the Symposium on Wheats for More Tropical Environments - cimmyt

253Tolerant vartettes-The yield ofvarieties with a wide range ofaluminum tolerance was alsodetennined in <strong>the</strong> trial with deep limeapplications; Table 4 includes yielddata for <strong>the</strong> aluminum-tolerant PF7748.It also responded to deeper liming up to30 cm. but its yields were increased bya factor of less than two; yields ofJupateco 73 were increased by a factorof seven. In <strong>the</strong>se trials. <strong>the</strong> increase inyield as a result of <strong>the</strong> use of <strong>the</strong>_tolerant variety in <strong>the</strong> absence of limewas approximately 800 kglha; whenlime was used. <strong>the</strong> difference was onlyabout 260 kg/ha.Table 3. Presence of aluminum four yearsafter application of lime to <strong>the</strong> top 15 cmof soil, Zambia, 1983Limeapplicationh/ha)o12468Aluminum (ppm)at soil depth15-30 cm 30-45 cm20139105118151919171Considerable effort is being placed on<strong>the</strong> selection of aluminum-tolerantvarieties in Zambia. So far. screeninghas been done in <strong>the</strong> field on unlimedland at Mbala. Lines are entered in anursery consisting of plots of2 x 2 meter rows spaced 20 cm apart ina randomized block design in threereplications. Three rows of each of twocontrol varieties. one tolerant (PF7748)and one nontolerant (Jupateco 73). areseeded along <strong>the</strong> paths between <strong>the</strong>replications at right angles to <strong>the</strong>direction of <strong>the</strong> nursery rows. The samecontrol varietie~ are also included in <strong>the</strong>nursery. Individual plots are scored foraluminum tolerance on a 1 to 9 scale.based on plant Vigor at <strong>the</strong> soft doughstage. relative to <strong>the</strong> controls seeded in<strong>the</strong> pathways (PF7748 set at 3 on <strong>the</strong>scale and Jupateco at 8). This enablesadjustments in scoring which take intoaccount <strong>the</strong> variability in pH andaluminum that occurs in <strong>the</strong> field. Thesame check varieties entered in <strong>the</strong>nursery itself give an added check.Table 4. Effect of depth of incorporation of lime on yields of two wheat cultivars,Zambia, 1983 and 1984!'Limeapplicationh/ha)Jupateco 73Yield % of 0(kg/ha) applicationPF 7748Yield % of 0(kg/ha) applicationMeanYield % of 0(kg/ha) applicationo3 t in top 15 em6 t in top 30 em9 tin top 45 em2221269158015661005727127051014152918551767100151183174618139917181667100226278270,E./ Mean of 1983 and 1984