the Symposium on Wheats for More Tropical Environments - cimmyt

262from <strong>the</strong> application of 1 to 8 tlha oflime (Table I); however, only 2 tlha canbe considered economic, and that onlymarginally so.A long-term trial investigated <strong>the</strong> effecton yield of single and split applicationsof lime over several years. Thetreatments included single applicationsof 2 and 4 tlha in 1979. In Table 2 <strong>the</strong>yield of <strong>the</strong> 2 tlha treatment in 1981 iscompared with <strong>the</strong> 1 tlha treatment in1979, plus 0.5 tlha in 1980 and 1981.Similarly, <strong>the</strong> yield in 1983 of <strong>the</strong> 4 tlhaTable 1. Effect of lime application atdifferent rates on wheat yield, Zambia,1979 to 1982Lime h/ha)o12468!./ Mean 1979 to 1982Yield (kg/ha)!.12785868689319811051treatment is compared with that of 2tlha in 1979, plus 0.5 tlha in each of1980, 1981, 1982 and 1983. Therewere no significant differences in yield.Heavy applications of lime (6 and 8tlha) to <strong>the</strong> top 15 cm of soil havecaused a downward movement ofcalcium through <strong>the</strong> soil profile overtime; <strong>the</strong> lower rates had <strong>the</strong> samereaction, as evidenced by <strong>the</strong> amount ofsoluble aluminum present (Table 3).However, this precipitation of <strong>the</strong>aluminum in <strong>the</strong> lower layers has notresulted in any fur<strong>the</strong>r increase inyield.Trials investigating deeperincorporation of lime have been carriedout for three seasons since 1982(10,11,12). Depths of 0 to 15,0 to 30and 0 to 45 cm have been investigated,with 3 tlha of lime being applied foreach 15 cm of soil. Wheat yields haveincreased with increasing depth ofincorporation, but <strong>the</strong>re has been nobenefit of incorporation to 45 cm ascompared with 30 cm (Table 4). Thepracticality and economics ofincorporation to <strong>the</strong>se depths on acommercial scale are, of course,questionable.Table 2. Comparison of single and split applications of lime on yields ofwheat, Zambia, 1981 and 1983LimeYieldTreatment h/ha) h/ha)1981Single application 2 738Split application!.1 1 +(0.5 x 2) 6851983Single application 4 950Split application!2.1 2 +(0.5 x 4) 969all ton in 1979 and.5 tin 1980 and 1981~/ 1 ton in 1979 and .5 t in 1980, 1981, 1982 and 1983