the Symposium on Wheats for More Tropical Environments - cimmyt

32Yield-The last character to bementioned here Is yield. Althoughcorrelation with latitude Is not high. itIs certain that yield Is. generallyspeaking. reduced in <strong>the</strong> tropics. Thisfact. however. must be viewed in <strong>the</strong>context of earliness or maturity.Measured in production per day. a 100­day crop of 2 t/ha in <strong>the</strong> tropicscorresponds to a ISO-day crop of 3 t/hain temperate zones. In many areas. thisforced maturity Is a major advantage ofwheat as it factlitates <strong>the</strong> grOwing ofasecond crop and sometimes even athird crop. It must also be rememberedthat <strong>the</strong> average yields of major wheatproducers such as Australia andArgentina were 1.2 and 1.5 tlha.respectively. for <strong>the</strong> 1979 to 1981period (4). What is most important forsmall farmers is <strong>the</strong> fact that smallmanagement mistakes. which wouldnormally cause minor yield reductionsin temperate climates. can lead tocomplete crop fallures in <strong>the</strong> tropics.AgroDomyAgronomic knowledge about wheatgrown in temperate environmentsneeds to be rechecked under hotclimate circumstances. The followingagronomic factors probably do notconstitute a complete list of <strong>the</strong>problems which will be encountered in<strong>the</strong> tropics.Weeds-Weed species are oftendifferent in <strong>the</strong> tropics. e.g.• volunteerrice in rice-wheat rotations. Highertemperatures may also cause <strong>the</strong> effectsof herbicides to be different.Ferttlizers-Fertilization Is generallyneeded. because tropical solls are oftenpoor in nutrients. The short growingseason but fast decomposition has to beconsidered in relation to basal versussplit applications.seed bed preparation-Special tnlagepractices may be necessary formoisture conservation. because ofwaterlogging problems or heavy solls.SoWing depth-Fur<strong>the</strong>r investigation isneeded here In relation to standestablishment and subsequent plantdevelopment.These factors are complicated by <strong>the</strong>strong interactions between <strong>the</strong>m andalso by nonagronomic factors. such asvariety and <strong>the</strong> socioeconomicconditions of <strong>the</strong> farmers grOwing <strong>the</strong>wheat.Seed productioDThe production of seed must receivespecial attention. since <strong>the</strong> seedmultiplication rate is slower undertropical conditions. because of reducedtillertng and generally lower yieldlevels. The short growing cycle. on <strong>the</strong>o<strong>the</strong>r hand. permits two crops per year.ifsuitable areas for off-season sowingcan be identified. This necessitatesmoving to high elevations. which areoften intensively cropped withvegetables or o<strong>the</strong>r high-value crops. orshipping seed between countries. whichcan be very expensive and involve agreat deal of logistical support.Seed .torageStorage Is a big problem in <strong>the</strong> tropics.especially under hot and humidconditions. Technical solutions suitablefor storage on-farm. in <strong>the</strong> village andat national levels would greatlyfactlitate <strong>the</strong> introduction of wheat Inmany areas. Grain storage is generallygiven high priority but. at harvest.many farmers do not know whe<strong>the</strong>r<strong>the</strong>y will use <strong>the</strong>ir grain for food or forseed. Therefore. <strong>the</strong> use of chemicalsfor pest control must be conSideredcarefully.NODtechDlcal problem.Previously. problems specific to tropicalconditions have been discussed. but <strong>the</strong>introduction of wheat Into a country