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时间:2018-11-18
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1、Chapter6HydroponicAquaculture:HowOneSystemWorks Thegrowingofplantswithoutsoilhasdevelopedfromexperimentscarriedouttodeterminewhatsubstances(likesoilandwater)makeplantsgrow.Growingplantsinwater(ratherthaninsoil)---inotherwords,hydroponics---datesbackmanymoreyearsthanyoumi
2、ghtthink.ScientistsbelievethathydroponicsoraquacultureisatleastasancientasthepyramidsofEgypt.ScientistsalsoknowthataprimitiveformofaquaculturehasbeenusedintheregionofKashmirforcenturies.Infact,scientistsbelievehydroponicgrowingactuallyprecededsoilgrowing.Theyevenbelieveth
3、atusinghydroponicsasafarmingtoolstartedintheancientcityofBabylonwithitsfamoushanginggardens.Thesehanginggardenswereprobablyoneofthefirstsuccessfulattemptstogrowplantshydroponically.However,returningtomoremoderntimes,researchersattheUniversityoftheVirginIslandshavedevelope
4、dasystemofhydroponicaquaculturethatisbothsimpleandlowcost.Thesystemusesgravitytocreaterecirculatingwatersystemsinwhichfishareraisedandvegetablesaregrown.LetmetakeaminutetoexplaintheprocessofhowthisparticularsystemofhydroponicaquacultureworksontheislandofSt.CroixintheVirgi
5、nIsland. Tostartwith,rainwateriscollectedinalarge3,000-gallontank.Thistankislocatedonthehighestpointoftheisland.Thetankissolargethatitmeasuresabout12feetindiameter.Oncethetankisfilledwithrainwater,fishareaddedtothetankandsubsequentlyraisedinalargetank.So,first,theresearc
6、herscollectrainwaterinalargetank,thentheyaddfish;thefishswimaroundandexcretewasteintothewater.Thenextstepintheprocesshappensinthisway.Therainwatercollectedinthelargetankslowlyrunsoutofthebottomofthelargefishtankandintoanothertank.Thisothertankholdsthewastefromthefish.Thew
7、ateristhenfiltered.Afterthewaterisfiltered,itispassedthrougha“bio-filter”thatcontainsbacteria.Thesebacteriaconvertanyharmfulammoniaproducedinthefishwasteintonitrates.Thesenitratesarethenusedtofeedtheplantsinthenextstageoftheprocess. So,whathappensnext?Well,afterthewaterh
8、aspassedthroughthisbio-filter,itenterstwo100-foot-longhydroponictanks.Justabovethe100-foot-longt
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