is an efficient hydraulicengineering approach to improve saline-alkali land which based on the theory of “saltmoving with water”. The technology is to lay pore pipes in a certain depth of subsurface.The salt in the soil could be leached into the pipe with rainwater or irrigational water andcould be removed by the subsurface pipe drainage system. And then the system couldrestrain salt moving up by controlling ground water table level. So the technology couldbe used to prevent the crop from waterlogging and salinity, to achieve the goal ofsaline-alkali land management.This paper put forward and researched a series of the water and soil resourcesmanagement measures based on laying subsurface pipe in view of the problems of shallowground water buried depth, high salinity of groundwater, high salt content of soil, lack offreshwater resource, spring drought and summer waterlogging, etc, in coastal saline-alkaliregions of Hebei Province. Taking Huanghua city as an example, researched themanagement and utilization for water and soil resources under subsurface pipe drainagesystem and analyzed the effect of those management measures. The main researchconclusions are as follows:(1) The water and soil resources management measure of groundwater depth controlcould improve the rate of groundwater depth increase by using subsurface pipe drainagesystem. The groundwater depth increased from ground to78.9cm with subsurface pipedrainage in three days after continuous heavy rain, but only reached to24.2cm withoutsubsurface pipe. When the groundwater depth is shallower than30cm, the land would bethreatened by water logging. The duration time of groundwater depth shallower than30cmdecreased from24d to9d by using preventing water logging technology with subsurfacepipe drainage system. The increase of groundwater depth could restrain the high saltcontent groundwater going up to the topsoil and causing the salt accumulation in topsoil.The study showed that the soil salinity would be controlled effectively when thegroundwater depth was deeper than80cm.(2) The water and soil resources management measures which are the salt leachingwith spring freeze-thaw water and the salt leaching with summer rain water under subsurface drainage system could decrease the soil salt content. After salt leaching withfreeze-thaw water in spring, the soil salt content decreased by66.7%in soil layer from0to10cm and69.1%in the layer from10to20cm. After salt leaching with rain waterunder subsurface drainage system in summer, the soil type of top soil changed frommiddle-heavy saline soil to light-middle saline soil.(3) According to the real situation and research results, four water resource utilizationtechnologies were proposed in this paper. They are rainwater runoff collecting and brackishwater irrigation technology, irrigation technology with saltwater and brackish water,high-frequency irrigation technology with saltwater and icing saltwater irrigationtechnology. The use of these technologies increased the amount of irrigation water andimproved the use efficiency of irrigation water and avoided the soil salinity accumulationby leaching salt with rain water under subsurface drainage system in summer based onlaying subsurface pipe.(4) Physical measures like subsoiling, deep plowing, sun mattress and land levelingcould improved the soil structure. Balancing soil nutrients measures like organic fertility,biological fertility and straw returning could increase the soil nutrient content.(5)The effect of water and soil resources management based on laying subsurface pipewas remarkable. It was promoting the efficiency of water and soil resources usage that tomake more reasonable use of limited water resources and increase16%of the arable land.It could improve cultivated land quality, reduce the soil salt content, increase theeffective soil moisture, improve the soil physical structure and increase the soil nutrientcontent, the soil salt content reduced35.2%, the soil bulk density of soil layer from10to40cm decreased3.7-5.8%, the soil porosity and saturated hydraulic conductivityincreased significantly, the soil total N, available P, available K and organic mattercontent compared with check area increased by68.6%,54.8%,46.9%and30.2%. Thefarmland cropping system has changed from one crop a year to two crops a year andthree crops two yeas. The crop yields of summer maize, winter wheat, millet and cottonin subsurface pipe area, respectively, compared with no pipe area increased by51.3%,21.9%,31.5%and21.9%. The surface vegetation has changed in subsurface pipearea,with the Shannon Wiener index and Pielou index higher than in no pipe area, and therelatively low salt resistance ability of pseudohalophytes and non-halophytes graduallyreplace euhalophyte.