Itisofpracticalsignificanceforthedecision-makingoncountryfoodsecurityandfarmlandprotectiontoanalyzetheconversionmarginsforthemajorusesofagriculturallandandtheirvariations.Basedonthepaneldataofwheat,corn,vegetable,fruit,andforestsproductionsfrom520investigatedfarmerhouseholdsof13investigatedvillagesinShandongProvincefrom2003to2009,andusingCobb-Douglasproductionfunction,therevenueconversionmarginscanbeobtainedseparately,betweendifferentgrain-crops(wheat,corn)anddifferentnon-graincrops(vegetable,fruit,forests),andtheconversionrelationshipbetweengrowinggrain(wheat,corn)andgoingoutfornon-farmwork.Theresultsshowthatfrom2003to2009,growingwheatandcornaremoreeconomicallyandreasonablyforfarmers,comparedwithgrowingvegetable,butgrowingwheatandcornarebecominglesseconomicallyandlessreasonablydaybyday,comparedwithplantingforests.Moreover,theconversionmarginbetweenwheatandfruitshowsobviousscissorsdifference.Justfrom2007,farmers'growingfruitbecameeconomicallyandreasonably,butuntil2009,comparedwithgoingouttoworkafterabandoningfarm8land,growingwheathadnoeconomicrationality.From2003to2009,farmers'growingcornismoreprofitablethangrowingfruitandgoingoutfornon-farmworkafterabandoningfarmland.Thesubsidiesforwheatandcornhaveincreasedfarmers'comparativeincomefromfoodproductionremarkably,butthesubsidiescannotchangethegeneraltendencythatfarmerstransformfood(wheat,corn)productionintonon-food(especiallyforests)production.Therevenuedifferencebetweengrowingwheat,cornandvegetableandgrowingfruitandforestsisbeingpulledceaselesslybigger,andthetendencythatfarmerstransformwheat,cornandvegetablegrowinglandsintofruitandforestsgrowinglandshasbecomeincreasinglyapparent.
