StudiesshowfarmlandinAfricaisoftenlackinginimportantnutrients.Butresearcherssaycombiningdifferentfarmingmethodsmayhelp.Sincetheworldfoodcrisisseveralyearsagoresearchershavedirectedmoreoftheirattentiontosma

　　StudiesshowfarmlandinAfricaisoftenlackinginimportantnutrients.Butresearcherssaycombiningdifferentfarmingmethodsmayhelp.

　　Sincetheworldfoodcrisisseveralyearsagoresearchershavedirectedmoreoftheirattentiontosmallfarms.MostfarmsinareassouthoftheSaharaDesertareonlyaboutoneortwohectares.Oneofthegoalsistoincreaseproductionwithoutnecessarilyclearingmorelandtogrowadditionalcrops.

　　Americanresearcherssaythatcanhappenwithgreateruseofanagriculturalsystemcalledperennation.Itmixesfoodcropswithtreesandperennialplants–thosethatreturnyearafteryear.

　　Mr.ReganoldwhoiswithWashingtonStateUniversitysayspoorsoilmayhaveresultedfromyearsofweatheringthatwashedawaymanynutrients.Hesayssomefarmersmayhavedonemoreharmthangood.

　　HeestimatesthatuptotwobilliondollarsworthofnitrogenphosphorousandpotassiumislostfromAfricansoileachyear.

　　ThescientistsaysthewordperennationdefinesthreesystemsthatarealreadyusedinAfrica.Theoldestofthethreeiscalledevergreenagriculture.Thisiswherefarmersplanttreeswiththeircrops.JohnReganoldsaysfarmersinAfricahavebeendoingthisforsixtyyearsbutitseemstobegrowinginpopularity.

　　ThemethodisgainingwidespreaduseincountriessuchasNigerBurkinaFasoMalawiandZambia.Thetreesareplantedamongmaizemilletorsorghumcrops.Theynotonlyaddnitrogentothesoilthroughtheirrootsbutalsothroughtheirleaveswhentheyfalloffandbreakdown.Atothertimesoftheyearthetreescanprotectplantsfromstrongsunlight.

　　Mr.Reganoldwasoneofthreeresearcherswhowroteareportaboutperennation.ItwaspublishedinthejournalNature.

　　小题1:FarmlandinAfrica________.A．isoftensmallinsizeB．canproducemorethanenoughcropsforAfricansC．isshortofimportantnutrientsD．hasgottheattentionofscientistsaroundtheworld小题2:Researchersfocusedtheirattentiononsmallfarmlandsforthereasonthat________.A．AfricawasgoingthroughafoodcrisisB．mostfarmsinareassouthoftheSaharaDesertaresmal